Right Ventricular Myocardial Oxygen Partial Pressure Is Reduced in Monocrotaline-induced Pulmonary Hypertension in the Rat and Restored by Myo-inositol Trispyrophosphate

Pulmonary arterial hypertension (PAH) initially results in compensatory RV hypertrophy, but eventually in RV failure. This transition is poorly understood, but may be triggered by hypoxia. Measurements of RV oxygen tension (pO 2 ) in PAH are lacking. We hypothesized that RV hypoxia occurs in monocrotaline-induced PAH in rats and that myo-inositol trispyrophosphate (ITPP), facilitating oxygen dissociation from hemoglobin, can relieve it. Rats received monocrotaline (PAH) or saline (control) and 24 days later echocardiograms, pressure-volume loops were obtained and myocardial pO 2 was measured using a fluorescent probe. In PAH mean pulmonary artery pressure more than doubled (35±5 vs. 15±2 in control), RV was hypertrophied, though its contractility was augmented. RV and LV pO 2 was 32±5 and 15±8 mmHg, respectively, in control rats. In PAH RV pO 2 was reduced to 18±9 mmHg, while LV pO 2 was unchanged. RV pO 2 correlated with RV diastolic wall stress (negatively) and LV systolic pressure (positively). Acute ITPP administration did not affect RV or LV pO 2 in control animals, but increased RV pO 2 to 26±5 mmHg without affecting LV pO 2 in PAH. RV oxygen balance is impaired in PAH and as such can be an important target for PAH therapy. ITPP may be one of such potential therapies.