Studies of induced malignant tumors of placental and uterine origin in the rat: I. Survival of placental tissue following fetectomy

Abstract

1. The survival of placental and embryonic tissues after fetectomy was studied in the rat. At the ninth, tenth, eleventh, or twelfth day of pregnancy, fetuses were removed from gestation sacs in the left uterine horn of 46 adult Long-Evans rats; after fetectomy, a beeswax pellet was inserted and the sac was ligated. At the eighteenth, twenty-fifth, thirty-second, or fortieth day after conception, the rats were sacrificed and the fetectomized gestation sacs were removed, sectioned, and examined histologically.2. Trophoblastic cells regressed within 3 weeks after fetectomy in most of the embryonic sacs (94.1 per cent) although they survived in the myometrium of 5.4 per cent for more than 4 weeks after fetectomy. Cortisone injection had no effect on trophoblast survival. Yolk sac epithelium survived only 2 weeks after fetectomy in 4.9 per cent.3. Embryonic cells, injected subcutaneously into the mothers at the time of operation or persistent in the uterine wall, survived to the fortieth day after conception in 36.4 per cent of the animals; fetal tissues had developed in all of these. The survival rate of embryonic cells was much higher than that of trophoblastic cells.4. No differences in the survival of trophoblast, yolk sac, or embryonic tissue were observed whether animals were fetectomized on the ninth, tenth, eleventh, or twelfth day of pregnancy.