Aminophylline does not attenuate histamine-induced airway constriction during halothane anesthesia

The effects of aminophylline on the release of endogenous catecholamines and on airway reactivity to aerosol histamine challenge were evaluated during halothane and thiopental/fentanyl anesthesia in basenji-greyhound dogs. Responses to histamine aerosol challenge (0.01, 0.03, 0.1, 0.3, 1.0, and 3.0 mg/ml) were measured during six conditions: 1) thiopental/fentanyl anesthesia (control), 2) thiopental/fentanyl with aminophylline infusion, 3) halothane anesthesia (1.5 MAC), 4) halothane anesthesia with aminophylline infusion, 5) thiopental/fentanyl anesthesia after pretreatment with iv propranolol, and 6) thiopental/fentanyl anesthesia with aminophylline infusion after pretreatment with iv propranolol. Prior to aerosol challenge baseline pulmonary resistance (RL) did not differ in the six groups. Aminophylline significantly attenuated the pulmonary response to histamine and increased catecholamine concentrations during thiopental/fentanyl anesthesia. Although halothane itself significantly attenuated the pulmonary response to histamine, the administration of aminophylline during halothane anesthesia produced no additional protective effect and no increases in catecholamines were noted. Moreover, no protective effect was seen after aminophylline administration during thiopental/fentanyl anesthesia in the same dogs pretreated with propranolol. These data suggest that the protective effect of aminophylline on histamine reactivity results from release of endogenous catecholamines and that the use of aminophylline during halothane anesthesia, which blocks this release, is not warranted.