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

Abstract

To further examine the role of the testes in determining the ontogeny of gonadotropin secretion in the male rhesus monkey, the time courses of circulating LH and FSH concentrations were determined using established RIAs in daytime and nighttime blood samples collected at weekly intervals from birth until 4 yr of age in intact animals (n = 7) and in males orchidectomized at approximately 1 week of age (n = 6). Estimates of plasma androgen (A) concentrations were obtained on nonchromatographed samples with a RIA that reacts with testosterone and other androgens. Plasma PRL concentrations were also determined by RIA, and body weight was monitored at weekly intervals. Testicular volumes were measured at weekly intervals after 1.8 yr of age in five animals. In intact animals, mean daytime plasma A concentrations during the first 3 months of infantile development ranged from 1-6 ng/ml. Daytime plasma A concentrations then declined to reach 0.5-1 ng/ml by 9 months of age, where they were maintained usually until 3 yr of age when circulating levels progressively increased to reach, by approximately 3.5 yr of age, mean levels (6 ng/ml) characteristic of fully mature males. During the transition from infantile to perpubertal development, circulating LH and FSH concentrations showed a pattern similar to that of A, with elevations during the first 2 months of life followed by a decline to undetectable concentrations. In contrast to A, however, distinct pubertal increments in circulating LH and FSH concentrations were not observed in daytime samples from intact animals. The first indication of the pubertal reactivation of the hypothalamic-pituitary-testicular axis was provided by a reemergence of nocturnal elevations in plasma A concentrations between 2-3 yr of age. These were followed shortly thereafter by detectable plasma LH concentrations in nighttime samples. Orchidectomy at 1 week of age resulted in a progressive and dramatic rise in circulating gonadotropin concentrations, which plateaued approximately 3 weeks later at values 1 order of magnitude greater than those observed in intact animals. This hypersecretion of LH and FSH was not sustained, however, and by 10 months of age, plasma gonadotropin concentrations in agonadal animals were indistinguishable from those in age-matched intact controls. These low levels of the gonadotropic hormones were maintained, in the absence of the testes, for approximately 2 yr until a second or "pubertal" postcastration hypersecretion of LH and FSH was observed.(ABSTRACT TRUNCATED AT 400 WORDS)