AJP - Regulatory, Integrative and Comparative Physiology, Vol 262, Issue 6 966-R974, Copyright © 1992 by American Physiological Society
Human placental vitamin B6 (pyridoxal) transport: normal characteristics and effects of ethanol
S. Schenker, R. F. Johnson, J. D. Mahuren, G. I. Henderson and S. P. Coburn
Department of Medicine, University of Texas Health Science Center, San Antonio 78284-7878.
The aims of this study were to define normal human placental transport of
pyridoxal, an important form of vitamin B6 in pregnancy, and to determine
the effect of short-term alcohol on this process. Our studies used the
isolated single cotyledon from the term placenta. Pyridoxal crossed the
human placenta readily in both directions, but the transfer was a little
less than half that of antipyrine and was significantly greater in the
direction of the fetus. Pyridoxine appeared to have a similar clearance
from the maternal compartment as pyridoxal, but transport of intact
pyridoxal 5'-phosphate was much smaller. There was no saturable transfer of
pyridoxal, and it was not transferred from the maternal to fetal
compartments against a concentration gradient. Placental concentration of
pyridoxal exceeded both maternal and fetal perfusate pyridoxal
concentrations, but this concentration was equal for both perfusion
directions. These composite data are most suggestive of passive transport
of pyridoxal across the placenta, binding of the vitamin in the placenta as
an explanation for its concentration there, and greater phosphorylation of
pyridoxal in the placenta when the compound is transferred in the fetal
direction, possibly displacing pyridoxal from its binding sites and
permitting its greater release into the fetal compartment. Alcohol, 400-250
mg/dl over 2.5 h, inhibited the transport of pyridoxal from the maternal to
fetal compartments by approximately 42% (P = 0.03) and resulted in a lower
transfer of pyridoxal 5'-phosphate into the fetal perfusate (P = 0.02).
