INHIBIN-B IN THE MALE RHESUS-MONKEY - IMPACT OF NEONATAL GONADOTROPIN-RELEASING-HORMONE ANTAGONIST TREATMENT AND SEXUAL DEVELOPMENT

We examined the effect of reversibly suppressing pituitary-testicular function during the neonatal period on developmental changes in inhibi n-B and FSH secretion in male rhesus monkeys. Infants were treated wit h either vehicle, a GnRH antagonist (Ant) or the Ant and androgen (Ant /And) for the first 4 postnatal months, and the effects on serum inhib in-B and FSH were monitored during the neonatal and peripubertal perio ds. In neonates, Ant or Ant/And treatment lowered both serum FSH and i nhibin-B levels. By 12 months of age, inhibin-B concentrations no long er differed across treatment groups. A major increase in inhibin-B occ urred between 27-36 months of age (late prepubertal period) in all gro ups, but levels were lower at 33 and 36 months of age in Ant/And-treat ed animals than in controls. These differences most likely were relate d to fewer Ant/And-treated animals achieving sexual maturity during th eir fourth year of life. Regardless of treatment, inhibin-B levels wer e higher in those that were destined to become mature (in year 4) than in those that were not. During the late prepubertal period, serum inh ibin-B was positively correlated with age and testicular volume, but n ot with serum LH or testosterone. After this period (39-52 months of a ge), inhibin-B no longer correlated with these parameters. FSH levels were near or below detection limits in most peripubertal animals, but FSH was detectable in fewer samples from control than treated animals. The data suggest that inhibin-B secretion in the neonate is driven by gonadotropin secretion, but during the juvenile hiatus in gonadotropi n secretion, the monkey testis continues to produce substantial amount s of this hormone.