Fetal responses to maternal infusions of angiotensin II

It is unclear whether the fetus is affected by maternal infusions of angiotensin II; therefore we studied maternal and fetal responses (n = 9) to angiotensin II (1.15, 2.29, 11.5 μg/min) infused 5 minutes into the vena cava of chronically instrumented sheep (129 to 137 days of gestation) while monitoring Po₂, Pco₂, pH heart rate, uterine blood flow, and arterial and umbilical venous pressures. Pregnant sheep demonstrated expected dose-related increases in mean arterial pressure and decreases in uterine blood flow (p < 0.05). Increases in fetal mean arterial pressure also correlated with the maternal dose of angiotensin II (r = 0.77, p < 0.001). Fetal heart rate appeared to increase with 2.29 μg/min; however, bradycardia was observed with 11.5 μg/min (p < 0.05) and was associated with decreased Pa_O2, 19.0 ± 1.0 to 14.3 ± 1.4 mm Hg (p, 0.05), increased Pa_O2 (p < 0.05), and decreased umbilical venous Po₂, 31.4 ± 2.3 to 27.0 ± 27.0 ± 1.9 mm Hg. The decreases in Po₂ correlated with decreases in uterine blood flow (r = 0.60, p < 0.002, and r = 0.75, p < 0.005, respectively). Nevertheless, changes in fetal mean arterial pressure also occurred in the absence of altered fetal oxygenation; thus decreased uterine blood flow and fetal oxygenation alone cannot explain the fetal cardiovascular responses. It is suggested that angiotensin II or an active metabolite may cross the ovine placenta.