REGIONAL CIRCULATORY CONTRIBUTIONS TO INCREASED SYSTEMIC VASCULAR CONDUCTANCE OF PREGNANCY

In pregnancy, maternal systemic vascular conductance increases, a new vascular circuit grows, and the maternal systemic circulation develops a diminished pressor response to angiotensin II (ANG II). However, the quantitative contributions of the latter two circulatory changes to the increased systemic vascular conductance of pregnancy have not been explored. In this experiment, we examined regional circulatory contributions to the increased systemic vascular conductance in conscious, late-gestation guinea pigs. Systemic arterial pressure, cardiac output (dye dilution), and regional blood flows (radiolabeled microspheres) were measured during baseline conditions and progressive ANG II infusion. Systemic and regional conductances were calculated from arterial pressure and cardiac output or regional blood flows. In pregnancy, maternal systemic vascular conductance increased from 3.2 to 5.0 ml.min-1.mmHg-1 (P < 0.001); increased nonuteroplacental conductance contributed 71% to the increase in whole body conductance. Pregnancy tended to decrease the nonuteroplacental conductance response (P = 0.072), but did not change the uteroplacental conductance response (P greater-than-or-equal-to 0.29), to ANG II. The increased uteroplacental blood flow of pregnancy was preserved during ANG II-induced vasoconstriction. We conclude that maternal systemic vascular conductance increased primarily because nonuteroplacental vascular conductance increased. Furthermore, the regional circulatory changes that increased maternal systemic vascular conductance in pregnancy 1) helped maintain blood flow to maternal nonreproductive organs, and 2) preserved uteroplacental blood flow during ANG II-induced vasoconstriction when blood flow to other maternal organs decreased.