Regular exercise enhances blood pressure lowering effect of acetylcholine by increased contribution of nitric oxide

This study is aimed to test the hypothesis, that short-term daily bouts of exercise alter the endothelial regulation of peripheral vascular resistance by nitric oxide. Rats ran on a treadmill once a day, 5 days a week, for an average of three weeks with gradually increasing intensity (EX), while a control group remained sedentary (SED). Dose dependent reductions in mean arterial blood pressure (resting MABP; SED: 120.0 +/- 3.4 and EX: 127.8 +/- 4.0 mm Hg) of pentobarbital anesthetized rats to intravenous endothelium independent dilator sodium nitropmsside (SNP; 0.6-3.0 microg/kg) were not different in EX and SED animals. In contrast, dose dependent reductions in MABP to endothelium dependent dilator acetylcholine (ACh) were significantly enhanced in EX compared to those in SED rats (at 0.5 and 1.0 microg/kg ACh: 60.3 +/- 2.4 and 66.5 +/- 1.8 vs 52.8 +/- 2.0 and 59.8 +/- 1.7 mmHg, respectively, p<0.01). There was no significant difference in the heart rate (HR) response to ACh and SNP in the two groups of rats. Intravenous administration of 20 mg/kg Nomega-nitro-L-arginine (L-NNA, a nitric oxide synthase inhibitor) elicited a similar increase (approximately 30%) in the MABP in the two groups and eliminated the difference between ACh-induced blood pressure lowering responses in EX and SED rats (at 0.5 and 1.0 microg/kg ACh: 44.6 +/- 4.7 and 56.3 +/- 4.4 vs 50.9 +/- 4.5 and 59.4 +/- 3.6 mm Hg, respectively). Thus, we suggest that the enhanced acetylcholine-induced decrease in systemic blood pressure following regular daily exercise is primarily due to the augmented synthesis of nitric oxide in the endothelium of peripheral vasculature. This change in the function of endothelium could be important in the adaptation of circulation to exercise training.