Effects of oral administration of medroxyprogesterone acetate and ethinyl estradiol on the transportation and development of rabbit eggs.

Abstract

Fifty-four rabbits in groups of 6 were subcutaneously injected with progesterone or fed medroxyprogesterone acetate (MPA) for 3 days either before or after artificial insemination and an ovulation-inducing injection of HCG. Feeding with progesterone (2 mg/rabbit/day) before or after ovulation, or by injection after ovulation, had no effect on the development of eggs when examined on day 6. Subcutaneous injection of progesterone or feeding with MPA at the same dose before ovulation, however, induced a complete degeneration of eggs. Oral administration of MPA before ovulation at doses less than 2 mg/rabbit/day for 3 days was progressively less effective. Fifty-six rabbits were fed ethinyl estradiol (EE) or MPA on various days before and/or after insemination, or with one compound before and the other after insemination. When examined on day 6, degeneration of eggs was observed whenever 0.05 mg/rabbit/day of EE was fed for 3 days after ovulation or MPA (2 mg/rabbit/day) for 3 days before ovulation. Although a single feeding with MPA on day - 1 (the day before insemination) and a single feeding with EE on day 1 were effective, a single feeding with MPA on day -1, a single feeding with EE on day 1, or 3 feedings with EE before ovulation and 3 injections of progesterone after ovulation, all produced less egg degeneration. Fifty-two rabbits were fed MPA before ovulation or with EE after ovulation. Although the majority of eggs were fertilized and normal when examined on day 2, the rate of recovery was slightly lower, and the eggs reached the uterus sooner than in the controls. Another 50 rabbits were fed MPA before and/or with EE after ovulation and were examined on days 2, 3 and 4. In these animals the recovery rate decreased as time elapsed, egg transport was speeded, and many eggs recovered at later times were neither at the expected stage of development nor developing normally. Finally, 1-day rabbit eggs were transferred into the ampullae of the fallopian tubes of estrous rabbits treated with MPA or EE. When examined at various times, the recovery rate was very low in the recipients treated with EE after transfer. Early entry of eggs into the uterus was observed in the control recipients, in those treated with MPA before transfer, and in those treated with EE after transfer. Retention of eggs in the tubes, however, was found in the recipients treated with MPA after transfer. It is concluded that endogenous or exogenous estrogen causes rapid egg transport from the tube to the uterus, while endogenous or exogenous progesterone counteracts the estrogenic effect and slows egg transport. Administration of progesterone before ovulation or of estrogen after ovulation speeds the transport of eggs and causes their degeneration or expulsion from the uterus. (Endocrinology79: 939, 1966)