title: 15O Radioactivity clearance is faster after intracarotid bolus injection of 15O-labeled oxyhemoglobin than after 15O-water injection.
abstract: The authors tested the hypothesis that the oxygen content of brain tissue is negligible by injecting an intracarotid bolus of 15O-labeled tracer into rats. Under the hypothesis, the clearance rates of 15O radioactivity from the brain after injections of both 15O-labeled water (H(2)15O) and 15O-labeled oxyhemoglobin (HbO15O) should be identical. However, the logarithmic slope of the 15O radioactivity curve after HbO15O injection (0.494 +/- 0.071 min-1) was steeper than that after H(2)15O injection (0.406 +/- 0.038 min-1) (P<0.001, n = 13), where the time range used in the comparison was between 60 and 120 seconds after the injection. A possible interpretation of this result is that nonmetabolized O15O may dwell in the brain tissue for a finite period of time before it is eventually metabolized or returned to the blood stream unaltered. These findings contradict assumptions made by models currently used to measure cerebral oxygen metabolism.
authors.affiliation: Akita Laboratory, Japan Science and Technology Corporation, Akita, Japan.
authors.forename: Chie
authors.initials: C
authors.lastname: Seki
authors.forename: Jeff
authors.initials: J
authors.lastname: Kershaw
authors.forename: Paule-Joanne
authors.initials: PJ
authors.lastname: Toussaint
authors.forename: Kenichi
authors.initials: K
authors.lastname: Kashikura
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Matsuura
authors.forename: Hideaki
authors.initials: H
authors.lastname: Fujita
authors.forename: Iwao
authors.initials: I
authors.lastname: Kanno
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002339:Carotid Arteries / Q000378:metabolism*; D002560:Cerebrovascular Circulation; D008297:Male; D010104:Oxygen Radioisotopes / Q000008:administration & dosage* / Q000737:chemistry / Q000378:metabolism*; D010108:Oxyhemoglobins / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014867:Water / Q000737:chemistry*
chemical_list: D010104:Oxygen Radioisotopes; D010108:Oxyhemoglobins; D014867:Water