RELAXATION KINETICS OF RAT AORTA DURING PREGNANCY

OBJECTIVE: To examine the hypothesis that kinetics of vasorelaxation a re altered during pregnancy. METHODS: Rings of aorta from rats at diff erent stages of pregnancy (early, late, and term) and from nonpregnant female rats were precontracted with high-K+ and then allowed to relax in normal-K+ physiologic saline solution. The time to reach 50% and 8 0% relaxation were determined in the absence or presence of a cyclooxy genase inhibitor (indomethacin) and a nitric oxide synthase inhibitor (N-omega-nitro-L-arginine methyl ester) or after removal of the endoth elium. RESULTS: The aortic relaxation was progressively faster in late r stages of gestation. N-omega-nitro-L-arginine methyl ester and indom ethacin had no significant effect whereas removal of the endothelium c aused a slowing of relaxation in all the groups. Even in the presence of N-omega-nitro-L-arginine methyl ester and indomethacin or after de- endothelization, the relaxation remained faster at term as compared wi th the other groups. CONCLUSION: Aortic relaxation is faster in the pr esence of endothelium. The effect of endothelium on relaxation is inde pendent of nitric oxide synthase or cyclooxygenase systems. Progressio n of gestation is associated with acceleration of aortic relaxation, w hich cannot be totally ascribed to an endothelial factor and may invol ve a change intrinsic to the vascular smooth muscle. Faster relaxation kinetics of the vasculature during pregnancy may be a mechanism to de crease peripheral vascular resistance. (C) 1998 by the Society of Gyne cologic Investigation.