J. Steroid Biochem. Molec. Biol. Vol. 40, No. 1-3, pp. 473-479, 1991 0960-0760/91 $3.00 + 0.00 Printed in Great Britain. All rights reserved Copyright © 1991 PergamonPress plc STRESS INDUCED CHANGES IN TESTIS FUNCTION A. L6PEZ-CALDER6N,* C. ARIZNAVARRETA,M. I. GONZ~LEz-QuIJANO, J. A. F. TRESGUERRES and M. D. CALDER6N Departamento de Fisiologia, Facultad de Medicina, Universidad Complutense, 28040 Madrid, Spain Summary--The mechanism through which chronic stress inhibits the hypothalamic-pituitary- testicular axis has been investigated. Chronic restraint stress decreases testosterone secretion, an effect that is associated with a decrease in plasma gonadotropin levels. In chronically stressed rats there was a decrease in hypothalamic luteinizing hormone-releasing hormone (LHRH) content and the response on plasma gonadotropins to LHRH administration was enhanced. Thus the inhibitory effect of chronic stress on plasma LH and FSH levels seems not to be due to a reduction in pituitary responsiveness to LHRH, but rather to a modification in LHRH secretion. It has been suggested that fl-endorphin might interfere with hypothalamic LHRH secretion during stress. Chronic immobilization did not modify hypothalamic fl-endor- phin, while an increase in pituitary fl-endorphin secretion was observed. Since we cannot exclude that changes in fl-endorphin secreted by the pituitary or other opioids may play some role in the stress-induced decrease in LHRH secretion, the effect of naltrexone administration on plasma gonadotropin was studied in chronically stressed rats. Naltrexone treatment did not modify the decrease in plasma concentrations of LH or FSH. These findings suggest that the inhibitory effect of restraint on the testicular axis is exerted at hypothalamic level by some mechanism other than opioids. INTRODUCTION It is well recognized that stress inhibits gonadal function in various animal species including humans (for review see [1]). Different stressful stimuli such as swimming, long-distance run- ning, surgery, electric foot shocks and psycho- logical stimuli have been shown to induce a decrease in plasma testosterone levels [2-8]. However, the precise mechanism through which stress decreases testosterone secretion is not well understood. It has been postulated that stress does not directly affect testicular testoster- one secretion, but rather inhibits gonadotropin secretion acting at pituitary or hypothalamic level [5,9]. Other authors have found that, although plasma concentrations of testosterone were decreased, there was no reduction in plasma LH levels after stress [10, 11]. Stress activates the hypothalamic-pituitary- adrenal axis and there is evidence suggesting a correlation between the degree of adrenal hyper- function and testicular atrophy after chronic stress [12]. Since stress increases the secretion of glucocorticoids, endogenous opioids and corticotropin-releasing factor (CRF), the inhi- Proceedings of the Vlllth International Congress on Hormonal Steroids, The Hague, The Netherlands, 16-21 September 1990. *To whom correspondence should be addressed. bition of the testicular axis caused by stress could be due to: (1) increased levels of gluco- corticoids during chronic stress, which may interfere with testosterone [13,14] or LH secretion[15, 16]; (2) increased release of en- dogenous opioids, which have been reported to inhibit luteinizing hormone-releasing hormone (LHRH) [17]; or (3) enhanced secretion of CRF, since this peptide is known to decrease LHRH release [18]. Therefore our studies were designed to exam- ine: the effect of stress on the different hormones of the testicular axis and the possible role of glucocorticoids and endogenous opioids in the chronic stress-induced inhibition of the testicular axis. EFFECT OF RESTRAINT STRESS ON THE TESTICULAR AXIS Adult male Wistar rats weighing around 350 g were stressed by restraint in a small flex- ible wire mesh container. All rats were killed at 16.00 h after being stressed for 0, 20, 45, 90, 180 or 360 min; or after 6 h of daily immobilization (from 10.00 to 16.00 h) over 4 consecutive days. As shown in Fig. 1, the testosterone response to stress is biphasic. An increase in plasma concentrations of testosterone at 45 min after immobilization can be observed, whereas at 180 SBMB 40/1 ~-FF 473