Ouabain enhances basal release of nitric oxide from carotid artery

The authors tested the postulate that ouabain releases nitric oxide (NO) from the vascular endothelium of porcine carotid arteries (PCAs) with the technique of perfusion-superfusion bioassay, in which the perfused PCA with endothelium served as the source of NO and superfused left circumflex coronary artery (CMFX) rings with rubbed endothelium served as the bioassay tissue. Selective exposure of the PCA to ouabain (10 microM) enhanced the basal release of NO but did not affect bradykinin-stimulated (BK; 0.1-100 picomoles) release of NO. The effect of ouabain on basal release of NO from PCA persisted after pretreatment of either PCA or circumflex coronary artery with propranolol (1 microM); ibuprofen (1 microM); and hydrocortisone (10 microM). Finally, selective pretreatment of the PCA with L-NG-monomethylarginine (LNMMA; 100 microM) to inhibit 1-arginine-derived NO synthesis inhibited the relaxation of the circumflex coronary artery to basal, BK, and ouabain-stimulated effluent. Since a nonspecific increase in intracellular calcium ion will enhance both basal and agonist-induced release of NO, the authors conclude that a ouabain-sensitive ATPase is involved in basal release of NO from the endothelium of the PCA. Alternatively, ouabain may act on an isozyme of NO synthase in the vascular endothelium. Speculatively, ouabain-induced stimulation of NO release from vascular endothelium may contribute to the beneficial effect of ouabain in congestive heart failure.