Effects of oestrogen and progesterone on the development, oviductal transport and uterine retention of eggs in hypophysectomized pregnant rats

Hypophysectomy of rats on day 1 of pregnancy resulted in expulsion of most eggs from the uterus between days 5 and 6, delayed entry of eggs into the uterus, and retarded development of eggs.

Expulsion of eggs was prevented with daily injections of 2 mg progesterone. Other regimes of progesterone administration were also beneficial, but not as effective as daily injections.

Daily injections of 2 or 4 mg progesterone, or of progesterone plus oestrone, restored egg transport to normal, whereas a single injection of progesterone did not. Daily injections of small amounts of oestrone caused total disappearance of eggs from the reproductive tract.

The development of eggs was significantly improved with daily injections of progesterone plus oestrone, but not with progesterone alone.

Combined treatment with progesterone and oestrone caused premature shedding of the zona pellucida in mature blastocysts, young blastocysts, and morulae.

Effects of ovariectomy or hypophysectomy on day one of pregnancy on development and transport of fertilized rat eggs

The development of fertilized eggs and their transport through the oviduct were studied in rats ovariectomized or hypophysectomized on day 1 of pregnancy. When killed on day 5 of pregnancy, 100%, 66% and 27% of the eggs were in the uterus of intact controls, ovariectomized and hypophysectomized rats, respectively. Thus both ovariectomy and hypophysectomy retarded transport of a proportion of the eggs. Ninety-nine per cent, 72% and 78% of the eggs were in the blastocyst stage in intact controls, ovariectomized and hypophysectomized rats. The remainder of the eggs were either morulae or degenerated.

Blastocysts and morulae recovered from the hypophysectomized rats were transferred to the uteri of pseudopregnant recipients: 52–57% developed into normal term foetuses compared to 57% for intact controls.

In hypophysectomized rats killed in the morning of day 6, the number of eggs recovered was greatly reduced as compared with rats killed on day 5. This loss of eggs was prevented by placing a ligature at the cervical end of the uterus in the morning of day 5. It was therefore concluded that the eggs had been expelled from the uterus into the vagina between days 5 and 6.