Abstract
Testosterone propionate injected into virgin $ rats during late estrus produced development of the acini in the mammary glands within 20 days. It is believed that this growth is caused by the secretion of progesterone from the hypertrophied corpora lutea. Such mammary glands are capable of lactating when exposed to a suckling stimulus. Copious'' milk production and successful fostering of 6- to 10-day-old rats were demonstrated. Continuation of treatment beyond 20 days resulted in a regression of hypertrophied corpora lutea, which was accompanied in the mammary glands by a marked increase in stored secretion resembling milk. The secretion increased with the regression of the corpora lutea.