Movements of 45Ca and 3H2O in maternal to fetal (M----F) and fetal to maternal (F----M) directions across the dually perfused isolated human placental lobule were measured under steady-state conditions. 2. M----F values of the clearances (CR) and extractions (ER) of 45Ca relative to 3H2O were 0.371 +/- 0.056 and 0.492 +/- 0.086 (mean +/- S.E. of mean) respectively. The corresponding values for F----M movements were 0.277 +/- 0.017 and 0.251 +/- 0.010 respectively. The F----M perfusion flow ratio (QF/QM) was 0.34 +/- 0.01 throughout. Comparison with previously published data indicated a significant degree of membrane limitation to Ca transfers. 3. There was evidence of a mismatch between tissues receiving a fetal and those receiving a maternal perfusion. 4. The relative extraction ER was markedly and reversibly enhanced when perfusate total Ca was reduced from 2.4 to 0.1 mM. The effect was present in both M----F and F----M transfers and provided evidence for carrier-mediated uptake of Ca on both aspects of the placental barrier. Small and transient decreases in the relative clearance CR were observed on changing from 2.4 to 0.1 mM-Ca in M----F and to a lesser extent F----M transfers while transient increases were seen on changing from 0.1 back to 2.4 mM-Ca. 5. Measurement of net changes in Ca levels in closed-circuit studies indicated a significant release of both ionized (Ca2+) and total (CaT) Ca into the fetal perfusate at total Ringer solution concentrations of 1.4, 1.9 and 2.4 mM-Ca. Release of Ca into the maternal circuit was also observed using 1.4 mM-Ca Ringer solution but when 1.9 and 2.4 mM-Ca Ringer solution was used a net uptake occurred. 6. These findings strongly suggest that mechanisms by which Ca is transferred from M----F circulations in vivo are at least partly preserved in the in vitro human placental preparation. They indicate that this preparation is suitable for the study of these mechanisms and their regulation by hormonal and other factors.
摘要
在稳态条件下，测量了45Ca和3H2O在母体到胎儿（M→F）以及胎儿到母体（F→M）方向上穿过双灌注离体人胎盘小叶的运动情况。2. 相对于3H2O，45Ca清除率（CR）和提取率（ER）的M→F值分别为0.371±0.056和0.492±0.086（均值±均值标准误）。F→M运动的相应值分别为0.277±0.017和0.251±0.010。F→M灌注流率（QF/QM）始终为0.34±0.01。与先前发表的数据比较表明，钙转运存在显著程度的膜限制。3. 有证据表明接受胎儿灌注的组织与接受母体灌注的组织之间存在不匹配。4. 当灌注液总钙浓度从2.4 mM降至0.1 mM时，相对提取率ER显著且可逆地增加。这种效应在M→F和F→M转运中均存在，为胎盘屏障两侧钙的载体介导摄取提供了证据。在M→F转运中，当从2.4 mM - Ca变为0.1 mM - Ca时，相对清除率CR出现小幅度短暂下降，F→M转运中下降幅度较小，而从0.1 mM - Ca变回2.4 mM - Ca时出现短暂上升。5. 在闭路研究中测量钙水平的净变化表明，在总林格氏液浓度为1.4 mM、1.9 mM和2.4 mM - Ca时，离子化钙（Ca2 +）和总钙（CaT）均有显著释放到胎儿灌注液中。使用1.4 mM - Ca林格氏液时也观察到钙释放到母体循环中，但使用1.9 mM和2.4 mM - Ca林格氏液时出现净摄取。6. 这些发现强烈表明，体内钙从M→F循环转运的机制在体外人胎盘制备中至少部分得以保留。它们表明该制备适用于研究这些机制及其受激素和其他因素的调节。
