Maintenance of pregnancy in rabbits treated with long-lasting progestins

Fertilized eggs from rabbits 1 or 2.5 days after insemination were transferred to the oviduct or uterine horn of recipients that had received a single subcutaneous injection of 20 or 30 mg of one of seven long-acting progestins. The rabbits were observed daily, and the number of implantation sites was determined 10 or 11 days after egg transfer. No implantation sites were recorded in the recipient does treated with progesterone or ZK-5623 (Schering AG, Berlin, West Germany), a nor-steroid compound. Thirty-nine percent and 51% of the transferred eggs implanted in the recipient does treated with ZK-5410 (Schering AG) and chloromadinone acetate (Eli Lilly & Company, Indianapolis, IN), respectively. However, most of the pregnant animals aborted 14 to 20 days after egg transfer. The pregnancy was either maintained to term or was prolonged beyond the normal gestation length in the does treated with other compounds, ZK-53915, ZK-9349 (Schering AG) or Depo-Provera (Upjohn Company, Kalamazoo, MI). The young delivered after a subcutaneous injection of 17 beta-estradiol and oxytocin were found normal and active.