Lactogen

Lactogen is a term historically used to describe a lactogenic hormone, most commonly placental lactogen produced by the placenta during pregnancy. In humans, this hormone is known as human placental lactogen (hPL) or chorionic somatomammotropin (CSH). It is synthesized by the placental syncytiotrophoblast and released into the maternal circulation as gestation progresses.

Physiology and function: hPL shares structural and functional features with the prolactin and growth hormone families. It has growth-promoting and metabolic effects, helping to modulate maternal nutrient use to favor fetal growth. Among its metabolic actions, hPL can increase maternal lipolysis and induce a degree of insulin resistance, thereby raising blood glucose availability for the fetus. It also acts on the mammary gland to prepare for lactation, contributing to mammary development and expression of lactation-related genes, though prolactin remains the primary lactogenic stimulant after birth.

Structure and genetics: Placental lactogen is encoded by the CSH genes (CSH1 and CSH2) in humans, producing two main isoforms that differ slightly in sequence. Like other placental hormones, hPL levels rise during the second and third trimesters and decline rapidly after parturition.

Clinical notes: Abnormal placental lactogen levels can reflect placental dysfunction or fetal growth concerns, though measurement is not routine in all prenatal screening protocols. Research continues into its precise roles in maternal metabolism and fetal development.