Production of Placentomata in Normal and Ovariectomized Guinea Pigs and Albino Rats.

The work of Loeb 1 in producing placentomata in the normal guinea pig by irritating the uterine mucosa between the fourth and ninth days after oestrum, suggested a comparable experiment in the albino rat. Negative results were obtained in the normal rat and were perhaps due to the oestrous cycle being so short that insufficient time elapses for a proliferation of decidual cells before the next cycle occurs. With the discovery that potent extracts of the corpus luteum could be prepared, as described by Hisaw 2 the problem was attacked from a different angle. The corpus luteum hormone when injected into the rat caused an inhibition of ovulation. This hormone was injected into rats for 2 days following oestrum, at which time the uterine mucosa was stimulated and the injections continued for 4 days. The rats were killed at this time and placentomata were found.

Ovariectomized rats were treated with corpus luteum hormone in the same manner and no placentomata were formed. If, however, such rats were first brought into oestrum artificially by injections of the follicular hormone and then treated as above, placentomata were formed. Apparently the follicular hormone is necessary to put the uterus in a proper physiological condition before it will respond to the corpus luteum hormone. Moreover in ovariectomized rats which have been injected first with follicular hormone followed by the corpus luteum hormone, stimulation of the uterine mucosa at any time during the interval between artificial oestrum and the fourth day after, produced these effects, while the normal rat is unresponsive until the third or fourth day after oestrum. Experiments are now being carried on to determine the length of time which may elapse before this physiological condition produced by the follicular hormone disappears so that placentomata can not be formed even though the corpus luteum hormone is present.