Effects of hypothermia for a short period on histologic outcome and extracellular glutamate concentration during and after cardiac arrest in rats.
OBJECTIVE
To evaluate the therapeutic effects of hypothermia for a short period (20 mins, 31 degrees C) using a cardiac arrest model (5 mins) in rats.


METHODS
Prospective animal study.


METHODS
Experimental laboratory in a university hospital.


METHODS
Male Wistar rats (n = 42).


METHODS
Direct current (DC) potential and extracellular glutamate concentrations (microdialysis) were monitored in the hippocampal region. Histologic observation was performed 7 days later.


RESULTS
No animal died or showed severe complications as a result of hypothermia for a short period. In nontreated animals (group F), extracellular glutamate concentration simultaneously increased with the onset of membrane depolarization and continued to increase during the reperfusion period (maximum, 212% +/- 40% of the pre-ischemia level) until the onset of DC recovery. In animals in which hypothermia was initiated before the onset of ischemia (group A), extracellular glutamate concentration did not increase during the ischemia period. When hypothermia was initiated at the onset of resuscitation (group B), the glutamate concentration immediately decreased. In animals in which hypothermia was initiated at 4.9 +/- 1.3 mins (immediately after DC recovery, group C), 10 mins (group D), and 20 mins (group E) after the onset of resuscitation, changes in extracellular glutamate concentration were the same as those in nontreated animals. The percentage of injured neurons was significantly attenuated (compared with group F, 82% +/- 10%) when hypothermia was initiated before DC recovery (group A, 5% +/- 3%; group B, 29% +/- 22%) or immediately after DC recovery (group C, 58% +/- 18%, 9.9 +/- 1.3 mins after the onset of ischemia).


CONCLUSIONS
Hypothermia for a short period decreased glutamate concentration when it was initiated before DC recovery and attenuated neuronal damage when it was initiated before or immediately after DC recovery. The therapeutic time window for hypothermia for a short period is about 10 mins after the onset of ischemia.
Takata
Ken
K
Department of Anesthesiology and Resuscitology, Okayama University Medical School, Okayama City, Okayama, Japan.
Takeda
Yoshimasa
Y
Sato
Tetsufumi
T
Nakatsuka
Hideki
H
Yokoyama
Masataka
M
Morita
Kiyoshi
K
D000818:Animals; D002545:Brain Ischemia / Q000209:etiology / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D002560:Cerebrovascular Circulation; D018698:Glutamic Acid / Q000378:metabolism*; D006323:Heart Arrest / Q000150:complications / Q000628:therapy*; D006624:Hippocampus / Q000378:metabolism / Q000473:pathology; D007036:Hypothermia, Induced; D008297:Male; D011446:Prospective Studies; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D018698:Glutamic Acid