Role of adenosine in the hypoxia-induced hypothermia of toads

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 teste d the hypothesis that adenosine mediates hypoxia-induced hypothermia in toa ds. Measurements of selected T-b were performed using a thermal gradient. A nimals were injected (into the lymph sac or intracerebroventricularly) with aminophylline (an adenosine receptor antagonist) followed by an 11-h perio d 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 no rmal thermoregulatory function. However, aminophylline (25 mg/kg) significa ntly 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 i njected into the fourth cerebral ventricle. Intracerebroventricular injecti on of aminophylline (0.25 mg/kg) caused no significant change in T-b under normoxia, but it abolished hypoxia-induced hypothermia. The present data in dicate that adenosine is a central and possibly peripheral mediator of hypo xia-induced hypothermia.