Some Effects of Progesterone and Related Compounds Upon Reproduction and Early Development in Mammals

In several publications we have indicated the rather remarkable role that progesterone, the characteristic corpus luteum hormone, plays in mammalian reproduction (1, 2, 3). Consider that progesterone: (a) is a significant conditioning substance for normal mating reflexes in a number of animals (4), (b) has its special effect upon both tubal and uterine contraction while the eggs and sperm are travelling through the oviducts (5), (c) may in certain dosages act as an inhibitor of fertilization in vivo (6), perhaps because of its effect on oviductal contractility, (d) is essential for ovum implantation, the maintenance of the fetus (7), and of normal uterine tone during pregnancy (5), (e) inhibits ovulation during normal pregnancy (8), and can do so on administration to preovulatory animals (9, 3), and (f) plays a role in parturition (8). Therefore, any experimental alteration of its normal action or abnormal intensification of certain of its effects may be expected to interfere with reproduction in the female. Experimental studies may take two courses: they may seek to antagonize or inhibit effects of progesterone e. g. by estrogens or specific progesterone antimetabolites, or they may be designed to induce progesterone effects at critical stages e. g. ovulation inhibition, during the follicular phase of the cycle by progesterone or other progestins.