INHIBITION OF ENDOTHELIUM-DERIVED RELAXING FACTOR ENHANCES MYOCARDIAL STUNNING IN CONSCIOUS DOGS

Background. Impaired endothelial-dependent vascular responses after coronary artery occlusion (CAO) and reperfusion (CAR) have been investigated extensively. However, it is not known whether impaired endogenous endothelium-derived relaxing factor production affects postischemic myocardial dysfunction, ie, myocardial stunning. Methods and Results. Eight dogs were instrumented with an intracoronary catheter and an hydraulic occluder on the left circumflex coronary artery. The effects of a Id-minute CAO randomized with and without intracoronary administration of N-G-nitro-L-arginine (L-NA), a nitric oxide (NO) synthesis inhibitor, were compared in the same conscious dogs. Postischemic regional contractile dysfunction in subendocardial and subepicardial as well as transmural wall thickening was measured with ultrasonic dimension crystals, and myocardial blood flow was measured with radioactive microspheres. Intracoronary infusion of L-NA did not affect systemic hemodynamics, and transmural myocardial blood how was reduced slightly (-8%), but significantly, only in the left circumflex territory. The recovery of wall thickening was significantly delayed in the presence of L-NA compared with the absence of L-NA, eg, at 30-minute CAR, not only in the subendocardium (-76+/-9% versus -49+/-9%) but also in the subepicardium (-52+/-8% versus -29+/-7%). During CAO, blood flow was decreased identically in both conditions, and during CAR, the differences in blood flow were minor (7%). Conclusions. Inhibition of NO synthesis enhanced myocardial stunning transmurally in conscious dogs, potentially independent of its effects on blood flow.