Pituitary role in the growth of metastasizing MRMT-1 mammary carcinoma in rats.

MRMT-1 is a mammary carcinoma induced in immunologically impaired female Sprague-Dawley rats fed 3-methylcholanthrene. Its biological characteristics include transplantability to syngeneic normal rats and spontaneous metastases to various organs. Hypophysectomy performed 48 hr after tumor inoculation resulted in tumor regression accompanied by the disappearance of the metastasis in lungs of all the animals. The hypophysectomized animals were given replacement treatments, such as transplantation of pituitary homogenates, pituitary homograft underneath the renal capsule, or prolactin administration, and the inhibited tumor growth was markedly reactivated, with the reappearance of lung metastasis. These results indicate that MRMT-1 mammary carcinoma is prolactin dependent.