Effects of Multiple Pituitary Homografts or Progesterone on 7,12-Dimethylbenz[a]an- thracene-Induced Mammary Tumors in Rats 1,2,3

SUMMARY-This investigation evaluates the effects of prolactin-secreting pituitary homografts and progasterone on the induction of mammary tumors in female rats subsequently treated withl7,12-dimethylbenz[a]anthracene (DMBA). Immature female Sprague-Dawley rats were divided into 5 groups: group I, intact controls; group II, ovariectomized; group III, intact and 4 pituitary homografts; group IV, ovariectomized and 4 pituitary homo-grafts; and group V, intact and given injection of 4 mg progesterone daily. Pituitary transplantation and/or ovariectomy were performed at age 25 days. Progesterone was injected beginning at 30 days of age and continued for 40 consecutive days. At age 55 days, all animals were given a single iv dose of 5 mg DMBA. At the end of the study, percent tumor incidence, average number of tumors per rat, and average total weight of tumors per rat (g) were: group 1,100%,12.2::1: 1.2,16.2::1: 3.5; group 11,0; group III, 73%, 4.7::I: 1.3, 5.4::I: 2.0; group IV, 0; and group V, 79%, 3.3::I: 0.7, 5.9::I: 4.6. Percentage of rats with tumors, average number of tumors pe