The purpose of this study was to investigate whether NO is involved in surfactant-induced vasodilatation in newborn piglets with surfactant deficiency. After repeated series of saline lung-lavage, Twenty-one anesthetized newborn piglets (2-6 days old) were randomly assigned to three groups (seven for each group): 1) Nω-nitro-L-arginine methyl ester (L-NAME) (3 mg/kg, iv.)+saline instillation; 2) L-NAME (iv.)+porcine surfactant (200 mg/kg) instillation; 3) saline (iv.)+surfactant instillation. Mean arterial blood pressure (ABP), mean pulmonary arterial pressure (PAP), mean left atrial pressure (LAP), mean central venous pressure (CVP) and cardiac output were measured. Systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR) were calculated. Mean±SD for ABP and PAP were: Table

Table 1
Full size table

ABP, PAP, SVR (P<0.001) and PVR (P<0.01) increased significantly 45 minutes after injection of L-NAME in group 1 and 2 while injection of saline did not modify any hemodynamic variable in group 3. After instillation of surfactant or saline, significant decreases in ABP, PAP, SVR (P<0.05) and PVR (P<0.05) were only observed in group 3. In the present model, by contrast to our previous findings, we found decreases in PAP and PVR after surfactant instillation. These data suggest that systemic and pulmonary vasodilatation caused by instillation of surfactant in newborn piglets with surfactant deficiency may be at least in part mediated by activation of NO synthase.