Stimulation of carcinogen-induced mammary tumor growth in rats by adrenalectomy

The effect of adrenalectomy on 7,12-dimethylbenz(a)anthracene-induced mammary tumor growth was studied in Sprague-Dawley female rats. Weekly measurements 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 7,12-dimethylbenz(a)anthracene-tumor bearing rats did not significantly alter tumor size, number, or serum prolactin levels but, when injected into adrenalectomized rats, it prevented increased tumor growth and prolactin release. Daily injection of ovine prolactin and hydrocortisone suppressed endogenous prolactin release but significantly increased tumore size and number. Ergocornine, a prolactin-inhibiting drug, blocked adrenalectomy-induced tumor growth and partially blocked prolactin release. These results indicate that adrenalectomy in rats stimulates tumor growth by increasing prolactin release.