The Urinary Excretion of Estrogens, 17-Ketosteroids, Creatine, and Creatinine in High and Low Mammary Tumor Strains of Mice*

Since the development of strains of mice with variations in the incidence of spontaneous mammary tumors, attempts have been made to demonstrate anatomic or physiologic differences between them that might be etiologically related to tumor formation. We have searched for such a variation in the urinary excretion rates of the so-called sex hormones because of the many observations linking these agents with mammary tumor formation in susceptible strains of mice. In the present communication, comparative studies on the rates of excretion of 17-ketosteroids, estrogens, creatine, and creatinine in the urine of high (C3H) and low (C57) mammary tumor strains of mice are reported. Urinary creatinine determinations were done in order to check the accuracy of the urine collections and, since creatine excretion is influenced to some extent by the sex hormones (35), urinary creatininecreatine ratios were obtained. Other attempts to detect metabolic variations between high and low mammary tumor strain animals are briefly reviewed. Anatomical observations on high, intermediate, and low mammary tumor strains of mice have been almost completely limited to the mammary glands and the endocrine system. In strains developing mammary tumors, the mammary glands develop and involute in a patchy fashion during the estrous cycle, pregnancy, and after lactation. Persistent hyperplastic areas may go on to tumor formation (13, 20, 25). Injected estrogens cause considerable proliferation in the mammary gland of a high mammary tumor strain male or female mouse, but only a minimal and variable response in the low tumor strains (22). The ovaries of the high tumor strains may show more corpora lutea as corn-