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 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.
Branco
L G
LG
Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, 14040-904, Ribeirão Preto, São Paulo, Brasil.
Steiner
A A
AA
Tattersall
G J
GJ
Wood
S C
SC
D000241:Adenosine / Q000378:metabolism*; D000628:Aminophylline / Q000008:administration & dosage; D000818:Animals; D001784:Blood Gas Analysis; D001831:Body Temperature / Q000187:drug effects / Q000502:physiology; D001833:Body Temperature Regulation / Q000187:drug effects / Q000502:physiology; D002025:Bufonidae / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006863:Hydrogen-Ion Concentration; D007035:Hypothermia / Q000209:etiology / Q000378:metabolism*; D000860:Hypoxia / Q000150:complications / Q000378:metabolism*; D007276:Injections, Intraventricular; D007279:Injections, Subcutaneous; D008208:Lymphatic System / Q000378:metabolism; D008297:Male; D058915:Purinergic P1 Receptor Antagonists
D058915:Purinergic P1 Receptor Antagonists; D000628:Aminophylline; D000241:Adenosine