The Effect of Estrogens and a Carcinogenic Chemical in Stimulating the Secretion of the Mammogenic Duct Growth Factor of the Anterior Pituitary*t

When estrogens are injected into normal immature and castrated male or female animals growth of the duct system of the mammary gland is stimulated. During the past several years increasing evidence has accumulated indicating that this mammary hyperplasia is due not to a direct action of estrogen upon the mammary gland but instead to an increased rate of secretion of anterior pituitary hormones which have been called mammogen (17, 23, i8). Data recently published 1 indicate that this consists of 2 factors: a ductgrowth factor and a lobule-alveolar-growth factor. A technic for the biological assay of the mammogenic duct-growth factor, in which young male mice are used, has been described (22). This method has now been extensively employed in assaying the mammogen content of pituitaries from dairy and beef cattle during several stages of growth, the sexual cycle, pregnancy, and lactation (23). The object of the present paper is to describe how this same assay technic may be used to advantage in the direct determination of the ability of various estrogenic chemicals to stimulate the secretion of mammogen (duct factor) by the pituitary. Such information is not only of interest as indicating the relative effectiveness on mammary hyperplasia of various types of chemical compounds which have estrogenic effects, but has a far greater value in measuring the effect of carcinogenic chemicals upon the secretion of mammogen. Lacassagne (21), Gardner, (i3, i4), and others ( I ) have shown that the injection of estrogens into male mice of cancer-susceptible strains will induce the formation of mammary tumors. As mammary growth is a prerequisite for mammary tumor formation, it would appear that the direct cause of such tumors is the secretion of mammogen by the pituitary rather