Luteinizing Hormone Release in the Cat in Response to Coitus on Consecutive Days of Estrus1

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Abstract
Domestic dats release an ovulatory LH [luteinizing hormone] surge in response to coitus. The LH release was determined following coitus on consecutive days of estrus. Variable responses to 2 matings were obtained as to the day of the ovulatory LH release: 6/14 on Day 1 (the 1st day of estrus), 3/14 on Day 2, 4/14 on Day 3 and 1/14 on Day 4 of estrus. The average amount of LH released during the ovulatory surge was 298 ng/ml per h (area units). The ovulatory surge was the greatest surge during estrus in 10/14 observations; 4/14 had a greater LH surge the following day. The average amount of LH released on the day of the greatest surge was .apprx. 338 ng/ml per h with significantly less (P < 0.05) LH released on subsequent days: 33, 14, 19, 7 and 14 ng/ml per h. This dramatic decrease in LH release indicates an apparent refractoriness of the hypothalamus/pituitary to coital stimulation following a major release of LH. Estradiol-17.beta. concentrations were always greater on the day of the coitus-induced ovulatory LH surge (.hivin.X = 51 .+-. 5 pg/ml) as compared to the previous day (.hivin.X = 34 .+-. 4 pg/ml) when coitus did not result in a significant LH release. The ability to release LH in response to coitus is in part a function of the duration of exposure to estrogen by the hypothalamus and/or anterior pituitary.