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 CO2variations, hypoxia, and reduced cerebral perfusion pressure. An intracerebral nitric oxide sensor was used in 10 pigs. Cerebral microcirculation was measured by laser Doppler flowmetry. Five pigs received 40mg/kg nitro-1-arginine methyl ester (L-NAME). Baseline NO concentration was 246 ± 42nM. Hypercapnia increased cerebral microcirculation (P< 0.05) and NO concentration (P< 0.05). Hypoxia decreased NO concentration (P< 0.05). During high intracranial 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 microcirculation (P< 0.05) and NO concentration (P< 0.05) to a new steady state, and L-NAME attenuated the changes in NO concentration after hypoxia (P< 0.05) and high intracranial pressure (P< 0.05). In conclusion, the electrochemical sensor appears to reliably detect changes in localised intracerebral NO concentration and seems to be a promising tool for direct measurement of this chemically unstable substance.