Effect of sodium nitrite on local control of contracting skeletal muscle microvascular oxygen pressure in healthy rats

Abstract

Exercise intolerance characteristic of diseases such as chronic heart failure (CHF) and diabetes is associated with reduced nitric oxide (NO) bioavailability from nitric oxide synthase (NOS), resulting in an impaired microvascular O2 driving pressure (PO2mv; O2 delivery/O2 utilization) and metabolic control. Infusions of the potent NO donor sodium nitroprusside augment NO bioavailability yet decrease mean arterial pressure (MAP) thereby reducing its potential efficacy for patient populations. To eliminate or reduce hypotensive sequelae, NO2- was superfused onto the spinotrapezius muscle. It was hypothesized that local NO2 administration would elevate resting PO2mv and slow PO2mv kinetics [increased time constant (τ) and mean response time (MRT)] following the onset of muscle contractions without decreasing MAP. In 12 anesthetized male Sprague-Dawley rats, PO2mv of the circulation-intact spinotrapezius muscle was measured by phosphorescence quenching during 180 s of electrically induced twitch contractions (1 Hz) before and after superfusion of sodium nitrite (NaNO2 30 mM). NO2- superfusion elevated resting PO2mv (control: 28.4±1.1 vs. NO2- : 31.6±1.2 mmHg; P=0.05), τ(control: 12.3±1.2 vs. NO2- : 19.7±2.2 s; P=0.05), and MRT (control: 19.3±1.9 vs. NO2- : 25.6 3.3 s; P=0.05). Importantly, these effects occurred in the absence of any reduction in MAP (103±4 vs. 105±4 mmHg, preand postsuperfusion respectively; P> 0.05). These results indicate that NO2- supplementation delivered to the muscle directly through NO2- superfusion enhances the blood-myocyte oxygen driving pressure without compromising MAP at rest and following the onset of muscle contraction. This strategy has substantial clinical utility for a range of ischemic conditions. NEW & NOTEWORTHY Ischemic conditions as diverse as chronic heart failure (CHF) and frostbite inflict tissue damage via inadequate O2 delivery. Herein we demonstrate that direct application of sodium nitrite enhances the O2 supply-O2 demand relationship, raising microvascular O2 pressure in healthy skeletal muscle. This therapeutic action of nitrite-derived nitric oxide occurred without inducing systemic hypotension and has the potential to relieve focal ischemia and preserve tissue vitality by enhancing O2 delivery.