Serum Progesterone Levels in Pregnant Rats Fed a Protein-Free Diet

Summary

Peripheral serum progesterone levels in rats fed a protein-free diet show a dramatic decrease on day 11 of pregnancy and remain low thereafter. This drop and the resultant abortion can be prevented by concomitant injections of prolactin and estrone in the intact or hypophysectomized animal. The decline in serum progesterone levels at day 11 of pregnancy suggests a defect in placental development and secretion of luteotrophin and that early secretion of adequate amounts of prolactin and ovarian steroids are required for placental formation and function.