Nitric oxide is the endothelium-derived relaxing factor in bovine pial arterioles

The purpose of this study was to investigate the formation and action of a nitric oxide-related endothelium-derived relaxing factor in cerebral arteries of cattle. Pial artery segments (0.6-1 mm o.d.) were incubated in oxygenated (20%) Krebs-Henseleit buffer containing indomethacin. Addition of acetylcholine (0.1 microM) to rings precontracted by serotonin (0.1 microM) resulted in a significant (p less than 0.05) relaxation. This response disappeared after removal of the endothelium and addition of hemoglobin, a nitric oxide scavenger, and NG-monomethyl-L-arginine, an inhibitor of L-arginine-derived nitric oxide biosynthesis. L-Arginine (10 microM) considerably attenuated the inhibitory action of NG-monomethyl-L-arginine. Relaxations induced by 3-morpholinosydnonimine and nitroglycerin (0.1 microM), two exogenous sources of nitric oxide, were unaffected by NG-monomethyl-L-arginine (10 microM) but abolished by hemoglobin. These data strongly suggest nitric oxide as the mediator of endothelium-derived relaxation in pial arteries of the cattle.