Prolactin-like activity of antiprolactin receptor antibodies in rat mammary tumor explants.
The effects of prolactin and a serum containing antiprolactin receptor antibodies on some lactogenic and mammogenic responses were investigated in nitrosomethylurea-induced mammary tumors in organ cultures. Prolactin was able to induce an increase in lactose synthetase activity, DNA synthesis, and prolactin-binding sites at moderate (i.e., physiological) concentrations of prolactin; at higher concentrations, desensitization of the tissues was observed for DNA synthesis and lactose synthetase activity, whereas the "down-regulation" of prolactin receptors occurred. Prolactin had no effect on casein synthesis. Antiprolactin receptor serum was capable of inducing an increase in lactose synthetase activity, DNA synthesis, and prolactin-binding sites, however, lower than that observed with prolactin, thus mimicking prolactin action. The antiserum did not induce any change in casein synthesis. These findings suggest that, in rat mammary tumors, as it has been observed in the normal mammary gland, the prolactin molecule is not required beyond the initial binding to its receptor for its action to be attained. It appears also that a differentiated function has lost its hormonal dependence in these tumors, although their hormonal dependence for other functions and growth is maintained.
D000818:Animals; D000906:Antibodies / Q000276:immunology*; D002364:Caseins / Q000096:biosynthesis; D003429:Cross Reactions; D004247:DNA / Q000096:biosynthesis / Q000276:immunology; D004305:Dose-Response Relationship, Drug; D005260:Female; D007788:Lactose Synthase / Q000032:analysis; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced / Q000276:immunology*; D008770:Methylnitrosourea; D009924:Organ Culture Techniques; D011388:Prolactin / Q000494:pharmacology*; D051381:Rats; D011956:Receptors, Cell Surface / Q000032:analysis / Q000276:immunology*
D000906:Antibodies; D002364:Caseins; D011956:Receptors, Cell Surface; D008770:Methylnitrosourea; D011388:Prolactin; D004247:DNA; D007788:Lactose Synthase