Canning J F, Stacey T E, Ward R H, Boyd R D
Am J Physiol. 1986 Jan;250(1 Pt 2):R112-9. doi: 10.1152/ajpregu.1986.250.1.R112.
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.
在33只经导管插入的清醒绵羊的胎儿和/或母体循环中注射放射性碘后，根据放射性碘的净通量计算单向经胎盘清除率。同时记录母胎电位差（PD）。推注后20分钟清除率达到稳定状态。胎儿向母体的清除率与电位差相关。在五个实验中测得的双向清除率与根据测得的电位差预测的被动通量值有显著差异，并且在四个实验中这些比率也显著不同于1，即使假设经胎盘电位差为零，该结果也与被动通量不相符。注射硫氰酸盐或碘会降低放射性碘的清除率。胎儿血浆碘浓度增加约0.1 mM时，胎儿向母体的放射性碘清除率减半。似乎存在一个可抑制的碘转运位点，能够双向进行主动转运。
