The Effect of Hypoxia on Neurohypophyseal Hormone Release in Fetal and Maternal Sheep

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Abstract
The effect of hypoxemia on arginine vasopressin (AVP) and oxytocin (OT) release was investigated in the chronically catheterized fetus and ewe. During 30 min of 10% maternal O2 delivery, mean (.+-. SEM [standard error of the mean]) arterial PO2 [O2 partial pressure] decreased from 105 .+-. 10.6 to 48 .+-. 3.5 mm Hg in the ewe and from 21 .+-. 1.3 to 12 .+-. 0.8 mm Hg in the fetus (each P < 0.001). Arterial PCO2 [CO2 partial pressure] decreased from 35 .+-. 4.4 to 29 .+-. 1.0 mm Hg in the ewe, while fetal PCO2 decreased from 43 .+-. 2.3 to 35 .+-. 3.5 mm Hg (P < 0.05). Blood pH increased from 7.44 .+-. 0.03 to 7.56 .+-. 0.04 in the ewe (P < 0.01) and from 7.36 .+-. 0.004 to 7.40 .+-. 0.006 in the fetuses (P < 0.01). Baseline mean AVP levels were identical in ewes and fetuses (0.7 .+-. 0.1 .mu.U/ml). After 30 min of hypoxia, plasma AVP levels remained unchanged in the ewes (0.9 .+-. 0.1), but increased dramatically in the fetuses (47 .+-. 21 .mu.U/ml) (P < 0.001). There was a highly significant correlation between the duration of hypoxia and log fetal AVP concentrations (r = 0.85). The log fetal plasma AVP also was inversely correlated to the log fetal PO2 values (r = 0.83). Mean baseline fetal and maternal plasma OT levels were 2.6 .+-. 0.5 .mu.U/ml and 2.2 .+-. 0.5 .mu.U/ml, respectively. After 30 min of hypoxia fetal and maternal OT values were 2.9 .+-. 0.8 .mu.U/ml (not significant).