Endogenous nitric oxide regulates right coronary blood flow during acute pulmonary hypertension in conscious dogs

Abstract.

This study investigated the role of nitric oxide (NO) in the control of right coronary (RC) blood flow at rest and during acute pulmonary hypertension. Experiments were performed in seven chronically instrumented, conscious dogs. NO synthesis was inhibited by systemic administration of N^ω-nitro-L-arginine (LNA, 35 mg/kg). Inflation of a balloon in the main pulmonary artery raised right ventricular (RV) peak systolic pressure from 34 ± 2 to 47 ± 3 mmHg before LNA and from 37 ± 2 to 47 ± 3 mmHg after LNA, but did not affect mean systemic arterial pressure. RV O₂ consumption (MVO₂) increased from 4.4 ± 0.7 to 6.1 ± 0.7 ml/min/100 g. 82 % of the elevated RV MVO₂ was provided by RC blood flow, which increased from 46 ± 7 to 61 ± 8 ml/min/100 g. After LNA, resting RV MVO₂ and RC flow fell. RC venous PO₂ fell, but RV lactate uptake was not altered. During pulmonary hypertension, the increase in RC blood flow was blunted by LNA, so that only 66 % of the elevated RV MVO₂ was supplied by increased RC flow. Analysis of O₂ supply variables as functions of RV MVO₂ further demonstrated a significant role of NO in regulating RC flow at rest and during moderate pulmonary hypertension. Conclusions NO is required for the RC hyperemic response to acute pulmonary hypertension as well as for normal resting RC blood flow. After blockade of NO synthesis, RV O₂ supply at rest and during pulmonary hypertension was sustained by increased RV O₂ extraction.