Role of α-adrenoceptors in the control of the cerebral blood flow response to hypoxia

This study assessed the role of vascular and central α-adrenoceptors in the regional cerebral blood flow response to moderate hypoxia. Studies were conducted in 21 rabbits using radioactive microspheres under normoxic and hypoxic (10% O₂ in N₂) conditions. Animals were divided into three groups and administered either saline, N-methyl chlorpromazine, or phenoxybenzamine. During normoxia, there were regional differences in cerebral blood flow distribution in the saline- and N-methyl chlorpromazine-treated rabbits which were eliminated by phenoxybenzamine. In control, hypoxia significantly increased average cerebral blood flow from 57 ± 22 to 132 ± 52 ml/min per 100 g. Flow to the hindbrain increased to a significantly greater extent than to the mid- or forebrain during hypoxia. The increase in average cerebral blood flow during hypoxia was significantly reduced to 97 ± 34 ml/min per 100 g by phenoxybenzamine. Both α-adrenoceptor antagonists prevented the significantly greater increase in hindbrain flow during hypoxia. The greater flow responsiveness of the hindbrain to hypoxia appears to be related at least in part to α-adrenoceptors found in the cerebral vasculature.