Showing papers on "Incubation published in 1983"

Putrescine and Acid Stress : Induction of Arginine Decarboxylase Activity and Putrescine Accumulation by Low pH.

Abstract: Incubation of peeled oat Avena sativa L var Victory leaf segments on media of pH 50 or below leads to a rapid and massive increase in the titer of putrescine while incubation at pH values above 50 causes little or no change The low pH effect is independent of the buffer system employed Putrescine levels rise within 3 hours and reach their peak 8 to 9 hours after acidification At this time, putrescine titer is eight times greater at pH 35 than at 60 None of the other polyamines shows a response to changes in external pH The increase in putrescine is blocked by the addition of cycloheximide or dl-alpha-difluoromethylarginine, a specific inhibitor of the putrescine biosynthetic enzyme, arginine decarboxylase In one experiment, arginine decarboxylase activity was 110% greater at pH 40 than at 60 after a 4-hour incubation, although the average increase over many experiments was 47% The activity of the other possible putrescine biosynthetic enzyme, ornithine decarboxylase, falls throughout the incubation period and is virtually equal at pH 40 and 60

Genetic control of scrapie and Creutzfeldt-Jakob disease in mice.

Abstract: Genetic control of experimental scrapie and Creutzfeldt-Jakob disease (CJD) was studied in inbred strains of mice by measuring the times from intracerebral inoculation with the agents to the onset of neurological dysfunction. Every strain of mice examined was susceptible to infection; however, a wide range of incubation times was found for both scrapie and CJD. New Zealand (NZ) mice, which eventually develop an autoimmune disorder, were inoculated intracerebrally with 10(6) ID50 units of the scrapie agent in a Chandler isolate. NZW mice showed incubation periods of less than 95 days; this is the shortest period recorded for any murine host with scrapie. In NZB and NZB X W F1 mice, the incubation periods were approximately 130 days and were similar to those in BALB/c and C57BL mice. Male and female NZ mice exhibited scrapie incubation periods of the same length. Similar results were obtained when B10.Q and C57BL/6J mice were inoculated intracerebrally with 10(4) ID50 units of the CJD agent in a K.Fu. isolate. These observations define a genetic locus or loci controlling the length of scrapie and CJD incubation periods; alleles coding for longer incubation times appear to be autosomal dominant. When congenic mice with a C57BL/10J background differing only in their H-2 haplotypes were studied, the results showed that the D subregion of the H-2 complex played a central role in controlling the length of the CJD incubation period. The q allele at the D subregion resulted in shorter incubation times, whereas the d allele resulted in long incubation times. The p, s, b, and k alleles gave intermediate incubation times. We propose the symbol PID-1 for designating this genetic locus which is located within the D subregion of the major histocompatibility (H-2) complex on murine chromosome 17. In addition, observations on congenic mice provide evidence for the influence of sex on CJD incubation periods. In some strains of inbred mice, males showed significantly shorter incubation periods compared with those for females with experimental CJD. These studies with inbred mice have defined previously unrecognized genes that control the length of scrapie and CJD incubation periods.

Effect of temperature of extrinsic incubation on the vector competence of Culex tarsalis for western equine encephalomyelitis virus.

Abstract: Culex tarsalis was a less competent vector of western equine encephalomyelitis (WEE) virus after 2-3 weeks' extrinsic incubation at 32 degrees C than after incubation at 18 degrees or 25 degrees C The high temperature itself was not directly detrimental to mosquito infection as all mosquitoes were initially infected, but subsequently some females were able to limit viral multiplication and/or dissemination Elevated maintenance temperatures enhanced the expression of modulation, and elevated larval rearing temperatures selected for those females with this trait This is the first report of an inverse relationship between temperature of extrinsic incubation within the range of 25 degrees-32 degrees C and vector competence of a mosquito for an arbovirus

Sulfur and nitrogen mineralization in soils compared using two incubation techniques

Abstract: Net mineralization of sulfur and nitrogen was studied in three Canadian Prairie soils using two commonly used incubation methods. In the open system technique, where the soils were leached periodically II.3n11.8 m g SO 2m 4n-S g m1nsoil was mineralized in 17 weeks. Little mineralization or a net immobilization of sulfur (from 1.4 to 1.3 m g SO 2m 4-S g m1nsoil) was observed in a closed system where the soils were left undisturbed throughout incubation. Changes in the specific activity ofn 35S-labelled soil solution sulfate during the closed incubation indicated that mineralization-immobilization processes were occurring simultaneously resulting in minimal net changes in CaCl 2-extractable SO 2m 4nconcentrations. The amounts of mineralized nitrogen (32.6n57.8 mg N g m1nsoil) were found to be independent of the incubation method employed.

Crocodylus johnstoni in the McKinlay River Area N. T, VI.* Nesting Biology

Abstract: In the McKinlay River area most female C. johnstoni mature at 74-78 cm snout-vent length (SVL), and 11-14 years of age, whereas maies are about 87 cm SYL and 16-17 years of age. Adult sex ratios in the field are lM:3-4F. There is a well defined, brief nesting period in late August and early September, and the nests are typical 'hole' nests excavated in sand or other friable substrates close to permanent water. Mean clutch size is 13.2 ± 3.2 eggs (± SD) and mean egg dimensions are: length 6.64 ± 0.26 cm, breadth 4.19 ± 0.19 cm and weight 68.2 ± 8.0 g. There is a variable but significant increase in egg size with clutch size, and large clutches of large eggs tend to be laid earlier in the nesting season than small clutches of small eggs. From 2 to 4% of eggs are infertile. Nest temperatures show considerable daily variation and baseline levels differ between shaded and exposed nest sites. Incubation times are temperaturedependent and range from 9 to 14 weeks. Females excavate nests at hatching time, but attend the nests little, ifat all, during incubation. Hatchlings are 11.2 ± 0.5 cm SVL and weigh 42.0 ± 6.1 g. Formulae for predicting egg and hatchling dimensions from each other are presented. A preliminary method for aging C. johnstoni embryos is described. Artificial incubation at 26°, 30° and 34°C, respectively, resulted in 0, 63% and 21% survival; at 26 and 34°C physically deformed embryos were common. Hatching success is correlated with the age at which eggs are transported to incubators. Sex determinantion is influenced by incubation temperature, and at temperatures we tested between 26 and 34°C, females predominated; males were produced at 31-32°C. Histological examination of females from high-temperature incubation (34°C) indicated slight hermaphroditic tendencies in two of 35 animals examined; their status remains to be clarified. The temperature-sensitive period for sex determination appears to be between 20 and 57 days of age (30°C equivalent ages), but this may well vary with incubation temperature, as in Alligator mississippiensis. Egg losses due to predators (particular varanid lizards) were estimated as 64%, although they may have been increased by our interference with nests. Eggs are also lost to flooding and overheating, and a 60-70% annual egg mortality may be common. In one experiment, hatchling mortality was estimated at 98% within the first year. An egg and/or hatchling harvest balanced by a proportional return to the wild of raised 1-year-olds (5% and 10% of eggs and hatchlings collected respectively) is a potential strategy through which sustained-yield harvesting could be introduced into a conservation-management program.

Calcium regulation of the secretion of α-amylase isoenzymes and other proteins from barley aleurone layers.

Abstract: The effect of calcium on the secretion of α-amylase (EC 3.2.1.1) and other hydrolases from aleurone layers of barley (Hordeum vulgare L. cv. Himalaya) was studied. Withdrawal of Ca2+ from the incubation medium of aleurone layers preincubated in 5 μM gibberellic acid (GA3) and 5 mM CaCl2 results in a 70–80% reduction in the secretion of α-amylase activity to the incubation medium. Agar-gel electrophoresis shows that the reduction in α-amylase activity following Ca2+ withdrawal is correlated with the disappearance of group B isoenzymes from the incubation medium. The secretion of isoenzymes of group A is unaffected by Ca2+. The addition of Ca2+ stimulates the secretion of group-B isoenzymes but has no measurable effect on either the α-amylase activity or the isoenzyme pattern of aleurone-layer extracts. Pulse-labelling experiments with [35S]methionine show that Ca2+ withdrawal results in a reduction in the secretion of labelled polypeptides into the incubation medium. Immunochemical studies also show that, in the absence of Ca2+, α-amylase isoenzymes of group B are not secreted into the incubation medium. In addition to its effect on α-amylase, Ca2+ influences the secretion of other proteins including several acid hydrolases. The secretion of these other proteins shows the same dependence on Ca2+ concentration as does that of α-amylase. Other cations can promote the secretion of α-amylase to less and varying extents. Strontium is 85% as effective as Ca2+ while Ba2+ is only 10% as effective. We conclude that Ca2+ regulates the secretion of enzymes and other proteins from the aleurone layer of barley.

Effect of influenza A virus on leukocyte histamine release.

Abstract: Viral respiratory infections provoke asthma in many patients. In the following study we examined the effect of an in vitro incubation of influenza A on leukocyte histamine release. After incubation with a live influenza A (H3N2) virus, calcium ionophore A23187 (0.5, 1.0, and 1.5 microgram/ml)-induced leukocyte histamine release (HR) was enhanced (p less than 0.05). This effect was also found with heat- or ether-inactivated virus. Similarly, influenza A-exposed leukocytes had augmented leukocyte HR during subsequent incubation with ragweed AgE. Incubation of the leukocyte suspension with interferon (800 IU/ml) for 24 hr was also associated with enhanced HR to ragweed AgE. In contrast, interferon did not alter the calcium ionophore A23187 HR. Therefore, although interferon may mediate the enhanced leukocyte HR when ragweed AgE is the inciting stimulus, it does not change HR to the calcium ionophore.

The rhythm of incubation from egg laying to hatching in Mountain White-crowned Sparrows

Abstract: The rhythm of incubation in Mountain White-crowned Sparrows developed gradually during the egg laying period and a consistent pattern began with laying of the penultimate egg. Behaviors of incubating females were highly flexible and adaptable to conditions at the nest. During environmental fluctuations females partitioned their activity to provide adequate time for foraging while maintaining egg temperature (Tegg) within "normal" limits. Abilities of embryos to withstand low and oscillating temperatures allowed females to forage during the coldest hours of the day. Both air temperature (Ta) and exposure of the nest to direct sun influenced the daily rhythm of incubation activities. Mean duration of periods on and off the nest increased with increasing Ta. In some individuals, however, length of periods off decreased with increasing Ta, especially when nests were exposed to sun. Females remained on the nest at such times to prevent heating of embryos to lethal temperatures. There are indications that the onset and cessation of daily incubation activity is cued by photoperiod or light intensity.

Effects of insulin in vitro on protein turnover in rat epitrochlearis muscle.

Abstract: Rates of protein synthesis and degradation were measured in the isolated rat epitrochlearis muscle by radiotracer techniques, by using the specific radioactivity of tRNA-bound amino acid as precursor for protein synthesis. The tissue maintained linear rates of protein synthesis for 3 h of incubation in the presence of amino acids and glucose and in the absence of insulin. Under these conditions, however, the muscles were in negative nitrogen balance, with rates of protein degradation exceeding rates of protein synthesis. Under steady-state conditions of labelling, the specific radioactivities of tRNA-bound leucine, phenylalanine and valine were significantly less than their respective values in the incubation medium, at concentrations in the medium varying from 1 to 10 times those in normal rat serum. Insulin caused a dose- and time-dependent increase in tRNA-based protein synthesis rates, more than doubling rates at 5 and 50 ng of insulin/ml. At the lower, physiological, concentration of insulin, the stimulation of protein synthesis was not observed until the third hour of incubation with the hormone, whereas the rate of protein synthesis at the higher concentration was elevated during the second hour. There were no delays in the stimulation by insulin of glucose conversion into glycogen. The delayed stimulatory effects of insulin on the rate of protein synthesis brought the tissue to a nitrogen balance near zero. The presence of the hormone also prevented the increase in the rate of protein degradation seen in the third hour of incubation in the absence of the hormone. These studies demonstrate the viability of the incubated rat epitrochlearis muscle with respect to protein metabolism and sensitivity to the protein anabolic effects of physiological concentrations of insulin, and indicate that the preparation is a suitable experimental model for the study of the control of protein metabolism in fast-twitch skeletal muscle.

Parrot Eggs, Embryos, and Nestlings: Patterns and Energetics of Growth and Development

Abstract: The Psittaciformes constitute a distinct and homogeneous order, members of which lay multiple egg clutches of relatively small eggs that have prolonged incubation periods. The chicks are altricial but nevertheless grow comparatively slowly. The contents of parrot eggs contain more solids (19.4%) than is typical for altricial or semialtricial species. The rate of embryonic oxygen consumption increases throughout incubation. The relative rate of increase in $\dot{V}O_{2}$ (percent per day) and the relative growth rate of the embryo decrease throughout incubation. The relative growth rate continues to decrease after hatching. In the six parrot species I studied, total embryonic energy metabolism is greater than predicted for altricial species owing to the prolonged incubation periods. Pre-pipping and hatching levels of oxygen consumption are lower than in the same size eggs of precocial species. In Agapornis roseicollis, mass-specific metabolism decreases through the first 15 days of incubation, then is rela...

Antibody penetration into living cells. IV. Different effects of anti-native DNA and anti-ribonucleoprotein IgG on the cell cycle of activated T gamma cells.

Abstract: Normal T cells bearing receptors for the Fc portion of IgG that were incubated in anti-RNP or anti-DNA at the time of activation with phytohaemagglutinin showed different effects on this activation as determined by flow cytometric analysis of acridine orange stained cells. Incubation in anti-RNP caused an arrest in the progression from the G0 + G1 to the S + G2 phases of the cell cycle. Incubation in anti-native DNA caused activated cells to have an increase in their RNA content without a concomitant increase in their DNA content (DNA block). These effects were not seen in T cells that were depleted of T gamma cells by means of their property of forming rosettes with high affinity for sheep erythrocytes. Use of F(ab')2 fragments of either autoantibody, pre-incubation with aggregated IgG, or incubation with the respective autoantibodies in the cold effectively prevented their effect on the nucleic acid content of T gamma cells. Despite their different effect on the cell cycle both antibodies caused similar increase of 51Cr release of low affinity T cells 6 h after incubation in them. Our findings show that different anti-nuclear antibodies seem to cause different effects upon the cells they penetrate. These differences may have pathogenetic significance in the diseases where these antibodies occur.

Effect of atmosphere and duration of incubation on primary isolation of group A streptococci from throat cultures.

Abstract: The optimal incubation conditions for isolation of group A streptococci from throat cultures are controversial. Therefore, we compared the effects of aerobic and anaerobic incubations after 24 and 48 h on the recovery of group A streptococci. Throat swabs submitted to the clinical laboratory were inoculated onto duplicate 5% sheep blood agar plates, incubated aerobically or anaerobically (GasPak jar) at 35 degrees C, and examined semiquantitatively after 24 and 48 h. Group A streptococci were identified by the fluorescent-antibody technique. Of 1,040 specimens, 506 (48.6%) grew beta-hemolytic streptococci, including 200 (19.2%) group A streptococci. Group A streptococci were recovered significantly more often with anaerobic incubation than with aerobic incubation after 24 h (182 versus 138; P less than 0.001) and after 48 h (193 versus 174; P less than 0.05). Non-group A beta-hemolytic streptococci also were recovered significantly more often with anaerobic incubation after 24 and 48 h (P less than 0.001). Colony counts were not affected by the incubation atmosphere. We conclude that incubation of throat cultures in an anaerobic atmosphere is superior to incubation in air for detection of group A streptococci. The greater sensitivity of anaerobic incubation, however, may not justify the extra laboratory effort and cost required to differentiate group A streptococci from the non-group A streptococci detected as a result of anaerobic incubation. Throat cultures should be examined after 24 and 48 h, especially if plates are incubated aerobically.

Microbial activity at the sediment-water interface in halifax harbor, Canada.

Abstract: The sediment-water interface in Halifax Harbor supports a microbial population of 6.95 × 109 cells per g (dry weight). As determined by the standard technique of suspending subsamples in filtered seawater, the uptake of added glutamic acid by this population is 113.5 ng g (dry weight)−1 h−1. An alternate technique was developed to measure the heterotrophic activity of the interface over longer periods of time, using undisturbed cores with the sediment-water interface intact. Under these conditions, the microbes in the water column and the interface increased exponentially in number, with mean doubling times of 9.6 and 4.5 days, respectively. The uptake of glutamic acid by the microbial population of the interface was determined to be 12.7 ng g (dry weight)−1 h−1, almost an order of magnitude less than the uptake determined by the previous method. This indicates that substrate diffusion and competition for substrate by the microbes in the water column are important factors when considering the heterotrophic activity of the sediment microbial population. After 48 h of incubation, uptake and respiration ceased, probably due to the exhaustion of labeled substrate. Additional substrate added after 48 h of incubation was taken up at a rate similar to that measured after the first addition. It appears that the microbial population of the interface is able to respond quickly and repeatedly to relatively large nutrient additions. After 10 days of incubation, the number of “viable” cells as determined by autoradiography was much smaller than the increase in numbers as determined by direct counts. Apparently a large part of the viable population is unaffected by nutrient addition.

Serum levels of luteinizing hormone, prolactin, estradiol and progesterone in laying and nonlaying mallards (Anas platyrhynchos).

Abstract: Temporal changes of circulating serum hormones were measured to compare the reproductive endocrinology of laying and nonlaying mallards. In this study all sixteen control mallards left with their mates laid eggs, while only one of sixteen mallards stressed by daily movement into new pens, laid eggs. Serum levels of luteinizing hormone (LH), prolactin, estradiol, and progesterone were significantly lower (P<0.05) in stressed nonlaying mallards than in laying mallards over the 7-week period. Within 1 week of the rotation treatment, LH concentrations in stressed mallards averaged (ii ± SEM) 2.72 ± 0.19 nglm! and were significantly lower (P<0.05) than LH levels in the controls (3.62 ± 0.18 ng/ml). After 7 weeks, injections of luteinizing hormone releasing hormone (LHRH) induced a greater change in circulating LH levels in stressed mallards (2.1 ± 0.3 ng/ml) than in breeding control mallards (0.9 ± 0.2 ng/m!). These data demonstrate that the lack of reproduction in stressed mallards was associated with LHRH-sensitive pituitary pools of LH, despite their low concentrations of serum LH. These data suggest that the block in reproduction is a failure of the hypothalamus to produce or release releasing hormones. The serum hormone levels of the control mallards varied temporally with stages in the nesting cycle. LH levels increased with the onset of nesting activity, and showed marked fluctuations during the laying period. LH levels fell at the onset of incubation but increased after loss of clutch. Estradiol levels were highest prior to the laying of the first egg and their peak coincided with the initial nest buildingbehaviorof the females. Progesterone levels increased sharply with the laying of the 2nd-4th eggs, decreased sharply with the laying of the 6th egg, and then increased slightly at the end of the nesting cycle. Prolactin levels were initially low but gradually increased with laying and incubation activity, declined with loss of clutch, and increased again with renesting activity. Prolactin levels in the stressed mallards also increased (P<0.01) over the 7-week period, but significantly less (P<0.05) than in layers.

Altered Scrapie Infectivity Estimates by Titration and Incubation Period in the Presence of Detergents

Abstract: Summary During experiments on the purification of scrapie infectivity, changes were found in the dynamics of scrapie titration. After exposure to detergent, infectivity estimates by both endpoint titration and incubation period were altered. The addition of detergent to the diluent used in titration resulted in at least a 100-fold increase in the infectivity estimate. This suggests that the amount of scrapie in a sample, as measured by serial dilution and titration, may be underestimated to different extents, depending on the biochemical milieu of the inoculum. Membrane fractions treated with detergents before dilution exhibited longer incubation periods than untreated fractions for the same number of infectious units of scrapie. This demonstrates that detergent treatments and possibly other biochemical manipulations can cause changes in the response of the host to the inoculum that are not detectable if incubation periods alone are used to estimate scrapie ‘titre’.

Secondary Dormancy, Growth - Regulator Effects, and Embryo Growth Potential in Curly Dock (Rumex crispus) Seeds'

Abstract: Curly dock (Rumex crispus L.) seeds failed to germinate in the dark, but germinated readily in light at 15, 20, and 25 C. A secondary dormancy was induced in these seeds by 6 days of dark or light incubation at 30C (thermodormancy), by 6 days of dark incubation at 15 C, or by a prolonged soaking in -15.7 bar polyethylene glycol- 6000 (PEG) solution at 15 C in light. The secondary dor- mancy induced at 15 C was partially removed by 2 - chloro - ethylphosphonic acid (ethephon) in presence of light; however, when the dormancy was induced at 30 C, an addition of gibberellin A4 +7 (GA4 +7) to ethephon was necessary for effective removal of the dormancy. The ability of growth regulators to remove the secondary dormancy induced by prolonged dark incubation at 15 C decreased progressively in light as the duration of dark incubation increased. The water - potential studies indicate that the thermodormancy can be attributed, at least in part, to the inability of the embryonic cells to lower their water potential to a level sufficient to cause radicle protrusion. Additional index words. Water potential (seeds), seed germi - nation, ethephon, GA4 + 7.

Protein synthesis by intact Coxiella burnetii cells.

Abstract: Coxiella burnetii was isolated from persistently infected fibroblast host cells by a rapid mechanical lysis technique. Macromolecular synthesis was initiated in these otherwise dormant cells by incubation at pH 4.5. The synthesis of protein proceeded for as long as 24 h. Initiation of protein synthesis in C. burnetii was dependent upon RNA synthesis. Approximately 24 species of polypeptides were synthesized, and some of these appeared to be major synthetic products. Increases in protein biomass of 15 to 30% were calculated to occur during incubation. Inhibition of DNA synthesis affected protein synthesis after 12 h of incubation. The results suggest that although these parasitic bacteria did not grow in the axenic media devised, significant biosynthetic processes occurred.

Protein synthesis by chloroplasts during the senescence of barley leaves

Abstract: Chloroplasts were isolated from senescent leaf segments of barley (Hordeum vulgare L. var. Mozoncillo) and assayed for protein synthesis. Protein synthesis activity of the chloroplasts greatly increased after 10–20 h of incubation of leaf segments in the dark in spite of an intense degradation of chloroplast rRNA. The rise in the activity of protein synthesis was more pronounced when kinetin was present in the incubation medium. However, as deduced from SDS-polyacrylamide gel electrophoresis of the products, different proteins were synthesized under the two conditions of incubation of the leaf segments. The activity of protein synthesis of the chloroplasts decreased during the first hours of incubation of the leaf segments in the light. Cutting and incubation in the dark of the leaf segments enhanced the synthesis of a few proteins also formed by chloroplasts in attached senescing leaves. Hormone and senescence treatments changed the type and the rate of the protein synthesized by chloroplasts, which suggests that hormones may control senescence through a modulation of the protein synthesized by the chloroplasts.

Volume regulation in the red coelomocytes ofGlycera dibranchiata: An interaction of amino acid and K+ effluxes

Abstract: Glycera dibranchiata red coelomocytes regulate cell volume during hypoosmotic stress by reducing the intracellular concentration of certain osmotically active solutes, principally free amino acids (FAA) and K+. The volume regulatory mechanisms found in other species, especially the bivalve molluscs, are sensitive to changes in external divalent cation concentrations and the depletion of intracellular ATP. TheGlycera coelomocyte volume regulatory mechanism also requires divalent cations, but the requirement is not specific; either Ca2+ or Mg2+ will suffice. Deletion of both Ca2+ and Mg2+ from the external medium caused leakage of both FAA and K+ from the coelomocytes. The presence of the cellular ATP synthesis inhibitor DNP potentiated the volume regulatory response. The enhanced volume regulation was caused by a potentiated decrease of intracellular K+ content while the salinity induced FAA efflux was unaffected. Incubation of the coelomocytes with ouabain did not affect volume regulation, indicating that control of intracellular K+ during hypoosmotic stress does not depend on the Na+−K+-ATPase. Thus, the volume regulatory mechanisms in theGlycera coelomocytes utilize two types of solute, FAA and K+, and separate permeability mechanisms that interact to control the solute contents during hypoosmotic stress.

Endocrine changes in the incubating and brooding turkey hen.

Abstract: Turkey hens were allowed to incubate eggs and to hatch and rear young. Plasma prolactin (Prl) levels increased prior to the start of continuous incubation and rose sharply as incubation progressed to reach a peak of 1178.2 +/- 221.8 ng/ml (mean +/- SEM) just before hatching. Prl levels then fell precipitously before the hens left the nest, and returned to preincubation levels (36.8 +/- 3.4 ng/ml) by the time the poults were 2 weeks old. These results show that the high plasma concentrations of Prl found during incubation are not initiated or maintained only by the stimulus of nesting. We suggest that the decline in Prl levels at the end of incubation could be related to the pipping and hatching of eggs, and the consequent shift to maternal behavior. Plasma growth hormone (GH) levels were significantly increased in hens which were brooding poults, but not in hens incubating eggs. An elevenfold, 1-day increase in plasma GH was observed immediately after the hens left the nests. Mean plasma GH levels rose from 12.0 +/- 4.7 ng/ml on the day that the hens left the nests to 133.0 +/- 32.0 ng/ml on the following day, and then declined to 23.1 +/- 9.6 ng/ml after an additional day. There were no significant changes in plasma thyroxine levels during laying, incubation and brooding. Plasma glucose concentration was significantly depressed during incubation.