The effect of althesin on plasma corticosterone levels

Althesin in doses which produced anesthesia (4 and 6 ml kg-1, i.p.) produced biphasic changes in plasma corticosterone levels. Plasma corticosterone showed an increase (p less than 0.05) due to the stress of injection but returned to basal levels by 30 min. Subsequent to the anesthetic effect (approximately 30 min) corticosterone levels increased markedly (p less than 0.01). Althesin's effectiveness showed time of day effects, i.e., Althesin was more effective in the A.M. Rats given 6 ml kg-1 Althesin showed graded plasma corticosterone responses to stresses of varying intensity. Blood withdrawal and surgical stress evoked significant increases in plasma corticosterone but a 2-min holding stress had no effect on plasma corticosterone levels. Instrumented rats receiving supplemental injections (i.p.) presented patterns of plasma corticosterone which were different from those receiving supplemental infusions (i.a.). Whereas plasma corticosterone levels of rats receiving the continuous infusion of Althesin remained relatively constant, corticosterone levels of those which received supplemental injections tended to increase. Collectively, these data suggest that Althesins usefulness as an experimental anesthetic is limited to those studies which are not compromised by stress-induced pituitary-adrenal activity.     

The effect of transdermal corticosterone application on plasma corticosterone levels in pregnant Lacerta vivipara

Relationships between hormones and behaviour can be explored by altering endogenous hormone levels, often through implantation of silastic tubing or osmotic pumps filled with a hormone or its agonists or antagonists. However, organisms in sensitive life-history stages (such as pregnancy) may be adversely affected by the surgical procedures associated with these manipulations, necessitating use of non-invasive techniques. We demonstrate that the application of a sesame oil-corticosterone mixture to the skin of pregnant female common lizards (Lacerta vivipara) elevates plasma levels of the hormone. Pregnant female L. vivipara were captured and treated daily for 1-20 days with the sesame oil-corticosterone mixture (experimental group) or with vehicle only (control group). Blood samples were collected and analyzed for corticosterone by radioimmunoassay. Baseline plasma corticosterone levels were elevated within 1 h in the experimental group. Similar levels ( approximately 145 ng/ml) were found over the subsequent 2 days, and by day 5 had risen significantly higher ( approximately 281.9 ng/ml), where they remained for the duration of the experiment. These increases are comparable to those found in other species using related techniques. No significant changes in plasma corticosterone levels occurred in the control group. Finally, corticosterone levels also were determined for untreated females that were captured, held overnight, sampled, and released to access to the natural range of basal corticosterone levels. Basal plasma levels of corticosterone in pregnant females varied among individuals independently of female body size or corpulence.     

Effects of intrahippocampal injection of chemicals on the levels of plasma corticosterone in rats.

The possibility that the hippocampus can influence the function of the hypothalamo-pituitary-adrenal axis was examined by injecting small quantities of various neurotransmitter substances into this brain structure. Injections of either noradrenaline or 5-hydroxytryptamine into the dorsal hippocampus had no effect on plasma concentrations of corticosterone (B). An injection of carbachol into the dorsal hippocampus elicited a significant rise in B concentrations, while that of hemicholinium into the same brain structure resulted in an inhibition of noise-induced rise of plasma B concentration. An injection of carbachol into the dorsal hippocampus counteracted dexamethsone-induced decrease in plasma B concentration, while that of hemicholinium enhanced it.     

慢性低氧对雄性大鼠血浆皮质酮及睾酮水平的影响

目的:研究低氧对雄性大鼠性腺及相关激素水平的影响。方法:分别检测3km、5km及杭州海拔水平雄性大鼠睾丸和附睾指数、血浆皮质酮和睾酮水平。结果:3km组体重、睾酮含量均显著下降,睾丸指数、血浆皮质酮显著上升;5km组体重、附睾指数和睾酮含量均显著下降,皮质酮含量显著上升。结论:慢性低氧能显著影响雄性成年大鼠性腺及血浆睾酮水平,该结果显示哺乳动物在慢性低氧条件下生殖内分泌功能呈现抑制状态。     

Effect of alpha-methyl-p-tyrosine and dihydroxyphenylalanine on plasma corticosterone levels in rats pretreated with prednisolone acetate

The effects on hypothalamic-pituitary-adrenal function and on negative feed-back action of a synthetic adrenal steroid, prednisolone acetate, have been studied in female Wistar rats treated with alpha-methyl-p-tyrosine (alpha MpT) and L-dihydroxyphenylalanine (L-DOPA) administered for six consecutive days. The parameter for study was taken from the plasmatic changes of corticosterone levels. alpha-MpT injection determines an increase of plasmatic corticosterone values, while L-DOPA injection produces the opposite effect, decreasing corticosterone levels as compared to the saline control group. The simultaneous administration of prednisolone acetate 250 micrograms/kg weight s.c. for six consecutive days to alpha-MpT or L-DOPA determines the following effects: a) With alpha-MpT the negative feed-back action of prednisolone was not modified. b) With L-DOPA this action of the steroid is cancelled and the plasmatic corticosterone values are increased significantly. These changes have been related to modifications of the catecholamines content in the brain. The importance of the catecholamines on the activity of the hypothalamic-pituitary-adrenal axis is discussed under experimental condition, specially the effects of L-DOPA, which depends for its activity on the presence or absence of prednisolone.     

The influence of oral corticosterone replacement on plasma prolactin levels of adrenalectomized female rats

The administration of 80 μg of corticosterone/ml of drinking solution to adrenalectomized (ADX) rats resulted in a 24 hour serum corticosterone pattern similar to that of intact animals except that the magnitude of the afternoon-nocturnal surge was one third. Basal plasma prolactin levels and the estrogen-induced afternoon prolactin surge were similar for intact and for ADX animals receiving corticosterone in the drinking solution. Adrenalectomized animals receiving 0.9% NaCl to drink, however, had an afternoon prolactin surge that was significantly lower than that of intact animals while basal levels were similar.     

Influence of intra-uterine growth retardation on plasma and adrenal corticosterone levels during development in rats]

The evolution of plasma and adrenals corticosterone was followed in normal rats, sham rats, IUGR rats and their controls, during the foetal and post-natal development. Adrenals weight was significantly reduced in IUGR rats. Corticosterone plasma levels were lower in IUGR rats up to 24 hours after birth.     

Effect of oxytocin and naloxone on the plasma levels of corticosterone in the rat

The effect of two doses of oxytocin (2 or 4 UI/kg i.p.) has been studied in the male Wistar rats, either preceded or not by a naloxone administration (10 mg/kg i.p.), on the response of the hypothalamus-pituitary-adrenal system, the latter being valued by changes produced in the plasmatic corticosterone levels. Oxytocin produced significant increases of the plasmatic corticosterone levels, this effect being stronger and longer lasting after the superior dose. Naloxone alone produced the same effect, but not as intense and stable as that of oxytocin. Pretreatment with naloxone modified the response of the hypothalamus-pituitary-adrenal system to oxytocin, producing partial blockade. The results suggest that the oxytocin action on the hypothalamus-pituitary-adrenal axis might be mediated by the endogenous opiates.     

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.     

Effect of clorgyline and of alpha-methyl-p-tyrosine on the plasma levels of corticosterone in the rat

The effect of a type A MAO inhibitor, clorgyline, injected alone or with alpha-methyl-p-tyrosine (aMpT) on the plasmatic corticosterone levels estimated at 9 a.m. and 5 p.m. has been studied in male Wistar rats. The clorgyline injected alone produced significant decreases in corticosterone values, especially at 5 p.m., determining a variation lack between the morning and the afternoon levels. When alpha-MpT is associated to IMAO, increases at both points of the day considered in this experiment take place. The amount of NA and 5-HT in the brain was also estimated; clorgyline high increases in Na and 5-HT contents, 5-HT; aMpT reduces the effect of clorgyline, especially as regards content. The results are discussed in relation to this highly specific MAO inhibitor and with the role of these amines as modulators of ACTH secretion. In view of the changes introduced by the aMpT injection, the modifications produced by clorgyline alone are related to NA, but to 5-HT, when the NA synthesis has been interrupted by the tyrosine hydroxylase inhibitor.     

Adrenocorticotropin and corticosterone levels in pre-weanling spontaneously hypertensive rats

Circulating plasma ACTH and corticosterone levels were measured in spontaneously hypertensive rats (SHR) and the corresponding, normotensive Wistar-Kyoto (WKY) strain at 10 and 20 days of age. In addition, stored levels of ACTH were measured in the pituitary glands of these animals. Circulating corticosterone levels were significantly lower, in both strains, at 10 days than at 20 days. Although the glucocorticoid was undetectable in WKY animals at 10 days, significant levels were observed in age-matched SHR. No difference in corticosterone concentrations was observed between the two strains at 20 days. Circulating ACTH levels did not reflect the values for circulating glucocorticoids. There were no significant differences in the levels of ACTH between strains or between age groups. Moreover, pituitary stores of ACTH between animals of different strains and ages were not found to be significantly different among any of the groups tested. These results demonstrate that there is a difference in circulating corticosterone levels between spontaneously hypertensive and Wistar-Kyoto rats at 10 days postnatally which is not evident just prior to weaning (20 days). This difference is not due to variations in stored or circulating ACTH. Indeed, ACTH levels are high at a time (10 days) when corticosterone is low - thus suggesting that the difference may reside within the responsiveness of the adrenal cortex.     

Plasma corticosterone levels during sexual behavior in male rats

The activity of the pituitary-adrenal (p-a) system, as reflected in plasma levels of corticosterone, was determined in 14 male Long Evans rats during copulation, exposure to an open field and in control conditions. Plasma corticosterone concentration during copulation was higher than in control conditions (13.3 ± 1.2 vs 9.4 ± 1.2 μm%, p < .01), but well below mean levels obtained in the open field (21.2 ± 0.8 μm%). Individual data indicated that some males gave no evidence of p-a activation during sexual activity. Furthermore, animals which showed increased steroid levels during copulation tended to have longer latencies to reinitiate copulation after ejaculation and were behaviorally less active in a subsequent open field test. It was suggested that neither sexual arousal nor copulatory performance necessarily activates the p-a system. Males showing p-a activation may be slow to habituate to a novel stimulus and thus the elevated steroid levels may reflect an insufficient number of habituation trials with the receptive female.     

The effect of glucocorticoids on plasma fibronectin levels in normal and arthritic rats

In vivo studies with normal and adjuvant-induced arthritic rats were undertaken in order to measure the effects of glucocorticoids on paw inflammation and plasma fibronectin (Fn) levels. Dexamethasone, methylprednisolone, and corticosterone all enhanced plasma Fn levels in normal animals. All drugs also significantly decreased inflammation in arthritic rats as measured by paw swelling. Of the three glucocorticoids, only corticosterone did not significantly enhance Fn levels in arthritic rats, possibly due to its lesser potency and narrow therapeutic window.