STRESS AND THE ENDOCRINE HYPOTHALAMUS-PITUITARY-TESTIS SYSTEM - A REVIEW

Stressors generally induce a depression of the hypothalamus-pituitary-testis (HPT) system, mediated by the activated hypothalamus-pituitary-adrenocortical (HPA) system, resulting in a fall in plasma luteinising hormone (LH) and testosterone levels. Hypothalamic gonadotrophin-releasing hormone (GnRH) secretion may be suppressed by endogenous opioid peptides (EOP) and/or corticosteroids. The latter dramatically enhance the negative feedback effects of testosterone on both the hypothalamus and pituitary. Pituitary gonadotrophin secretion may be reduced by adrenocorticotrophic hormone or by EOP of hypothalamic or pituitary origin. Decreases in plasma concentrations of testosterone, independent of gonadotrophins, can be induced by corticosteroids. These hormones might reduce the number of Leydig-cell LH-receptors or occupation of LH-receptors. Testicular steroidogenesis may also be inhibited by pro-opiomelanocortin-derived (opioid) peptides secreted by the Leydig cells. There are some indications of increases in LH and testosterone during acute stress and, in dominant male animals, during the stress of social conflict. The latter finding indicates a difference in stress response between dominant and subordinate males. In subordinate males, decreased feedback sensitivity may allow hypersecretion throughout the HPA system. As a result, corticotrophin releasing hormone may induce the release of EOP from the hypothalamus, which inhibit the HPT axis. This inhibition may be enhanced by a corticosteroid-induced decrease in testosterone feedback.