Stimulation by estrogen and progesterone of the in vivo growth of transformed murine Leydig cells only at the limited early phase of growth.

Abstract B-1 F is a cell line established from estrogen-responsive murine Leydig cell tumor and maintained in vitro. We investigated the effects of steroid hormones on the growth of tumors produced by the inoculation of B-1 F cells into mice. When tumor tissues were transplanted into castrated male mice, injections of estradiol-17 beta (E2) or progesterone shortened the period before tumors became palpable, but did not affect the growth rates of tumors after tumors became palpable. Injections of E2 or progesterone from the time when tumors became palpable did not affect the growth of tumors, and the discontinuation of injections of E2 or progesterone during the middle growth phase showed no effect on the growth of tumors. E2 or progesterone also did not increase the mitotic indices of tumors after they became palpable. E2 and progesterone did not stimulate the proliferation of dispersed tumor cells in vitro. The present results suggested that steroid hormones might exert their actions only at the limited early phase of growth of transplanted steroid hormone-responsive tumors in vivo.