Role of adenosine in the hypoxia-induced hypothermia of toads |
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Authors: | Branco L G Steiner A A Tattersall G J Wood S C |
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Affiliation: | Faculdade de Odontologia de Ribeir?o Preto, Universidade de S?o Paulo, 14040-904, Ribeir?o Preto, S?o Paulo, Brasil. |
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Abstract: | The concept that hypoxia elicits a drop in body temperature (T(b)) in a wide variety of animals is not new, but the mechanisms remain unclear. We tested the hypothesis that adenosine mediates hypoxia-induced hypothermia in toads. Measurements of selected T(b) were performed using a thermal gradient. Animals were injected (into the lymph sac or intracerebroventricularly) with aminophylline (an adenosine receptor antagonist) followed by an 11-h period of hypoxia (7% O(2)) or normoxia exposure. Control animals received saline injections. Hypoxia elicited a drop in T(b) from 24.8 +/- 0.3 to 19. 5 +/- 1.1 degrees C (P < 0.05). Systemically applied aminophylline (25 mg/kg) did not change T(b) during normoxia, indicating that adenosine does not alter normal thermoregulatory function. However, aminophylline (25 mg/kg) significantly blunted hypoxia-induced hypothermia (P < 0.05). To assess the role of central thermoregulatory mechanisms, a smaller dose of aminophylline (0.25 mg/kg), which did not alter hypoxia-induced hypothermia systemically, was injected into the fourth cerebral ventricle. Intracerebroventricular injection of aminophylline (0.25 mg/kg) caused no significant change in T(b) under normoxia, but it abolished hypoxia-induced hypothermia. The present data indicate that adenosine is a central and possibly peripheral mediator of hypoxia-induced hypothermia. |
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