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)-adre noreceptor 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 rimes, and lethal body temperatures that occur during the exposure of anesthaetized rats to 35 GHz microwaves. 2 Forty Sprague-Dawley rats, anaesthetized with ketamine, were expose d 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 hea rt rate. In experiments in which esmolol was infused and microwave exp osure was continued until death, drug-treated animals survived for sig nificantly shorter periods and died at significantly lower body temper atures. The change in survival may have been related to the lower bloo d pressure due to esmolol treatment.