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

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 O-2 delivery/O-2 utilization ratio (microvascular PO2, PmvO(2)) and raise the PmvO(2) during the rest-contractions transition. Rats were administered BR (similar to 0.8 mmol/kg/day, n=10) or water (control, n=10) for 5 days. PmvO(2) was measured during 180s of electrically induced (1 Hz) twitch spinotrapezius muscle contractions. There were no changes in resting or contracting steady-state PmvO(2). However, BR slowed the PmvO(2) fall following contractions onset such that time to reach 63% of the initial PmvO(2) 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 PmvO(2) fall (Delta(1)PmvO(2)/tau(1); control: 1.9 +/- 0.3, BR: 1.2 +/- 0.2 mmHg/s, p < 0.05). Despite no significant changes in contracting steady state PmvO(2), BR supplementation elevated the O-2 driving pressure during the crucial rest-contractions transients thereby providing a potential mechanism by which BR supplementation may improve metabolic control. (C) 2013 Elsevier B.V. All rights reserved.