Inhibitory effect of prostaglandin F2 alpha on the growth of a hormone-dependent rat mammary tumor.

Growth of the rat hormone-dependent mammary adenocarcinoma MTW-9 was inhibited by prostaglandin F2alpha (PGF2alpha) This inhibition of tumor growth was associated with a marked reduction in serum progesterone concentrations. The inhibitory effect of PGF2alpha on tumor growth was abolished by concomitant injections of progesterone. The growth rates of coimplanted prolactin-secreting pituitary tumor MtTW-5 and plasma concentrations of prolactin and estradiol were not affected significantly by PGF2alpha. Our data imply that the effect of PGF2alpha on growth of rat mammary adenocarcinoma is mediated by progesterone.