NITRIC OXIDE (NO) SYNTHASE INHIBITION PREVENTS SURFACTANT-INDUCED CEREBRAL VASODILATATION IN NEWBORN PIGLETS WITH SURFACTANT DEFICIENCY. 2123

Our previous study has shown that a significant decrease in cerebral vascular resistance (CVR) without fluctuation of cerebral blood flow (CBF) is observed 3-5 minutes after instillation of surfactant in newborn piglets with surfactant deficiency. To investigate whether this change is related to activity of NO synthase, fourteen anesthetized newborn piglets were studied. Following repeated series of saline lung-lavage, animals were randomly assigned to two groups: 1) N^ωnitro-L-arginine methyl ester(L-NAME) (3 mg/kg, iv.)+porcine surfactant (200 mg/kg) instillation; 2) saline(iv.)+porcine surfactant instillation. Cerebral blood flow (CBF) was estimated by blood flow in the internal carotid artery measured by a transit-time ultrasound flow probe, and corrected by brain weight. Mean arterial blood pressure (ABP) was measured. Arterial blood gases were analyzed. CVR was calculated. Mean±SD for CBF (ml/min/100g) and CVR (mmHg/ml/min/100g) were: Table

Table 1

ABP (P<0.001) increased significantly 45 minutes after injection of L-NAME whereas none of the variables were modified by saline injection. Five minutes after instillation of surfactant, significant decreases in ABP(P<0.01) and CVR (P<0.05) were observed only in group 2. CBF was not modified by injection of L-NAME (or saline) and instillation of surfactant in both groups. These data suggest that this cerebral vasodilatation after instillation of surfactant in newborn piglets with surfactant deficiency may be associated with either inducible NO synthase or the intact autoregulation of cerebral circulation.