The nature of pressor responsiveness to angiotensin II in human pregnancy

The purpose of this investigation was to siudy the determinants of the pressor response to infused angiotensin II in normal pregnant women near term. In these subjects acute plasma volumc expansion was accomplished by the rapid intravenous infusion of normal saline or 6% dextran. Uniformly this treatment was effective in reducing the venous hematocrit and plasma renin activity but failed to alter the amount of intravenously infused angiotensin II dose required to elicit a pressor response. The same treatment of nonpregnant women resulted in a marked decrease in the dose of angiotensin II required to elicit the same pressor response after volume expansion compared to that required before. The rapid infusion of the same amount of NaCI as a 5% solution to normal pregnant women near term did result in a marked decrease in angiotensin II pressor resistance. The results suggest that the principal determinant of pressor response to angiotensin II in pregnancy is arteriole response and not alterations in plasma volume or renin plasma levels.