Independence of brain and trunk temperature during hypothermic preconditioning in rats.
Hypothermic preconditioning is rapid cooling and warming to induce tolerance to ischemia. The purpose of the study was to examine differences in brain and trunk temperature during hypothermic preconditioning.


METHODS
Rats (n=18) were implanted with telemetric probes for simultaneous measure of brain and trunk temperature. Hypothermic preconditioning was produced by exposing rats to cool and warm environments that produced rapid cooling to 30 degrees C and warming to 35 degrees C.


RESULTS
Brain temperature was warmer (37.56+/-0.45 degrees C) than trunk (37.17+/-0.29 degrees C) temperature in unanesthetized, free roaming rats at room temperature (t-test p=0.04). The brain cooled (0.59+/-0.1 degrees C/min) quicker than the trunk (0.44+/-0.19 degrees C/min) during cooling cycles of hypothermic preconditioning and the brain (0.28+/-0.04 degrees C/min) warmed quicker than the trunk (0.18+/-0.07 degrees C/min) during the warming cycle of hypothermic preconditioning (t-test p<0.0001). When the trunk temperature probe was designated to reach the target temperature of 35 degrees C during warming, the brain temperature (38.1+/-0.44 degrees C) was warmer than trunk temperature (34.95+/-0.16 degrees C) during the peak of warming (t-test p<0.0001).


CONCLUSIONS
The brain cools and warms quicker than the trunk during hypothermic preconditioning. Failure to anticipate these differences could lead to unrecognized brain hyperthermia during warming. Appreciation of differences in rates of change between brain and trunk temperature may be important when designing hypothermic preconditioning experiments.
University of North Carolina School of Medicine, Department of Emergency Medicine, CB 7594, Neurosciences Hospital Ground Floor, 101 Manning Drive, Chapel Hill, NC 27599, USA. Lkatz@med.unc.edu
Laurence M
LM
Katz
Jonathan E
JE
Frank
Anne
A
Dvorak
Alex
A
Finch
Adam
A
Szymanowski
Christopher J
CJ
Gordon
D018685:Anesthetics, Inhalation / Q000494:pharmacology; D000818:Animals; D016477:Artifacts; D001831:Body Temperature / Q000502:physiology*; D001921:Brain / Q000098:blood supply / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology; D007036:Hypothermia, Induced / Q000379:methods*; D020925:Hypoxia-Ischemia, Brain / Q000503:physiopathology / Q000517:prevention & control; D019194:Ischemic Preconditioning / Q000379:methods*; D007530:Isoflurane / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017694:Rewarming / Q000379:methods; D013686:Telemetry / Q000379:methods; D013821:Thermometers; D013997:Time Factors
D018685:Anesthetics, Inhalation; D007530:Isoflurane