Pinealectomy in agonadal infantile male rhesus monkeys (Macaca mulatta) does not interrupt initiation of the prepubertal hiatus in gonadotropin secretion.

The present study was undertaken to determine whether pineal hormones are responsible for initiation of the prepubertal hiatus in gonadotropin secretion that is observed between 2-3 months of age in the infantile male rhesus monkey. Six neonatally orchidectomized rhesus monkeys were pinealectomized at 4-6 weeks of age using a microneurosurgical technique. The time courses of circulating LH and FSH concentrations during the first 36 weeks of life in these animals were determined in weekly samples by RIA and compared to those observed in sham pinealectomized animals (n = 2) and in agonadal infantile males with an intact central nervous system (n = 3). The completeness of pinealectomy was verified by an absence of pineal rests in serial coronal sections of the brain. The absence of nocturnal elevations in circulating immunoreactive melatonin concentrations in pinealectomized monkeys was consistent with the foregoing histological findings. The developmental pattern of gonadotropin secretion in pinealectomized animals was unremarkable. Of particular interest in the context of the present question was the failure of pinealectomy to interrupt or to delay the decline in plasma LH and FSH concentrations that characteristically occurs in neonatally orchidectomized monkeys between 2-8 months of age. These findings suggest that, in the rhesus monkey, the pineal gland plays no major role in mediating the onset of the inhibition of LH and FSH secretion that occurs during transition from the infantile to the prepubertal phase of development and, therefore, is not responsible for initiating the protracted delay in the advent of puberty in this higher primate.