Production and regulation of progesterone in bovine corpus luteum and placenta in mid and late gestation: a personal review.

In late pregnancy the secretory activity of the corpus luteum of the cow is markedly diminished. This reduced secretion is due to a decline in the number of viable luteal cells as well as reduction in the secretory activity and responsiveness of the cells to trophic agents. The principal extra-ovarian source of progesterone in late gestation appears to be the placenta, especially the fetal cotyledon, which was shown to produce progesterone throughout gestation. Uniquely, this progesterone biosynthesis is cyclic-nucleotide independent, but Ca2+ dependent. It therefore appears that the Ca2(+)-second messenger and protein kinase C systems are responsible for regulation of sterol biosynthesis in the cow placenta.