Effect of L-NAME on the VO2 Response to Incremental Cycle Exercise

Abstract

1587 Nitric oxide is believed to play a role both in muscle vasodilatation and in the regulation of oxidative metabolism during exercise. However, surprisingly few studies have investigated the effect of nitric oxide synthase (NOS) inhibition on oxygen uptake (VO2) during exercise in humans. PURPOSE: To determine the effect of NOS inhibition on the VO2 response to incremental cycle exercise. METHODS: Seven healthy males (aged 25 ± 4 yrs; mass 78.5 ± 9.2 kg) completed an incremental exercise test to exhaustion on an electrically braked cycle ergometer (work rate (WR) increment: 30 W.min−1) following prior intravenous infusion of either the NOS inhibitor L-NAME (4 mg.kg−1 body mass in 50 ml saline) or 50 ml saline as a placebo. Pulmonary gas exchange was measured nreath-by-breath. The gas exchange threshold (GET) was determined with the V-slope method and peak VO2 was defined as the average VO2 recorded over the last 30 s of the test. The ΔVO2-/ΔWR slope was calculated for the region from 1 min into exercise to the GET (S1) and from the GET to the attainment of peak VO2 (S2). The results were analysed using paired ttests. RESULTS: L-NAME resulted in an increase in mean arterial blood pressure immediately before exercise (mean ± S.D. L-NAME: 109 ± 10 vs. CON: 97 ± 8 mmHg; P<0.05) and within 30 s of the completion of exercise (L-NAME: 123 ± 9 vs. CON: 105 ± 15 mmHg; P<0.05). L-NAME also resulted in a reduction in heart rate immediately before exercise (L-NAME: 79 ± 8 vs. CON: 84 ± 10 b.min−1; P = 0.10), during exercise, and at exhaustion (L-NAME: 178 ± 7 vs. CON: 186 ± 10 b.min−1; P<0.01). L-NAME resulted in a significant reduction in peak VO2 (L-NAME: 3.80 ± 0.34 vs. CON: 4.02 ± 0.41 L.min−1; P<0.05). However, L-NAME did not significantly influence the GET (L-NAME: 2.01 ± 0.41 vs. CON: 1.94 ± 0.47 L.min−1), the ΔVO2−/ΔWR slopes S1(L-NAME: 8.7 ± 0.9 vs. CON: 8.7 ± 0.6 ml.min−1. W−1. W) or S2 (L-NAME: 9.1 ± 0.8 vs. CON: 9.2 ± 0.6 ml.min−1. W-1. W), or the time to exhaustion (L-NAME: 12.0 ± 1.1 vs. CON: 12.2 ± 1.3 min; P = 0.09). CONCLUSIONS: Inhibition of NOS with L-NAME reduces peak VO2 during incremental cycle exercise in man, presumably by altering central or peripheral components of muscle O2 delivery.