A Study of the Role of the Postnatal Testes in Determining the Ontogeny of Gonadotropin Secretion in the Male Rhesus Monkey (Macaca mulatto)*

Publisher Website
Google Scholar
Abstract
The time courses of circulating LH [luteinizing hormone] and FSH concentrations were determined in daytime and nighttime blood samples from birth until 4 yr of age in intact animals (n = 7) and in males orchidectomized at .apprx. 1 wk of age (n = 6). Plasma androgen concentrations plasma androgens [A], PRL (prolactin), body weight and testicular volumes were measured. These observations provided further evidence to support the view that, in higher primates, the hiatus in gonadotropin secretion during prepubertal development is occasioned by mechanisms of extragonadal origin. Thus, it would appear that the gonadostat hypothesis, which proposes that the restraint of LH and FSH secretion during prepubertal development is occasioned by the inhibitory action of gonadal hormones on a hypersensitive hypothalamic-hypophysial apparatus, should no longer be invoked as the fundamental mechanism underlying the protracted delay in the onset of puberty in higher primates. The reactivation of the hypothalamic-pituitary apparatus in neonatally orchidectomized monkeys at an age (2 1/2 yr) when the initiation of the pubertal process may have been anticipated had the animals remained intact also suggests that testicular hormones have little impact on the postnatal ontogeny of central neural mechanisms that govern the intermittent release of hypothalamic gonadotropin releasing hormone. Striking circannual like fluctuations in serum PRL concentrations were observed, after 1 yr of age, in both intact and agonadal animals throughout prepubertal and peripubertal development. On several occasions, the 1st evidence of a pubertal reactivation of gonadotropin secretion, i.e., the onset of nocturnal A secretion in intact animals and the reinitiation of FSH secretion in agonadal animals, was associated with a nadir in plasma PRL concentrations. Thus, it is possible that PRL may play a role in determining the precise timing of the onset of the pubertal process in this species.