Tolazoline Decreases Survival Time During Microwave-Induced Lethal Heat Stress in Anesthetized Rats

Abstract

Effects of alpha-adrenergic antagonists have been studied during environmental heating but not during microwave-induced heating. Tolazoline may exert some of its effects via alpha-adrenegic blockade. In the present study, ketamine-anesthetized Sprague-Dawley rats were exposed to 2450-MHz microwaves at an average power density of 60 mW/cm2 (whole-body specific absorption rate of approximately 14 W/kg) until lethal temperatures were attained. The effects of tolazoline (10 mg/kg body weight) on physiological responses (including changes in body temperature, heart rate, blood pressure, and respiratory rate) were examined. Survival time was significantly shorter in the tolazoline group than in saline-treated animals. In general, heart rate and blood pressure responses were similar to those that occur during environmental heat stress. Heart rate, however, was significantly elevated in animals that received tolazoline, both before and during terminal microwave exposure. It is possible that changes associated with the elevated heart rate (e.g., less cardiac filling) in tolazoline-treated animals resulted in greater susceptibility to microwave-induced heating and the lower survival time.

Cardiovascular and thermal effects of microwave irradiation at 1 and/or 10 GHz in anesthetized rats

“…The gradual rise in heart rate throughout the exposure period and the biphasic change in mean arterial blood pressure (exhibited in all groups) were similar to changes observed by other investigators during experiments of lethal environmental heat stress in anesthetized rats [Kregel and Gisol®, 1990]. In our earlier studies of terminal exposures of anesthetized rats to 350-MHz , 2.45-GHz [Jauchem and Frei, 1994;Jauchem et al, 1995;Jauchem et al, 1996], 2.8-GHz [Jauchem et al, 1984b], 5.6-GHz [Jauchem et al, 1983;, and 35-GHz MWs [Ryan et al, 1996;, the patterns of heart rate and mean arterial blood pressure changes were comparable.…”

“…As in the present study, previous results of respiratory rate changes during lethal MW exposures have shown either no consistent pattern or a respiratory rate that initially remained relatively constant (or slightly increased) and then decreased until death [Jauchem and Frei, 1994;Jauchem et al, 1983Jauchem et al, , 1995Jauchem et al, , 1996.…”

“…In our earlier studies of terminal exposures of anesthetized rats to 350-MHz , 2.45-GHz [Jauchem and Frei, 1994;Jauchem et al, 1995;Jauchem et al, 1996], 2.8-GHz [Jauchem et al, 1984b], 5.6-GHz [Jauchem et al, 1983;, and 35-GHz MWs [Ryan et al, 1996;, the patterns of heart rate and mean arterial blood pressure changes were comparable.…”

Body heating induced by sub-resonant (350 MHz) microwave irradiation: Cardiovascular and respiratory responses in anesthetized rats

“…This phenomenon was seen in conjunction with MW animals exposed to microwaves (MWs) are related to both the whole-body average temperature increase and studies performed at frequencies of 700 [Frei et al, 1989], 1200 [Jauchem et al, 1990], 2450 [Jauchem et localized temperature increases (hot spots). These temal., 1995, 1996], 2800 [Frei and Jauchem, 1989; Frei perature changes are dependent on the MW carrier et al, 1988;Jauchem andFrei, 1991, 1994; (additional frequency. At very low frequencies, a biological specireferences are cited in Jauchem and Frei, 1992], 5600, men absorbs relatively little electromagnetic energy; it and 9300 MHz (references cited in Jauchem and Frei, is highly transparent.…”

“…Higher is inversely related to frequency, larger HR changes average specific absorption rates (SARs) and faster were elicited at frequencies that produced greater pecore heating for equivalent incident power densities ripheral heating and, therefore, greater cutaneous theroccur during irradiation at or near the resonant fremoreceptor stimulation. Blood pressure and respiratory quency than during irradiation to frequencies well changes during MW exposure at different frequencies above whole-body resonance [D'Andrea et al, 1977, have been summarized previously [Frei, 1995[Frei, ]. 1985[Frei, , 1987[Frei, , 1988Frei et al, 1989;Jauchem et al, Lotz and Saxton [1988] suggested that frequen-1990].…”