The Rhesus Monkey Corpus Luteum Is Dependent on Pituitary Gonadotropin Secretion throughout the Luteal Phase of the Menstrual Cycle*

Abstract

Experiments were conducted in rhesus monkeys to determine whether the corpus luteum of the menstrual cycle requires pituitary gonadotropin for progesterone production and normal functional lifespan. Eight adult females were rendered anovulatory by placement of radiofrequency lesions in the arcuate region of the medial basal hypothalamus. Endogenous gonadotropin secretion and ovulatory cycles were reestablished by chronic pulsatile infusion of GnRH [gonadoliberin]. Control luteal phases exhibited typical plasma progesterone patterns and ranged from 14-17 days in length. In experimental cycles, endogenous gonadotropin secretion was interrupted during the luteal phase by stopping the infusion of GnRH. When the GnRH infusion was stopped in the early luteal phase (3 days after the preovulatory estradiol peak; day 3), plasma LH [luteinizing hormone] fell to undetectable levels within 90 min. Plasma progesterone concentrations (1.5 .+-. 0.4 ng/ml) declined to undetectable levels (< 0.2 ng/ml) by the afternoon of day 5 (P < 0.05). Premature menses occurred 2-5 days later. When the GnRH infusion was stopped in the midluteal phase (day 8), plasma LH fell below the limits of detectability within 150 min. Circulating progesterone (4.5 .+-. 1.0 ng/ml) declined to undetectable levels by the afternoon of the following day. Premature menses occurred 3 days after the fall in plasma LH, 11 days after the preovulatory estradiol peak. Plasma LH and progesterone remained undetectable as long as exogenous GnRH was withheld (18 days), and progesterone did not reappear until the next GnRH-induced ovulatory cycle. The normal functional lifespan of the primate corpus luteum requires the presence of circulating pituitary gonadotropin during both the early (developmental) and middle (fully functional) stages of the nonfertile luteal phase.