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This Article Full Text Full Text (PDF) All Versions of this Article: 295/3/R991    most recent 00142.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Miyazawa, S. Articles by Takewaki, T. PubMed PubMed Citation Articles by Miyazawa, S. Articles by Takewaki, T.

TEMPERATURE AND FEVER

Central A1-receptor activation associated with onset of torpor protects the heart against low temperature in the Syrian hamster

¹Department of Basic Veterinary Sciences, Laboratory of Physiology, The United Graduate School of Veterinary Sciences; and ²Department of Physiology, School of Medicine, Gifu University, Gifu, Japan

Submitted 27 February 2008 ; accepted in final form 24 June 2008

Body temperature drops dramatically during hibernation, but the heart retains the ability to contract and is resistant to induction of arrhythmia. Although adaptive changes in the heart prior to hibernation may be involved in the cold-resistant property, it remains unclear whether these changes are sufficient for maintaining cardiac pulsatility under an extreme hypothermic condition. We forcibly induced hypothermia in Syrian hamsters by pentobarbital anesthesia combined with cooling of the animals. This allows reproduction of a hypothermic condition in the absence of possible hibernation-specific reactions. Unlike hypothermia in natural hibernation, the forced induction of hypothermia caused atrioventricular block. Furthermore, J-waves, which are typically observed during hypothermia in nonhibernators, were recorded on an ECG. The origin of the J-wave seemed to be related to irreversible injury of the myocardium, because J-waves remained after recovery of body temperature. An abnormal ECG was also found when hypothermia was induced in hamsters that were well adapted to a cold and darkened environment or hamsters that had already experienced hibernation. These results suggest that acclimatization prior to hibernation does not have a crucial effect at least on acquisition of cardiac resistance to low temperature. In contrast, an abnormal ECG was not observed in the case of hypothermia induced by central administration of an adenosine A1-receptor agonist and subsequent cooling, confirming the importance of the adenosine system for inducing hibernation. Our results suggest that some specific mechanisms, which may be driven by a central adenosine system, operate for maintaining the proper cardiac pulsatility under extreme hypothermia.

arrhythmia; electrocardiogram; hypothermia; J-wave; torpor