Modulation of α-adrenergic-induced contractions by endothelium-derived relaxing factor in rat aorta

Abstract

1. 1. In rat thoracic aorta, endothelium removal produced a significant increase of the maximal contraction ( E max) and of the pD 2 value (−log ED 50) induced by norepinephrine, phenylephrine and clonidine, and did not affect the maximal contractile response to 70 mM KCl. 2. 2. Clonidine did not induce a contraction in aorta with intact endothelium, but after endothelium removal, the contractile response was 94.8% of the E max produced by norepinephrine in aorta with endothelium. 3. 3. Pre-incubation with methylene blue (10 −5 M) and hemoglobin (0.02%), which inhibit EDRF effects, produced the same effects as the mechanical removal of endothelium on the contractile responses to α-adrenergic agonists. 4. 4. These results suggest that EDRF formation and release is an important factor in the modulation of α-adrenergic-induced vasoconstriction.