Effects of Different Levels of Exercise Volume on Endothelium-Dependent Vasodilation: Roles of Nitric Oxide Synthase and Heme Oxygenase

Abstract

The objective of this study was to examine the effects of moderate and high levels of exercise volume on endothelium-dependent vasodilation and associated changes in vascular endothelial/inducible nitric oxide synthase (eNOS and iNOS) and heme oxygenase (HO). Male Sprague-Dawley rats were assigned to sedentary control, acute (2 weeks), or chronic (6 weeks) treadmill running at moderate intensity (50% maximal aerobic velocity) with different durations of exercise episodes: 2 h/d (endurance training, moderate volume) and 3 h/d (intense training, high volume). Endothelium-dependent vascular function was examined in isolated thoracic aorta. Co-localization and contents of aortic eNOS/iNOS and HO-1/HO-2 were determined with immunofluorescence and Western blotting. Compared with sedentary controls, rats subjected to acute and chronic endurance training showed enhanced endothelium-dependent relaxation (p<0.01). Whereas acetylcholine-induced dilation was inhibited completely by NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) in sedentary controls, the dilation in the training groups was only partly blocked by L-NAME (inhibition was 98+/-3%, 79+/-6%, and 77+/-5% in sedentary control, acute, and chronic training groups, respectively, p<0.01). The remnant dilation in the training groups was further inhibited by HO inhibitor protoporphyrin IX zinc, with concomitant elevation in aortic eNOS as well as HO-1 and HO-2. In contrast to endurance exercise, high-volume intense training resulted in mild hypertension with significant impairment in endothelium-dependent vasodilation and profuse increases in aortic iNOS and eNOS (p<0.01). In conclusion, endothelium-dependent vasodilation is improved by endurance exercise but impaired by chronic intense training. Elevations of vascular eNOS and HO-1/HO-2 may contribute to enhanced vasodilation, which can be offset by intense training and elevation in vascular iNOS.