Placental transfer of glucose and amino acids in intrauterine growth retardation: studies with substrate analogs in the awake guinea pig.

After experimentally inducing growth retardation by unilateral uterine artery ligation in midpregnancy, placental blood flow (PBF) (microsphere technique) and placental transfer of 14C-aminoisobutyric acid (AIB) and 3H-methylglucose (MG) were studied at d 44, 50, or 63 of gestation in 19 chronically catheterized awake guinea pigs. At d 44, fetal wt (FW) and placental wt were reduced by 16 and 18%, respectively, in the ligated horn and FW/PBF was increased by 122%. Placental efficiency to transfer MG and AIB (fetal dpm/g placenta) was maintained in the ligated horn, feto-placental extraction (feto-placental dpm/PBF) was increased, and placental transfer of the substrate analogs (fetal dpm/g fetus) was unchanged. At d 50 and 63, placental wt and FW were reduced in proportion (approximately 40%) in the growth-retarded group and FW/PBF was increased by 80 and 51%, respectively. Placental transfer of AIB was reduced by 33% at d 50 and by 18% at d 63. In addition, placental efficiency to transfer AIB was reduced by 36% at d 50 and by 22% at d 63 in the growth-retarded group. Fetal uptake of MG per g fetus was slightly reduced (-6%) at d 50 of gestation, but unaffected at d 63. Extraction of MG from the maternal PBF was increased, whereas the wt-specific transfer capacity of the placenta was unaltered.(ABSTRACT TRUNCATED AT 250 WORDS)