Metabolic clearance of angiotensin II in pregnant and nonpregnant sheep

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Abstract
Reduced vascular responsiveness to infused angiotensin II (ANG II) was observed during pregnancy. Infusions produce lower circulating concentrations of ANG II in pregnancy, due to an increase in the metabolic clearance rate of ANG II (MCRANG II). The MCRANG II and the arterial plasma concentrations of ANG II were measured during constant infusions of 1.15 .mu.g ANG II/min into chronically instrumented pregnant (n = 6) and nonpregnant (n = 9) sheep. Although the pressor responses were significantly less in the pregnant than in the nonpregnant sheep (17.5 .+-. 0.5 vs. 34.9 .+-. 3.2 mm Hg, P < 0.001), the values for MCRANG II were not different: 56.2 .+-. 6.3 ml/min per kg in nonpregnant and 55.9 .+-. 4.3 ml/min per kg in pregnant sheep. The steady-state plasma ANG II concentrations during the infusions were slightly less in pregnant than in nonpregnant sheep (388 .+-. 36 vs. 454 .+-. 36 pg/ml); this difference would be responsible for only a 2-mm Hg reduction in the pressor response. Apparently, the reduced pressor response to infused ANG II in pregnancy is not due to an increase in MCRANG II nor to lower plasma ANG II concentrations.