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J. K. Hodges, D. I. Green, P. G. Cottingham, M. J. Sauer, C. Edwards, and S. L. Lightman

Summary. Doses of 100 or 200 μg of a novel GnRH antagonist ([N-acetyl-dβNall-d-pCl-Phe2-d-Phe3-d-Arg6-Phe7-Arg8-d-Ala10]NH2 GnRH) (4 animals/dose) were administered on Days 10/11 of the luteal phase and induced a marked suppression of circulating bioactive LH and progesterone concentrations within 1 day of treatment (P < 0·01). Thereafter, progesterone concentrations remained low or undetectable until after the next ovulation. Similar results were obtained when 200 μg antagonist were given on Days 5/6 of the luteal phase (N = 4). The interval from injection of antagonist (200 pg but not 100 μg to ovulation (based on a rise in progesterone above 10 ng/ml) was significantly longer than that from prostaglandin-induced luteal regression to ovulation in control cycles (N = 4/treatment) (range, 13–15 days after antagonist vs 8–10 days after prostaglandin, P < 0·01). This delay of 4–5 days was equivalent to the duration for which LH concentrations were significantly suppressed by 200 μg antagonist when administered to ovariectomized animals (N = 3). Corpus luteum function during the cycle after GnRH antagonist treatment appeared normal according to the pattern of circulating progesterone. These results show that corpus luteum function and preovulatory follicular development in the marmoset monkey are dependent on pituitary gonadotrophin secretion.

Keywords: GnRH antagonist; monkey; corpus luteum