Chronic hypoxia decreases arterial and venous compliance in isolated perfused rat lungs: an effect that is reversed by exogenous L-arginine.

Chronic hypoxia (CH)-induced pulmonary hypertension is characterized by vasoconstriction and vascular remodeling, leading to right ventricular dysfunction. Given the role of arterial compliance (C(a)) in right ventricular work, a decrease in C(a) would add to right ventricular work. Nitric oxide (NO) is a potent vasodilator made by NO synthases from L-arginine (L-Arg). However, little is known of the effect of L-Arg on vascular compliance (C(v)) in the lung. We hypothesized that exposure to CH would decrease C(a) and that this effect would be reversed by exogenous L-Arg. Sprague-Dawley rats were exposed to either normoxia or CH for 14 days; the lungs were then isolated and perfused. Vascular occlusions were performed and modeled using a three-compliance, two-resistor model. Pressure-flow curves were generated, and a distensible vessel model was used to estimate distensibility and a vascular resistance parameter (R(0)). Hypoxia resulted in the expected increase in arterial resistance (R(a)) as well as a decrease in both C(a) and C(v). L-Arg had little effect on R(a), C(a), or C(v) in isolated lungs from normoxic animals. L-Arg decreased R(a) in lungs from CH rats and redistributed compliance to approximately that found in normoxic lungs. CH increased R(0), and L-Arg reversed this increase in R(0). L-Arg increased exhaled NO, and inhibition of L-Arg uptake attenuated the L-Arg-induced increase in exhaled NO. These data demonstrate that the CH-induced decrease in C(a) was reversed by L-Arg, suggesting that L-Arg may improve CH-induced right ventricular dysfunction.