Dual effects of estradiol on normal and tumor pituitary cell multiplication

Abstract

We have compared the effects of estradiol on the [ 3H]thymidine (TdR) incorporation into the DNA of 2 rat tissues whose growth is controlled by estradiol in vivo in 2 opposite directions: the normal anterior pituitary and the MtF 4 pituitary tumor transplanted under the kidney capsule. Small pieces of pituitary or tumor from Fischer rats, treated or not by estradiol in silastic tubing, were incubated in vitro with [ 3H ]TdR. The [ 3H]TdR incorporated per μg DNA was decreased in tumor after 2 to 8 day-estradiol treatment while simultaneously, in the same rats, it was increased in the pituitary. In addition, we studied the effect of estradiol in vitro on the F 4C 1 cell line obtained from the MtF 4 tumor. A dose-dependent decrease of both the [ 3H ]TdR incorporated into DNA and the DNA amount was observed between 10 −6 and 10 −5 M estradiol. These results suggest that the control of the pituitary or MtF 4 tumor growth by estradiol in vivo is in part due to an inhibition of cell multiplication. Although estradiol inhibits the growth of a clone of MtF 4 tumor cells in vitro we cannot decide whether or not the in vivo effect of estradiol is direct.