Influence of suckling on gonadotropin secretion in the female rhesus monkey (Macaca mulatta)

The ability of exogenous estrogen to elicit gonadotropin surges was determined at approximately monthly intervals in postpartum female rhesus monkeys nursing their infants, in postpartum females whose infants were weaned at birth, and in pregestational females that served as foster mothers to these weaned infants. The stimulatory action of estrogen on gonadotropin secretion was abolished or severely inhibited for the first 6 months of nursing in both natural and foster mothers. In contrast, the administration of estrogen to postpartum females, whose infants were weaned at birth, elicited luteining hormone (LH) and follicle stimulating hormone (FSH) surgers on the first trial 30 days after delivery. The abolition of the positive feedback action of estrogen in nursing mothers was associated with a suppression of basal serum gonadotropin levels. These findings demonstrate that the protracted inhibition of gonadotropin secretion in lactating female rhesus monkeys is occassioned by the presence of a suckling infant and is independent of antecedent events associated with gestation and parturition.