Microvascular angioadaptation after endurance training with L-arginine supplementation in rat heart and hindleg muscles

This study was designed to examine whether dietary L-arginine supplementation modulates exercise-induced angiogenesis and vascular endothelial growth factor (VEGF) expression in female Wistar rats. Exercise training (running) lasted for 6 weeks at 25 m min-1 on a 20% gradient for 10-60 min day-1. Rats in the L-arginine-treated groups drank water containing 4% L-arginine. Histochemical identification of capillary profiles showed that training with L-arginine significantly increased the capillary/fibre (C/F) ratio in the subendocardium of the left ventricle, whereas training alone did not. Because of a significantly higher fibre cross-sectional area, a concomitant, but not significant, decrease in capillary density was also observed. In the hindleg muscles, training with L-arginine significantly increased the C:F ratio, although the degree of change was the same as that observed after training alone. Western blot analysis showed that training with L-arginine significantly increased VEGF protein expression by 1.7-fold in the left ventricle, while the increase with training alone was insignificant. In the soleus muscle, although VEGF protein expression was elevated insignificantly after training (2.8-fold), training with L-arginine significantly increased the protein levels (3.8-fold). Tissue endothelial nitric oxide synthase protein levels did not changed after either training or L-arginine treatment. The present results suggest that L-arginine supplementation causes additional effects on exercise-induced angiogenesis in the rat heart by promoting VEGF expression.