The ontogeny of pulsatile growth hormone secretion and its temporal relationship to the onset of puberty in the agonadal male rhesus monkey (Macaca mulatta).

Abstract

The pubertal amplification of GH secretion in primates has been thought to reflect an increase in gonadal steroid hormones due to gonadotropin stimulation induced by hypothalamic GnRH release. Previous studies in agonadal, peripubertal, male rhesus monkeys have estimated the age of GnRH activation (defined as d 0) using analyses of nocturnal, pulsatile LH patterns derived from sequential blood samples. Using samples from these earlier studies, secretory patterns of GH were analyzed using Cluster at approximately 30-d intervals in the youngest prepubertal ages and at approximately 10- to 20-d intervals in the period immediately preceding and following the onset of puberty. Pulse frequency, amplitude, and mean GH increased significantly between early prepubertal ages (up to 30 d before d 0) and the late prepubertal period (between -20 d and d 0). Pulsatile GH activity increased earlier than pulsatile LH secretion in four of five animals. These findings support the conclusion that pulsatile GH secretion increases developmentally in the absence of gonadal steroids. Furthermore, the present observation that the developmental increase in GH secretion occurs earlier than previously reported is consistent with the possibility that GH itself either directly or indirectly participates in the pubertal reinitiation of GnRH pulse generator activity.