[D-Phe2, Phe3, D-Phe6]-LH-RH, a potent antagonist of LH-RH, was injected during the different stages of the estrous cycle in rats at a dose of 1.5 mg/rat. When it was administered at noon or proestrus, a 100% blockade was observed. This decreased to 33% and 17% when the analogue was injected at 9 AM on proestrus and diestrus 2, respectively. No blockade of ovulation was observed after the injection of the analogue on diestrus 1 or on the previous estrus. The sequential administration of the analogue twice daily on E, D1 and D2, brought about almost complete suppression of LH surge on proestrus and an 86% blockade of ovulation without altering the cyclic vaginal smear pattern. In this case, serum levels of estradiol were not modified but progesterone levels were significantly lower on proestrus and higher on diestrus 1 in the analogue treated group as compared to control rats. This higher level of progesterone on diestrus 1 might account in part for the inhibition of the LH-surge and blockade of ovulation by the inhibitory analogues of LH-RH.
|Original language||English (US)|
|Number of pages||4|
|Journal||Proceedings of the Society for Experimental Biology and Medicine|
|State||Published - Oct 1978|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)