AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 1 112-R119, Copyright © 1986 by American Physiological Society
Radioiodide transfer across sheep placenta
J. F. Canning, T. E. Stacey, R. H. Ward and R. D. Boyd
Unidirectional transplacental clearances of radioiodide were calculated
from the net radioiodide fluxes after injection into fetal and/or maternal
circulations of 33 catheterized conscious sheep. Maternofetal potential
difference (PD) was also recorded. Clearance reached a steady state 20 min
after bolus injection. Fetomaternal clearance was related to PD.
Bidirectional clearance ratios measured in five experiments showed a
significant divergence from the value for passive flux predicted from the
measured PD, and in four experiments these ratios were also significantly
different from unity, this result being incompatible with passive flux even
if the transplacental PD is assumed to be zero. Injection of thiocyanate or
iodide reduced radioiodide clearance. Fetomaternal clearance of radioiodide
was halved by an increase in fetal plasma iodide concentration of
approximately 0.1 mM. There appears to be an inhibitable
iodide-transporting site capable of active transport in either direction.
