Correlation between in vivo inhibition of gonadotropin release induced by LH-RH and the blockade of ovulation by synthetic analogues of LH-RH.

Several antagonists of LH-RH were examined for their anti-LH/FSH releasing activities in an immature male rat assay and for their ability to block ovulation. The in vivo inhibition of the release of LH and FSH induced by LH-RH over a 4-h period of time and the antiovulatory activity of these analogues were parallel to each other. The analogues that exhibited at least a 95% inhibition of LH and 77% of FSH release at 1 h and 75% and 40% of FSH release at 4 h in immature male rats, gave high blockade of ovulation. [D-Phe2, D-Trp3, D-Phe6]-LH-RH was the most potent analogue of the series and it seems to be active in men.