Maternal muscle mass may influence system A activity in human placenta.

During pregnancy, nutrient partitioning between the mother and fetus must balance promoting fetal survival and maintaining nutritional status of the mother for her health and future fertility. The nutritional status of the pregnant woman, reflected in her body composition, may affect placental function with consequences for fetal development. We investigated the relationship between maternal body composition and placental system A amino acid transporter activity in 103 term placentas from Southampton Women's Survey pregnancies. Placental system A activity was measured as Na(+)-dependent uptake of 10 mumol/L (14)C-methylaminoisobutyric acid (a system A specific amino acid analogue) in placental villous fragments. Maternal body composition was measured at enrollment pre-pregnancy; in 45 infants neonatal body composition was measured using dual-energy x-ray absorptiometry. Term placental system A activity was lower in women with smaller pre-pregnancy upper arm muscle area (r = 0.27, P = 0.007), but was not related to maternal fat mass. System A activity was lower in mothers who reported undertaking strenuous exercise (24.6 vs 29.7 pmol/mg/15 min in sedentary women, P = 0.03), but was not associated with other maternal lifestyle factors. Lower placental system A activity in women who reported strenuous exercise and had a lower arm muscle area may reflect an adaptation in placental function which protects maternal resources in those with lower nutrient reserves. This alteration may affect fetal development, altering fetal body composition, with long-term consequences.