Effects of nitrate supplementation via beetroot juice on contracting rat skeletal muscle microvascular oxygen pressure dynamics

•Dietary NO3− (via beetroot juice, BR) augments exercising muscle blood flow.•We examined the effects of BR on contracting rat muscle microvascular O2 pressure (PmvO2) dynamics.•BR slowed the PmvO2 fall across the crucial rest-contractions transition.•There was no effect of BR on contracting steady-state PmvO2.•This elevated O2 driving pressure may improve metabolic control during exercise.

NO3− supplementation via beetroot juice (BR) augments exercising skeletal muscle blood flow subsequent to its reduction to NO2− then NO. We tested the hypothesis that enhanced vascular control following BR would elevate the skeletal muscle O2 delivery/O2 utilization ratio (microvascular PO2, PmvO2) and raise the PmvO2 during the rest-contractions transition. Rats were administered BR (~0.8 mmol/kg/day, n = 10) or water (control, n = 10) for 5 days. PmvO2 was measured during 180 s of electrically induced (1 Hz) twitch spinotrapezius muscle contractions. There were no changes in resting or contracting steady-state PmvO2. However, BR slowed the PmvO2 fall following contractions onset such that time to reach 63% of the initial PmvO2 fall increased (MRT1; control: 16.8 ± 1.9, BR: 24.4 ± 2.7 s, p < 0.05) and there was a slower relative rate of PmvO2 fall (Δ1PmvO2/τ1; control: 1.9 ± 0.3, BR: 1.2 ± 0.2 mmHg/s, p < 0.05). Despite no significant changes in contracting steady state PmvO2, BR supplementation elevated the O2 driving pressure during the crucial rest-contractions transients thereby providing a potential mechanism by which BR supplementation may improve metabolic control.