Changes in the adrenal steroidogenic responsiveness of the mallard duck (Anas platyrhynchos) during early post-natal development

1. Plasma concentrations of corticosterone (B), aldosterone (Aldo) and deoxycorticosterone (DOC) were measured in mallard ducklings immediately before and after exposure to acute immobilization stress. 2. Except for transient declines in B and DOC between the 4th and 14th days after hatching, the resting concentration of each hormone did not change significantly during post-natal development. 3. The stress-induced in Aldo was maximal at hatching while maximal increases in B and DOC did not occur until one day later. 4. Thereafter the magnitude of the stress-induced increases in the concentrations of all of the hormones decreased steadily and on the 21st and 28th days after hatching only B increased significantly in response to stress.     

Dynamics of the fecal corticosterone content in males of red,gray-sided,and bank voles (<Emphasis Type="Italic">Myodes</Emphasis>, Rodentia,Cricetidae) upon sexual maturation

The dynamics of the corticosterone content in feces of males are analyzed in red (M. rutilis), graysided (M. rufocanus), and bank (M. glareolus) voles. The ontogenetic dynamics of the corticosterone content in feces of these species collected on the 20th and 40th days are shown to depend differently on the month of their birth. At the same time, the fecal corticosterone content is similar in males of all species that originated from litters with various sizes and shares of males in it. The fecal corticosterone content in the 40-day-old animals is related to the month of birth for all three species. The species-specific features of adrenal activity are found on the 20 and 40 days after the birth of animals. The males of the May and August generations have the highest corticosterone level in feces. The fecal corticosterone content in the red vole males also correlates with the social environs; in addition, socially isolated single males have a higher rate of maturation. The fecal corticosterone in the gray-sided vole males related to the season of start maturation and to the date of birth negatively correlates with sexual maturation. The mature males of those species are found only among the spring–early summer generation. Thus, population factors are important only for maturing males that were born in the current year. Moreover, sexual maturation at a high population density is accompanied by a smaller decrease in the adrenocortical activity.     

A correlated stereological and functional studies on the long-term effects of ACTH on rat adrenal cortex

The aim of the study was to investigate the effect of prolonged ACTH administration on quantitative structural changes of the rat adrenal cortex and on function of its cells with particular emphasis on correlation of the results of biochemical estimations with stereologic parameters. Daily injections of 20 micrograms ACTH (Synacthen, Depot) for 35 days results in a marked enlargement of the cortex due to an increase in the volume of all the zones. This increase depends upon hypertrophy and hyperplasia of parenchymal cells. At day 21 of experiment the number of parenchymal cells markedly decreased if compared with day 14, the lost of cells being observed mainly in the zona reticularis. Prolonged ACTH treatment only insignificantly changed serum corticosterone concentration and--if calculated per mg of adrenal weight--did not change adrenal corticosterone concentration and 11 beta-hydroxylase activity and decreased corticosterone output by adrenal homogenate. If expressed per adrenocortical cell or per pair of glands, ACTH increased corticosterone concentration and 11 beta-hydroxylase activity while the drop in corticosterone output occurred only at days 28 and 35 of experiment. The striking differences in and among various functional parameters depicting adrenal steroidogenesis show for necessity--in case of long-term experiments leading to hypertrophy or atrophy of the gland--of using coupled stereologic and biochemical techniques which better evaluate the cytophysiological state of adrenocortical cells.     

Plasma amino acid concentrations in pregnant rats and in 21-day foetuses.

Plasma amino acid concentrations were determined in virgin female rats, in pregnant rats (12 and 21 days after impregnation) and in 21-day foetuses. The total amino acid concentration in plasma decreases significantly with pregnancy, being lower at 12 than at 21 days. Alanine, glutamine+glutamate and other 'gluconeogenic' amino acids decrease dramatically by mid-term, but regain their original concentrations at the end of the pregnancy. With most other amino acids, mainly the essential ones, the trend is towards lower concentrations which are maintained throughout pregnancy. These data agree with known nitrogen-conservation schemes in pregnancy and with the important demands on amino acids provoked by foetal growth. In the 21-day foetuses, concentrations of individual amino acids are considerably higher than in their mothers, with high plasma foetal/maternal concentration ratios, especially for lysine, phenylalanine and hydroxy-proline, suggesting active protein biosynthesis and turnover. All other amino acids also have high concentration ratios, presumably owing to their requirement by the foetuses for growth. Alanine, glutamine+glutamate, asparagine+aspartate, glycine, serine and threonine form a lower proportion of the total amino acids in foetuses than in the virgin controls or pregnant rats, probably owing to their role primarily in energy metabolism in the adults. The results indicate that at this phase of foetal growth, the placental amino acid uptake is considerable and seems to be higher than immediately before birth.     

Perinatal changes in amylase and serum corticosterone levels in rats

In rats amylase activity in the pancreas increased greatly from day 15 of gestation to a maximum on day 21. Then it decreased to less than one-tenth of this maximum value on about day 5 after birth. It increased again about 15 days after birth and reached the adult level about 30 days after birth.No amylase activity was in the parotid gland before birth: it appeared about 12 days after birth and reached the adult level, which was higher than that in the pancreas, about 30 days after birth.The serum corticosterone level was as high as the adult level before birth. Then it decreased to less than one-tenth of the adult level 5 days after birth and increased again from 15 to 25 days after birth to the adult level. The developmental change in the serum corticosterone level seemed to influence amylase activity in the pancreas both before and after birth, and that in the parotid gland only after birth.The serum contained both pancreatic and paratoid type isozymes of amylase until 1 day after birth but only the parotid type from 3 days after birth.     

Neonatal handling enhances contextual fear conditioning and alters corticosterone stress responses in young rats

Previous studies have indicated that neonatal handling influences development of hypothalamic-pituitary-adrenal (HPA) control of corticosterone. In addition, corticosterone influences memory consolidation processes in contextual fear conditioning. Therefore, neonatal handling may affect hippocampal-dependent memory processes present in contextual fear conditioning by influencing the development of HPA control of corticosterone. To investigate the effects of neonatal handling on early learning, rat pups were either handled (15-min removal from home cage) on the first 15 days after birth or left undisturbed in their home cage. Handled rats and nonhandled rats were fear conditioned at 18, 21, or 30 days of age and then tested at two time points--24 h following conditioning and at postnatal day 45. Subsequently, at approximately postnatal day 60, rats were exposed to restraint stress and corticosterone levels were assessed during restraint and recovery. Handled and nonhandled rats did not differ significantly in their freezing response immediately following footshock on the conditioning day. However, when tested for contextual fear conditioning at 24 h following conditioning and at postnatal day 45, handled rats showed more freezing behavior than nonhandled rats. When exposed to restraint stress, handled rats had a more rapid return of corticosterone to basal levels than nonhandled rats. These results indicate that neonatal handling enhances developmentally early memory processes involved in contextual fear conditioning and confirms previously reported effects of neonatal handling on HPA control of corticosterone.     

Daily rhythms of pituitary-ovarian function in the immature hamster are independent of adrenal and pineal influence

In female hamsters, the daily rhythm of LH appeared on the 15th or 16th day after birth with a peak occurring at about 16:00 h (14L:10D, lights on 06:00 h). Progesterone concentrations increased and became rhythmic a few days later. In serum samples collected at 14, 16, 18, 20, 25, 30, 40 and 60-62 days of age between 13:00 and 23:00 h, significant rhythms of serum cortisol and corticosterone concentrations were not detected before 25 days of age; furthermore, the phase of the rhythms did not stabilize to the adult pattern until about 40 days of age. As in the adult, significant rhythms were present in both sexes and the levels of cortisol were greater than those of corticosterone. Injection of pig ACTH (50 i.u./kg body wt, i.p.) significantly increased serum cortisol by 10 days of age, but corticosterone did not respond until 25 days of age. Thus, for cortisol at least, the appearance of 24-h rhythms in the serum is probably not dependent on the ability of the adrenal to respond to ACTH. Ovariectomy had no effect on the late afternoon surge of serum cortisol; similarly, adrenalectomy of immature females did not abolish the surge of LH. Ovariectomy did not alter the daily rhythm of pineal melatonin content and pinealectomy had no effect on the daily afternoon surge of LH. These results demonstrate functional independence of circadian rhythms in the pituitary-gonadal axis and the pituitary-adrenal axis of the immature hamster and also independence of daily rhythms of pineal melatonin and pituitary release of LH.     

Early age cold conditioning in broiler chickens (Gallus domesticus): thermotolerance and growth responses

The influence of short repetitive cold exposure at an early age (cold conditioning—exposure to 15°C for 3 h at 3 and 4 days of age) on chickens’ thermotolerance during cold challenge (15°C) at 21 days of age was examined. The first cold exposure elicited a dramatic decline in body temperature (T_b) and a significant elevation in stress response (plasma corticosterone concentration); the second cold exposure resulted in moderate T_b and stress responses. Thereafter, the corticosterone concentration remained at a significantly lower level. Acute cold challenge of conditioned broilers at 21 days of age revealed better T_b and stress recovery during the first 24 h, and a significantly lower mortality rate thereafter. Conditioned chickens exposed to optimal conditions (22°C) achieved significantly higher body weights than others. It may be concluded that early cold conditioning improves thermotolerance in broiler chickens in later life.     

Chronic administration of corticosterone impairs LH signal transduction and steroidogenesis in rat Leydig cells

The mechanism involved in the inhibitory actions of chronic corticosterone treatment on Leydig cell steroidogenesis was studied in adult Wistar rats. Rats were treated with corticosterone-21-acetate (2 mg/100 g body weight, i.m., twice daily) for 15 days and another set of rats was treated with corticosterone plus ovine luteinizing hormone (oLH) (100 microg/kg body weight, s.c., daily) for 15 days. Chronic treatment with corticosterone increased serum corticosterone but decreased serum LH, testosterone, estradiol and testicular interstitial fluid (TIF) testosterone and estradiol concentrations. Administration of LH with corticosterone partially prevented the decrease in serum and TIF testosterone and estradiol. Leydig cell LH receptor number, basal and LH-stimulated cAMP production were diminished by corticosterone treatment which remained at control level in the corticosterone plus LH treated rats. Activities of steroidogenic enzymes, 3beta- and 17beta-hydroxysteroid dehydrogenase (3beta-HSD and 17beta-HSD) were significantly decreased in corticosterone treated rats. LH plus corticosterone treatment did not affect 3beta-HSD activity but decreased 17beta-HSD activity, indicating a direct inhibitory effect of excess corticosterone on Leydig cell testosterone synthesis. The indirect effect of corticosterone, thus, assume to be mediated through lower LH which regulates the activity of 3beta-HSD. Basal, LH and cAMP-stimulated testosterone production by Leydig cells of corticosterone and corticosterone plus LH treated rats were decreased compared to control suggesting the deleterious effect of excess corticosterone on LH signal transduction and thus steroidogenesis.     

Production of corticosterone in male homozygous Brattleboro rats

Plasma concentration, metabolic clearance rate and in vitro adrenal production of corticosterone were measured in Brattleboro male rats homozygous for diabetes insipidus (DI) and in Long-Evans male rats (LE) as controls in resting conditions, under stress caused by pentobarbitone anesthesia and surgery and after three days water deprivation. In resting animals, plasma concentrations and in vitro adrenal production of corticosterone were higher in DI rats than in LE rats. Under pentobarbitone anesthesia and surgery, plasma concentrations and metabolic clearance rate of corticosterone were slightly but not statistically lower in DI rats; however, the in vivo production rate of corticosterone was significantly lower. After three days water deprivation, increasing plasma corticosterone level was consistently higher in DI than in Le rats. These results are not in favour of a reduced glucocorticoid activity of the adrenal of DI rats and of an important role played by vasopressin on the stimulation of the hypothalamopituitary adrenal activity at least in resting conditions; its role may depend upon stressful circumstances.     

The Effect of Corticosterone on the Growth of Perinatal Rat Lung Fibroblasts in Culture: Modulation by the Extracellular Matrix

Third passage lung fibroblasts from rat pups between the ages of fetal day 17 and postnatal day 15 were allowed to attach onto either tissue culture plastic or an endothelial cell-derived matrix, and were then exposed to different concentrations of corticosterone in culture medium containing 1% charcoal-stripped serum. The effect of the hormone on growth of these cells was assessed after 48 hours of exposure by radiothymidine incorporation into DNA. Lung fibroblasts on plastic responded to the hormone in an age-dependent manner; thus, cells which were obtained during late gestation (days 19–21) and after the third day of extrauterine life were consistently growth-inhibited by corticosterone, whereas those which were obtained from fetal donors prior to day 19 and from neonatal donors (days 0–3 after birth) were stimulated to grow in response to the hormone. On the other hand, cells that were plated onto an endothelial cell-derived matrix showed a different age-related response to the hormone. Thus, lung fibroblasts from all fetal donors and from postnatal donors up until 4–5 days of age were stimulated to grow in response to corticosterone. This modulatory effect of the matrix on the fibroblast response to corticosterone was also seen in early passage fibroblasts. In an attempt to identify the modulatory agent(s) in the extracellular matrix, fibroblasts from day 19 fetal rat lung were challenged with corticosterone in the presence of laminin, fibronectin, type IV collagen, type I collagen, heparin, or chondroitin sulfate. None of these agents exerted a modulatory effect resembling that seen with the extracellular matrix. These results suggest the existence during lung development of a fibroblast-endothelial interaction, the nature of which remains to be elucidated, which may serve to modify the effects of circulating hormones.     

Repeated stress at the same time of day does not mimic timed feeding in its effects on the plasma corticosterone rhythm in rats

The present study examined whether mild restraint stress occurring at the same time each day would entrain an anticipatory peak in the circadian plasma corticosterone rhythm associated with the time of stress. Rats were stressed by tube restraint for 2 h in the morning on 23 consecutive days, and plasma corticosterone concentrations were measured at 4h intervals over the next 2 days. Plasma corticosterone patterns were similar in control and restrained rats, and no anticipatory corticosterone peak occurred in stressed rats before the time when stress would have occurred. However, periodic regression analysis of the data indicated that timed stress did advance the acrophase of the circadian corticosterone rhythm by 1.7 h. This effect was minimal and could not explain the anticipatory rise in corticosterone concentrations seen in restricted feeding paradigms. Thus, it is unlikely that any stress associated with restricted feeding entrains corticosterone rhythms to anticipate the time of feeding, and some aspect of feeding per se is likely involved in producing the corticosterone peak that anticipates the time of restricted feeding.     

Effects of L-serine supplementation on the daily rhythms of growth hormone and corticosterone concentrations in mice

The impact of L-serine on the daily rhythms of growth hormone (GH) and corticosterone remains unknown. We explored whether the daily rhythms of these hormones were affected by L-serine supplementation as well as the supplementation time. The results showed that plasma GH concentration at Zeitgeber time (ZT)4 and 8 were significantly increased by L-serine supplementation at ZT22, while the diurnal rhythms peaks of plasma corticosterone at ZT12 were suppressed by L-serine supplementation at ZT10. After the supplementation was stopped, the effects of L-serine on the diurnal rhythms of plasma GH and corticosterone lasted for 2 days then they were fading on day 4. L-serine concentrations in plasma and hypothalamus after supplementation at ZT22 was lower than those after supplementation at ZT10. In conclusion, L-serine modulates the daily rhythms of GH and corticosterone depending on its supplementation time. The modulation effect might be association with the daily rhythms of L-serine metabolism.     

Plasma concentrations of arginine vasotocin, prolactin, aldosterone and corticosterone in relation to oviposition and dietary NaCl in the domestic fowl

The osmolality and concentrations of Na, K, Cl and the hormones arginine vasotocin (AVT), prolactin, aldosterone and corticosterone were measured in plasma as functions of time in relation to oviposition, changing NaCl content of the diet, and feeding-inanition. AVT was significantly increased immediately after oviposition (but not during the hour before) with a calculated average value of 38.0 +/- 4.1 pg/ml at oviposition. A moderate increase in concentrations of prolactin and corticosterone were observed immediately after oviposition. Oviposition was not associated with detectable changes in plasma osmolality (and electrolyte concentrations) nor with the concentration of aldosterone. After a sudden change from a high NaCl diet to a low NaCl diet the plasma osmolality and concentrations of NaCl, AVT and prolactin reached new stable levels in 24 hr, whereas the plasma aldosterone concentration required more than 4 days to reach a steady level. After resalination plasma aldosterone was suppressed in less than 8 hr. Both osmolality and concentrations of AVT and prolactin showed transient overshoots during the first 24 hr. NaCl depletion resulted in a transient increase of corticosterone.     

Investigation of thyroxine monodeiodinase activity in the liver, kidney and brown adipose tissue of foetal and neonatal rabbit

The maturation of the 5'- and 5-monodeiodinase system in liver, kidney and brown adipose tissue of rabbits, during the foetal period (from 21 days of gestation to birth) and the neonatal period (from birth to 3 weeks of life) was studied. A sudden increase of 5'- and 5-monodeiodinase activity in liver and kidney 3 days before birth was observed, falling to a nadir at day 3 after birth. Foetal and neonatal serum T4, T3 and rT3 concentration were very low and rose progressively with age, reaching adult values at about day 21. In the foetal brown adipose tissue high 5'-monodeiodinase and low 5-monodeiodinase activity was found. The 5'-monodeiodinase decreased during the first days of life whereas the 5-monodeiodinase activity remained at a low stable level until day 3 when the activities of both enzymes increased. The increase of conversion rate of T4 to T3 and rT3 in liver and kidney well correlate with the triiodothyronines concentration in serum from day 3 after birth.     

Hormonal studies of young lean and obese Zucker rats

Plasma concentrations of insulin, corticosterone, T3, T4 and glucose were measured at 6 hour intervals throughout 24 hours in undisturbed, 34-day-old lean (Fa/?) and genetically obese (fa/fa) Zucker rats. fa/fa rats had higher plasma concentrations of insulin at all sampling times and higher plasma concentrations of corticosterone at 0300 and 0900 hours. Neither T3 nor T4 levels differed between phenotypes at any sampling time. Fasting for 24 hours at 34 days abolished the hyperinsulinaemia of fa/fa rats and raised the plasma corticosterone concentrations of both phenotypes. Before weaning there were no phenotypic differences in the plasma insulin or corticosterone concentrations measured at two sampling times in undisturbed rats. Following an intra-gastric glucose load however, fa/fa rats became hyper-insulinaemic compared with similarly treated Fa/? animals. Pancreatic insulin contents were higher in fa/fa rats at 34 days of age, but not before weaning. Somatostatin contents of the pancreas, hypothalamus and cerebral cortex did not differ between phenotypes at either 18 or 34 days of age. In conclusion, the elevated plasma concentrations of insulin and corticosterone in young fa/fa rats may contribute to their greater lipid deposition and lower protein deposition.     

Plasma and adrenal corticosterone concentrations and liver glycogen content in premature mice at birth and during neonatal development

The concentrations of corticosterone in the plasma and adrenal glands and the content of glycogen in the liver were estimated from birth to day 6 after birth in surviving premature mice removed by Caesarean section on day 19 of pregnancy and submitted to reanimation during 30 min; the neonates were nourished by nursing mothers from 30 min after birth. A group of full-term newborns was removed by Caesarean section on day 20 of pregnancy and killed 30 min after reanimation. Premature mice were characterized by neonatal changes of three parameters used. The plasma corticosterone level reached a peak in the first 6 h after birth, then decreased until day 6. The adrenal corticosterone level did not vary significantly 30 min after birth, then decreased progressively until day 2. The liver glycogen content, very high on day 19 of pregnancy, increased 30 min after birth, then fell sharply until day 2. In full-term newborns removed by Caesarean section and killed 30 min after reanimation the plasma corticosterone level increased, whereas the adrenal corticosterone level and the liver glycogen content did not decrease. The adrenal gland of surviving premature mice was able to respond to the stress induced by the reanimation; the stimulation of glucocorticoid function was similar in both neonates.     

Increased hypothalamic-pituitary-adrenal axis activity and hepatic insulin resistance in low-birth-weight rats

Individuals born with a low birth weight (LBW) have an increased prevalence of type 2 diabetes, but the mechanisms responsible for this association are unknown. Given the important role of insulin resistance in the pathogenesis of type 2 diabetes, we examined insulin sensitivity in a rat model of LBW due to intrauterine fetal stress. During the last 7 days of gestation, rat dams were treated with dexamethasone and insulin sensitivity was assessed in the LBW offspring by a hyperinsulinemic euglycemic clamp. The LBW group had liver-specific insulin resistance associated with increased levels of PEPCK expression. These changes were associated with pituitary hyperplasia of the ACTH-secreting cells, increased morning plasma ACTH concentrations, elevated corticosterone secretion during restraint stress, and an approximately 70% increase in 24-h urine corticosterone excretion. These data support the hypothesis that prenatal stress can result in chronic hyperactivity of the hypothalamic-pituitary-adrenal axis, resulting in increased plasma corticosterone concentrations, upregulation of hepatic gluconeogenesis, and hepatic insulin resistance.     

Variation in the amounts of hepatic copper, zinc and metallothionein mRNA during development in the rat.

Amounts of hepatic metallothionein mRNA were assessed in RNA from foetal and neonatal rat livers by using dot-blot hybridization. Metallothionein mRNA began to increase about day 15 of gestation and reached a foetal maximum of 5-fold higher than adult values between 18 and 21 days of gestation. The amounts fell significantly for the first 3 days after parturition, and rose again to 6-fold above adult values 6 days after birth. By 15 days after birth the metallothionein mRNA had declined to adult amounts. In comparison, amounts of ornithine transcarbamoylase mRNA did not vary greatly during development. Hepatic zinc concentrations increased from day 14 of gestation to a maximum just before birth, and remained above adult values until 30 days after birth. From 14 days of gestation to 8 days after birth, hepatic copper concentrations were about 4-fold higher than in the adult, but a substantial increase (to about 9-fold higher than in the adult) occurs between 10 and 15 days after birth. CdCl2 administered to pregnant rats on day 18 of gestation was shown to block placental transfer of zinc, and we found decreased foetal hepatic zinc concentration after the CdCl2 treatment, but this failed to cause a significant decrease in metallothionein mRNA, suggesting that zinc may not be the primary inducer of hepatic metallothionein mRNA during foetal life.     

Circaseptan rhythm of corticosterone and lipids in the serum of male rats

After adaptation to standard conditions and to a 12:12 h light: dark regimen, groups of young SPF male Wistar rats were killed at 8 h on 17 consecutive days and their serum corticosterone and lipid concentrations were determined. Using a combination of a Fourier harmonic analysis and an analysis of variance, the circaseptan rhythm of corticosterone, total cholesterol and triacylglycerol oscillations was determined; it is unlikely that the nonesterified fatty acid concentration has a 7-day rhythm. The circaseptan variation of metabolic and hormonal indicators is evidently adaptive in character and its existence ought to be taken particularly into account in the evaluation of long-term experiments.