Effects of Prolactin, Progesterone and Estrogen on Reactions of Nonpregnant Rats to Foster Young

Abstract

In one experiment 3 virgin rats were given 5 daily injections of 20 mg. of prolactin, 3 were given 5 injections of 10 mg. of the same hormone, and 3 received control injections of sterile water. At the end of treatment each female was tested on 3 days for tendencies to retrieve foster young a few days old. Some retrieving occurred, but it was confined to 2 of the 3 control females. The 3 rats previously serving as controls were next injected for 5 days with 20 mg. of prolactin, while the 6 animals that had received prolactin were shifted to water injections. The reversal of treatment conditions was not accompanied by any change in responsiveness to foster young. In a second experiment 9 multiparous females were given 20 daily injections of estrogen followed by 10 daily injections of 10 mg. of prolactin (4 rats) or control injections of water (5 rats). These treatments were followed by 3 daily tests for retrieving behavior. Estrogen followed by prolactin or by water had no clear-cut effect upon the responses to foster young. The same 9 females were placed with fertile males for impregnation which occurred in 8 of the 9 animals. The tendency to retrieve their own litters was tested on the first day postpartum. Seven of the 8 mothers retrieved part or all of the young within 10 min. The litters of these 7 were removed after the test and the females were re-tested with foster young 4 weeks later. No retrieving occurred. Finally, the 7 females which had previously shown postpartum retrieving were given 21 daily injections of estrogen followed by 7 injections of prolactin plus progesterone. None of these rats retrieved foster young during the test conducted one day after the final injection. It is evident (1) that some nulliparous rats will retrieve foster young without special treatment and (2) that this tendency is not induced in other females by prolactin, estrogen, or progesterone as used in the present experiment.