Male rat behavior, endocrinology and reproductive physiology in a mixed-sex, socially stressful colony.

Previous research suggests that social stress in the absence of females disrupts male reproductive functioning. The presence of females often increases intermale aggression and, presumably, the probability that fighting----social stress----hyperadrenalism----reproductive disruption. Colony membership of male rats was manipulated in the present research to provoke high or low aggression and the consequent environments that were characterized as high or low socially stressful. The principle comparisons were between all-male and mixed-sex colonies. Results were that the presence of females predictably increased aggressive behavior in both high and low stress environments, yet the adrenal response was different in the two environments. When females were present, adrenal weights and circulating corticosterone levels of males increased in the low stress setting but decreased in the high stress setting. Males cohabitating with females in both environments, on the other hand, experienced elevated titers of circulating testosterone, increased activity of various androgen-sensitive tissues and greater epididymal sperm reserves. The conclusion is that the profound changes in males with sexual contact can attenuate the stress----reproductive disruption relationship.