Cerebral nitric oxide concentration and microcirculation during hypercapnia, hypoxia, and high intracranial pressure in pigs

Intracerebral nitric oxide (NO) concentration was measured to establish the technique and to investigate the response of the NO concentration to CO2 v ariations, hypoxia, and reduced cerebral perfusion pressure. An intracerebr al nitric oxide sensor was used in 10 pigs, Cerebral microcirculation was m easured by laser Doppler flowmetry. Five pigs received 40 mg/kg nitro-1-arg inine methyl ester (L-NAME), Baseline NO concentration was 246 +/- 42 nM. H ypercapnia increased cerebral microcirculation (P < 0.05) and NO concentrat ion (P< 0.05). Hypoxia decreased NO concentration (P < 0.05). During high i ntracranial pressure, cerebral microcirculation decreased (P < 0.05) before the NO concentration decreased (P < 0.05), and after normalisation of the intracranial pressure the NO concentration increased, but more slowly than the cerebral microcirculation. L-NAME caused a decrease in cerebral microci rculation (P< 0.05) and NO concentration (P< 0.05) to a new steady state, a nd L-NAME attenuated the changes in NO concentration after hypoxia (P < 0.0 5) and high intracranial pressure (P< 0.05). In conclusion, the electrochem ical sensor appears to reliably detect changes in localised intracerebral N O concentration and seems to be a promising tool for direct measurement of this chemically unstable substance. (C) 2000 Harcourt Publishers Ltd.