Effects of female hormonal condition on body weight of male partners: dependence on testicular factors.

Four experiments explored the short-term effects of female estrous condition or gonadal hormones on male body weight. Body weights of male guinea pigs and their ovulating female partners were initially found to show a significant periovular suppression relative to those of female cagemates that were not ovulating at that time. Similar effects in male rats have been hypothesized to result from postcopulatory increases in circulating testosterone and the conversion of that testosterone to estradiol. For evaluation of the probable role of the guinea pig testes in the observed phenomenon, intact and castrated male guinea pigs were housed with ovariectomized females. Female estrus, induced by injecting the females with estradiol and progesterone, resulted in an immediate decline in body weight of the intact male partners, but the body weight of castrated male partners was unaffected. Additional tests evaluated the direct effects of estradiol and testosterone on body weight of male guinea pigs. Injections of up to 1 mg per day of testosterone propionate were insufficient to produce short-term suppression of body weight in either intact or castrated males. However, treatment of the males with estradiol readily reduced their body weight. Overall, these results are not consistent with the hypothesis that short-term reductions in body weight of mated males result from immediate postcopulatory increases in circulating testosterone. It is suggested that other, possibly more estrogenic, testicular factors may play a role in the observed phenomenon.