System A amino acid transporter activity in human placental microvillous membrane vesicles in relation to various anthropometric measurements in appropriate and small for gestational age babies

Fetal growth and development is dependent on the transfer of amino acids from maternal to fetal blood across the microvillous plasma membrane (MVM) and basal plasma membrane of placental syncytiotrophoblast. The aim of this study was to determine the relationship of system A amino acid transporter (SysA) activity in MVM to a variety of measurements of size at birth in a group of term small for gestational age (SGA) babies and in a group of appropriate for gestational age (AGA) babies. Mean SysA activities (nmol/mg vesicle protein/30 s +/- SEM) were: SGA, 0.027 +/- 0.004 (n = 25) and AGA, 0.045 +/- 0.005 (n = 24); p = 0.006. Spearman rank correlations were calculated for SGA (n = 19-25) and AGA (n = 21-24) groups for SysA activity against the following anthropometric measurements: abdominal circumference, birth weight, length, midarm circumference (MAC), head circumference, midarm circumference:head circumference ratio, placental weight (PW), placental ratio (placental weight:birth weight), birth weight:length ratio, Ponderal index (birth weight/length(3)) and triceps and subscapular skin-fold thicknesses (tsft and ssft). In SGA babies, SysA activity was positively correlated (p < 0.05) with subscapular skin-fold thicknesses (r = 0.48), triceps skin-fold thicknesses (r = 0.42), PW (r = 0.42), and placental ratio (r = 0.46). In AGA babies, the only significant correlation was an inverse one with placental ratio (r = -0.50). These data suggest there are differences in the relationship between placental SysA activity and fetal proportion in term AGA compared with SGA babies.