Effects of Estrone and Progesterone on Male Rabbit Mammary Glands. I. Varying Doses of Progesterone

Eighteen doses of 0.25, 1.0, 4.0 and 8.0 I.U. of crystalline progesterone were given, simultaneously with 120 I.U. of estrone, to immature male rabbits during a period of 4 weeks. Of these 4 levels of progesterone, the 1.0 I.U. dose synergized best although the prolactational proliferation induced was not maximal. The 4.0 and 8.0 I.U. doses of progesterone were apparently inhibiting as shown by the relatively poor mammary growth obtained.