Vascular Effects of Bradykinin and Sodium Nitroprusside During Pregnancy in the Rat

Abstract

The vascular reactivity of pregnant rats to vasodilator agents was determined by measuring their in vivo and in vitro responses to bradykinin (BK) and sodium nitroprusside (SNP) at mid-term (9 days) and at term-pregnancy (21 days), by comparison to non-pregnant rats. In conscious, unrestrained and catheterized rats, the dose-response curves of bolus SNP and BK injections were progressively shifted to the left in both groups of pregnant rats, but this increased sensitivity reached significance only in term-pregnant rats. The baroreceptor reflex influence on blood pressure response to these agents was similar in the three groups of rats and cannot explain the increased response to the vasodilators observed. The in vitro vasorelaxation produced by SNP on NE (6 × 10^-6 M) pre-contracted mesenteric bed was not changed in mid-term and term-pregnant rats. In contrast, the vasorelaxant responses of BK were significantly reduced in the pre-contracted mesenteric bed of term-pregnant animals in comparison to non-pregnant and 9-day pregnant rats. These data suggest that vascular reactivity to vasodilator agents are specifically modified during pregnancy in the rat and that the increased responses to BK and SNP observed in vivo may be the consequence of decreased vasoconstrictor influences on the vasculature.