27Moderate physical exercise does not cause any changes in the plasma levels of the catabolic hormone cortisol and the anabolic hormone testosterone compared with the concentrations during a control day. In studies on army recruits, however, fit compared to unfit men tended to have smaller mean decreases in plasma testosterone and free testosterone index during the day both during a control day and during a day with submaximal marching exercise. After 4 months training, the mean plasma testosterone and free testosterone index tended to decrease less during both control and marching exercise days, and this was more evident in the well-conditioned subjects. However, very fit male athletes, who have been training for many years, and sedentary men have identical plasma testosterone levels and serum sex hormone binding globulin binding capacities (SHBG). Intense physical exercise invariably leads to an increase in plasma cortisol and a decrease in plasma testosterone compared with the concentrations during a control day. However, the percentage of free testosterone seems to increase cornpensatorily, which in many individuals keeps the absolute free testosterone level constant or even higher despite no change or slight increase in SHBG. Prolonged exhaustive physical exercise in men results in a decrease in plasma testosterone even down to normal female levels, and there is a constant increase in SHBG resulting in very low free testosterone concentrations. It is known from studies in rats that a low level of androgens results in an increase in the binding of cortisol in muscle tissue probably due to an increase in the number of cortisol receptors. This in combination with the high level of cortisol during prolonged exhaustive physical exercise may lead to a situation in which the protein catabolic events in the muscle cells supersedes the anabolic ones. Rats trained on a treadmill and sedentary rats have identical plasma and testicular testosterone concentrations, identical plasma LH levels, and training has no effect on Leydig cell LH and prolactin receptors. When these rats ran until exhaustion, the trained rats were able to run much longer (up to 3 h) than the untrained rats. In this experiment, the decrease in plasma testosterone was greater in the trained rats compared with the untrained ones, and also the testicular concentration of testosterone, androstenedione, and progesterone fell to lower levels in the trained rats after the exhaustive exercise. The plasma LH levels remained unchanged. This suggests that the decrease in plasma testosterone is due to a reduction in testicular testosterone production and a depletion of the testosterone stores and that the testosterone-LH feedback mechanism is no longer functioning in these exhausted animals. However, when the Leydig cells were incubated in vitro with HCG at different concentrations, it could be shown that in trained rats Leydig cell testosterone and cyclic AMP production was significantly greater than in sedentary rats. All these results are in good agreement w...

The effects of 4-6 days of food deprivation on the pituitary-testicular function of adult male rats were studied. Fasting decreased body weights on average by 23% (P less than 0.01) and those of seminal vesicles by 55% (P less than 0.01) in 4 days. No consistent changes were found in testicular and ventral prostate weights. The pituitary levels of gonadotrophin-releasing hormone (GnRH) receptors decreased by 50% (P less than 0.01). Serum and pituitary levels of LH, FSH and prolactin decreased by 25-50% (P less than 0.01 for all). Testicular and serum levels of testosterone decreased by 70-80%, testicular LH receptors by 26%, those of prolactin by 50% (P less than 0.01 for all), but those of FSH remained unaffected. Acute (2 h) stimulation by a GnRH agonist (buserelin, 10 micrograms/kg i.m.) resulted in similar LH, FSH and testosterone responses in the fasted and control animals, and human chorionic gonadotrophin (hCG) stimulation (30 IU/kg i.m.) in similar increases in testosterone. A 42% decrease was found in pituitary content of mRNA of the common alpha subunit (P less than 0.05), but the mRNAs of the LH- and FSH-beta chains and prolactin were unaffected by fasting for 4 days. When the same mRNAs were measured after 6 days of fasting, the decrease of the mRNA of FSH-beta also became significant (50%, P less than 0.01). In contrast, the mRNA of LH-beta was increased twofold (P less than 0.01) at this time and serum LH levels were similar in control and starved animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Objective: Orexins have been implicated in the regulation of several physiological functions including reproduction, energy balance and vigilance state. For successful reproduction, the precisely timed hormonal secretions of the estrous cycle must be combined with appropriate nutritional and vigilance states. The steroid-and nutritional state-dependent modulation of LH release by orexins, as well as an increase of vigilance, suggest that orexins may co-ordinate these functions in the course of the estrous cycle. Design: We studied the brain tissue levels of orexins in the course of the estrous cycle in young and middle-aged rats. Young cycling rats (3 months old) and irregularly/non-cycling (7 -9 months old) female rats were inspected for vaginal smears and serum hormone levels. Methods: Tissue concentrations of orexin A and B were measured in the hypothalamus and lateral hypothalamus on different days of the estrous cycle. Results: Orexin A concentration in the hypothalamus of young cycling rats was higher on the day of proestrus 5-6 h after the lights were switched on than on the other days of the estrous cycle at the same circadian time. Orexin B concentration was higher on both the day of proestrus and the day of estrus as compared with the days of diestrus. The hypothalamic concentrations of both orexin A and B in the non-cycling middle-aged rats were lower than those in cycling rats on the days of proestrus and estrus. Conclusions: We have concluded that the high hypothalamic concentration of orexins on the day of proestrus may contribute to the LH and prolactin surges. High orexin A levels may also contribute to the decreased amount of sleep on the day of proestrus.European Journal of Endocrinology 150 737-742

The sequence of appearance of FSH and LH receptors, and response of cyclic AMP (cAMP) production to these hormones and cholera toxin, were studied in the fetal and neonatal rat ovary. Specific binding of radiolabelled human (h)FSH and chorionic gonadotrophin (CG) to ovarian homogenates was first detectable on day 7 of life. The content of FSH receptors per ovary increased tenfold between days 7 and 16, and that of LH receptors 27-fold. A significant response of cAMP production in vitro to FSH appeared on day 4 of life, but no significant effect of hCG on cAMP was achieved until day 7. In contrast, cholera toxin had a marked effect on cAMP production by day 17 of fetal life. Although both FSH and LH receptors were detectable in the neonatal rat ovary by day 7, the present findings indicate that the FSH responsiveness of the ovary appears earlier than that of LH. The post-receptor machinery of cAMP production is already functional in the fetal ovary as shown by the experiments with cholera toxin. The appearance of the receptor may therefore be the last link in the ontogeny of the gonadotrophin signal transduction system in the ovary. To study the hormone dependence of the appearance of gonadotrophin responsiveness, neonatal female rats were treated on days 1-6 or 1-9 of life with a potent gonadotrophin-releasing hormone antagonist, and killed on the following day. In both treatment groups, the pituitary LH and FSH contents were suppressed.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract