Synergistic effects of nitric oxide and exercise on revascularisation in the infarcted ventricle in a murine model of myocardial infarction

Abstract

It has been shown that density of microvessels decreases in the left ventricular after myocardial infarction (MI). The change of angiogenic and angiostatic factors as the main factors in revascularisation after exercise training in area at risk is not determined yet in MI. Therefore, the aim of the present study was the effect of exercise training and L-arginine supplementation on area at risk angiogenesis in myocardial infarction rat. Four weeks after surgery (Left Anterior Descending Coronary artery Ligation), myocardial infarction rats were divided into 4 groups: Sedentary rats (Sed-MI); L-arginine supplementation (La-MI); Exercise training (Ex-MI) and Exercise + L-arginine (Ex+La). Exercise training (ET) lasted for 10 weeks at 17 m/min for 10-50 min day(-1). Rats in the L-arginine-treated groups drank water containing 4 % L-arginine. After ET and L-arginine supplementation, ventricular function was evaluated and angiogenic and angiostatic indices were measured at ~1 mm from the edge of scar tissue (area at risk). Statistical analysis revealed that gene expression of VEGF as an angiogenic factor, angiostatin as an angiostatic factor and caspase-3 at area at risk decrease significantly in response to exercise training compared to the sedentary group. The capillary and arteriolar density in the Ex groups were significantly higher than those of the Sed groups. Compared to the Ex-MI group, the Ex+La group showed a markedly increase in capillary to fiber ratio. No significant differences were found in infarct size among the four groups, but cardiac function increased in response to exercise. Exercise training increases revascularization at area at risk by reduction of angiostatin. L-arginine supplementation causes additional effects on exercise-induced angiogenesis by preventing more reduction of VEGF gene expression in response to exercise. These improvements, in turn, increase left ventricular systolic function and decrease mortality in myocardial infarction rats.

Keywords: L-arginine; angiogenesis; cardiac function; exercise training; myocardial infarction.

Table 1. General characteristics at the end of protocol

Table 2. Doppler echocardiographic assessment of left ventricular geometry and function at 4 and 14 weeks post MI

Figure 1. Level of serum nitric oxide in different groups. * Significant difference from the Sed-MI group at the level of P < 0.05, & significant difference from the Ex-MI group at the level of P < 0.05.

Figure 2. The graph represents the relative expression levels of VEGF mRNA, after exercise training and L-arginine treatment, compared to Sed-MI animals. * Significant difference from the Sed-MI group at the level of P < 0.001. & Significant difference from the Ex-MI group at the level of P < 0.05

Figure 3. The graph represents the relative expression levels of angiostatin mRNA, after exercise training and L-arginine treatment, compared to Sed-MI animals. * Significant difference from the Sed-MI group at the level of P < 0.01

Figure 4. The graph represents the relative expression levels of caspase-3 mRNA, after exercise training and L-arginine treatment, compared to Sed-MI animals. * Significant difference from the Sed-MI group at the level of P < 0.001

Figure 5. (a) Effects of exercise on area at risk capillary density. (b) The capillary to fiber ratio at area at risk. (c) Microscopic representative images of area at risk capillary diensity stained with H & E. Scale bar represents 100 µm, original magnification x 200. * Significant difference from the Sed-MI group at the level of P < 0.05, & significant difference from the Ex-MI group at the level of P < 0.05

Figure 6. (a) Effects of exercise on area at risk arteriolar density. (b) Representative images of arterioles stained with antibodies against smooth muscle (SM) α-actin obtained from heart failure sedentary and exercised rats at 14 weeks after MI in the antero-lateral free wall of the left ventricle. Scale bar represents 100 µm, original magnification x 200. * Significant difference from the Sed-MI group at the level of P < 0.05, & significant difference from the Ex-MI group at the level of P < 0.05

Figure 7. No significant differences were found in infarct size among the four groups.

Figure 8. Survival rate at 14 weeks following myocardial infarction. Kaplan-Meier analysis revealed a trend of lower mortality in the training groups compared with the Sed groups. * Significant difference from the Ex groups at the level of P < 0.05