Nitric oxide synthesis inhibition during cerebral hypoxemia and reoxygenation with 100% oxygen in newborn pigs.

The objective of our study was to evaluate the effects of N(sigma)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of the nitric oxide (NO) pathway, on cerebral microcirculation during hypoxemia and reoxygenation with 100% oxygen in newborn pigs. Twenty-two pigs were randomized to hypoxemia [inspired fraction of oxygen (FIO(2)) 0.08; 20 min] and reoxygenation (FIO(2) 1.0; 60 min) or normoxia. The hypoxemic animals were further randomized to receive either an intravenous bolus injection of 5 mg/kg L-NAME (n = 8) or a corresponding volume of isotonic saline (n = 8) 30 min before the onset of hypoxemia. The normoxemic group (n = 6) received the same pretreatment with L-NAME. Cerebral hemodynamics were assessed by laser Doppler flowmetry and intracranial pressure monitoring. The cerebral NO concentration was continuously measured using an electrochemical sensor. Pretreatment with L-NAME resulted in a more severe systemic hypotension and reduced cerebral microcirculation during the period of hypoxemia compared with the saline/hypoxemia group. NO synthesis inhibition during reoxygenation with 100% oxygen, however, blunted the increase in NO concentration (p < 0.05) without reduction of cerebral blood flow and cerebral perfusion pressure. In conclusion, in this newborn pig model, pretreatment with a bolus infusion of L-NAME induced severe hypotension and reduced cerebral microcirculation during hypoxemia. However, it appears to have no significant adverse effect on cerebral hemodynamics during the period of reoxygenation with 100% oxygen. This deleterious effect during hypoxemia limits the use of L-NAME as a preventive drug but suggests beneficial effects during reoxygenation with 100% oxygen.