Effects of esmolol on 35 GHz microwave-induced lethal heat stress

1. The purpose of this study was to examine effects of the beta(1)-adrenoreceptor antagonist esmolol (infused at 2 or 4 mg kg-1 body wt min-1) on heart rate, blood pressure, respiratory rate, localized body temperature changes, survival times, and lethal body temperatures that occur during the exposure of anaesthetized rats to 35 GHz microwaves. 2. Forty Sprague-Dawley rats, anaesthetized with ketamine, were exposed to 35 GHz microwaves at a level that resulted in heating and death. During irradiation, a continuous increase in heart rate and a biphasic response in blood pressure (initial increase followed by a decrease) were observed in all groups of animals. 3. Esmolol caused a significant dose-dependent decrease in blood pressure, relative to saline-treated animals, but only a small attenuation of the heat-induced rise in heart rate. In experiments in which esmolol was infused and microwave exposure was continued until death, drug-treated animals survived for significantly shorter periods and died at significantly lower body temperatures. The change in survival may have been related to the lower blood pressure due to esmolol treatment.