ABSTRACT
Other Placental Hormones During the last third of pregnancy in several animal species, another pituitary-like hormone, PL (also called chorionic somatomammotropin (CS), or chorionic growth hormone-prolactin (CGP)), is secreted by the placenta (Part B and Ch. 55). Secretion occurs in direct proportion to placental size and maturity, and 2 PLs occur in rodents (PL-I & PL-II). One is secreted early in pregancny (PL-I), the other later. They are found in high concentrations in the maternal circulation; however, little reaches the fetus. There are some mammals, including rabbits, dogs, and pigs, that apparently do not express a PL, and it is thought that in these species pituitary PRL secretion is elevated throughout the latter half of gestation in lieu of PL.
