Human placental lactogen (hPL)
Also known as: hPL, human chorionic somatomammotropin, hCS
A GH/prolactin-like protein from the syncytiotrophoblast, rising in proportion to placental mass, that makes the mother insulin-resistant so more glucose reaches the fetus and helps prepare the breasts for lactation.
Overview
hPL is structurally ≈85 % similar to GH and also resembles prolactin. Its secretion increases steadily through pregnancy, so by term the placenta produces ≈1–3 g per day — more than any other hormone. Acting through prolactin (and GH) receptors, it shifts maternal metabolism: increased lipolysis and free fatty acids for maternal fuel, reduced maternal glucose uptake (insulin antagonism), and so increased glucose and amino-acid availability for the fetus. Together with progesterone, cortisol, placental GH and prolactin, this "diabetogenic" effect of late pregnancy unmasks gestational diabetes in women with limited β-cell reserve. hPL also contributes to mammary growth.
- Location
Source: syncytiotrophoblast. Targets: maternal adipose tissue, liver, muscle and breast.
Function
- Induces maternal insulin resistance and lipolysis, sparing glucose for the fetus.
- Promotes breast development.
- Stimulates maternal β-cell expansion.
- Physiology
Class: protein (191 aa, GH family). Receptor: prolactin receptor (JAK–STAT).
- Regulation
Proportional to placental mass; increased by maternal hypoglycaemia and fasting.
Clinical significance
Gestational diabetes
Placental hormones raise insulin requirements 2–3-fold in the third trimester; women who cannot compensate develop gestational diabetes (screened with an OGTT at 24–28 weeks), which resolves after delivery of the placenta but signals a high lifetime risk of type 2 diabetes.
Compiled from standard anatomy and physiology references — see the Endocrine System sources. For education only; not medical advice.