Maternal-Fetal Cyst(e)ine Transfer

Abstract

In order to investigate the mechanisms by which cyst(e)ine (referring in the following to the mixture, in any proportion, of the sulfhydryl form of this compound – cysteine -and the disulfide form – cystine) transfer across the placenta to the fetus might be limited we first assessed the original observation that cyst(e)ine concentrations in fetal plasma are less than or equal to maternal cyst(e)ine concentrations. Second, we determined the capacity of the placenta to concentrate cyst(e)ine. And third, using an animal model, we determined the effects of providing excess cysteine to maternal rats on maternal-fetal cyst(e)ine transfer. Our data confirm (1) that cyst(e)ine is present in concentrations in human cord plasma that are equal to maternal plasma cyst(e)ine concentrations; (2) establish that cyst(e)ine is concentrated in the placenta, and (3) suggest that the incorporation of cyst(e)ine into glutathione in the placenta may limit the transfer of cyst(e)ine to the fetus.

Human Growth

“…Since the uptake in vitro ofPSS]cystine by slices of human fetal liver was less than that of [ 35 S]methionine (Gaull et al, 1972), it seemed unlikely that the failure to maintain a plasma concentration that is higher in the fetus than in the mother is a result of avid uptake of cystine by fetal tissues. Malloy et al (1983) have restudied this problem and confirm that the cyst(e)ine concentrations in human cord plasma are equal to those in maternal plasma and that cyst(e)ine is concentrated by the placenta. These workers show that the incorporation of cyst( e )ine into glutathione in placenta may limit the transfer of cyst(e)ine to the fetus.…”