Effect of exogenous sex steroids upon the number of germ cells and the growth of foetal ovaries grafted under the kidney capsule of adult ovariectomized hamsters

The effect of estradiol E, progesterone P and testosterone propionate T upon growth and germ cell population of foetal ovaries transplanted under the kidney capsule of adult ovariectomized hamsters was examined. Foetal ovaries were obtained 15 days postcoitum and the host received daily subcutaneous injections of E (1 µg/day), P (5 mg/day), T (500 µg/day) or E + P in 0·1 ml oil for 25 days beginning 5 days before grafting. One day after the last injection, the size of the ovary, the germ cell population and plasma steroid levels were assessed. The results of hormone assays indicate that daily steroid administration was able to maintain continuously elevated plasma levels of the corresponding hormone. Interconversions or steroid secretion by the graft, if any, were not reflected in the peripheral circulation. The growth of the graft was stimulated by T and inhibited by P, in comparison with E and oil-treated controls. All germ cells were at the stage of primary oocyte forming part of a primordial or growing follicle. Their absolute number was significantly increased by T and E and significantly decreased by P and E + P. The number of oocytes per mm 3 of ovary was increased 80 %, 48 % and 40 % with E, T and E + P, respectively. It is concluded that, in the hamster, exogenous sex steroids given to the host can exert specific effects upon the growth and oocyte population of a grafted foetal ovary. Whether ornot the action of steroids upon the graft is a direct one and whether they influenced oogonial mitosis, the evolution of the meiotic prophase or atresia of primary oocytes remains to be determined.