Effects of a vasorelaxing factor liberated by the rat isolated atria on rat aortic rings with and without endothelium

In 1993, IIlanes et ar. described a vasoactive factor, the auricular vasore laxing factor (AVF), by controlled distension of rat isolated atria. This f actor produces vasodilation, antagonizing the vasoconstrictor action of phe nylephrine. We now report assays by using isolated rat aortic rings and nor epinephrine as a vasoconstrictor. Isolated thoraxic aortic rings were mecha nically deprived of endothelium and subjected to the effects of increasing, cumulative concentrations of 6.6 x 10(-11) M to 6.6 x 10(-7) M norepinephr ine. AVF significantly decreases the constrictor effect of norepinephrine a ssayed afterward, shifting the-vasoconstrictor dose-response relation to th e right. The effect was the same in rat aortic rings with or without endoth elium. Subjecting aortic rings to control vehicle samples did not alter the dose-response curve to norepinephrine. We conclude that AVF antagonizes th e norepinephrine vasoconstrictor effect in rat isolated aortic rings and th at the mechanism of this vasorelaxing effect is independent of any contribu tion from the endothelial cells. (C) 1999 Elsevier Science Inc. All rights reserved.