Luteinizing hormone release in the cat in response to coitus on consecutive days of estrus

Domestic cats are known to release an ovulatory LH surge in response to coitus. In this study, we determined the LH release 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 first 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 X 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 approximately 338 ng/ml X h with significantly less (P less than 0.05) LH released on subsequent days: 33, 14, 19, 7 and 14 ng/ml X 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 (mean = 51 +/- 5 pg/ml) as compared to the previous day (mean = 34 +/- 4 pg/ml) when coitus did not result in a significant LH release. These data suggest that 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.