EXPERIMENTAL INDUCTION OF MAMMOGENESIS AND LACTOGENESIS IN THE DWARF MOUSE

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Abstract
The response of the mammary glands to exogenous hormones was studied in genetically hormone-deficient intact dwarf mice. Some ductal growth was observed after the administration of thyroxin alone or in combination with ovarian and adrenocortical steroids. Combinations of steroids without thyroxin did not induce appreciable growth of the mammary gland. Addition of pituitary somatotrophin or mam-motrophin to the combinations containing steroids and thyroxin resulted in further ductal stimulation and some alveolar development. Lactogenesis could be induced in the mammary glands of dwarf mice by injecting an initial hormone combination which would result in lobulo-alveolar development and following this by a combination of pituitary and adrenocortical hormones which induces milk secretion. The most effective treatment for the induction of lactogenesis was oestradiol-17[beta] + progesterone + cortisol acetate + mammotrophin + somatotrophin + thyroxin followed by mammotrophin + somatotrophin + cortisol acetate. Mammotrophin and somatotrophin were observed to be equally effective in inducing mammogenesis and lactogenesis in the dwarfs. The response of the mammary gland of the dwarf mouse to exogenous pituitary hormones (excluding thyroxin-containing combinations) seems similar to that of hypophysectomized mice of various strains in which the mammary cancer incidence is high in virgin as well as breeding females. The significant growth of mammary glands as a result of thyroxin treatment alone and the increased mammogenic effect of thyroxin-containing steroid combinations suggest that thyroxin promotes manufacture and/or release of somatotrophin and gonadotrophin from the anterior pituitary glands of dwarf mice.

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