Increased incidence of mammary tumors in the female rat grafted with multiple pituitaries.

This study evaluates the role of pituitary homografts on mammary tumorigenesis in the female Sprague-Dawley rat. 5 pituitaries were grafted unilaterally over the inguinal, abdominal, and thoracic region of the mammary gland, and 2 pituitaries were grafted underneath the kidney capsule of each rat. Number and percentage of rats with mammary tumors 9 months after grafting were: Group 1, 13/45 (30%), Group II, 9/12 (75%), and Group III, 8/13 (61%). Since pituitary homografts secrete relatively large amounts of prolactin and small amounts of other pituitary hormones, the results indicate that an additional source of prolactin significantly enhances mammary tumorigenesis in the female rat.