McGrath J C, MacLennan S J, Mann A C, Stuart-Smith K, Whittle M J
J Physiol. 1986 Nov;380:513-9. doi: 10.1113/jphysiol.1986.sp016299.
The O2 tension of umbilical arterial blood in utero is 15 mmHg. The contractile effect of increasing the O2 tension above this value was studied quantitatively in vitro in preparations of human umbilical artery and vein. The umbilical arterial smooth muscle was contracted in a concentration-related manner by stepped increments in O2 tension. The threshold for O2-induced contraction was estimated to be 36 mmHg at pH 7.28 and the maximum contraction occurred at 297 mmHg. The sensitivity of the preparations to low O2 tensions (less than 100 mmHg) was reduced by increasing the pH of the bathing medium from 7.28 to 7.36, at which the threshold was 69 mmHg and the maximum contraction occurred at 282 mmHg. Reducing the pH to 7.18 did not significantly change the sensitivity from that found at pH 7.28. Indomethacin (0.1 microM) virtually abolished responses to O2. The results indicate that the increase in the physiological O2 tension at birth, from 15 to 100 mmHg, may be an adequate stimulus to effect the closure of the umbilical artery. In the physiological range O2 did not contract the umbilical venous smooth muscle. This may allow the transfusion of blood from the placenta to the fetus at birth when the O2 tension of umbilical cord blood increases after the onset of breathing.
子宫内脐动脉血的氧分压为15 mmHg。在人体脐动脉和静脉制剂中，对将氧分压提高到该值以上的收缩效应进行了体外定量研究。随着氧分压逐步升高，脐动脉平滑肌以浓度相关的方式收缩。在pH 7.28时，氧诱导收缩的阈值估计为36 mmHg，最大收缩发生在297 mmHg。将浴液介质的pH从7.28提高到7.36，可降低制剂对低氧分压（低于100 mmHg）的敏感性，此时阈值为69 mmHg，最大收缩发生在282 mmHg。将pH降至7.18，与pH 7.28时相比，敏感性无显著变化。吲哚美辛（0.1 microM）几乎完全消除了对氧的反应。结果表明，出生时生理氧分压从15 mmHg升高到100 mmHg，可能是促使脐动脉关闭的充分刺激因素。在生理范围内，氧不会使脐静脉平滑肌收缩。这可能使得出生时呼吸开始后脐带血氧分压升高时，胎盘的血液能够输送给胎儿。
