Sodium nitrate supplementation alters mitochondrial H 2 O 2 emission but does not improve mitochondrial oxidative metabolism in the heart of healthy rats

Supplementation with dietary inorganic nitrate (NO3-) is increasingly recognized to confer cardioprotective effects in both healthy and clinical populations. While the mechanism(s) remain ambiguous, in skeletal muscle, the oral consumption of sodium nitrate has been shown to improve mitochondrial efficiency. Whether sodium nitrate has similar effects on mitochondria within the heart is unknown. Therefore, we comprehensively investigated the effect of sodium nitrate supplementation on in vivo left ventricular (LV) function and mitochondrial bioenergetics. Healthy male Sprague Dawley rats were supplemented with sodium nitrate (1 g L-1) in their drinking water for 7 days. Echocardiography and invasive hemodynamics were used to assess LV morphology and function. Blood pressure (BP) was measured by tail-cuff and invasive hemodynamics. Mitochondrial bioenergetics were measured in LV isolated mitochondria and permeabilized muscle fibers (PmFBs) using high-resolution respirometry and fluorometry. Nitrate decreased ( P < 0.05) BP, LV end-diastolic pressure and maximal LV pressure. Rates of LV relaxation (when normalized to mean arterial pressure) tended ( P = 0.13) to be higher with nitrate supplementation. However, nitrate did not alter LV mitochondrial respiration, coupling efficiency or oxygen affinity in either isolated mitochondria or PmFBs. In contrast, nitrate increased ( P < 0.05) the propensity for mitochondrial H2O2 emission in the absence of changes in cellular redox state and decreased the sensitivity of mitochondria to ADP (apparent Km). These results add to the therapeutic potential of nitrate supplementation in cardiovascular diseases and suggest that nitrate may confer these beneficial effects via mitochondrial redox signaling.