Effects of megestrol acetate on growth and secretion of a pituitary tumor

Abstract

The effect of the administration of the 6-methylated progestagen megestrol acetate on the growth of the estrogen-induced transplantable PRL/ACTH-secreting rat pituitary tumor 7315a was investigated. A significant inhibition of tumor growth was observed only during the last week of a four week period of drug administration ( 6 mg/kg). Administration of megestrol acetate suppressed the total content and the ability to release PRL, ACTH and LH of the pituitary gland of tumor bearing rats. Further, a significant suppression of the anterior pituitary, ovarian and uterine weights was observed in the megestrol acetate treated animals. Megestrol acetate did not exert a direct effect on PRL, ACTH and LH secretion by normal rat pituitary glands incubated in vitro. We conclude that megestrol acetate exerts in the model used a suppressive effect on PRL, ACTH and LH release and led to a diminution of the pituitary content of these hormones, while it has also anti-estrogenic and anti-androgenic properties. The effects of the drug help further explain its beneficial effects in metastatic breast, endometrial, renal and prostatic cancer in man.