[Effects of EDRF on the vasoconstrictor action of phenylephrine in rat aorta]

The influence of endothelium-derived relaxing factor (EDRF) on the vasoconstrictor effect of phenylephrine on rings of rat aorta was studied in this paper. Rings of rat aorta, with or without endothelium, were suspended in organ chambers for the measurement of contractive force and contractive speed. All experiments were performed in the presence of indomethacin (10 mumol/L) to prevent the production of vasoactive prostanoids. When the preparations with intact endothelium were treated with methylene blue (10 mumol/L), an inhibitor of the target enzyme of EDRF, or NG-nitro-L-arginine (30 mumol/L), an inhibitor of EDRF formation, dose-contractive force curves of phenylephrine shifted to left: the EC30 value decreased 5-fold and the maximal response ratios were 1.6 +/- 0.4 and 1.6 +/- 0.5 (n = 8) respectively. These results were similar to those observed after mechanical removal of the endothelium: a 3-fold decrease in the EC30 value and the maximal response ratio was 1.0 +/- 0.2 (n = 8), The latter results may be related to a little EDRF produced by vascular smooth muscle. Our results suggest that the vasoconstrictive effect induced by phenylephrine may also be regulated by EDRF production from vascular endothelium and smooth muscle.