Prolactin receptors in 7,12-dimethylbenz(a) anthracene-induced mammary tumors following endocrine ablation.

We have determined the effect of ovariectomy and hypophysectomy on prolactin receptors in 7,12-dimethylbenz(a)anthracene-induced mammary tumors. Growing tumors from intact rats show a wide range in the number of prolactin receptors. Ovariectomy causes a slight (approximately 30%) decrease in receptors regardless of whether tumors regress or continue to grow, while the affinity of the receptor for prolactin remains unchanged. Hypophysectomy, which causes a prompt 10-fold decrease in prolactin receptors in rat liver, causes only a slight reduction in prolactin receptors in tumors from these same animals. We conclude that autonomous and ovariectomy responsive 7,12-dimethylbenz(a)anthracene-induced mammary tumors cannot be distinguished on the basis of prolactin receptor sites and that endocrine regulation of prolactin receptors is distinctly different in normal liver and neoplastic mammary tissue.