male rats carrying a pituitary tumor graft showed an in creased incidence of mammary tumors, and attributed this to prevention of milk production and enhancement of cellu

The effect of adrenalectomy on 7,12-dimethyl benz(a)anthracene-induced mammary tumor growth was studied in Sprague-Dawley female rats. Weekly measure ments revealed that adrenalectomy significantly increased both mammary tumor size and number and elevated serum prolactin levels as compared to the intact controls. Daily injection of 1 mg hydrocortisone acetate into the intact 7,12dimethylbenz(a)anthracene-tumor bean ng rats did not sig nificantly alter tumor size, number, or serum prolactin levels but, when injected into adrenalectomized rats, it prevented increased tumor growth and prolactin release. Daily injec tion of ovine prolactin and hydrocortisone suppressed en dogenous prolactin release but significantly increased tu more size and number. Engocornine, a prolactin-inhibiting drug, blocked adrenalectomy-mnduced tumor growth and partially blocked prolactin release. These results indicate that adrenalectomy in rats stimulates tumor growth by in creasingprolactin release.