Inhibition by 2-bromo-alpha-ergocriptine and tamoxifen of the growth of an estrogen-dependent transplantable pituitary tumor (MtT/F84) in F344 rats.

A new transplantable pituitary tumor, designated MtT/F84, was induced in estrogenized female F344 rats and has been serially passaged in 17 beta-estradiol-treated females. It grew well in rats treated with estrone, 17 beta-estradiol, or estriol but not in intact females or in rats given progesterone or testosterone. The growth of MtT/F84 in rats grafted with up to 1.6 X 10(6) tumor cells and given 17 beta-estradiol was inhibited by orally administered high dose bromocriptine (37.5 mg/kg in food) or by intraperitoneal injection of tamoxifen citrate but was not inhibited by low dose bromocriptine (3.75 mg/kg in food). The tumors grown in intact females contain high amounts of estrogen receptor, and they were greatly reduced in the tumors grown either in 17 beta-estradiol or 17 beta-estradiol-plus-tamoxifen loaded rats. However, administration of bromocriptine resulted in estrogen receptor levels significantly higher than those of tumors grown in 17 beta-estradiol. The existence of dopamine receptor was also confirmed. Growth inhibition of MtT/F84 either by high dose bromocriptine or by tamoxifen may be a direct action and may be an estrogen and dopamine receptor-mediated phenomenon.