title: Microwave-induced lethal heat stress: effects of phentolamine, prazosin and metoprolol.
abstract: Previous studies have shown that adrenergic antagonists can alter physiological responses to microwave-induced heating. In the present experiments, 33 ketamine-anesthetized Sprague-Dawley rats were exposed to 2450-MHz microwaves at an average power density of 60 mW/sq cm (whole-body average specific absorption rate of approximately 14 W/kg) until death occurred. The effects of intraarterial injections of the nonselective alpha-adrenoceptor antagonist phentolamine (10 mg/kg body weight), the alpha 1-adrenoceptor antagonist prazosin (5 mg/kg), and the beta 1-adrenoceptor antagonist metoprolol (2 mg/kg) on physiological responses (including changes in body temperature, heart rate, blood pressure, and respiratory rate) were examined. A group of saline-injected animals was included for comparison. There were no significant differences in lethal temperatures, survival times, or rates of temperature change among the different groups. In all groups, heart rate increased continuously during exposure; mean arterial blood pressure increased until colonic temperature reached 41-41.5 degrees C, and then decreased. These heart rate and blood pressure changes were similar to those that occur during environmental heat stress. Despite differences in absolute values of heart rate and mean arterial blood pressure among groups, there were no significant differences in changes from baseline levels among groups. From these results, taken together with previous findings in our laboratory, it may be hypothesized that selective alpha 1 blockade (without concurrent alpha 2 blockade) and beta 2 blockade (with or without concurrent beta 1 blockade) are effective in altering physiological responses to microwave exposure.
mesh_terms: D058668:Adrenergic alpha-1 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D058671:Adrenergic beta-1 Receptor Antagonists; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D001831:Body Temperature / Q000187:drug effects; D001833:Body Temperature Regulation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006358:Hot Temperature / Q000009:adverse effects*; D008297:Male; D008790:Metoprolol / Q000494:pharmacology*; D008872:Microwaves; D010646:Phentolamine / Q000494:pharmacology*; D011224:Prazosin / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D058668:Adrenergic alpha-1 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists; D058671:Adrenergic beta-1 Receptor Antagonists; D000319:Adrenergic beta-Antagonists; D008790:Metoprolol; D011224:Prazosin; D010646:Phentolamine