Growth hormone-secreting variants of a mammotropic tumor.

Abstract

Three investigators described independently somatotropic variants (mutants) of the originally typical mammotropic MtT.W5, which was isolated from a rat that had been X-rayed (800 R) over the head and neck. Studies of one of these variants (W5/St.H) led us to conclude that the three variants are basically identical; all possess high somatotropic hormone (growth hormone, StH) and very low mammotropic hormone (prolactin, MtH) activity. However, persistence of secretion of some MtH is indicated by our tests with the highly sensitive radioimmunoassay and immunohistochemical staining. The mammary gland stimulation of the variant studied by us is characterized by slight to moderate alveolar hyperplasia with some milk secretion, periglandular and perivascular fibrosis, some ability to support the growth of a hormone-responsive mammary tumor, and serum levels of MtH elevated 8 to 23 times normal. The variant is stable and fully autonomous, growing equally well in rats of both sexes. StH secretion was about as high as that of the original tumor as judged by similar criteria. StH serum levels were increased to about 220 times normal in rats of both sexes. Immunohistochemical staining of the tumors was distinct for StH but not for MtH. Staining of the pituitaries of tumor hosts for MtH was reduced as compared with normal pituitaries. These findings suggest that the quantity of this hormone secreted per cell in the tumors was very small. This study supports our earlier findings of the intimate relation of MtH and StH production and is consistent with the hypothesis that the same neoplastic acidophils can produce both hormones.