[Participation of the adenyl cyclase system in estradiol-activated growth of tumors in rat mammary glands].

Early effects of estradiol on the adenylate cyclase system in target tissues were investigated. The proliferative processes in the estradiol-dependent mammary tumours and uterus of the rat were arrested by ovariectomy. Subsequent hormonal treatment resulted in adenylate cyclase activation and the increase of the cAMP level in these tissues, probably to be connected with the initiation of the cell growth. These events were followed by a decrease of the cAMP content necessary for active proliferation of tumour cells. cAMP phosphodiesterase is not responsible for the increase in the cyclic nucleotide content, but provides for its further hydrolysis. The stimulation of the adenylate cyclase system at early steps of estradiol action is typical both for normal and transformed estradiol-dependent tissues.