GROWTH-HORMONE MESSENGER-RNA IN MAMMARY-GLAND TUMORS OF DOGS AND CATS

We have shown recently that in the dog progestin administration result s in mammary production of immunoreactive growth hormone (GH). At pres ent me demonstrate the expression of the gene encoding GH in the mamma ry gland of dogs and cats using reverse-transcriptase PCR. GH mRNA was found in the great majority of normal mammary tissues as well as beni gn and malignant mammary tumors of the dog and was associated with the presence of immunoreactive GH in cryostat sections, The mammary PCR p roduct proved to be identical to that of the pituitary. The highest ex pression levels were found after prolonged treatment with progestins. In carcinomas GH mRNA was also found in progesterone receptor-negative tissue samples, indicating that after malignant transformation GH gen e expression may become progestin independent. GH mRNA was also presen t in mammary tissues of cats with progestin-induced fibroadenomatous c hanges. It is concluded that GH gene expression occurs in normal, hype rplastic, and neoplastic mammary tissue of the dog, The expression in normal tissue is stimulated by progestins and might mediate the proges tin-stimulated development of canine mammary tumors. The demonstration of progestin-stimulated GH expression in mammary tissue of cats indic ates that the phenomenon is more generalized among mammals.