Dietary nitrate does not acutely enhance skeletal muscle blood flow and vasodilation in the lower limbs of older adults during single-limb exercise

Abstract

Purpose: Blood flow (BF) and vasodilator responses to knee-extension exercise are attenuated in older adults across an exercise transient (onset, kinetics, and steady-state), and reduced nitric oxide bioavailability (NO) has been hypothesized to be a primary mechanism contributing to this attenuation. We tested the hypothesis acute dietary nitrate (NO3−) supplementation (~ 4.03 mmol NO3− and 0.29 mmol NO2−) would improve leg vasodilator responses across an exercise transient during lower limb exercise in older adults. Methods: Older (n = 10) untrained adults performed single and rhythmic knee-extension contractions at 20% and 40% work-rate maximum (WRmax) prior to and 2-h after consuming a NO3− or placebo beverage in a double-blind, randomized fashion. Femoral artery BF was measured by Doppler ultrasound. Vascular conductance was calculated using BF and mean arterial pressure. Results: Acute ingestion of dietary NO3− enhanced plasma [NO3−] and [NO2−] (P < 0.05). Neither dietary NO3− or placebo enhanced vasodilator responses at the onset of exercise or during steady state at 20% and 40% WRmax (P > 0.05). Leg vasodilator kinetics during rhythmic exercise remained unchanged following NO3− and placebo ingestion (P > 0.05). Conclusions: The key findings of this study are that despite increasing plasma [NO3−] and [NO2−], acute dietary NO3− intake had no effect on (1) rapid hyperaemic or vasodilator responses at the onset of exercise; (2) hyperaemic and vasodilator responses during steady-state submaximal exercise; or (3) kinetics of vasodilation preceding steady-state responses. Collectively, these findings suggest that low dose dietary NO3− supplementation does not improve hyperaemic and vasodilator responses across an exercise transient in older adults.