In VivoGonadotropin-Releasing Hormone Release and Serum Luteinizing Hormone Measurements in Ovariectomized, Estrogen-Treated Rhesus Macaques*

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Abstract
The push-pull perfusion technique was used to measure GnRH [gonadotropin-releasing hormone] release in unanesthetized female rhesus macaques (M. mulatta) and to examine the dynamic relationship between GnRH release and LH [luteinizing hormone] levels during the estrogen-induced LH surge. Each ovariectomized macaque was anesthetized and stereotaxically fitted with a push-pull cannula directed into the median eminence (ME). After at least 1 wk of recovery, each animal received an estradiol benzoate (E2B) injection (42 .mu.g/kg [body wt]) or an oil (OIL) injection and underwent push-pull perfusion of the ME and blood sampling for at least 5 h between 28 and 56 h postinjection. Continuous 10 min push-pull perfusates were collected and prepared for GnRH radioimmunoassay. Peripheral venous blood smaples were obtained either hourly or every 10 min; serum LH levels were determined by Leydig cell bioassay. GnRH release was detectable and pulsatile in areas in or adjacent to the ME or arcuate nucleus. In 8 OIL monkeys, GnRH pulses were regular (.apprx. 1 pulse every 60 min) and of low amplitude (14.7 .+-. 12.0 pg) with mean GnRH release rate of 4.0 .+-. 1.7 pg/10 min. In 5 E2B-treated monkeys, GnRH release during the rising phase of the LH surge occurred as an apparent burst of high amplitude GnRH pulses. The mean GnRH release rate (37.5 .+-. 17.9 pg/10 min) and mean GnRH pulse amplitude (170.0 .+-. 90.0 pg) during the 5 h before the peak LH level in E2B-treated monkeys were greater than OIL values (P < 0.025, mean release; P < 0.05, mean amplitude). Within individual E2B-treated monkeys, hourly mean GnRH release rates were significantly correlated with LH levels during the ascending limb of the LH surge (r = 0.75 .+-. 0.11; P < 0.025). Apparently, an increase an GnRH neurosecretion occurs in E2B-treated monkeys; it is associated with generation of the LH surge. Evidently, the primate hypothalamus, through changes in GnRH secretion, activity participates in the E2B-induced LH surge.

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