The transport of thiamine, riboflavin and pyridoxal 5'-phosphate by human placenta.

In the present examination the concentrations of thiamine, riboflavin and pyridoxal 5'-phosphate in blood plasma of pregnant women and venous and arterial cord plasma were determined. In maternal plasma the concentration was 4.5 nmol/l (thiamine), 22.2 nmol/l (PLP), 8.7 nmol/l (free riboflavin) and 84.5 nmol/l (FAD + FMN). In venous cord plasma the concentration was 45.9 nmol/l (thiamine), 112.1 nmol/l (PLP), 40.6 nmol/l (free riboflavin) and 49.1 nmol/l (FAD + FMN). Therefore the gradients of concentration between maternal plasma and venous cord plasma were 1:10 for thiamine, 1:4.7 for free riboflavin and 1:5 for PLP. For the coenzyme forms of vitamin B2 the maternal circulation showed the higher concentration (1.7:1). Therefore an active transplacentar transport mechanism was assumed. The vitamin concentrations in cord arteria were significantly lower than that in cord vene, indicating a massive retention by the fetus.