The Hx-xanthine oxidase system is an important generator of free radical which are reported to induce pulmonary hypertension. In vitro studies have shown that NO is an important free radical scavenger, and inhibition of NO synthase enhances production of superoxide anion in adult rats. The purpose of this study was to investigate the effect of NO synthase inhibition on plasma Hx in newborn piglets with surfactant deficiency, and to study a possible relationship between plasma Hx and pulmonary arterial pressure (Ppa). Methods: Nineteen anesthetized and instrumented newborn piglets were subjected to repeated lung lavages, and then randomly assigned to two groups: the L-NAME group (n = 12) received 3 mg/kg of L-NAME i.v; and the control group (n = 7) received same volume of saline i.v. Ppa was continuously recorded. Plasma Hx was analyzed with HPLC. Results: Plasma Hx was not modified by the repeated lung lavages, but increased significantly 45 minutes after L-NAME i.v. (p < 0.01)(fig). Saline injection, however, did not modify plasma Hx. Furthermore, the differences in Δ-plasma Hx between the two groups after L-NAME and saline i.v. were also significant (p < 0.05). Ppa was not changed after saline i.v., but increased significantly after L-NAME i.v. The change in Ppa after L-NAME i.v. was significantly correlated to plasma Hx (n = 24, r = 0.43, p < 0.05). Conclusion: These data show that inhibition of NO synthase may augments plasma Hx. We speculate that inhibition of NO synthase may potentiate production of free radicals during reperfusion which may contribute to pulmonary hypertension.

figure 1