Endocrinology, Vol 133, 1650-1656, Copyright © 1993 by Endocrine Society

ARTICLES

Preovulatory gonadotropin-releasing hormone surge in ovarian-intact rhesus macaques

KY Pau, M Berria, DL Hess and HG Spies
Oregon Regional Primate Research Center, Beaverton 97006.

The occurrence and profile of the preovulatory hypothalamic GnRH surge in relation to plasma profiles of LH and ovarian steroids, i.e. 17 beta- estradiol (E2) and progesterone (P4), were examined in ovarian intact, freely moving rhesus macaques. Nine monkeys with active ovarian cycles were each fitted with a jugular venous catheter and two push-pull cannulae directed to separate sites within the median eminence (ME). Each female was connected continuously to a tether/swivel device through which daily blood samples or frequent blood samples and ME perfusates (simultaneously at 10- to 20-min intervals for 18-24 h) were obtained without disturbing the animals. An increment in the plasma E2 level (> 150 pg/ml) during the follicular phase (FP) was selected as the preovulatory ovarian signal and served as the index for initiating the ME push-pull perfusion (PPP). Daily increased P4 concentrations of more than 1 ng P4/ml plasma for several consecutive days were consistent with the assumption of ovulation and subsequent formation of a corpus luteum after PPP. A total of 18 PPP trials were completed; each in a fresh ME site. Five of these PPPs were performed during the mid- and late FP (3 were between 6-8 days before and 2 were 4 days before the E2 peak). The remaining 13 PPPs, each of 18- to 24-h duration, were performed between 24 h before and 48 h after the highest daily plasma E2 level, i.e. time zero. Of these 13 PPPs, 2 started within 12 h before (-12 to 0 h), 8 began within 12 h after (0-12 h), and 3 started between 12-24 h after this peak E2 value. During the FP, mean levels of GnRH and LH were less than 2 pg/ml and 20 ng/ml, respectively. During the periovulatory interval (-24 to 48 h around time zero), the release of hypothalamic GnRH (expressed in picograms per ml) increased to 6.63 +/- 2.35 between -12 to 0 h (n = 2), peaked at 20.70 +/- 6.09 between 0-12 h (n = 10), declined to 3.25 +/- 1.39 between 12-24 h (n = 11), and further declined to 0.89 +/- 0.18 between 24-36 h (n = 3). The mean GnRH value from 0-12 h was higher (P < 0.05) than other means (including those during the FP), except for the value between -12 to 0 h. Changes in mean plasma LH values during the same periods paralleled those in GnRH.(ABSTRACT TRUNCATED AT 400 WORDS)

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