NOVEL TECHNIQUE TO BIOASSAY ENDOCARDIUM-DERIVED NITRIC-OXIDE FROM THEBEATING HEART

Nitric oxide is a potent vasodilator and antiplatelet substance releas ed by the vascular endothelium. In the current study, isolated rabbit hearts were perfused retrograde in the aortic root with a balanced sal t solution using a Langendorff technique. To perfuse the right cardiac chambers, an inflow cannula was placed in the superior vena cava and an outflow cannula in the right ventricular apex via the pulmonary art ery. To detect endocardial vasodilator production, right heart perfusa te was used to bathe a ''bioassay'' segment of canine coronary artery denuded of endothelium. Perfusate from unstimulated hearts did not alt er smooth muscle tone in the bioassay tissue. Calcium inophore, a pote nt stimulus for endothelial nitric oxide production, produced relaxati on of the bioassay smooth muscle when added to the cardiac perfusate b ut not when applied directly to the bioassay segment. Cardiac effluent vasodilator activity was abolished by removal of the endocardium or a ddition of nitric oxide synthesis inhibitors, but not by prostanoid in hibitors. These experiments describe a practical method to bioassay en docardial nitric oxide production in the beating heart.