Hemodynamic responses of the sheep fetus to vasopressin infusion.

The effects of intravenous infusion vasopressin on the circulation the fetus were studied in lambs utero with chronically maintained intravascular catheters. Vasopressin infused doses of 0.91-2.26 mU/min per kg fetal weight resulted in plasma levels arginine vasopressin of 6.8-36.4 /μU/ml; these levels are similar to those achieved during fetal hypoxia. Petal mean arterial blood pressure increased from control levels of 47 ± 1.7 to 56 1.9 nun Hg, and heart rate fell from 174 4.1to 144 ± 4.4 beats/min. Fetal cardiac output and its distribution actual organ blood flows were measured before and during vasopressin infusion by the radionuclide-labeled microsphere technique. Combined ventricular output did not change significantly, but there was a redistribution of flow, with a marked reduction of the proportion cardiac output to gastrointestinal and peripheral circulations and an increase in the percent of cardiac output to umbilical-placental, myocardial, and cerebral circulations. This redistribution was associated with a significant increase in fetal arterial Po» from 22 to 24 torr. Changes in heart rate, cardiac output, and distribution of cardiac output to various fetal organs are similar to those seen during fetal hypoxia and suggest that vasopressin release may play an important role in the fetal cardiovascular response to stress. cire Res 44: 430-436, 1979