15O Radioactivity clearance is faster after intracarotid bolus injection of 15O-labeled oxyhemoglobin than after 15O-water injection.
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.
Seki
Chie
C
Akita Laboratory, Japan Science and Technology Corporation, Akita, Japan.
Kershaw
Jeff
J
Toussaint
Paule-Joanne
PJ
Kashikura
Kenichi
K
Matsuura
Tetsuya
T
Fujita
Hideaki
H
Kanno
Iwao
I
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*
D010104:Oxygen Radioisotopes; D010108:Oxyhemoglobins; D014867:Water