Showing papers on "Incubation published in 1989"

Incubation period of AIDS in San Francisco.

Abstract: In a closed population, the distribution of AIDS diagnoses over time is the convolution of the distributions of human immunodeficiency virus (HIV) infections and the incubation period. This has motivated estimates of the infection distribution, assuming known diagnosis and incubation distributions, but the usefulness of this method is limited by uncertainty about incubation. The large amount of information on the distribution of HIV infections in San Francisco's gay community suggests the opposite approach--estimating the incubation distribution, assuming known infection and diagnosis distributions. A non-parametric implementation of this strategy produced an estimate with a median at 9.8 years, increasing hazard rates, and less uncertainty than previous estimates.

The genomic identity of different strains of mouse scrapie is expressed in hamsters and preserved on reisolation in mice.

Abstract: 263K is the most widely used strain of agent in scrapie research because it produces very short incubation periods in golden hamsters and exceptionally high infectivity titres in clinically affected brain. 263K is also remarkable in having a very low pathogenicity for mice. Evidence is presented that 263K originated as a mutant that was strongly selected on passage in hamsters. Seven new passage lines have been established in hamsters using well characterized strains of mouse scrapie representing the 'drowsy goat' and SSBP/1 families of scrapie strains, and one natural scrapie source. Considerable differences between scrapie strains were found in hamsters using incubation period criteria alone. There was evidence that the parent strain of 263K might be 79V or a strain like it in the 'drowsy goat' family. Four of the hamster passage lines were established from scrapie strains that had been cloned in mice. Reisolates in mice were compared with original strains. By the criteria used, two of the reisolates were the same as the original strains. Two others were mutants with incubation periods longer than those of their parental strains but the mutants were different from one another. It is concluded that passage between mice and hamsters can select mutants that would otherwise be lost but there is also clear evidence that the genotypic identity of some scrapie strains is preserved on passage between different host species. These findings are important in the search for the putative nucleic acid genome of the scrapie agent.

Incubation temperature has long-term effects on behaviour of young Pine snakes ( Pituophis melanoleucus )

Abstract: Eggs of pine snakes (Pituophis melanoleucus) were incubated at constant temperatures of 21°, 23°, 26°, 28°, 30° and 32° C to determine behavioural differences as a function of incubation temperature. For all behavioural and physiological measures hatchlings from medium incubation temperatures (26°, 28°) performed tests better than those hatchlings from eggs incubated at low temperatures (21°, 23°). For some behavioural tests hatchlings from eggs incubated at high temperature (30°, 32°) performed less well than medium temperature hatchlings. These differences were not due to ambient temperatures or age of testing since these were held constant. Some of the behavioural differences persisted for 24 weeks.

Nutritional Characteristics of a Mixotrophic Nanoflagellate, Ochromonas sp.

Abstract: Autotrophic and heterotrophic growth characteristics of a nano-flagellate were investigated. The flagellate,Ochromonas sp., was isolated from the northern Baltic Sea. Autotrophic growth was poor. Axenically pregrown flagellates did not increase significantly in cell number during incubation in different inorganic media. The number of flagellates remained constant 3–5 weeks in cultures kept in the light (100μmol m−2 sec−1), whereas in the dark, a high mortality rate was found. Uptake of inorganic14C into an acid-stable fraction indicated thatOchromonas had a functional photosynthetic apparatus. Heterotrophic growth in both liquid medium and medium containing bacteria was rapid. The maximum growth rate corresponded to a generation time of 5.3 hours. Light had no effect on heterotrophic growth. Cells pregrown onEscherichia coli minicells survived without additional bacteria as food when kept in the light, but rapid death occurred in darkness. In conclusion, heterotrophy is the major mechanism to support growth in this species ofOchromonas, but under poor environmental conditions photoautotrophy might be a strategy for survival rather than growth.

Phosphorylation-dependent activation of the adenovirus-inducible E2F transcription factor in a cell-free system.

Abstract: Adenovirus infection induces a large increase in the DNA binding activity of a cellular transcription factor that is utilized by the viral E2 promoter and termed E2F. Using cell-free extracts, we have developed an assay for the in vitro activation of DNA binding activity of E2F. E2F activity is undetectable in HeLa extracts but upon incubation with a fraction from adenovirus-infected cells, there is an ATP-dependent increase in E2F DNA binding activity. This increase does not occur using an equivalent fraction from dl312 (E1A-)-infected cells. Incubation of E2F with phosphatase inactivates E2F binding activity. Incubation of the phosphatase-inactivated E2F with an infected cell fraction restores E2F activity as does incubation with a known protein kinase. In contrast, incubation with an extract from mock-infected cells does not restore activity. We conclude that the DNA binding activity of E2F is regulated by phosphorylation in an E1A-dependent manner.

Characteristics of unturned eggs: Critical period, retarded embryonic growth and poor albumen utilisation

Abstract: 1. The physiological effects of egg turning during incubation are described. 2. There was a critical period for turning, from days 3 to 7 of incubation, which affected hatchability, embryo growth and utilisation of extra-embryonic fluids. 3. Failure to turn eggs retarded formation of allantoic and amniotic fluids, restricted alumen uptake and retarded growth of the embryo, but only after day 12 of incubation.

Sex Determination and Sex Ratios in Crocodylus palustris

Abstract: Incubation temperature determines sex in the mugger crocodile, Crocodylus palustris . Exclusively females are produced at constant temperatures of 28.0°C through 31°C. At 32.5°C, only males are produced. Both sexes are produced in varying proportions at 31.5, 32.0, and 33.0°C. Embryo survival is not affected within this range, but developmental rate and total incubation time are strongly temperature dependent. In natural nests laid in breeding enclosures, cool incubation temperatures produced only females whereas males were produced only in warm nests. Clutch sex ratios were female or male biased. Yearly sex ratios (=percent male) varied from 0.05 to 0.58; overall sex ratio during six nesting seasons was 0.24 (1 male: 3 females). Sex ratio and incubation time vary with nest location and temperature in a manner consistent with the constant temperature results. Incubation time decreases with increasing incubation temperature, and is an accurate predictor of sex ratio in the field and laboratory. To date, temperature-dependent sex determination (TSD) has been reported in five species of Crocodylus and in three species of Alligatorinae; but the TSD patterns in these groups differ. The TSD pattern of C. palustris is similar to that of C. porosus . Nesting in C. palustris is synchronized with the seasonal availability of thermal regimes suitable for incubation. Resultant sex ratios are a consequence of when and where eggs are laid. Early nests are located in warm, sunny sites; in contrast, late season nests are located in the shade. An egg transplant experiment demonstrated that sex ratios could be altered by simple manipulations of nest temperatures in the field. The adaptive significance of TSD in crocodilians may relate to the influence of incubation temperature on various hatchling attributes, particularly growth.

Primary structure of prion protein may modify scrapie isolate properties.

Abstract: Scrapie is an infectious neurodegenerative disease caused by unusual pathogens called prions, in which no scrapie-specific nucleic acid has been detected to date. The only known component of the prion is the scrapie isoform of prion protein (PrPSc), which is encoded by a host gene (Prn-p). Isolates of scrapie agent were prepared by passage of infectivity through inbred strains of mice that differ in scrapie incubation time and produce PrPSc molecules differing by two amino acids. Both the length and variability of the incubation period were increased by inocula containing allogeneic PrPSc. For example, Prn-pb I/Ln mice inoculated with scrapie isolate passaged through Prn-pa NZW mice had incubation times of 283 +/- 21 days compared with a 193 +/- 6 day incubation time seen with isolate passaged once through isologous I/Ln mice. No further shortening of incubation time was observed following further isologous passage. NZW incubation times were prolonged by inoculation with prions from I/Ln mice. Results from (NZW x I/Ln)F2 mice and from using inocula from donors isologous for Prn-p but otherwise allogeneic with respect to the recipient suggest that the primary structure of PrPSc is responsible for these incubation time results. Incubation times in (NZW x I/Ln)F1 mice were constant regardless of the passage histories of the scrapie isolates and were equivalent to those of I/Ln mice inoculated with I/Ln prions, contending that prolongation of scrapie incubation time by the prion incubation time gene Prn-i is fully dominant. I/Ln incubation times longer than those in F1 hybrids may reflect a reduced efficiency of allogeneic PrPSc in initiating disease. Although some investigators propose that differences in behavior among scrapie isolates reflect host selection and argue for a nucleic acid genome, we suggest that the variation observed among our scrapie isolates is epigenetic, reflecting host-directed differences in the amino acid sequence of PrPSc.

Induction of developmental abnormalities in larval goldfish, Carassius auratus L., under cool incubation conditions

Abstract: Compared with incubation at a constant 22° C, exposure of goldfish embryos and larvae to 13° C, under a variety of thermal protocols, caused increased frequencies of abnormal development and, in some cases, reduced survival to hatching. The low-temperature incubation conditions were particularly deleterious when eggs were incubated at 13° C from the outset, regardless of the temperature at which the donor female ovulated and the eggs were fertilized. Significantly higher frequencies of developmental abnormalities were also noted when embryos were transferred from 22°C to 13°C at 6, 24, 128 and, in one case, 175 h after fertilization. In three of five experiments, subjecting embryos and larvae to diel fluctuations between 22 and 13° C, with a 5-h hold at the lower temperature, caused an increase in development abnormalities. These results demonstrate that the thermal requirements of goldfish embryos and larvae necessitate a delay in ovulation and spawning until water is sufficiently warm. Developmental abnormalities can be induced by exposure to cool (13° C) conditions, at least up to the time that swimbladder inflation occurs.

Effects of incubation temperature on growth and development of embryos ofAlligator mississippiensis

Abstract: Eggs ofAlligator mississippiensis were incubated at 30 °C and 33 °C throughout incubation up to hatching. Every four days several eggs were opened and the albumen, yolk and extra-embryonic fluids removed and weighed. The embryo was removed and fixed prior to being staged, weighted and measured for various morphometric criteria. Development at 33 °C was accelerated compared with 30 °C in terms of yolk and albumen utilization and embryo growth. Significant losses in yolk mass did not occur until stage 22 at 33 °C but occurred at stage 18 at 30 °C. Different patterns in growth were observed in embryos at the two temperatures at similar morphological stages: between stages 18 and 22 embryos at 33 °C were smaller (in mass and length) compared with embryos at 30 °C despite being morphologically similar. The differences in growth and physiology between embryos at 30 °C (females) and 33 °C (males) were dependent on incubation temperature but not sex. Incubation at 33 °C accelerated both growth and development inAlligator; initially morphogenesis was accelerated by the higher temperature but later, growth rate was accelerated.

Importance of sub-embryonic fluid and albumen in the embryo's response to turning of the egg during incubation.

Abstract: 1. The effects of removal of sub-embryonic fluid and albumen on the development of the fowl embryo were investigated. 2. A deficiency of sub-embryonic fluid on day 7 of incubation resulted in a reduction in the volume of the yolk sac and of allantoic fluid, and a reduction in the mass of the embryo later in incubation. 3. A deficiency of albumen on day 3 of incubation led to a reduction in allantoic fluid and embryo mass after day 12 incubation. 4. The results suggest that the physiology of embryos in unturned eggs is better modelled by eggs deprived of albumen than by eggs deprived of sub-embryonic fluid.

Female nutritional state affects the rate of male incubation feeding in the pied flycatcher Ficedula hypoleuca

Abstract: Male pied flycatches Ficedula hypoleuca regularly feed their mates during incubation. By experimentally supplying some females with extra food we studied how the female's nutritional state affected her incubation schedule and the rate at which her mate fed her. Females that received extra food spent more time on the nest and shorter periods away from it, compared with control females. This suggests that nest attentiveness is governed by the amount of energy available to the female. When females reccived extra food, males decreased their rate of incubation feeding. They also did so in response to increasing ambient temperatures, whereas incubation schedules were unaffected. We, therefore, conclude that our results support the “female nutrition hypothesis”, i.e., that the food provided by the male constitutes a significant nutritional contribution to the incubating female.

Differential phytotoxicity among species and cultivars of the genus Brassica to wheat

Abstract: Classhouse and laboratory studies were conducted to investigate the effect of microorganisms on the activity of water-soluble phytotoxins from Brassica residues, and on the persistence of the phytotoxins Warm temperatures (20–24°C) and long incubation periods (20 to 40 days) were conductive to reduced phytotoxicity while low temperatures (0–4°C, regardless of incubation time), or short incubation time (regardless of temperature) resulted in levels of phytotoxicity similar to that found without incubation The removal of microbial populations by micro-filtration resulted in the maintenance of phytotoxicity, regardless of the incubation conditions The quantity of residues or extracts from residues used in a pot experiment and the soil type (sand or clay soil) determined the degree of phytotoxicity Generally, the greater the quantity of residues or extracts, the greater the toxicity, with residues being more toxic than extracts from the same rate of residue These observations agree with the general literature that the level of toxicity is determined by the quantity of residue present, and the rate of decline in the toxicity of water-soluble toxins is dependent on the microbial populations present, and their level of activity

An endogenous digitalis-like factor derived from the adrenal gland: studies of adrenal tissue from various sources.

Abstract: We have previously reported that the adrenal gland is the probable origin of the digitalis-like immunoreactive material (DLI) present in the plasma of rats and other species which have never received cardiac glycoside drugs. The present study demonstrates that adrenal glands removed from rats and then chopped release an immunoreactive digitalis-like material into a serum-free minimal incubation medium. HPLC studies indicated that this immunoreactivity was not homogeneous. Since such material may be a mammalian steroidal ligand for the glycoside receptor on the sodium pump, we investigated whether release of this material could be inhibited by antagonizing the conversion of cholesterol to pregnenolone through the addition of aminoglutethimide (AG) to the incubation medium. Our observations indicate that this manipulation successfully inhibited pregnenolone production during both of our 2-h serial incubation periods. However, in neither incubation period was AG able to inhibit the release of DLI in...

Mineralization of nitrogen in the presence of a nitrification inhibitor

Abstract: The influence of a nitrification inhibitor, dicyandiamide (DCD). on nitrogen processes was studied by incubation of soil with ammonium sulfate labelled with 15 N. During the early days of the incubation, the amount of nitrate-N was higher in the control than in the treatment with DCD, but after 6 months, there was no significant difference. The decrease in nitric-N attributable to dicyandiamide, resulted from selective inhibition of the nitrification process. Moreover, an increase in the immobilization of the N from the labelled ammonium was observed, while the mineralization of N from the soil organic compartments was of similar magnitude in both treatments.

Reproductive ecology of three ocypodid crabs II. Incubation sites and egg mortality

Abstract: Mortality of eggs during incubation was estimated for three ocypodid crabs,Scopimera globosa, Ilyoplax pusillus andMacrophthalmus japonicus, and the influence of incubation sites was discussed. These crabs all lived in isolated burrows and fed on sediments during day time low tide.S. globosa andI. pusillus inhabited the upper intertidal sandflats, whereasM. japonicus inhabited the lower intertidal mudflats. Females of bothS. globosa andI. pusillus remained in their plugged burrows without feeding throughout incubation and the mortality of eggs was low despite large broods relative to body size. On the other hand, females ofM. japonicus fed actively on surface mud during incubation and the mortality of eggs was high despiite small broods relative to body size. InS. globosa andI. pusillus, the ovaries of ovigerous females were small until egg-hatching, whereas inM. japonicus, the ovaries grew rapidly during incubation and females were able to produce consecutive broods. I conclude that incubation of eggs in burrows may be advantageous in species which inhabit the upper interidal sandflats, even though the crabs cannot forage during incubation, since otherwise their eggs would be exposed to strong heat stress and desication during the summer. Furthermore, such species may produce few large broods because of less frequent interruption of feeding than that associated with production of many small broods.

RQ of benthic marine invertebrates

Abstract: This study investigated an incubation method which employed simultaneous measurement of CO2 production and O2 consumption rates to calculate the RQ (respiratory quotient; CO2 production rate: O2 consumption rate) of individual benthic marine invertebrates. Carbon dioxide production rates were calculated from changes in CO2 concentration determined using seawater pH. O2 consumption rates were calculated from changes in O2 concentration with a correction applied for O2 flux across the air/water interface due to gaseous exchange. Species examined were Triphyllozoon sp. cf. moniliferum (MacGillivray 1860), a bryozoan; Herdmania momus (Savigny), a solitary ascidian; Poneroplax albida (Blainville 1825), a chiton; and Haliotis roei (Gray 1826), an abalone. Six individuals of each were collected on 14 November 1985 from the limestone walls of a cave in a nearshore reef off Marmion, Western Australia. After acclimation for 6 h in experimental conditions, rates of CO2 production and O2 consumption were measured. A minimum period of 4 h was required to obtain consistent RQ values for each species. The standard error (SE) of the (calculated) RQ ratio was 14 to 33% of the mean in incubations of 4 h, and less than 14% in incubations of 4 to 12 h. The RQ is commonly used as an indicator of unknown catabolic substrates by comparing it with biochemically determined limits for known substrates. This study provides a strong argument against using the RQ of individual animals to draw any conclusions about catabolic substrates. Unexplained variation in the components of the RQ of an individual, measured over short time periods, and the potential involvement of stored reserves in catabolism, over longer time periods, obscure the relationship between the RQ of individual animals and the ratio's biochemically determined limits.

Sequential sampling of plasma cholinesterase in mallards (Anas platyrhynchos) as an indicator of exposure to cholinesterase inhibitors

Abstract: The use of sequential measurements of plasma cholinesterase (ChE) activity for monitoring exposure to organophosphorus pesticides was investigated in the mallard (Anas platyrhynchos). At the onset of incubation, birds were assigned to treated (400 ppm methyl parathion in the diet), pair-fed (same daily food allotment on a g/kg/d basis as consumed by the treated bird of the pair), control or nonincubating control groups. Blood samples were collected weekly during egglaying and every 3 d during incubation periods. Both plasma and brain samples were taken on day 24 of incubation. Plasma ChE was more variable than brain ChE among the birds and there were no significant correlations (p > 0.05) between plasma and brain samples within treatment groups. Reduced food consumption during incubation did not affect plasma ChE activity (p = 0.77). Birds that abandoned their nests had significantly increased (paired t = -2.39, d.f. = 9, p < 0.05) ChE activity at the time of abandonment. There were significant differences (p < 0.01) in plasma ChE activity between untreated birds, but within-bird variation was 2 and 11 times less than betweenbird variation during egg-laying and incubation, respectively. Methyl parathion significantly (p < 0.0001) reduced plasma ChE activity. Measurement of plasma ChE activity provides a noninvasive, nonlethal technique for assessing the exposure of animals to ChE inhibitors.

The temperature dependence of embryonic and larval development in Protonemura intricata (Plecoptera: Nemouridae)

Abstract: SUMMARY. 1. Egg development and larval growth of Protonemura intricata (Ris, 1902) (Plecoptera: Nemouridae) were studied in the laboratory and in the Breitenbach, a small stream-in Germany (F.R.G.). 2. The mean number of eggs in batches collected from the field was 627 (S=314). 3. Mean batching success in the laboratory was 60–100% at 2–18°C. Cumulative hatch in individual batches could be described by asymmetrically sigmoid curves. The length of the hatching period was positively correlated with the length of the incubation period. 4. The incubation period of I', intricata normally consists of an initial dormancy followed by subsequent development. The length of embryonic development (Y. days) is strongly inversely temperature (T, °C) dependent and can be described by the equation: 5. The length of dormancy is dependent on oviposition dale, and is shorter the later that the eggs are laid. It also depends on temperature during incubation and is increased by rising temperatures. As a consequence, larvae hatch more or less synchronously in the field during autumn. Total incubation period, i.e. dormancy and actual development, exhibits a complex dependence on both incubation temperature and oviposition date. Under constant laboratory temperatures, a late sharp fall in temperature can terminate dormancy earlier. 6. Photoperiod probably induces dormancy and may already act on the last larval instars of the parent generation. The dormancy of P. intricata is classified as an oligopause (Muller. 1970, 1976). 7. In the laboratory. P. intricata larvae from early batches with long dormancy grew faster than larvae from late batches with direct development. Final size was the same in both cases. This acted against the population synchrony induced through egg dormancy. Benthos samples suggest the same in the field. 8. Avoidance of the suboptimal summer conditions in streams by the cold stenothermous P. intricata is suggested to partly explain the success of the species, which contributes more to total emergence biomass than do other Plecoptera in the Breitenbach.

Egg Temperatures and Parental Behavior during the Transition from Incubation to Brooding in the American White Pelican

Abstract: -I monitored incubation behavior and egg temperatures (Ti) recorded with agarfilled eggs before and during hatching in American White Pelicans (Pelecanus erythrorhynchos) to determine if embryos were subject to more extreme temperature conditions at this critical period than at other stages of development. Before pipping, mean Te was 35.2?C. It did not change significantly in the presence of a pipped egg or newly hatched young. Diurnal variations in T, were absent prior to hatching, despite a slight but significant correlation between Te and ambient temperature (Ta). A small drop in Te (about 2?C) occurred in early morning at nests containing one newly hatched young. T, minima at these nests correlated significantly with Ta. Range and variance in T, increased with onset of pipping and again when the first young hatched. Increasing variability in T, was associated with progressive changes in relevant incubation behaviors. Eggs exposed by the removal of foot webs at the onset of pipping were subject to cooling when the parent raised to preen or settled with an egg protruding from the nest. The embryos were exposed to greater temperature extremes during the pipped-egg stage than in other stages. By calling when cold, embryos in pipped eggs may influence parental behavior and hence their own thermal environment. Received 1 March 1988, accepted 29 July 1988. NEST and egg temperatures during incubation have been examined in a wide range of species (Drent 1973, Webb 1987). Recent studies (e.g. Grant 1982, Zerba and Morton 1983, Morton and Pereyra 1985) have provided detailed egg temperature data from continuous or frequent recordings within eggs throughout the 24-h day and, in some studies, over most of the incubation period. In the Pelecaniformes, egg temperatures have been recorded for two tropical species, the Red-tailed Tropicbird (Phaethon rubricauda) and Red-footed Booby (Sula sula) (Howell and Bartholomew 1962, Whittow and Grant 1985) and data have been obtained for a temperate population of the Double-crested Cormorant (Phalacrocorax auritus) (Van Scheik 1985). Apparently nothing has been reported on egg temperatures for the American White Pelican (Pelecanus erythrorhynchos). Most studies of egg temperatures have been confined to the prehatching stages of incubation. Less is known about temperatures subsequent to the onset of pipping (Webb 1987). The period between pipping and hatching is particularly important and is associated with a range of changes in gaseous exchange and metabolic rate (Vleck et al. 1980, Whittow 1980). In the altricial White Pelican, as in many precocial species, this period also marks the onset of embryonic vocalizations, which make it possible for the embryo, still confined within the egg, to influence its own environment through the incubation behavior of the parent (Evans 1988, in press). A potentially adaptive function of communication between embryo and parent during the transition from incubation to brooding is to ensure the parent maintains suitable incubation temperatures for the pipped egg(s). In the White Pelican, cooling of a pipped egg is a potent stimulus that elicits embryonic calls. In the laboratory I found that pelican embryos could thermoregulate behaviorally (by calling when cold) for periods of up to 5 h of otherwise continuous cold stress (Evans in press). Cooling of the pipped eggs from 38 to 37?C was sufficient to initiate calling, which then increased as cooling continued down to 33?C. Calling normally ceased in under 1 min when warmth was reapplied, regardless of the temperature reached by the cooled egg. This degree of behavioral sensitivity to temperature coupled with the long persistence of the reaction suggests that the pelican embryo is well-equipped after pipping to regulate its thermal environment by communication with the incubating parent. An obvious objection to the hypothesis that communication from embryos influences the 26 The Auk 106: 26-33. January 1989 This content downloaded from 207.46.13.122 on Fri, 01 Apr 2016 04:44:13 UTC All use subject to http://about.jstor.org/terms January 1989] Pelican Egg Temperatures 27 incubation environment during the pipped egg stage is that, prior to pipping, parents evidently incubate the eggs adequately without recourse to specific vocal communication from the embryos. For the embryonic communication hypothesis to have any biological relevance, it is necessary to show that incubation behavior and thermal or other relevant conditions at the nest normally change as pipping and hatching proceed. In particular, I will show that pipped eggs become exposed to a range of temperatures below those normally experienced prior to pipping, and that these temperatures are at least as low as those known from laboratory work to elicit a strong level of calling. Evidence for the occurrence of low incubation temperatures during the pipped-egg stage is scant. At the onset of pipping in some Charadriiformes, however, changes in incubation behavior which can lead to partial neglect and lower temperatures of the last-hatched egg have been documented (Beer 1962, Drent 1970, Norton 1972). In the Herring Gull (Larus argentatus), hatching of the first 2 eggs can result in a decrease in parental incubation attentiveness and a drop in temperature of the remaining pipped egg by as much as 12?C (S. Lee pers. comm.). In pelicans, as in gannets and boobies (Nelson 1978), parents normally incubate by placing the eggs under the inner webs of their feet. With the onset of pipping of the first egg, there is an abrupt change in incubation mode. Parents elevate the feet and shift both eggs back between the legs where incubation is completed and brooding of the newly hatched young begun (Evans 1988). Details of other relevant changes in incubation or associated behavior of pelicans at this stage, and any effects of the changing mode of incubation on the temperature of unhatched eggs at the nest, are un-

Glucagon-induced changes in fructose 2,6-bisphosphate and 6-phosphofructo-2-kinase in cultured rat foetal hepatocytes.

Abstract: The sensitivity of 6-phosphofructo-2-kinase to glucagon and cyclic AMP was studied during the perinatal period. In liver homogenates from foetal and neonatal rats, incubation with cyclic AMP produced inactivation of 6-phosphofructo-2-kinase 3 h after birth. The maximal effect was obtained 12 h after birth. In primary cultures of hepatocytes from 22-day-old foetuses, glucogon induced an inhibition of 6-phosphofructo-2-kinase that required 45 min to reach the half-maximal effect. Cycloheximide prevented the glucagon-induced changes in this activity from cultured foetal hepatocytes. These results suggest that the adult form of 6-phosphofructo-2-kinase is rapidly induced after birth, probably by the hormonal changes that occur in this period.