Gaseous molecules controlling metabolic systems

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Enhancement of cerebral blood flow by hypoxia is critical for brain function, but signaling systems underlying its regulation have been unclear. We report a novel pathway mediating hypoxia-induced cerebral vasodilation in studies monitoring vascular disposition in cerebellar slices as well as in intact mouse brains employing two-photon intravital laser scanning microscopy. In this cascade, hypoxia elicits cerebral vasodilation via the coordinate actions of hydrogen sulfide(H_2S) formed by cystathionine.-synthase(CBS) and carbon monoxide(CO) generated by heme oxygenase(HO)-2. Hypoxia diminishes CO generation by HO-2, an oxygen(O_2) sensor. The constitutive CO physiologically inhibits CBS, so that hypoxia leads to increased levels of H_2S that mediate the vasodilation of pre-capillary arterioles. Mice with targeted deletion of HO-2 or CBS display impaired vascular responses to hypoxia. Thus, in intact adult brain cerebral cortex of HO-2-null mice, imaging mass spectrometry reveals an impaired ability to maintain ATP levels on hypoxia.