ABSENCE OF AN INHIBITORY VASOPRESSINERGIC TONE ON LH-RELEASE IN PUBERTAL MALE RHESUS MACAQUES

During puberty, primates begin to secrete LH, and presumably GnRH, at night and then eventually throughout the day as they mature. We examin ed the role of vasopressin, a putative inhibitor of the GnRH pulse gen erator, on LH secretion in pubertal male macaques both during the day when the GnRH pulse generator was not active and during the night when pulsatile LH secretion was observed. As has been found in other prima tes, LH and testosterone levels were low during the day and elevated a t night. A potent vasopressin receptor antagonist (VPa) was administer ed during the middle 5 h of a 15-hour daytime or nighttime blood colle ction period to determine the effects on LH, testosterone and cortisol secretion. Both during the day and night, cortisol secretion was elev ated during VPa infusion, suggesting that this Via receptor antagonist has agonist activity on the V1b receptor in the pituitary involved in vasopressin-stimulated corticotropin release. Mean LH levels during V Pa infusion were not different from the control period for that group during the day when LH secretion was absent. Mean LH levels were signi ficantly higher (p < 0.05) than pre-VPa LH levels at night when pulsat ile LH secretion was observed. However, LH levels at night during VPa were not higher than levels in untreated animals at the same time. The results of these studies demonstrate that LH and testosterone profile s are similar to those observed in human males during the pubertal tra nsition and suggest that the absence of daytime gonadotropin release d uring puberty is not due to inhibitory vasopressinergic tone on the Gn RH pulse generator.