Pregnancy-terminating action of a luteinizing hormone-releasing hormone agonist D-Ser(But)6desGly10ProEA in baboons.

Subcutaneous injections of luteinizing hormone-releasing hormone agonist D-Ser(But)6desGly10ProEA given to six pregnant baboons at 8-hour or 12-hour intervals over a period of 4 to 6 days around the time of the appearance of chorionic gonadotropin in the circulation diminished the plasma progesterone (P) to very low levels, leading to termination of pregnancy in all animals. The same amount of the agonist, given in a similar manner in the early luteal phase, although succeeding in reducing the plasma P levels by more than half, failed to abrogate pregnancy. The time and frequency of administration of the agonist appear to be important for interception of pregnancy.