The development of daily change in serum corticosterone in pre-weanling rats

The development of daily changes in serum corticosterone (B) values was followed in maturing Sprague-Dawley derived rats raised from birth on a 14 hour light:10 hour dark cycle or received from the breeder on the day of weaning, and placed in a 14:10 cycle, In shipped rats., initial values of B were high at 8 AM on day 22 but had dropped by day 26. Evening values of B(8 PM) were similar in 22 and 26 day old rats. A significant difference between the noon and 8 pm values of B was obtained at 18 days of age in females and 19 days of age in males. Samples taken every 4 hours on days 19 and 20, before weaning, revealed a daily pattern similar to that of adults except that high values were obtained at 8 AM on day 19 and on day 20 at the time of a trough period in older rats. The evening peak was also longer in duration, failing to fall at midnight as in 26 day old rats. It is concluded that the pattern of the adrenal rhythm matures over a three or four day period in the preweanling rat.     

Influence of light regimen and time of year on circadian oscillations of insulin and corticosterone in rats.

Male SPF bred Wistar rats were adapted to natural light (N) and to a 12:12 h (light-dark) artificial light (A) regimen in the course of the year. The rats were analyzed at 3 h intervals during 24 h approximately at the time of the vernal and autumnal equinox and at the winter and summer solistice. Serum insulin circadian oscillations depended on the season, being different in various light regimens. The mesors were the highest during summer, the lowest during winter in both regimens. The external acrophases of insulin in the N differed from those in the A group, contrary to the computative ones. The annual mean of serum insulin concentration was lower in the N than in the A group. The circadian oscillations of corticosterone were influenced primarily by the time of year. The mesors were the highest during summer, lower in winter and spring in N and A group. The computative acrophases were similar in both groups in all seasons except spring. The external acrophase was similar in both regimens during the year. The response of insulin, a major anabolic hormone, to various light regimens during the day and year was different from that of corticosterone, a major hormone of the stress reaction.     

The effect of acute and chronic ethanol administration on serum corticosterone concentration in rats

The effect of intraperitoneally (i.p.) and intragastrically (i.g.) administered ethanol solution, and the influence of voluntary ethanol uptake (20% v/v) on adrenocortical activity of adult male rats was studied. Both i.p. and i.g. ethanol administration resulted in a significant activation of adrenocortical mechanisms, while voluntary ethanol uptake failed to induce elevation of serum corticosterone concentration. No difference was found in blood ethanol concentration among these groups. The responsiveness of adrenocortical mechanisms was also tested in rats which were given the free choice between ethanol solution (5% v/v) and tap-water for three weeks. Unavoidable electric foot-shocks, as stressor, resulted in an elevation of serum corticosterone concentration in control animals, but this response was found to be significantly reduced in chronically ethanol drinking rats.     

Circadian oscillations of thyroid hormones and insulin in the serum of fasting rats

Adult male Wistar rats adapted to a 12:12 h light:dark regimen, fed or after a 24- or 48-h fast, were decapitated at 3-h intervals during a single day. They were deprived of food at day-time intervals ensuring that on decapitation they had fasted for the same length of time, i.e. 24 or 48 h. Thyroid hormones, insulin and glucose concentrations were determined in their serum. Fasting did not significantly affect circadian thyroxine, triiodothyronine and reverse triiodothyronine rhythms compared with the findings in fed animals; 24, but not 48 hours' fasting led to a shift in the acrophase of circadian insulin and glucose oscillations compared with fed rats. The maintenance of original circadian thyroid hormones and insulin rhythm in rats which fasted for short lengths of time testifies to a dependence of the stimulus on the time of day.     

The effect of chronic food and water restriction on open-field behaviour and serum corticosterone levels in rats

In operant conditioning experiments, two methods are commonly used to motivate laboratory rats to perform designated tasks. The first is restricting food so that rats are forced to lose 20% of body weight within one week, followed by maintenance at 80% of the baseline weight for the remainder of the experiment. The second is restricting access to water to 15 min in each 24 h period. These methods are effective in motivating the animals. There is, however, little information available on the effects on performance in tests of behaviour that are not related to operant conditioning. In addition, it is not clear if these commonly used methods of food and water restriction will lead to physiological stress as indicated by an elevation of serum corticosterone. Male rats were either food-restricted to reduce and maintain their weight at 80% of baseline weight, or were restricted to 15 min access to water every 24 h. Activity in the open field was significantly greater in food-restricted rats than in water-restricted or control rats, but freezing behaviour was similar in all experimental groups. Food-restricted rats had a higher mean serum corticosterone level than water-restricted and control rats 37 days after the start of the experimental period. These data suggested that chronically restricting food and maintenance of body weight at 80% of baseline body weight led to significant behavioural changes and physiological stress. In contrast, water restriction did not lead to changes in behaviour or corticosterone levels. A second experiment was conducted to compare the effects of food restriction to 80% of baseline body weight, as described above, with a less stringent protocol in which test rats were initially reduced to 80% of baseline weight, but were then maintained at 80% of an ad libitum fed control rat's weight. Serum corticosterone levels and adrenal gland weights were measured after the initial week of forced weight loss and after maintenance for 21 days. Forced loss of 20% of body weight in the first week led to significantly increased serum corticosterone levels and adrenal gland weights compared to ad libitum fed controls. Serum corticosterone levels and adrenal gland weights in rats maintained at 80% of their initial body weight for 21 days remained higher than ad libitum fed control rats. However, rats maintained at 80% of an ad libitum fed control rat's weight did not differ from control rats in serum corticosterone levels or adrenal gland weights at the end of the 21-day study period. Adjustment of the feeding regimen in this manner eliminated physiological evidence of chronic stress.     

Postnatal maturation patterns of serum corticosterone and growth hormone in rats: effect of chronic thyroxine administration.

The effects of chronic neonatal hyperthyroidism in rats on the ontogenic pattern of serum corticosterone and growth hormone (GH) were studied. Thyroxine (T4) treated and saline injected rat pups were sacrificed under basal and stress conditions. In comparison to saline control animals, daily T4 administration (0.4 micrograms/gram body weight) produced a sustained elevation in basal corticosterone levels by day 12 and a significant elevation of serum corticosterone in response to stress by day 4. The serum GH levels in non-stressed animals were moderately decreased in response to T4 administration as compared to saline injected animals with a greater reduction in GH measured in samples obtained from stressed animals. The results indicate that chronic T4 administration influences the developmental pattern of serum corticosterone and GH under both non-stress and stress conditions.     

The in vitro effect of corticosterone on insulin binding and glucose metabolism in mouse skeletal muscles

We studied the in vitro effect of corticosterone on insulin binding, uptake of 2-deoxy-D-glucose, glycolysis, and glycogenesis in the soleus and extensor digitorum longus (EDL) of Swiss-Webster mice. In each experiment, one muscle (soleus/EDL) was incubated with corticosterone (0.1, 1, 50, and 100 micrograms/mL) and the respective contralateral muscle was incubated without corticosterone, but at the same insulin and pH levels. Corticosterone did not affect insulin binding in both muscles. However, corticosterone decreased the uptake of 2-deoxy-D-glucose and the rate of glycolysis and glycogenesis in both muscles when the dose was pharmacologic (50 and 100 micrograms/mL), but not when it was physiologic (0.1 and 1 microgram/mL). For glycolysis and glycogenesis, the suppression was greater in the EDL when compared with the soleus. This suppression was seen in both basal and insulin-stimulated conditions. In this in vitro system, where the experimental muscle is not exposed to prior hyperinsulinemia as in the in vivo model, corticosterone, at pharmacologic doses, affects postreceptor events without altering the insulin binding in the skeletal muscle.     

Arylalkylamine N-acetyltransferase gene expression in retina and pineal gland of rats under various photoperiods

The present study examines how the circadian oscillators in the retina and the suprachiasmatic nucleus (SCN) respond to changes in photoperiod. Arylalkylamine N-acetyltransferase (aa-nat) gene expression studied by quantitative RT-PCR revealed that in adult Sprague-Dawley rats kept under different light-dark (LD) cycles for two weeks the temporal pattern of AA-NAT mRNA expression was identical in retina and pineal gland. In both tissues, the time span between the onset of darkness and the nocturnal rise in AA-NAT mRNA expression was 3 h under LD 20:4, 6 h under LD 12:12, and 15 h under LD 4:20. As aa-nat expression in the pineal gland is regulated by the circadian oscillator in SCN, the results suggest that the photoperiodic differences accompanying the seasons of the year are imprinted in more than one oscillator and that this may accentuate the important message regarding 'time of year.'     

Effect of corticosterone treatment on muscle protein turnover in adrenalectomized rats and diabetic rats maintained on insulin

The effect of corticosterone on protein turnover in skeletal muscle was investigated in growing rats. Protein synthesis was measured in vivo by the constant infusion of [(14)C]tyrosine. The extent to which any effect of corticosterone is modulated by the hyperinsulinaemia induced by steroid treatment was examined by giving the hormone not only to adrenalectomized rats but also to streptozotocin-induced diabetic rats maintained throughout the treatment period on two dosages of insulin by an implanted osmotic minipump. Approximate rates of protein degradation were also estimated in some cases as the difference between synthesis and net change in muscle protein mass. Measurements were also made of free 3-methylhistidine concentration in muscle and plasma. At 10mg of corticosterone/100g body wt. per day, growth stopped and muscle wasting occurred, whereas at 5 mg of corticosterone/100g body wt. per day no net loss of protein occurred. However, this low dose did induce muscle wasting when insulin concentration was regulated by a dose of 1.2 units/day. Protein synthesis was markedly depressed in all treated groups, the depression in the insulin-maintained rats being marginally more than in the hyperinsulinaemic adrenalectomized rats. The oxidative soleus muscle appeared to be less susceptible to the effect of the corticosterone than was the more glycolytic plantaris or gastrocnemius muscle. Any effect of the corticosterone on protein degradation was much less than its effects on protein synthesis. Where increases in the degradation rates appeared to occur in the rats treated with 10mg of corticosterone/100g body wt. per day, the increases were less than 20%. The free intracellular 3-methylhistidine concentrations were doubled in all groups treated with 5 mg of corticosterone/100g body wt. per day and increased 5-fold in the adrenalectomized rats treated with 10mg of corticosterone/100g body wt. per day, with no change in plasma concentration in any of the groups. It is therefore concluded that: (a) the suppression of protein synthesis is the main effect of glucocorticoids in muscle; (b) marked increases in insulin afford only minor protection against this effect; (c) stimulation of protein degradation may occur, but to a much lesser extent.     

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.     

The effect of sex on central histaminergic responses and corticosterone bioperiodicity in Sprague-Dawley rats

Male and female rats demonstrate a difference in the relationship between food intake and H(1) receptor binding, which may be due to hormonal differences that exist. The relationship between the endocrine and histaminergic regulation and synchronization of food intake needs to be elucidated. Male and female rats fed 25% protein displayed bioperiodicity in mean corticosterone levels of 148.95+/-33.71 and 288.48+/-47.84 ng/ml, respectively. Accompanying bioperiodic times were of 22.43+/-1.35 h (males) and a period of 21.42+/-1.96 h (females). Central H(1) receptors in male rats had a mean bioperiodic value of 102.37+/-1.95 pmol/g protein with a period of 21.66+/-1.85 h, while that for females was 97.42+/-4.19 pmol/g protein with a period of 10.23+/-0.95 h. Central histaminergic activity affects feeding in rats with distinct gender variation that is bioperiodic in nature and functions as a major regulatory mechanism.     

The effect of intrahippocampal injection of kainic acid on corticosterone release in rats

The aim of the present study was to investigate whether the hiopocampus exerts a modulatory effect on the activity of the hypothalamic-pituitary-adrenal (HPA) axis. Kainic acid was stereotaxically injected into the CA1 pyramidal cell layer of the dorsal hippocampus, causing histological and behavioural changes typical of kainic acid toxicity. The CA3 pyramidal cells of the dorsal hippocampus were selectively lesioned. Rats treated with kainic acid were hyperactive, executed clockwise rotatory movements and displayed epileptic seizures. The acute excitatory effect of kainic acid on glutamatergic receptors in the hippocampus resulted in an elevation in plasma corticosterone levels, suggesting a stimulation of HPA axis activity. Direct or indirect stimulation of the CA1 pyramidal cells of the dorsal hippocampus appeared to have caused the increase in corticosterone secretion.     

Genistein administration decreases serum corticosterone and testosterone levels in rats

The phytochemical flavonoid genistein has been shown to act as a potent competitive inhibitor of human adrenocortical 3beta-hydroxysteroid dehydrogenase and cytochrome P450 21-hydroxylase activities in vitro [J. Steroid Biochem. Molec. Biol. 2002; 80: 355-363]. In the present study, we evaluated the effects of large amounts of genistein continuously administered to weanling rats, particularly on steroidogenesis at the pubertal stage in vivo. Serum concentrations of free and total genistein were significantly higher in the 40 mg/kg genistein administration group when compared with the control group. In genistein administered rats, adrenal weight was significantly higher. Furthermore, a clear expansion of cells was observed in hematoxylin and eosin stained tissue at the zona fasciculata and zona reticularis of the adrenal cortex. However in the testis, no differences in weights or histologic changes were observed. Serum corticosterone concentration significantly decreased to 50% of control levels by 40 mg/kg genistein administration and testosterone also tended to decrease with this dose of genistein. On the other hand, although serum follicle stimulating hormone was unchanged, adrenocorticotropic hormone and luteinizing hormone levels increased with genistein administration. These results suggest a significant effect of genistein on steroidogenesis in the adrenal gland and testis of rats, and this effect appeared to be more evident on steroid production in adrenals than in testis in vivo.