The hemodynamic response to nitrite is acute and dependent upon tissue perfusion

In the vasculature, nitric oxide (NO) is produced in the endothelium by endothelial nitric oxide synthase (eNOS) and is critical for the regulation of blood flow and blood pressure. Blood flow may also be regulated by the formation of nitrite-derived NO catalyzed by hemoproteins under hypoxic conditions. We sought to investigate whether nitrite administration may affect tissue perfusion and systemic hemodynamics in WT and eNOS knockout mice. We found that global eNOS KO mice show decreased tissue perfusion compared to WT mice by using laser speckle contrast imaging. To study both the acute and long-term effects of sodium nitrite (0, 0.1, 1, and 10 mg/kg) on peripheral blood flow and systemic blood pressure, a bolus of nitrite was delivered intraperitoneally every 24 h over 4 consecutive days. We found that nitrite administration resulted in a dose-dependent and acute increase in peripheral blood flow in eNOS KO mice but had no effects in WT mice. The nitrite induced changes in tissue perfusion were transient, as determined by intraindividual comparisons of tissue perfusion 24-h after injection. Accordingly, 10 mg/kg sodium nitrite acutely decreased blood pressure in eNOS KO mice but not in WT mice as determined by invasive Millar catheterization. Interestingly, we found the vasodilatory effects of nitrite to be inversely correlated to baseline tissue perfusion. These results demonstrate the nitrite acutely recovers hypoperfusion and hypertension in global eNOS KO mice and suggest the vasodilatory actions of nitrite are dependent upon tissue hypoperfusion.