Endothelial NOS is Upregulated in the Heart During the Second Window of Protection

Abstract

The role of eNOS in the heart during the second window of protection (SWOP) is a matter of debate. Fourteen dogs were chronically instrumented to measure aortic pressure, left ventricular dP/dt max, coronary blood flow, and wall thickening. In half the animals, preconditioning was induced by 10-min occlusion of left circumflex (CX) artery. Following 24 hr of reperfusion (during SWOP), hearts were excised. Western blot analysis was used to assess eNOS level in the myocardium. Coronary microvessels were obtained from CX bed and incubated in presence of endothelium-dependent agonists [carbachol (10 −8–10−5M) and bradykinin (10−5M)]; calcium ionophore A23187 (10−5M). Nitrite (NT), a metabolite of NO, was measured spectrophotometrically. Findings during SWOP were compared to those in normal hearts. The level of eNOS protein was 3-fold higher in SWOP group. Under baseline (no agonist present), NT production by coronary microvessels from SWOP group was 30% higher than that from Normal group. NT production in response to agonists was enhanced in coronary microvessels from SWOP group. These enhanced responses were abolished by L-NAME. The present findings provide evidence for an upregulation of eNOS leading to increased NO production during SWOP. This NO would be expected to provide protection to the endothelium, as well as to the surrounding myocytes, during ischemia-reperfusion.