Ihibition of the pre-ovulatory proestrous gonadotropin surge, ovulation and pregnancy with a peptide analogue of luteinizing hormone releasing hormone.

D-[PHE]-2-D[ALA]-6-LRH (Wy-18,185), an analogue of synthetic hypothalamic LRH, was evaluated for its anti-fertility properties. The compound dampens the preovulatory proestrous surge of serum LH and FSH in rats, is an active anti-ovulatory agent in both rats and rabbits and prevents pregnancy when administered pre-coitally to rats. Additionally, the compound suppresses the ovulatory event in rats only during the cycle in which it is acutely administered, does not interfere with the rat vaginal cycle and is devoid of any effects on body, ovarian and uterine weights when given acutely. The compound is a moderate LRH agonist in rats but does not induce ovulation in rats or rabbits.