Pulsatile secretion of bioactive luteinizing hormone in adult male rhesus macaques: Acute and chronic effects of orchidectomy

Serum concentrations of bioactive luteinizing hormone (LH) and of testosterone were measured in adult male rhesus macaques at the time of, and at least 6 wk after orchidectomy. The effects of anesthesia alone and of sham surgery on the secretion of these hormones were also studied. Contrary to expectations based on current notions of the negative feedback actions of testosterone on gonadotropin secretion, pulsatile LH release was absent for an average of 9.3 h immediately after removal of the testes. Animals that were subjected to sham surgery or anesthesia alone showed a delay of 4.4 h in the reappearance of LH secretion, similar to the lull in LH pulsations normally observed at that time of day. When LH secretion resumed in the acutely castrated animals, the pulses continued for the remainder of the sampling period and did not show the midmorning decrease in activity characteristic of intact or sham-operated animals. In the animals that were castrated, circulating cortisol was elevated approximately twofold above levels observed in sham-operated animals for a period of 8 h, beginning immediately after castration. In the long-term (>6 wk) castrated male macaques, circulating bioactive LH levels were eightfold greater (24 μ/ml) than levels observed in intact animals (3 μg/ml). The frequency of LH pulses in the castrated animals, as determined by PULSAR analysis, was significantly influenced by sampling frequency. When blood samples were taken at 15-min intervals for 24 h, LH pulse frequency averaged 7 pulses/12 h. If samples were collected every 7 min for 12 h, the frequency increased to 13 pulses/12 h. These findings concerning the control of gonadotropin secretion in male rhesus macaques show that removal of the testes results in an acute cessation of LH secretion that outlasts the suppressive effects of anesthesia and sham surgery; that the cessation of LH secretion in castrated animals is associated with a decline in circulating testosterone and a sustained elevation in circulating cortisol; that the escape from the negative feedback action of testicular secretions, evidenced by the absence of an early morning lull in LH secretory episodes in orchidectomized animals, can be observed within 16-18 h after removal of the testes; and that the frequency of episodic LH secretion increases from 14 pulses/24 h in intact animals to 26 pulses/24 h after orchidectomy.