Histidine transfer across the human placenta: Characteristics in the isolated perfused human placenta and the effect of ethanol

Abstract

Histidine is essential to normal fetal growth. In vivo, the fetal-to-maternal (F-to-M) plasma concentration ratio for histidine is the highest of any amino acid. Previously, we have shown that histidine uptake by human placental microvillous membrane vesicles (MMV) occurs by a specific, Na(+)-dependent system. In this study, we have examined the maternal-to-fetal (M-to-F) transfer characteristics of histidine, using the isolated perfused human placental cotyledon. In addition, the effect of ethanol on net transfer of histidine in this human tissue model has been assessed. During 4 h of perfusion a 1.8:1 fetal-to-maternal perfusate ratio formed for histidine. In the perfused placentae, net M-to-F transfer of histidine was saturable with an apparent Km of 0.09 mM. The perfusion experiments suggest that the F-to-M histidine gradient observed in vivo is due primarily to active transport across the placenta. The presence of 300 per cent (65 mM) ethanol in the maternal perfusate did not alter the transfer characteristics of histidine, nor that of the diffusion markers, antipyrine and L-glucose.