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PubMed1981

Pulsatile pituitary gonadotropin secretion during maturation of the dominant follicle in monkeys: estrogen positive feedback enhances the biological activity of LH.

In the follicular phase of the menstrual cycle, pulsatile patterns of LH and FSH secretion in monkeys change during maturation of the dominant follicle. At the preovulatory surge, the most striking event is the prodigious elevations of bioassayable LH, rising up to 50-fold within 24 h. Principally, establishment of the surge is due to marked enhancement of the amplitude of LH secretory pulses. In contrast, LH and FSH measured by RIA enter, in parallel, the surge modes of secretion approximately 5 h later than bioassayable LH and rise more slowly; the B:I ratio may reach 10:1. This same disparity between bioassayable versus immunoassayable LH was induced in castrate monkeys under estrogen positive feedback stimulation. We conclude that the preovulatory estrogen surge promotes the secretion of an LH molecule(s) having enhanced biological activity.

Animals↗

PubMed1980

Asymmetrical ovarian function during recruitment and selection of the dominant follicle in the menstrual cycle of the rhesus monkey.

Despite similar exposure to pituitary gonadotropins by perfusion of both ovaries with the same peripheral blood, only 1 of the 2 ovaries sponsors the single dominant follicle in the typical menstrual cycle. In the present study was examined the initiation of asymmetrical ovarian function during recruitment and selection of the dominant follicle in the primate ovarian cycle by comparison of steroid hormones in the ovarian venous effluent. Thirty-four adult female rhesus monkeys were selected because of high estimated fertility based on their reproductive performance. These monkeys underwent laparotomy for ovarian inspection and collection of ovarian venous blood on 1 of days 1, 3, 5, 7, 9, and 11 after the onset of menses. In addition, femoral blood was collected daily. Repeat laparotomies were performed in the midluteal phase to assess the location of the functional corpus luteum. Concentrations of 17 beta-estradiol, androstenedione, and progesterone were determined in all sera, as well as LH and FSH in peripheral sera, by RIA. In all, 17 of 19 ovulatory monkeys manifested clear asymmetry of 17 beta-estradiol 5 days before the LH/FSH midcycle surges. Often, asymmetry of androstenedione levels was not apparent until 3 days before the midcycle gonadotropin surge. Uniformly, in ovulatory monkeys, the ovary associated with significantly greater concentrations of 17 beta-estradiol and androstenedione in ovarian venous serum ultimately bore the functional corpus luteum observed in the midluteal phase and confirmed by elevated progesterone in peripheral serum. We interpret these findings to indicate that asymmetrical ovarian steroid secretion, especially of 17 beta-estradiol, may be among the earliest indicators that the dominant follicle, or at least the ovary destined to bear it, is already selected by 5 days before the preovulatory FSH/LH surge in the typical menstrual cycle.

Androstenedione↗