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Although Ca<jats:sc>o<\/jats:sc><jats:sub>2<\/jats:sub>can be reduced to equal levels by hypoxia or hemodilution, intravascular P<jats:sc>o<\/jats:sc><jats:sub>2<\/jats:sub>is reduced only during hypoxia. We therefore tested the hypothesis that K<jats:sub>ATP<\/jats:sub>channels would be unlikely to contribute to cerebrovasodilatation during hemodilution.<\/jats:p><jats:p><jats:italic>Methods<\/jats:italic>\u2014Glibenclamide (19.8 \u03bcg) or vehicle was injected into the cisterna magna of barbiturate-anesthetized rats. The dose of glibenclamide was chosen to yield an estimated CSF concentration of 10<jats:sup>\u22124<\/jats:sup>M. Thirty minutes later, some animals underwent either progressive isovolumic hemodilution or hypoxia (over 30 minutes) to achieve a Ca<jats:sc>o<\/jats:sc><jats:sub>2<\/jats:sub>of \u22487.5 mL O<jats:sub>2<\/jats:sub>\/dL. Other animals did not undergo hypoxia or hemodilution and served as controls. Six groups of animals were studied: control\/vehicle (n=4), control\/glibenclamide (n=4), hemodilution\/vehicle (n=10), hemodilution\/glibenclamide (n=10), hypoxia\/vehicle (n=10), and hypoxia\/glibenclamide (n=10). CBF was then measured with<jats:sup>3<\/jats:sup>H-nicotine in the forebrain, cerebellum, and brain stem.<\/jats:p><jats:p><jats:italic>Results<\/jats:italic>\u2014In control\/vehicle rats, CBF ranged from 72 mL \u00b7 100 g<jats:sup>\u22121<\/jats:sup>\u00b7 min<jats:sup>\u22121<\/jats:sup>in forebrain to 88 mL \u00b7 100 g<jats:sup>\u22121<\/jats:sup>\u00b7 min<jats:sup>\u22121<\/jats:sup>in the brain stem. Glibenclamide treatment of control animals did not influence CBF in any brain area. Hemodilution increased CBF in all brain areas, with flows ranging from 128 mL \u00b7 100 g<jats:sup>\u22121<\/jats:sup>\u00b7 min<jats:sup>\u22121<\/jats:sup>in forebrain to 169 mL \u00b7 100 g<jats:sup>\u22121<\/jats:sup>\u00b7 min<jats:sup>\u22121<\/jats:sup>in the brain stem. Glibenclamide treatment of hemodiluted animals did not affect CBF in any brain area. Hypoxia resulted in a greater CBF than did hemodilution, ranging from 172 mL \u00b7 100 g<jats:sup>\u22121<\/jats:sup>\u00b7 min<jats:sup>\u22121<\/jats:sup>in forebrain to 259 mL \u00b7 100 g<jats:sup>\u22121<\/jats:sup>\u00b7 min<jats:sup>\u22121<\/jats:sup>in the brain stem. Glibenclamide treatment of hypoxic animals significantly reduced CBF in all brain areas (<jats:italic>P<\/jats:italic>&lt;0.05).<\/jats:p><jats:p><jats:italic>Conclusions<\/jats:italic>\u2014Both hypoxia and hemodilution increased CBF. Glibenclamide treatment significantly attenuated the CBF increase during hypoxia but not after hemodilution. This finding supports our hypothesis that K<jats:sub>ATP<\/jats:sub>channels do not contribute to increasing CBF during hemodilution. Because intravascular PO<jats:sub>2<\/jats:sub>is normal during hemodilution, this finding supports the hypothesis that intravascular PO<jats:sub>2<\/jats:sub>is an important regulator of cerebral vascular tone and exerts its effect in part by activation of K<jats:sub>ATP<\/jats:sub>channels in the cerebral circulation.<\/jats:p>","DOI":"10.1161\/01.str.30.9.1942","type":"journal-article","created":{"date-parts":[[2011,6,17]],"date-time":"2011-06-17T20:08:03Z","timestamp":1308341283000},"page":"1942-1948","update-policy":"https:\/\/doi.org\/10.1161\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":52,"title":["Cerebral Blood Flow During Hemodilution and Hypoxia in Rats"],"prefix":"10.1161","volume":"30","author":[{"given":"Yoshinobu","family":"Tomiyama","sequence":"first","affiliation":[{"name":"From the Department of Anesthesia, University of Iowa College of Medicine, Iowa City."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"suffix":"Jr","given":"Johnny E.","family":"Brian","sequence":"additional","affiliation":[{"name":"From the Department of Anesthesia, University of Iowa College of Medicine, Iowa City."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Michael M.","family":"Todd","sequence":"additional","affiliation":[{"name":"From the Department of Anesthesia, University of Iowa College of Medicine, Iowa City."}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"276","reference":[{"key":"e_1_3_1_1_2","doi-asserted-by":"publisher","DOI":"10.1016\/0163-7258(94)00058-B"},{"key":"e_1_3_1_2_2","doi-asserted-by":"publisher","DOI":"10.1016\/0006-8993(95)01105-6"},{"key":"e_1_3_1_3_2","doi-asserted-by":"publisher","DOI":"10.1038\/jcbfm.1993.26"},{"key":"e_1_3_1_4_2","doi-asserted-by":"publisher","DOI":"10.1161\/atvb.15.10.1641"},{"key":"e_1_3_1_5_2","doi-asserted-by":"publisher","DOI":"10.1038\/jcbfm.1994.25"},{"key":"e_1_3_1_6_2","doi-asserted-by":"crossref","first-page":"616","DOI":"10.1016\/S0022-3565(25)12736-5","volume":"254","year":"1990","unstructured":"Pearce WJ, Reynier-Rebuffel A-M, Lee J, Aubineau P, Ignarro L, Seylaz J. 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