Showing papers in "Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology in 1991"

Metabolic responses to flight and fasting in night-migrating passerines

Abstract: 1. Small passerine migrants achieve endurance flight while fasting, together with one of the highest mass-specific energy rates. Metabolic responses to flight and fasting were examined in three species of free-living migrants (Sylvia borin, Ficedula hypoleuca, Erithacus rubecula) by measuring plasma concentrations of glucose, uric acid, triglycerides, glycerol, free fatty acids (FFA), and β-hydroxybutyrate (β-OHB) in three main physiological situations (feeding, overnight fasting, nocturnal flight) and while changing between these situations. 2. Overnight-fasted birds showed low triglyceride and uric acid levels. Contrary to mammals, FFA and glycerol levels were not increased in agreement with published data on birds. The transition from feeding to fasting (post-feeding) was distinguished by a temporary rise in FFA and a drop in glucose levels. 3. Birds utilize fat during migratory flight, indicated by high levels of FFA, glycerol, and β-OHB. For the first time, high triglyceride levels were found in an exercising vertebrate. The use of protein during flight was demonstrated by high uric acid levels. 4. Birds kept inactive after flight showed a more pronounced reduction of the fat and protein utilization and post-exercise ketosis than naturally landed birds. 5. Differences among the three species in the metabolic pattern suggest that the garden warbler shows the greatest metabolic adaption to endurance flight, having the highest levels of fat metabolites and the highest body fat reserves.

Daily torpor in the Djungarian hamster (Phodopus sungorus): interactions with food intake, activity, and social behaviour

Abstract: In Djungarian hamsters,Phodopus sungorus, daily torpor occurs spontaneously in winter in the presence of abundant food, but individuals show different tendencies to enter torpor. The results show that in hamsters fed rodent chow ad libitum individual torpor frequencies were negatively correlated with both food consumption and the amount of nocturnal locomotor activity. Provision of cafeteria diet at ambient temperatures below thermoneutrality significantly lowered torpor frequencies and induced body weight gains. However, in hamsters fed seeds with a high fat or carbohydrate content (i.e., sunflower seeds or wheat, respectively) neither a decrease of torpor frequencies nor an increase of body weights was observed. The results suggest that in Djungarian hamsters, daily torpor is an intrinsic component of energy balance control and is functionally linked to individual physiological adjustments of food consumption and foraging activity. In addition, the employment of daily torpor can be affected by social interactions, since the long-term pattern of alternations between torpor and normothermia was found to be synchronized in breeding pairs caged together.

Changes in whole body concentrations of thyroid hormones and cortisol in metamorphosing conger eel

Abstract: To clarify the hormonal regulation of metamorphosis of the conger eel (Conger myriaster), changes in whole body concentrations of thyroid hormones, thyroxine (T4) and triiodothyronine (T3), and cortisol during metamorphosis were examined, as well as the changes in the histological activity of the thyroid gland. In larvae before metamorphosis, T4 and T3 levels were less than 5 and 0.15 ng·g-1 respectively. Levels of T4 increased to about 30 ng·g-1 during early metamorphosis, and decreased subsequently. Levels of T3 increased gradually in early metamorphosis, and then increased abruptly to about 2.0 ng·g-1 in late metamorphosis. Before metamorphosis, cortisol levels of the leptocephali less than 11 cm in total length were greater than 200 ng·g-1. Cortisol levels decreased rapidly in larger premetamorphic leptocephali, and low levels were maintained throughout the metamorphic period. Histological observation revealed an activation of the thyroid gland in early metamorphosis; thyroid follicle epithelial cells became columnar and their nuclei larger. Active uptake of colloid by these cells and intensive vascularization of the gland were also observed. By the end of metamorphosis, follicle epithelial cells became squamous, indicating a low level of glandular activity. These results suggest that thyroid hormone plays an important role in regulation of conger eel metamorphosis.

The effect of submergence on heart rate and oxygen consumption of swimming seals and sea lions

Abstract: Respiratory, metabolic, and cardiovascular responses to swimming were examined in two species of pinniped, the harbor seal (Phoca vitulina) and the California sea lion(Zalophus californianus).

Changes in lipid and carbohydrate metabolism during starvation in adult Manduca sexta.

Abstract: Adult Manduca sexta feed very irregularly in the laboratory, and many adult males never feed. Feeding adults live longer and feeding females lay many more eggs; however, in both feeding (sugar water) and starving adults a decrease of metabolic reserves is observed. Carbohydrates disappear from hemolymph and from fat body. Fat body lipid also decreases, while hemolymph lipid concentration increases strongly in starving adults. The activity of fat body glycogen phosphorylase increases strongly in starving adult M. sexta. The activity of glycogen phosphorylase is correlated inversely with hemolymph sugar concentration. Injected trehalose inactivates glycogen phosphorylase within 2 h. and lowers the hemolymph lipid level within 6 h. In starving adult M. sexta, neither the activation of glycogen phosphorylase nor the increase of hemolymph lipid concentration depends on adipokinetic hormone, since cardiacectomy does not prevent the activation of glycogen phosphorylase nor the increase of hemolymph lipid level.

Basal and stress-induced corticosterone levels of garden warblers, Sylvia borin, during migration

Abstract: Plasma levels of the metabolically and behaviorally active corticosteroid hormone, corticosterone, were studied in garden warblers in the laboratory and in the field during the autumnal migratory phase. Garden warblers showing nocturnal migratory activity in the laboratory had elevated levels of corticosterone at the end of the dark phase and low levels during daytime. When nocturnal migratory activity was experimentally disrupted by food deprivation and subsequent refeeding or after spontaneous termination of migratory activity this rhythm was absent. Garden warblers stopping over in the Sahara desert during autumnal migration had low levels of corticosterone. Levels were negatively correlated with fat stores and body mass in birds sampled throughout the day. These levels were generally lower than those associated with stress in response to repeated handling and blood sampling. The results suggest (1) the existence of diel changes in adrenocortical hormonal activity that could be involved in regulation of migration, and (2) that garden warblers carrying large fat depots are not stressed by prolonged flight or lack of appropiate feeding areas during migration over the desert.

The effect of unsaturated and saturated dietary lipids on the pattern of daily torpor and the fatty acid composition of tissues and membranes of the deer mouse Peromyscus maniculatus.

Abstract: Dieary lipids strongly influence the pattern of torpor and the body lipid composition of mammalian hibernators The object of the present study was to investigate whether these diet-induced physiological and biochemical changes also occur in species that show shallow, daily torpor Deer mice, Peromyscus maniculatus, were fed with rodent chow (control diet) or rodent chow with either 10% sunflower seed oil (unsaturated diet) or 10% sheep fat (saturated diet) Animals on the unsaturated diet showed a greater occurrence of torpor (80–100% vs 26–43%), longer torpor bouts (45 vs 225 h), a lower metabolic rate during torpor (096 vs 225 ml O2·g-1·h-1), and a smaller loss of body mass during withdrawal of food (235 vs 390 g) than animals on the saturated diet; controls were intermediate These diet-induced physiological changes were associated with significant alterations in the fatty acid composition of depot fat, leg muscle and brain total lipids, and heart mitochondrial phospholipids Significant differences in the total unsaturated fatty acid (UFA) content between animals on saturated and unsaturated diet were observed in depot fat (557% vs 811%) and leg muscle (564% vs 721%) Major compositional differences between diet groups also occurred in the concentration of n6 and/or n3 fatty acids of brain and heart mitochondria The study suggests that dietary lipids may play an important role in the seasonal adjustment of physiology in heterothermic mammals

Interadult feeding of jelly in honeybee (Apis mellifera L.) colonies

Abstract: Honeybee nurses (8 days old) were injected with 14C-phenylalanine. These bees then dispensed the 14C-labelled protein-rich products of their hypopharyngeal glands to the queen and the brood, and also to young drones and workers of all age classes. In small colonies containing 400–800 bees, nearly one-quarter of the radioactivity which could not be recovered in the nurses was fed by them in a protein-bound form to other members of the worker caste. During one night, one nurse fed an average of 4–5 foragers with proteinaceous food. The role of nurses in the work allotment system of honeybee colonies therefore needs a new, extended definition. Nurses are largely responsible for preparing nutrients from pollen, which is difficult to digest. They then distribute the nutritionally valuable protein produced by their hypopharyngeal glands to practically all hive mates.

The effect of corticosterone on standard metabolic rates of small passerine birds.

Abstract: Resting metabolic rates of Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii) and pine siskins (Carduelis pinus) were evaluated at thermoneutral temperatures before and after administration of corticosterone (B) at physiological doses. There was no effect of B on basal metabolic rate of either species, but nocturnal metabolic rate varied significantly less over the 3-h period of measurement in B-treated sparrows and siskins than in control birds. These results, coupled with observations of caged birds, suggest that corticosterone has no direct effect on avian resting metabolism but does reduce the responsiveness of birds to external stimuli and thus promotes nocturnal restfulness.

Short-chain fatty acids and CO2 as regulators of Na+ and Cl- absorption in isolated sheep rumen mucosa.

Abstract: Unidirectional 22Na+ and 36Cl− fluxes were determined in short-circuited, stripped rumen mucosa from sheep by using the Ussing chamber technique. In both CO2/HCO − 3 -containing and CO2/HCO − 3 -free solutions, replacement of gluconate by short-chain fatty acids (SCFA, 39 mM) significantly enhanced mucosal-toserosal Na+ absorption without affecting the Cl− transport in the same direction. Short-chain fatty acid stimulation of Na+ transport was at least partly independent of Cl− and could almost completely be abolished by 1 mM mucosal amiloride, while stimulation of Na+ transport was enhanced by lowering the mucosal pH from 7.3 to 6.5. Similar to the SCFA action, raising the PCO2 in the mucosal bathing solution led to an increase in the amiloride-sensitive mucosal-to-serosal Na+ flux. Along with its effect on sodium transport, raising the PCO2 also stimulated chloride transport. The results are best explained by a model in which undissociated SCFA and/or CO2 permeate the cell membrane and produce a raise in intracellular H+ concentration. This stimulates an apical Na+/H+ exchange, leading to increased Na+ transport. The stimulatory effect of CO2 on Cl− transport is probably mediated by a Cl−/HCO − 3 exchange mechanism in the apical membrane. Binding of SCFA anions to that exchange as described for the rat distal colon (Binder and Mehta 1989) probably does not play a major role in the rumen.

Energetics of under-water swimming in Adélie penguins (Pygoscelis adeliae)

Abstract: The energy consumption of Adelie penguins while at rest in water (8.4 W·kg-1 at 4°C) or swimming below the surface was determined using a 21 m long canal fitted with respiration chambers at each end. Penguins chose to swim 86% of the time at speeds recorded in nature. Cost of transport was lowest (7.9 J·kg-1·m-1) at 1.7–2.3 m·s-1, corresponding to a power input of 15.8 W·kg-1, and only 50% as high as previously reported. Assuming a muscle efficiency of 0.25, propulsion efficiency is 0.4 and overall efficiency is 0.1. Calculated food requirements vary between 1060 g krill per adult and foraging trip at the beginning of the breeding season and 2500 g at the period of highest demand, prior to creching of the chicks.

Changes in expression of provasotocin and proisotocin genes during adaptation to hyper- and hypo-osmotic environments in rainbow trout.

Abstract: The physiological roles of neurohypophysial hormones, vasotocin (VT) and isotocin (IT), are not yet clear in teleosts. Since information on responsiveness of hypothalamic neurosecretory neurons to environmental stimuli may contribute to an understanding of their physiological roles, effects of environmental hyper- and hypo-osmotic stimuli on expression of VT and IT precursor (proVT and proIT) genes in rainbow trout were investigated, using an in situ hybridization technique in which 46 mer synthetic oligonucleotides were used as hybridization probes. The probes corresponded to the mRNA loci encoding chum salmon proVT (-5 to 11) and proIT (-5 to 11), and were labeled at the 3′-end with 35S. Autoradiographic silver grains which represent the hybridization signals of proVT and proIT mRNAs were localized in both magnocellular and parvocellular neurons in the nucleus preopticus magnocellularis (NPOmg). Localizations of proVT and proIT hybridization signals coincided with those of VT- and IT-immunoreactive neurons in adjacent sections, and showed that proVT and proIT genes are expressed in separate neurons. The intensity of proVT hybridization signals as determined by grain counting in magnocellular neurons in the NPOmg was conspicuously decreased after transfer from fresh water (FW) to 80% seawater (SW). The proVT mRNA levels in SW trout were consistently lower than those of FW trout for up to 2 weeks. After return from 80% SW to FW, the proVT mRNA level increased, attaining the initial FW level. The proIT mRNA levels in SW trout were not statistically different from those in FW trout, except for the 1st day after transfer to SW. These results suggest that synthesis of proVT was elevated by transfer from higher to lower salinity, and that VT may have a physiological role in salmonid osmoregulation, especially in adaptation to a hypo-osmotic environment.

Two lectins on the surface of Helix pomatia haemocytes: a Ca2+-dependent, GalNac-specific lectin and a Ca2+-independent, mannose 6-phosphate-specific lectin which recognises activated homologous opsonins

Abstract: Haemocytes of the gastropod mollusc, Helix pomatia, possess on their surface a membrane-integrated GalNac-specific lectin which binds to and stimulates phagocytosis of GalNac-bearing target cells (human A erythrocytes) only in the presence of extracellular calcium ions. Target cells without GalNac moieties on their surface (human B and bovine erythrocytes) are not recognised. Helix haemocytes also possess a Ca2+-independent mannose-6-phosphate-specific lectin on their surface which, in the absence of extracellular calcium ions, enables recognition and phagocytosis of A rbc opsonised with agglutinins isolated from either the snail's albumin gland or serum. These opsonins, however, bind to host haemocytes only after binding to GalNac moieties on the surface of test particles. Our results indicate that such a ligand-specific opsonin/target cell interaction apparently induces a conformational change in the opsonin, resulting in exposure of mannose 6-phosphate moieties that are recognised by the Ca2+-independent lectin on the surface of the haemocytes.

Differential survival of Venus gallina and Scapharca inaequivalvis during anoxic stress: Covalent modification of phosphofructokinase and glycogen phosphorylase during anoxia

Abstract: Biochemical mechanisms underlying anaerobiosis were assessed in two Mediterranean bivalve species, Scapharca inaequivalvis and Venus gallina, with widely differing tolerances for oxygen lack These species displayed LT50 values for anoxic survival at 17–18°C of 17 and 4 d, respectively Succinate and alanine were the major products of 24 h anaerobic metabolism in both species but only S inaequivalvis further metabolized succinate to propionate Both species reduced metabolic rate while anoxic but metabolic arrest was more pronounced in S inaequivalvis Calculated ATP turnover rate (MATP) during exposure to N2-bubbled seawater was only 451% of the aerobic rate in S inaequivalvis but was 1268% in V gallina To counteract a greater load of acid end products, V gallina foot showed a significantly greater buffering capacity, 2338±020 slykes, compared to 196±079 slykes in S inaequivalvis The two species also differed distinctly in the enzymatic regulation of anaerobiosis In V gallina anoxia exposure caused only a small change in PFK kinetic parameters (a decrease in Ka AMP) and had no effect on glycogen phosphorylase By contrast, S inaequivalvis foot showed a strong modification of enzyme properties in anoxia The percentage of glycogen phosphorylase in the a form dropped significantly only in S inaequivalvis Other changes included alterations in the properties of PFK leading to a less active enzyme form in anoxia Compared to the aerobic enzyme form, PFK from anoxic foot showed a reduced affinity for fructose-6-P (Km increased 24-fold), greater inhibition by ATP (I50 decreased 68-fold), and an increase in sensitivity to AMP activation (Ka decreased by 50%) These enzyme changes appear to be key to a glycolytic rate depression during anaerobiosis in S inaequivalvis foot muscle

Developmental and metabolic changes induced by anoxia in diapausing and non-diapausing flesh fly pupae

Abstract: Anaerobic metabolism was compared in nondiapausing (ND) and diapausing (D) pupae of the flesh fly,Sarcophage crassipalpis using in vivo13C NMR spectroscopy. Anoxia-induced changes in the development of ND and D pupae were correlated with oxidative metabolism and mitochondrial integrity. ND pupae tolerated 1 day of anoxia without any obvious developmental effect, while D pupae tolerated up to 6 days of anoxia. Longer exposure to anoxia (3 days in ND pupae and up to 14 days in D pupae) allowed development to the pharate adult stage but precluded eclosion. Four-day anoxia applied to ND pupae during 4–6 days post-pupariation arrested development in a stage indistinguishable from diapause. This morphological stasis was accompanied by 80% suppression of oxidative metabolism and a 100% increase in glycerol concentration. However, unlike a true diapause, this arrest could not be terminated with 20-hydroxyecdysone or hexane. Four-day anoxia treatment applied to D pupae stimulated development and raised their oxygen consumption. The anoxia-induced changes in oxidative metabolism were not accompanied by mitochondrial changes. Exposure to 95%PO2 atmosphere had no apparent developmental or metabolic effects on ND or D pupae. Major metabolites (lipids, trehalose, glycogen, glycerol, glutamine, and alanine) were detected in the ND and D pupae but their rates of turnover differed. Anoxia induced synthesis of glycerol and alanine in both D and ND pupae. Injected labeled glucose was incorporated primarily into trehalose and glycogen by both D and ND pupae. The rate of incorporation in ND pupae was approximately twice that observed in D pupae. Anoxia resulted in glycerol and alanine synthesis in both groups of pupae, but more glycerol was labeled in ND pupae and more alanine in D pupae. Glycogen and trehalose were depleted in the D pupae under anoxia. Cold acclimation had no effect on the steady-state or rate of synthesis of metabolites.

Na+-independent, electrogenic Cl- uptake across the posterior gills of the Chinese crab (Eriocheir sinensis): Voltage-clamp and microelectrode studies

Abstract: Single gill lamellae from posterior gills of Chinese crabs (Eriocheir sinensis) were isolated, separated into halves and mounted in a modified Ussing chamber. Area-related short-circuit current (Isc) and conductance (Gtot) of this preparation were measured. Epithelial cells were impaled with microelectrodes through the basolateral membrane and cellular potentials (Vi under open- and Vsc under short-circuit conditions) as well as the voltage divider ratios (Fi, Fo) were determined. With NaCl salines on both sides an outside positive PDte (22±2 mV) and an Isc (-64±13 μA·cm-2) with a polarity corresponding to an uptake of negative charges (“inward negative”) were obtained. “Trough”-like potential profiles were recorded across the preparation under open- as well as short-circuit conditions (Vo=-101±5 mV, external bath as reference; Vi=-78±2 mV, internal bath as reference; Vsc=-80±2 mV, extracellular space as reference). The voltage divider ratios of the external (apical membrane plus cuticle) and internal (basolateral membrane) barrier were Fo=0.92±0.01 and Fi=0.08±0.01, respectively. To investigate a Cl--related contribution to the above parameters, Na+-free solutions in the external bath (basolateral NaCl-saline) were used. “Inward negative” Isc under these conditions almost completely depended on external Cl-. Elimination of Cl- in the external bath reversed Isc, and Gtot decreased substantially. Concomitantly, Vsc depolarised and Fo increased. Cl--dependent current and conductance showed saturation kinetics with increasing external [Cl-]. Addition of 20 mmol·1-1 thiocyanate to the external bath had similar, although less pronounced, effects as Cl- substitution. Equally, external SITS (1 mmol·1-1) inhibited the current and, concomitantly, Gtot decreased substantially. Addition of 1 mmol·1-1 acetazolamide to, and omission of NaHCO3 from, the basolateral bath resulted in a decrease of Isc while Gtot remained unchanged. The Cl--channel blocker DPC inhibited Isc almost completely when added to the basolateral saline, whereas Gtot decreased moderately; however, Vsc depolarised without significant change of Fi. Ouabain had no influence on Isc and Gtot. Increasing the basolateral [K+] resulted in a decrease in Isc, while Gtot was not affected. At the same time Vsc largely depolarised and Fi decreased. Addition of the K+-channel blocker Ba++ (5 mmol·1-1) to the basolateral solution resulted in a two-step alteration of the transepithelial (Isc, Gtot) and cellular (Vsc, Fi) parameters. The results are discussed with regard to (i) the mechanisms responsible for active transbranchial Cl- uptake, and (ii) the technical improvement of being able to perform transport studies with crab gill preparations in an Ussing chamber.

The effects of nitrite on chloride regulation in the crayfish Pacifastacus leniusculus Dana (Crustacea: Decapoda)

Abstract: Nitrite in the external freshwater medium was found to be toxic to Pacifastacus leniusculus Dana (48 h LC50∼0.7 mM NO 2 − ). It produced significant changes in haemolymph ionic concentration and acid-base status. Exposure to 1.0 mM NO 2 − resulted in a rapid, active accumulation of nitrite in the haemolymph (to 25 mM NO 2 − after 24 h) and caused the partial inhibition of Cl− uptake. Some reduction in Cl− efflux rate was seen. In 1.0 mM NO 2 − a rapid depletion of haemolymph [Cl−] was observed (∼50 mM decrease in 27 h). Nitrite competitively inhibited active Cl− uptake (Km increased from 0.42 to 1.22 mM; Ki=0.45 mM). To achieve Cl− balance in this medium, depleted crayfish would require a two-fold increase in external [Cl−]. A lesser decrease in haemolymph [Na+] was found while osmotic pressure was relatively unaffected. Haemolymph [HCO 3 − ] showed a significant increase and was accompanied, unexpectedly, by an acidosis. Possible sources of the excess HCO 3 − , perhaps by inhibition of normal Cl−/HCO 3 − branchial exchange or release from CaCO3 stores, are discussed. Haemolymph clearance of NO 2 − was slower than uptake as was the restoration of [Cl−] on recovery in nitrite-free medium.

Effects of direct transfer from freshwater to seawater on respiratory and circulatory variables and acid-base status in rainbow trout

Abstract: The effects of increased ambient salinity (35 mg · ml-1) were studied at 1, 6, and 24 h after direct transfer of rainbow trout from freshwater to seawater. Two series of experiments were carried out successively. The first series was designed to simultaneously study all the respiratory (except Hb affinity for O2), circulatory, and acid-base variables in each fish. In this series, fish were fitted with catheters chronically inserted into the cardiac bulbus, the dorsal aorta, and the opercular and buccal cavities. In the second series, designed to study haemoglobin O2 affinity, fish were fitted with only a dorsal aorta catheter. The ventilatory flow ( $$\dot V_w $$ ) was markedly increased just after transfer (by 55% at 1 h), then more moderately (by 20% at 6 h and 32% at 24 h). The initial hyperventilation peak was associated with frequent couphing motions. These ventilatory changes resulted essentially from increase in ventilatory amplitude. Initially, standard oxygen consumption (MM}O2) decreased slightly, the moderately increased (by 12% at 24 h), so that the oxygen convection requirement ( $$\dot V_W /\dot MO_2 $$ ) increased substantially. In spite of an increased ventilation, the partial pressure of oxygen in arterial blood (P aO2) decreased slightly at 1 h, prior to returning to control levels, while partial pressure of carbon dioxide in arterial blood (P aCO2) was not significantly decreased. Gill oxygen transfer factor decreased substantially at 1 h (by 35%) then more moderately (by 7% at 1 h and 12% at 24 h). These results suggest a decrease in gas diffusing capacity of the gills. As P aCO2 remained approximatively unchanged, the gradual decrease in arterial pH (pHa) from 7.94 to 7.67 at 24 h must therefore be regarded as a metabolic acidosis. The strong ion difference decreased markedly because the concentration of plasma chloride increased more than that of sodium. Arterial O2 content (C aO2) gradually decreased (by 38% at 24 h) simultaneously with the decrease in pHa, while the ratio P aO2/C aO2 increased. In parallel, seawater exposure induced a marked decrease in affinity of haemoglobin for O2, so that at 24 h, P50 was increased by 26% above the value obtained in freshwater-adapted trout. The increase in $$\dot V_w $$ could be ascribed initially (at 1 h) to the decrease of P aO2 and later to a stimulation of respiratory neurons resulting from the lowered medullary interstitial pH. The decrease in C aO2 could be interpreted mainly as a consequence of a decreased affinity of haemoglobin for O2, likely to be due to the blood acidosis and a predictable increase in chloride concentration within erythrocytes. Cardiac output ( $$\dot Q_c $$ ) slightly decreased at 1 h, then progressively increased by 30% at 24 h. Branchial vascular resistance increased at 1 h by 28%, then decreased by 18% of the control value at 24 h. Systemic vascular resistance decreased markedly by 40% at 24 h. As heart rate (HR) remained significantly unchanged, the cardiac stroke volume initially decreased then increased in relation to the changes in $$\dot Q_c $$ . The increase of $$\dot Q_c $$ , allowing compensation for the effect of decreased C aO2 in tissue O2 supply, was interpreted as a passive consequence of the decrease in total vascular resistance occurring during seawater exposure.

Cloning and sequence analyses of cDNAs encoding vasotocin and isotocin precursors of chum salmon, Oncorhynchus keta: evolutionary relationships of neurohypophysial hormone precursors.

Abstract: The nucleotide sequences of cloned cDNAs were used to determine the primary structures of the precursors of vasotocin (sVT) and isotocin (sIT) from the hypothalamus of the chum salmon,Oncorhynchus keta. Two different cDNAs were obtained for each of sVT and sIT precursors (sVT-I and sVT-II; sIT-I and sIT-II). Both sVT and sIT precursors were found to contain a signal peptide and hormone that is connected to a neurophysin by a Gly-Lys-Arg sequence. Northern and Southern blot analyses showed that the sVT and sIT genes are expressed by the same chum salmon hypothalamus, but not by the liver and kidney. Microheterogeneity was found in the nucleotide and amino acid sequences of sVT precursors between our results and the previously reported data (Heierhorst et al. 1990). The conspicuous difference is the occurrence of a stop codon in the middle of sVT-II cDNA. The carboxyl termini of both sVT and sIT neurophysins are about 30 amino acids longer than neurophysins of toad and mammalian neurohypophysial hormone precursors. Although these extended regions do not contain a glycosylation site, they show striking similarity with the glycopeptide moiety (copeptin) of toad vasotocin and mammalian vasopressin precursors. The central portion of the neurophysins shows highest homology among corresponding regions of sVT and sIT precursors. Moreover, calculation of nucleotide substitution rates suggests that a recent gene conversion may have occurred which encompasses the exon that encodes the central segment of the sVT and sIT precursors. A possible pathway for the evolution of precursor molecules of neurohypophysial hormones is discussed.

Absorption of bioactive human growth hormone after oral administration in the common carp (Cyprinus carpio) and its enhancement by deoxycholate.

Abstract: Recombinant human growth hormone was administered orally to carp and serum levels of absorbed bioactive hormone were investigated using a highly sensitive Nb2 rat lymphoma cell bioassay and radioimmumoassay. Serum levels of bioactive hGH reached maximum values 30 min after oral intubation and then gradually decreased. Co-administration of the hormone with deoxycholate to fasted carp resulted in up to a 1000-fold increase in absorption compared to aqueous solutions of the hormone, but had no effect on the kinetics of the absorption process. Absorption of the hormone in starved fish was significantly greater than in fed fish. A linear dose-response relationship was observed for hGH in starved fish and the level of absorption in fed fish was influenced by the time interval from the last meal. The ratio of bioactive to immunoactive hGH in fasted fish indicated little loss of bioactivity and also that deoxycholate may be protective against hGH degradation. The present study demonstrates for the first time that biologically active hGH is absorbed in the common carp after oral intubation. Furthermore, the use of a biological detergent dramatically increased the extent of hGH absorption. Additional studies are required to establish the approapriate conditions (diet composition, feeding level, and frequency, etc.) in which polypeptide hormones could be introduced orally to fish.

Two-substrate kinetic analysis : a novel approach linking ion and acid-base transport at the gills of freshwater trout, Oncorhynchus mykiss

Abstract: The novel application of a two-substrate model (Florini and Vestling 1957) from enzymology to transport kinetics at the gills of freshwater trout indicated that Na+/acidic equivalent and Cl-/basic equivalent flux rates are normally limited by the availability of the internal acidic and basic counterions, as well as by external Na+ and Cl- levels. Adult rainbow trout fitted with dorsal aortic and bladder catheters were chronically infused (10–16 h) with isosmotic HCl to induce a persistent metabolic acidosis. Acid-base neutral infusions of isosmotic NaCl and non-infused controls were also performed. Results were compared to previous data on metabolic alkalosis in trout induced by either isosmotic NaHCO3 infusion or recovery from environmental hyperoxia (Goss and Wood 1990a, b). Metabolic acidosis resulted in a marked stimulation of Na+ influx, no change in Cl- influx, positive Na+ balance, negative Cl- balance, and net H+ excretion at the gills. Metabolic alkalosis caused a marked inhibition of Na+ influx and stimulation of Cl- influx, negative Na+ balance, positive Cl- balance, and net H+ uptake (=base excretion). Mean gill intracellular pH qualitatively followed extracellular pH. Classical one-substrate Michaelis-Menten analysis of kinetic data indicated that changes in Na+ and Cl- transport during acid-base disturbance are achieved by large increases and decreases in Jmax, and by increases in Km. However, one-substrate analysis considers only external substrate concentration and cannot account for transport limitations by the internal substrate. The kinetic data were fitted successfully to a two-substrate model, using extracellular acid-base data as a measure of internal HCO 3 - and H+ availability. This analysis indicated that true Jmax values for Na+/acidic equivalent and Cl-/basic equivalent transport are 4–5 times higher than apparent Jmax values by one-substrate analysis. Flux rates are limited by the availability of the internal counterions; transport Km values for HCO 3 - and H+ are far above their normal internal concentrations. Therefore, small changes in acid-base status will have large effects on transport rates, and on apparent Jmax values, without alterations in the number of transport sites. This system provides an automatic, negative feedback control for clearance or retention of acidic/basic equivalents when acid-base status is changing.

A role played by the vitelline diverticulum in the yolk sac resorption in young post-hatched chickens

Abstract: Yolk sac resorption, with special reference to the role of the vitelline stalk, was studied in young post-hatched chickens (0, 1, and 2 days old) using a radioactive (14C-PEG-4000) and coloured (Evans Blue) marker injected into the yolk sac lumen of conscious birds. When the animals were newly-hatched and 1 day old, the radioactive material was recovered from the lumen of the gastrointestinal tract, but not when the vitelline diverticulum was tied. These results suggest a role played by the vitelline diverticulum in the removal of vitelline contents during the first post-hatching 48 h of chick life.

Activation of antifreeze proteins from larvae of the beetle Dendroides canadensis

Abstract: Purified antifreeze proteins (AFPs) from the larvae of the beetle Dendroides canadensis do not produce the high levels of antifreeze activity seen in the hemolymph of overwintering larvae, even when the purified AFPs are assayed at very high concentrations. However, addition of certain proteins or agar (at concentrations sufficiently low that the gel state does not result) to the Dendroides AFP resulted in a 2–3-fold increase in activity. A 70-kDa protein with AFP-activating capabilities was purified from Dendroides larvae. Addition of this endogenous activator protein to a 4 mg·ml-1 solution of AFP increased the activity of the AFPs to values comparable to those of the hemolymph of overwintering larvae. Data derived from a modified immunoblot technique demonstrate that the activators bind to the AFP, or vice versa. Formation of this association must allow the AFP to block ice crystal growth by binding to the surface of potential seed crystals in the normal fashion. However, because the AFP-activator complex is much larger than the AFP alone, the complex probably blocks a greater surface area of the crystal and is thus a more efficient antifreeze.

Effect of cooling rate on the survival of frozen wood frogs, Rana sylvatica.

Abstract: Wood frogs (Rana sylvatica) were frozen to -2.5 degrees C under five distinct cooling regimes to investigate the effect of cooling rate on survival. Frogs survived freezing when cooled at -0.16 degrees C.h-1 or -0.18 degrees C.h-1, but mortality resulted at higher rates (-0.30 degrees C.h-1, -1.03 degrees C.h-1, and -1.17 degrees C.h-1). Surviving frogs in the latter groups required longer periods to recover, and transient injury to the neuromuscular system was evident. Some of the frogs that died had patches of discolored, apparently necrotic skin; vascular damage, as indicated by hematoma, also occurred. It is concluded that slow cooling may be critical to the freeze tolerance of wood frogs. Additional studies examined the effect of cooling rate on physiological responses promoting freeze tolerance. Mean glucose concentrations measured in plasma (15-16 mumol.ml-1) and liver (42-45 mumol.g-1) following a 2-h thaw did not differ between slowly- and rapidly-cooled frogs but in both groups were elevated relative to unfrozen controls. Thus, freezing injury to rapidly-cooled frogs apparently was not mitigated by the presence of elevated glucose. Water contents of liver tissue, measured 2 h post-thawing, did not differ between slowly-cooled (mean = 77.6%) and rapidly-cooled (mean = 78.5%) frogs. However, the mean hematocrit of slowly-cooled frogs (48%) was significantly higher than that (37%) of frogs cooled rapidly, possibly owing to differences in the dynamics of tissue water during freezing.

Seasonal changes in daily metabolic patterns of Lacerta viridis

Abstract: Lacerta viridis maintained under natural photoperiodic conditions show daily and seasonal changes in metabolic rates and body temperature (T b) as well as seasonal differences in sensitivity to temperature change. At all times of the year lizards have a daily fluctuation in oxygen consumption, with higher metabolic rates during the light phase of the day when tested at a constant ambient temperature (T a) of 30°C. Rhythmicity of metabolic rate persists under constant darkness, but there is a decrease in the amplitude of the rhythm. Oxygen consumption measured at various Tas shows significant seasonal differences at T as above 20°C. Expressed as the Arrhenius activation energy, metabolic sensitivity of Lacerta viridis shows temperature dependence in autumn, which changes to metabolic temperature independence in spring at T as above 20°C. The results indicate a synergic relationship between changing photoperiod and body temperature selection, resulting in seasonal metabolic adjustment and seasonal adaptation.

Purification and characterization of antifreeze proteins from larvae of the beetle Dendroides canadensis

Abstract: Four antifreeze proteins (AFPs) were purified from larvae of the beetle Dendroides canadensis The AFPs are similar in amino acid compositions, having high contents of hydrophilic amino acids (45–55 mol%) and cysteine (∼16 mol% Cys) Approximately half of the Cys residues form disulfide bridges, and both the disulfide bridges and free sulfhydryls are essential for activity The N-terminals of the AFPs are blocked The pH optimum of the AFPs is ∼78, but major loss of activity occurred only at very high pH (120) The detergents SDS and Triton X-100 did not inactivate the AFPs Circular dichroism spectra indicate the presence of both α and β secondary structures in the AFPs, in addition to a large random structure component

Steady-state sodium absorption and chloride secretion of colon and coprodeum, and plasma levels of osmoregulatory hormones in hens in relation to sodium intake.

Abstract: The plasma levels of four osmoregulatory hormones and their target ion-transport systems in the lower intestines of the domestic fowl were determined in order to elucidate their interrelationship and their setpoints in relation to NaCl intake. White Plymouth Rock hens were adapted to six intake levels of NaCl (0.20 +/- 0.02-24.7 +/- 1.9 mmoles Na+.kg bw-1.day-1) for 6 weeks. The Na+ absorption and the Cl- secretion of colon and coprodeum were characterized in vitro by the effects of hexoses, amino acids, amiloride, and theophylline on the short-circuit current (SCC) and electrical potential difference (PD). The NaCl-conserving system of the adult chicken is set at low intake levels of NaCl as the 80% range (quantized by non-linear, logistic regression analyses) of the change in the plasma [ALDO], the amiloride-inhibitable Na+ absorption of coprodeum and colon (delta SCC), occurred from 0.18 to 2.3, from 0.9 to 4.3, and from 1.2 to 7.3 mmoles Na+.kg bw-1.day-1, respectively. These results demonstrate that the amiloride-inhibitable Na+ absorption of coprodeum is more closely linked to plasma [ALDO] than that of colon. The aminoacid-Na+ coabsorption of colon increased over exactly the same range of Na+ intake as the colonic amiloride-inhibitable Na+ absorption decreased, whereas the hexose-Na+ coabsorption increased at higher levels of Na+ coabsorption increased at higher levels of Na+ intake, from 2 to 11 mmoles Na+.kg bw-1.day-1. Both these Na+ absorption types had reached their maximums at 24.7 mmoles Na+.kg bw-1.day-1, whereas the plasma [AVT] and plasma [PRL], although significantly increased, apparently had not; their 80% range of change occurred from 9.9 to 99 mmoles Na+.kg bw-1.day-1, and the main changes in plasma osmolality were predicted to occur from 5.4 to 107 mmoles Na+.kg bw-1.day-1. These results suggest that these colonic and hormonal variables conserve osmotically-free water and operate at high NaCl intake. The theophylline-induced colonic Cl- secretion did not change with NaCl intake, whereas the stimulation of SCC in coprodeum decreased with increasing NaCl intake: the main change occurred between 0 and 3.2 mmoles Na+.kg bw-1.day-1. Thus, all ion-transport capacity (although the nature of the Na+ transport changes). It is suggested that hormones defending the extracellular volume and composition are regulated close to zero input and output of both NaCl and water, regardless of whether they are NaCl conserving or free-water conserving.(ABSTRACT TRUNCATED AT 400 WORDS)

Temperature adaptation and the contractile properties of live muscle fibres from teleost fish

Abstract: The contractile properties of swimming muscles have been investigated in marine teleosts from Antarctic (Trematomus lepidorhinus, Pseudochaenichthys georgianus), temperate (Pollachius virens, Limanda limanda, Agonis cataphractus, Callionymus lyra), and tropical (Abudefduf abdominalis, Thalassoma duperreyi) latitudes. Small bundles of fast twitch fibres were isolated from anterior myotomes and/or the pectoral fin adductor profundis muscle (m. add. p). Live fibre preparations were viable for several days at in vivo temperatures, but became progressively inexcitable at higher or lower temperatures. The stimulation frequency required to produce fused isometric tetani increased from 50 Hz in Antarctic species at 0°C to around 400 Hz in tropical species at 25°C. Maximum isometric tension (Po) was produced at the normal body temperature (NBT) of each species (Antarctic, 0–2°C; North Sea and Atlantic, 8–10°C; Indo-West Pacific, 23–25°C). P0 values at physiological temperatures (200–300 kN·m−2) were similar for Antarctic, temperate, and tropical species. A temperature induced “tension hysteresis” was observed in muscle fibres from some species. Exposure to temperate>tropical species. Relaxation was generally much slower at temperatures <10°C in fibres from tropical than temperate fish. Q10 values for these parameters at NBTs were 1.3 2.1 for tropical species, 1.7–2.6 for temperate species, and 1.6–3.5 for Antarctic species. The forcevelocity (P-V) relationship was studied in selected species using iso-velocity releases and the data below 0.8 P0 iteratively fitted to Hill's equation. The P-V relation at NBT was found to be significantly less curved in Antarctic than temperate species. The unloaded contraction velocity (Vmax) of fibres was positively correlated with NBT increasing from about 1 muscle fibre length·s−;1 in an Antarctic fish (Trematomus lepidorhinus) at 1°C to around 16 muscle fibre lengths·s−1 in a tropical species (Thalassoma duperreyi) at 24°C. It is concluded that although muscle contraction in Antarctic fish shows adaptations for low temperature function, the degree of compensation achieved in shortening speed and twitch kinetics is relatively modest.

Fuel homeostasis in the harbor seal during submerged swimming

Abstract: 1. The turnover rates and oxidation rates of plasma glucose, lactate, and free fatty acids (FFA) were measured in three harbor seals (average mass = 40 kg) at rest or during voluntary submerged swimming in a water flume at 35% (1.3 m.s-1) and 50% (2 m.s-1) of maximum oxygen consumption (MO2max). 2. For seals resting in water, the total turnover rates for glucose, lactate, and FFA were 23.2, 26.2, and 7.5 mumols.min-1.kg-1, respectively. Direct oxidation of these metabolites accounted for approximately 7%, 27%, and 33% of their turnover and 3%, 7%, and 18% of the total ATP production, respectively. 3. For swimming seals, MO2max was achieved at a drag load equivalent to a speed of 3 m.s-1 and averaged 1.85 mmol O2.min-1.kg-1, which is 9-fold greater than resting metabolism in water at 18 degrees C. 4. At 35% and 50% MO2max, glucose turnover and oxidation rates did not change from resting levels. Glucose oxidation contributed about 1% of the total ATP production during swimming. 5. At 50% MO2max, lactate turnover and anaerobic ATP production doubled, but the steady state plasma lactate concentration remained low at 1.1 mM. Lactate oxidation increased 63% but still contributed only 4% of the total ATP production. Anaerobic metabolism contributed about 1% of the total ATP production at rest and during swimming. 6. The plasma FFA concentration and turnover rate increased only 24% and 37% over resting levels, respectively, at 50% MO2max. However, the oxidation rate increased almost 3.5-fold and accounted for 85% of the turnover.(ABSTRACT TRUNCATED AT 250 WORDS)

Caste-specific modulation of juvenile hormone III content and ecdysteroid titer in postembryonic development of the stingless bee, Scaptotrigona postica depilis

Abstract: Juvenile hormone III content and ecdysteroid titer were analyzed for larval and pupal development of the stingless bee,Scaptotrigona postica depilis. Castespecific differences in juvenile hormone III content were detected at three developmental phases: at the transition from the fourth to the fifth larval stadium, in the spinning phase of the fifth larval stadium, and shortly after the imaginal moult. During the fifth larval stadium, juvenile hormone content closely reflects corpora allata activity. Juvenile hormone synthesis may thus be responsible for the elevated hormone titer in spinning-phase queen larvae, a phase of known sensitivity for induction of queen characters by exogenous juvenile hormone. For ecdysteroids, two phases of caste-specific differences were found: in the pre-pupal phase, and shortly after the imaginal moult. In both periods the titer in queens is distinctly higher compared to workers.