Abstract
Summary
1. Injections of approximately 3.7 to 60 I.U. of prolactin daily for 5 to 10 days, beginning on the 16th day of gestation, prolonged pregnancy in rats. The largest doses and longer treatment were most effective in preventing parturition, resulting in death of most of the young when pregnancy was extended beyond 23 days. 2. Prolactin failed to prolong pregnancy in rats ovariectomized on the 19th or 20th day of pregnancy, while injections of progesterone into intact rats extended pregnancy. These results as well as histological examination of corpora lutea, suggest that prolactin acts by extending functional activity of corpora lutea of pregnancy. 3. Lactation was usually initiated in prolactin-injected rats by the 21st day of gestation, independent of the occurrence of parturition. However, milk secretion was not as marked in rats which failed to be delivered of their young as in parturient rats.
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