Synergism between psychosocial and metabolic stressors: impact on reproductive function in cynomolgus monkeys

The role of energy imbalance versus psychosocial stress in the pathogenesis of female reproductive dysfunction characterized by anovulation and amenorrhea remains controversial. In women, functional hypothalamic amenorrhea can develop in the absence of significant weight loss, excessive exercise, or profound psychosocial disruption. We posited, therefore, that commonplace, seemingly minor stressors that alone would have minimal impact upon reproductive function might interact synergistically such that combinations of stressors would cause a greater impairment of the reproductive axis than any single stressor alone. We then developed a monkey model to test this hypothesis. Adult female cynomolgus monkeys with normal menstrual cycles were randomized into three experimental groups and studied over four menstrual cycles. The groups were: low-level psychosocial stress (i.e., moving to a new housing environment; Move, n = 8), moderate energy imbalance (Exercise + Diet, n = 9); and all stressors in combination (Move + Exercise + Diet, n = 10). Food intake, body weight, menstrual cyclicity, and reproductive hormones were assessed for two control menstrual cycles followed by two experimental cycles during which the monkeys experienced the stressors. Abnormal cycles were considered to be abnormally long or anovulatory cycles. Few abnormal cycles occurred in the Move group (1 of 8 monkeys) and in the Exercise + Diet group (1 of 9 monkeys). In contrast, 7 of 10 monkeys in the Move + Exercise + Diet group displayed at least one abnormal cycle (chi(2) = 9.61, P = 0.008). These findings suggest that infertility due to hypothalamic hypogonadism can result from the combination of commonplace, seemingly minor stressors that often escape clinical attention.