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The effects of N-omega-nitro-L-arginine methyl ester (L-NAME) on basal cerebral vascular tone, the vasodilatory effects of acetylcholine (ACh), and the cerebrovascular response to alterations in arterial carbon dioxide tension (CBVR) were investigated using near-infrared spectroscopy. Seven newborn piglets were anesthetized and mechanically ventilated; mean arterial blood pressure (MAP) was monitored and near-infrared spectroscopy used to measure changes in total cerebral Hb concentration. At the beginning of the experiment, CBVR was measured and then 10, 20, 30, and 100 mg.kg-1 L-NAME were administered sequentially; ACh (1, 2, 3, and 5 micrograms) was given before and after each injection of L-NAME. At the end of this sequence, CBVR was measured again and finally sodium nitroprusside (1.5 mg.kg-1) was administered. Ten and 20 mg.kg-1 L-NAME caused a significant decrease in total cerebral Hb concentration of -0.59 (-3.21 to -0.02) and -1.46 (-6.50 to -0.15) mumol.L-1 (median and range), respectively (Wilcoxon p &lt; 0.05), but subsequent injections did not. Ten, 20, and 100 mg.kg-1 L-NAME caused an increase in MAP (Wilcoxon p &lt; 0.05). ACh caused an increase in total cerebral Hb concentration and a decrease in MAP that was impaired but not abolished by L-NAME (ANOVA p &lt; 0.05). CBVR was not affected by L-NAME. Sodium nitroprusside caused a reduction in mean (SD) MAP of 4.7 (1.6) kPa, and a slower rise in [tHb] of 13.44 (2.03) mumol.L-1. Postmortem examination of three animals revealed NADPH-diaphorase staining in neurons, cerebral blood vessels, carotid artery, and jugular vein.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of N-ω-Nitro-L-Arginine Methyl Ester on the Cerebral Circulation of Newborn Piglets Quantified In Vivo by Near-Infrared Spectroscopy