Dose-dependent effects of angiotensin II on the ovine fetal cardiovascular system

The purpose of this experiment was to establish dose-response relationships for the effects of angiotensin II on arterial pressure, venous pressure, heart rate, and blood volume in the ovine fetus. Chronically catheterized fetal sheep at 132 ± 1 (SE) days' gestational age were infused with angiotensin II at 4.8 ± 1.1 (n = 7), 27.7 ± 4.6 (n = 7), 102.2 ± 16.7 (n = 6), or 239.0 ± 30.9 (n = 4) ng/min/kg fetal body weight for 30 minutes. Fetal arterial pressure increased at the three highest doses. Fetal venous pressure, heart rate, and blood volume responded only at 102.2 and 239.0 ng/min/kg. At 239.0 ng/min/kg, arterial pressure increased by 17.7 ± 1.6 mm Hg (p < 0.00001), venous pressure increased by 1.5 ± 0.3 mm Hg (p < 0.0005), blood volume decreased by 7.8 ± 2.2% (p < 0.0001), and heart rate initially decreased by 14 ± 4 beats/min, followed by an increase of 52 ± 17 beats/min from control (p < 0.0005) at the end of angiotensin II infusion. Thus this study shows that angiotensin II affected multiple fetal cardiovascular variables in a dose-dependent manner, suggesting that it is an important regulatory hormone for the entire fetal cardiovascular system.