Functions of Placental Lactogen (PL) in the Placenta
Placental Lactogen (PL) plays a critical role in regulating maternal metabolism and fetal growth during pregnancy by modifying insulin sensitivity, promoting nutrient availability, and directly stimulating fetal development.
Primary Functions of Placental Lactogen
Maternal Metabolic Regulation
- Induces maternal insulin resistance to facilitate mobilization of maternal nutrients for fetal growth 1
- Increases maternal food intake by inducing central leptin resistance 1
- Promotes maternal beta-cell expansion and insulin production to defend against gestational diabetes mellitus 1
- Acts as the "growth hormone of pregnancy" with regulation distinct from normal growth hormone 2
- Coordinates maternal metabolism to ensure optimal nutrient supply to the fetus during the latter half of pregnancy 2
Fetal Growth and Development
- Exerts direct growth-promoting effects on the fetus, particularly during early and mid-gestation 2
- Is secreted preferentially into the fetal circulation during early and mid-gestation when fetal linear growth is maximal 2
- May modulate fetal insulin-like growth factor (IGF) production, which is essential for maintaining normal fetal growth rate 3
- Shows positive correlation with birth weight, suggesting its importance in regulating fetal growth 4
Placental Function
- Acts through distinct PL receptors to regulate and coordinate growth and metabolism in both mother and fetus 2
- Contributes to the placenta's role as an active endocrine organ, secreting hormones that influence maternal and fetal physiology 3
Clinical Implications of PL Dysregulation
Metabolic Conditions
- Maternal obesity is associated with lower PL serum concentrations 4
- Diabetes results in increased PL blood levels 4
- Dysregulation of PL in pathologic pregnancy conditions may adversely impact fetal growth and postnatal metabolic function 1
Fetal Growth Abnormalities
- Disruptions in PL secretion are associated with increased prevalence of placental dysfunction and abnormalities in fetal growth 4
- Impaired regulation of PL secretion could contribute to both growth retardation and fetal macrosomia 4
- Dysregulation during intrauterine period may affect metabolic status in adulthood 4
Mechanism of Action
- PL effects are mediated through diverse signaling pathways and are potentiated by glucose 1
- In ruminants, PL appears to mediate effects through unique receptors, though this remains controversial in humans 3
- PL works in concert with other placental hormones to integrate metabolic adaptations of pregnancy with the demands of fetal development 1
PL measurement could potentially be useful in predicting fetal macrosomia in women with normal glucose tolerance or in evaluating the risk of fetal growth restriction, though its clinical application is currently limited compared to ultrasonography 4.