Effect Of L-arginine Supplementation On Nitric Oxide And VO2 Max In Healthy Males

Abstract

INTRODUCTION: Previous research has focused on the effects of IV or orally administered L-arginine (L-arg) and its subsequent enzymatic reduction by nitric oxide synthase to nitric oxide (NO) in respect to benefits for patients with various forms of heart disease. However, L-arg supplementation has not been widely investigated in terms of its possible cardiovascular effect in healthy populations. The benefits of using this supplement in cardiovascular training are related to the vasodilatory effect of NO, and the possible increase in oxygen delivery to the muscles during exercise. PURPOSE: The purpose of this study was to investigate the effects of varying doses of oral L-arg supplementation on NO concentration and maximal oxygen consumption in normal healthy male subjects. METHODS: Twenty-five healthy males 18-30 yrs of age were recruited. Subjects completed an informed consent and health history questionnaire and were measured for anthropometric measured. Testing trials occurred on three separate occasions seven days apart with dosing (HD - high dose [6 g],LD - low dose [3 g], or PLA- placebo) randomly assigned. Testing trials consisted 3 blood draws: pre-supplementation, 25 min post-supplementation, a VO2 max test, and a post-exercise test. NO concentration was measured via venous blood draw and separated with a centrifuge for plasma. Plasma was then analyzed for NO utilizing a total nitric oxide assay kit. RESULTS: No significant effect was observed following L-arg supplementation at rest; however L-arg concentrations did increase from post-treatment to post-exercise (PLA: 29.69 mol/L vs 39.18 μµmol/L; LD: 27.63 μmol/L vs 32.65 μmol/L; HD: 19.53 μmol/L vs 45.58 μmol/L). L-arg supplementation did demonstrate statistical significance within the treatments (p< 0.05) on VO2 max scores within treatments (PLA= 47.524 ml/kg/min, LD= 48.46 ml/kg/min, HD= 48.54 ml/kg/min). CONCLUSIONS: Since no significance was observed when examining NO measures between treatments, the increase in VO2 max scores might be related to other SNS effects not related to NO concentrations. Further research is needed in this particular subject matter to further explain the physiological rationale for the positive impact that was demonstrated by L-arg on cardiovascular endurance and to provide further information in this area.