Correlation Between Serum Prolactin Levels and Incidence of Mammary Tumors Induced by 7,12-Dimethylbenz[ a ]anthracene in the Rat

Summary

The administration of 5 mg 7,12-dimethylbenz[a]anthracene (DMBA) to otherwise untreated female Sprague-Dawley rats, 52 days old, induced tumors with an average latency period of 79-2±2.2 days in all animals. Only 60% of the rats given DMBA, followed by the taking of daily vaginal shears and weekly blood sampling under heavy ether anesthesia, developed tumors. The average latency time of this group was 93.4±4.5 days. The difference between the groups in latency time was statistically significant (P<0.05). Tumor regression for experimental animals was 40% and 18% for control animals, Ether-stressed serum prolactin levels were significantly higher (P<0.001) in animals not developing tumors than in those that did. At each stage of the estrous cycle the serum prolactin level was higher for animals without tumors. Prolactin levels within groups of animals that did not develop tumors, that developed tumors which regressed, or that developed tumors which were maintained and continued to grow did not vary significantly when examined at different times after DMBA administration. The data indicated that animals with the capacity to secrete high levels of prolactin, stimulated by ether stress, did not develop DMBA-induced mammary tumors. Whether this is a mechanism related specifically to prolactin or involves other hormones is not known, but prolactin appears to be involved in protecting the animals against induction of mammary tumors by DMBA.