Evidence that inhibin plays a major role in the regulation of follicle-stimulating hormone secretion in the fully adult male rhesus monkey (Macaca mulatta).

In the juvenile male rhesus monkey in which an adult-like pattern of endocrine activity in the pituitary-testicular axis is imposed by pulsatile stimulation with exogenous GnRH, administration of inhibin antiserum elicits a marked and selective hypersecretion of FSH. This finding suggests that in the monkey, testicular inhibin plays a major role in the postpubertal regulation of this gonadotropin. The purpose of the present study was to confirm this view more directly. To this end, 10 adult male rhesus monkeys were implanted with indwelling venous catheters and housed in specialized cages that permit continuous access to the venous circulation with minimal restraint and without tranquilization. Six of the males received a continuous infusion of an ovine antiserum to the alpha-subunit of human inhibin (iv bolus injection of 2.22 ml/kg BW, followed by a continuous infusion of serum at 0.62 ml/kg BW.24 h), and 4 animals received a similar infusion of control ovine immune serum. The duration of the infusion of the inhibin antiserum ranged from 2.5-7.5 days, and that for the control serum was 7.5 days. The FSH response to immunoneutralization of circulating inhibin was determined by measuring concentrations of this gonadotropin in sequential plasma samples collected between 1900-2300 h on the day before initiation of the anti-serum infusion and, depending on the duration of the infusion, on days 0.5, 1.5, 2.5, 4.5, and 6.5 of antiserum administration. In 5 of the 6 animals that received the inhibin antiserum, a progressive hypersecretion of FSH was observed during the initial 2.5 days of the infusion. This increase in circulating FSH concentration, which reached, by day 2.5 of treatment, a value 2- to 3-fold greater (P less than 0.05) than the pretreatment control level, was not associated with changes in either LH or testosterone levels. Continuation of the infusion of the inhibin antiserum beyond 2.5 days invariably resulted in a marked decline in LH and testosterone secretion, suggesting that the hypophysiotropic drive to the pituitary-testicular axis may have been compromised, presumably by a mechanism related to the infusion of heterologous serum. Infusion of the control immune serum for 2.5 days was not associated with an elevation of circulating FSH concentrations, and changes in circulating concentrations of plasma LH and testosterone were, as expected, unremarkable. Continuation of the infusion of control serum, like that of antiserum, generally resulted in a temporary but precipitous decline in LH and testosterone secretion.(ABSTRACT TRUNCATED AT 400 WORDS)