Dimethylbenzanthracene-induced rat
carcinomas possess activities binding cyclic
adenosine 3':5'-monophosphate (cAMP) and
estrogen. When dimethylbenzanthracene-induced
tumors regress after
ovariectomy of the host, a change in the specific binding of cAMP and
estrogen occurs in the
tumors. Six days after
ovariectomy, cAMP binding increases 5-fold in the nuclei and 2-fold in the cytosol of
tumors, while nuclear and cytoplasmic
estrogen binding decreases by 80% and 50%, respectively. These changes in activities binding cAMP and
estrogen are detectable within 1 day after
ovariectomy and the changes are reversed when resumption of
tumor growth is induced by the injection of 17beta-estradiol. When dimethylbenzanthracene-induced
tumors fail to regress after
ovariectomy, the change in activities binding cAMP and
estrogen does not occur. Significant increases in the cAMP level as well as in
adenylate cyclase and
cAMP-phosphodiesterase activities are also found in the regressing
tumors. Concomitant with the increase of cAMP-binding activity is an increase in
histone kinase activity in the regressing
tumor. These data suggest the involvement of cAMP in the growth control of a
hormone-dependent mammary rumor.