CHRONIC EXERCISE IN DOGS INCREASES CORONARY VASCULAR NITRIC-OXIDE PRODUCTION AND ENDOTHELIAL-CELL NITRIC-OXIDE SYNTHASE GENE-EXPRESSION

Recently, we have shown that chronic exercise increases endothelium-de rived relaxing factor (EDRF)/nitric oxide (NO)-mediated epicardial cor onary artery dilation in response to brief occlusion and acetylcholine . This finding suggests that exercise can provide a stimulus for the e nhanced production of EDRF/NO, thus possibly contributing to the benef icial effects of exercise on the cardiovascular system. Therefore, the purpose of the present study was to examine whether chronic exercise could influence the production of NO (measured as the stable degradati on product, nitrite) and endothelial cell NO synthase (ECNOS) gene exp ression in vessels from dogs after chronic exercise. To this end, dogs were exercised by running on a treadmill (9.5 km/h for 1 hour, twice daily) for 10 days, and nitrite production in large coronary vessels a nd microvessels and ECNOS gene expression in aortic endothelial extrac ts were assessed. Acetylcholine (10(-7) to 10(-5) mol/L) dose-dependen tly increased the release of nitrite (inhibited by nitro-L-arginine) f rom coronary arteries and microvessels in control and exercised dogs. Moreover, acetylcholine-stimulated nitrite production was markedly enh anced in large coronary arteries and microvessels prepared from hearts of dogs after chronic exercise compared with hearts from control dogs . One potential mechanism that may contribute to the enhanced producti on of nitrite in vessels from exercised dogs may be the induction of t he calcium-dependent ECNOS gene. Steady-state mRNA levels for ECNOS we re significantly higher than mRNA levels for von Willebrand's factor ( VWF, a specific endothelial cell marker) and glyceraldehyde-3 -phospha te dehydrogenase (GAPDH, a constitutively expressed gene) in exercised dogs. Densitometric analysis of ECNOS gene expression compared with v WF (to normalize for endothelial cell RNA isolation) or GAPDH expressi on revealed a twofold to threefold increase in ECNOS gene expression i n exercised dogs relative to control dogs. Collectively, these data de monstrate that chronic exercise, presumably by increasing endothelial shear stress, increases EDRF/NO production and ECNOS gene expression a nd may contribute to the beneficial effects (ie, antihypertensive) of exercise on the cardiovascular system.