Adenosine decreases the minimum alveolar concentration of halothane in dogs.
Adenosine has sedative properties, and adenosine-receptor agonists have been found to reduce anesthetic requirements in rodents. This study determined whether adenosine, in hypotensive doses, reduces anesthetic requirements in halothane-anesthetized dogs. In seven animals, minimum alveolar concentration (MAC) for halothane was determined by a tail-clamp technique at three time points: after 2 h of halothane anesthesia, during adenosine-induced hypotension (mean arterial pressure: 55 mmHg), and 1 h after adenosine was discontinued. In other dogs, the effects of aminophylline, dipyridamole, or the specific adenosine-receptor antagonist 8-phenyl-theophylline (8-PT) on the halothane-adenosine interaction were studied. Adenosine significantly reduced halothane MAC, by 49%, from 0.76 +/- 0.05 to 0.39 +/- 0.05 vol% (mean +/- SEM). This effect was blocked by the concurrent administration of aminophylline (n = 5, P less than 0.05) or 8-PT (n = 4 of 4). When dipyridamole, which increases the plasma concentrations of endogenous adenosine, was administered alone, halothane MAC was reduced from 0.79 +/- 0.03 to 0.67 +/- 0.05 vol% (n = 5, P = 0.09). We conclude that exogenous adenosine substantially reduces halothane MAC in dogs and that this effect is blocked by the concurrent administration of the adenosine-receptor antagonists aminophylline or 8-PT. Relatively small alterations of endogenous adenosine concentrations, however, do not substantially reduce halothane MAC.
Seitz
P A
PA
Department of Anesthesiology, University of Florida College of Medicine, Gainesville 32610-0254.
ter Riet
M
M
Rush
W
W
Merrell
W J
WJ
D000241:Adenosine / Q000494:pharmacology*; D000628:Aminophylline / Q000494:pharmacology; D000758:Anesthesia; D000818:Animals; D004176:Dipyridamole / Q000494:pharmacology; D004285:Dogs; D006221:Halothane / Q000493:pharmacokinetics*; D011650:Pulmonary Alveoli / Q000378:metabolism*; D011983:Receptors, Purinergic / Q000187:drug effects; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology
D011983:Receptors, Purinergic; D000628:Aminophylline; D004176:Dipyridamole; D013806:Theophylline; C028322:8-phenyltheophylline; D000241:Adenosine; D006221:Halothane