VASCULAR SMOOTH-MUSCLE RELAXATION BY ENDOTHELIUM-DEPENDENT BETA-1-ADRENERGIC ACTION

1. Norepinephrine (NE) (10(-5) M) in rabbit aorta relaxed ring segments with endothelium precontracted with 10(-6) M NE, but not segments without endothelium. 2. The relaxation was inhibited with metoprolol and methylene blue, but not inhibited with yohimbine and indomethacin. 3. NE (10(-5) M) significantly elevated tissue c-GMP levels in segments with endothelium. 4. These studies suggest that the vascular relaxation by high doses of NE is mediated by the release of endothelium-derived relaxing factor (EDRF) induced by the stimulation of beta-1-adrenoceptor.