Repeated exposure of C3H/HeJ mice to ultra-wideband electromagnetic pulses: lack of effects on mammary tumors.

It has been suggested that chronic, low-level exposure to radiofrequency (RF) radiation may promote the formation of tumors. Previous studies, however, showed that low-level, long-term exposure of mammary tumor-prone mice to 435 MHz or 2450 MHz RF radiation did not affect the incidence of mammary tumors. In this study, we investigated the effects of exposure to a unique type of electromagnetic energy: pulses composed of an ultra-wideband (UWB) of frequencies, including those in the RF range. One hundred C3H/HeJ mice were exposed to UWB pulses (rise time 176 ps, fall time 3.5 ns, pulse width 1.9 ns, peak E-field 40 kV/m, repetition rate 1 kHz). Each animal was exposed for 2 min once a week for 12 weeks. One hundred mice were used as sham controls. There were no significant differences between groups with respect to incidence of palpated mammary tumors, latency to tumor onset, rate of tumor growth, or animal survival. Histopathological evaluations revealed no significant differences between the two groups in numbers of neoplasms in all tissues studied (lymphoreticular tissue, thymus, respiratory, digestive and urinary tracts, reproductive, mammary and endocrine systems, and skin). Our major finding was the lack of effects of UWB-pulse exposure on promotion of mammary tumors in a well-established animal model of mammary cancer.

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

Relatively large thermal gradients may exist during exposure of an animal to microwaves (MWs), particularly at high frequencies. Differences in thermal gradients within the body may lead to noticeable differences in the magnitude of cardiovascular changes resulting from MW exposure. This study compares the thermal distribution and cardiovascular effects of exposure to a single MW frequency with effects of simultaneous exposure to two frequencies. Ketamine-anesthetized male Sprague-Dawley rats (n = 58) were exposed individually to one of three conditions: 1-GHz, 10-GHz, or combined 1- and 10-GHz MWs at an equivalent whole-body specific absorption rate of 12 W/kg. The continuous-wave irradiation was conducted under far-field conditions with animals in E orientation (left lateral exposure, long axis parallel to the electric field) or in H orientation (left lateral exposure, long axis perpendicular to the electric field). Irradiation was started when colonic temperature was 37.5 degrees C and was continued until lethal temperatures were attained. Colonic, tympanic, left and right subcutaneous, and tail temperatures, and arterial blood pressure, heart rate, and respiratory rate were continuously recorded. In both E and H orientations, survival time (i.e., time from colonic temperature of 37.5 degrees C until death) was lowest in animals exposed at 1-GHz, intermediate in those exposed at 1- and 10-GHz combined, and greatest in the 10-GHz group (most differences statistically significant). At all sites (with the exception of right subcutaneous), temperature values in the 1- and 10-GHz combined group were between those of the single-frequency exposure groups in both E and H orientations. During irradiation, arterial blood pressure initially increased and then decreased until death. Heart rate increased throughout the exposure period. The general, overall patterns of these changes were similar in all groups. The results indicate that no unusual physiological responses occur during multi-frequency MW exposure, when compared with results of single-frequency exposure. Bioelectromagnetics 21:159-166, 2000. Published 2000 Wiley-Liss, Inc.

Cardiovascular and thermal responses in rats during 94 GHz irradiation.

We investigated the thermal distribution and cardiovascular effects produced by sustained exposure of rats to 94 GHz radio-frequency electromagnetic radiation (RFR). Sixteen ketamine-anesthetized Sprague-Dawley rats were exposed individually at a power density of 75 mW/cm2 under far-field conditions in E orientation. Irradiation began when colonic temperature was 37 degrees C and continued until death. Large, immediate increases in subcutaneous temperature on the irradiated side were accompanied by more moderate, delayed increases in colonic temperature. These body-temperature responses were similar to previous results obtained during 35 GHz RFR exposure. During irradiation, arterial blood pressure initially increased and then precipitously decreased until death. The heart rate increased throughout the exposure period. When comparing the results of these 94 GHz exposures with those in previous studies of lower RFR frequencies, it appears that the patterns of heart-rate and blood-pressure changes that occur before death are similar. We conclude that exposure to 94 GHz RFR produces extreme peripheral heating without similar levels of core heating and that this pattern of heat deposition is sufficient to produce circulatory failure and subsequent death.

Lack of effects on heart rate and blood pressure in ketamine-anesthetized rats briefly exposed to ultra-wideband electromagnetic pulses.

Fourteen Sprague-Dawley rats were exposed to pulses produced by a Bournlea ultra-wideband (UWB) pulse generator (rise time, 318-337 ps; maximum E field, 19-21 kV/m). Exposures at a repetition frequency of 1 kHz for 0.5 s or to repetitive pulse trains (2-s exposure periods alternating with 2 s of no exposure, for a total of 2 min) resulted in no significant changes in heart rate or mean arterial blood pressure. These results suggest that acute whole-body exposure to UWB pulses does not have a detrimental effect on the cardiovascular system.

Chronic, low-level (1.0 W/kg) exposure of mice prone to mammary cancer to 2450 MHz microwaves.

In a previous study (Frei et al., Bioelectromagnetics 19, 20-31, 1998), we showed that low-level (0.3 W/kg), long-term exposure of mice prone to mammary tumors to 2450 MHz radiofrequency (RF) radiation did not affect the incidence of mammary tumors, latency to tumor onset, tumor growth rate or animal survival when compared to sham-irradiated animals. In the current study, the specific absorption rate (SAR) was increased from 0.3 W/kg to 1.0 W/kg. The same biological end points were used. One hundred C3H/HeJ mice were exposed in circularly polarized waveguides for 78 weeks (20 h/day, 7 days/week) to continuous-wave, 2450 MHz RF radiation; 100 mice were sham-exposed. There was no significant difference between exposed and sham-exposed groups with respect to the incidence of palpated mammary tumors (sham-exposed = 30%; irradiated = 38%), latency to tumor onset (sham-exposed = 62.0 +/- 2.3 weeks; irradiated = 62.5 +/- 2.2 weeks) and rate of tumor growth. Histopathological evaluations revealed no significant difference in numbers of malignant, metastatic or benign neoplasms between the two groups. Thus long-term exposures of mice prone to mammary tumors to 2450 MHz RF radiation at SARs of 0.3 and 1.0 W/kg had no significant effects when compared to sham-irradiated animals.

Ultra-wideband electromagnetic pulses: lack of effects on heart rate and blood pressure during two-minute exposures of rats.

Exposure to fast-rise-time ultra-wideband (UWB) electromagnetic pulses has been postulated to result in effects on biological tissue (including the cardiovascular system). In the current study, 10 anesthetized Sprague-Dawley rats were exposed to pulses produced by a Sandia UWB pulse generator (average values of exposures over three different pulse repetition rates: rise time, 174-218 ps; peak E field, 87-104 kV/m; pulse duration, 0.97-0.99 ns). Exposures to 50, 500 and 1000 pulses/s resulted in no significant changes in heart rate or mean arterial blood pressure measured every 30 s during 2 min of exposure and for 2 min after the exposure. The results suggest that acute UWB whole-body exposure under these conditions does not have an immediate detrimental effect on these cardiovascular system variables in anesthetized rats.

Chronic exposure of cancer-prone mice to low-level 2450 MHz radiofrequency radiation.

The purpose of this study was to determine whether chronic, low-level exposure of mammary-tumor-prone mice to 2450 MHz radiofrequency radiation (RFR) promotes an earlier onset (decreased latency), a greater total incidence, or a faster growth rate of mammary tumors. One hundred C3H/ HeJ mice were exposed in circularly polarized waveguides (CWG) for 18 months (20 h/day, 7 days/wk) to continuous-wave, 2450 MHz RFR at a whole body average specific absorption rate (SAR) of 0.3 W/kg; 100 mice were sham exposed. Before exposure, SARs were determined calorimetrically; during experimentation, SARs were monitored by differential power measurement. All animals were visually inspected twice daily and were removed from the CWG cages for a weekly inspection, palpation, and weighing. From the time of detection, tumor size was measured weekly. Animals that died spontaneously, became moribund, or were killed after 18 months of exposure were completely necropsied; tissues were fixed and subjected to histopathological evaluations. Results showed no significant difference in weight profiles between sham-irradiated and irradiated mice. Concerning mammary carcinomas, there was no significant difference between groups with respect to palpated tumor incidence (sham = 52%; irradiated = 44%), latency to tumor onset (sham = 62.3 +/- 1.2 wk; irradiated = 64.0 +/- 1.6 wk), and rate of tumor growth. In general, histopathological examination revealed no significant differences in numbers of malignant, metastatic, or benign neoplasms between the two groups; a significantly greater incidence of alveolar-bronchiolar adenoma in the sham-irradiated mice was the only exception. In addition, survival analysis showed no significant difference in cumulative percent survival between sham and irradiated animals. Thus, results indicate that under the conditions of this study, long-term, low-level exposure of mammary-tumor-prone mice to 2450 MHz RFR did not affect mammary tumor incidence, latency to tumor onset, tumor growth rate, or animal longevity when compared with sham-irradiated controls.

Administration of a nitric oxide donor does not affect hypotension induced by 35-GHz microwave heating.

Sustained whole body exposure to 35-GHz radiofrequency radiation produces localized hyperthermia and hypotension, leading to circulatory failure and death. We previously demonstrated that pressor responses to nitric oxide (NO) synthesis inhibition are reduced following 35-GHz microwave (MMW) heating, implying that NO levels might also be reduced. This study therefore sought to determine whether administration of S-nitroso-N-acetylpenicillamine (SNAP), a NO donor, influences MMW-induced hypotension in ketamine-anesthetized rats. First, rats were exposed to MMW until mean arterial pressure (MAP) fell to 75 mmHg. MMW exposure was then discontinued and either SNAP (300 micrograms/kg/h) or saline was infused. SNAP infusion affected neither the hypotension nor the survival time following MMW exposure. In a second protocol, SNAP (300 micrograms/kg/h) or saline was infused prior to and throughout MMW exposure, which was continued until death. SNAP infusion did not alter either the onset or the magnitude of terminal hypotension. Therefore, we conclude that exogenous NO does not affect cardiovascular responses to 35-GHz MMW heating.

Long-term, low-level exposure of mice prone to mammary tumors to 435 MHz radiofrequency radiation.

The purpose of this study was to determine if chronic, low-level exposure of mice prone to mammary tumors to 435 MHz radiofrequency (RF) radiation promotes an earlier onset, a faster growth rate or a greater total incidence of mammary tumors than in sham-exposed controls. Two hundred female C3H/HeJ mice were exposed for 21 months (22 h/day, 7 days/week) to a horizontally polarized 435 MHz pulse-wave (1.0 micros pulse width, 1.0 kHz pulse rate) RF radiation environment with an incident power density of 1.0 mW/cm2 (SAR = 0.32 W/kg). An additional 200 mice were sham-exposed. Animals that died spontaneously, became moribund or were euthanized after 21 months of exposure were completely necropsied; tissues were subjected to histopathological examinations. Concerning mammary carcinomas, there were no significant differences between the two groups with respect to latency to tumor onset, tumor growth rate and overall tumor incidence. Histopathological examination revealed no significant differences in numbers of malignant, metastatic or benign neoplasms between groups. Survival probability was estimated by the Kaplan-Meier method; no significant difference between groups was noted (Cox's test). Under the conditions of this long-term study, low-level exposure of mice prone to mammary tumors to 435 MHz RF radiation did not affect the incidence of mammary tumors, tumor growth rate, latency to tumor onset or animal longevity when compared to sham-exposed controls.

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.

Frequency of micronuclei in the peripheral blood and bone marrow of cancer-prone mice chronically exposed to 2450 MHz radiofrequency radiation.

C3H/HeJ mice, which are prone to mammary tumors, were exposed for 20 h/day, 7 days/week, over 18 months to continuous-wave 2450 MHz radiofrequency (RF) radiation in circularly polarized wave guides at a whole-body average specific absorption rate of 1.0 W/kg. Sham-exposed mice were used as controls. The positive controls were the sentinel mice treated with mitomycin C during the last 24 h before necropsy. At the end of the 18 months, all mice were necropsied. Peripheral blood and bone marrow smears were examined for the extent of genotoxicity as indicated by the presence of micronuclei in polychromatic erythrocytes (PCEs). The results indicate that the incidence of micronuclei/1,000 PCEs was not significantly different between groups exposed to RF radiation (62 mice) and sham-exposed groups (58 mice), and the mean frequencies were 4.5 +/- 1.23 and 4.0 +/- 1.12 in peripheral blood and 6.1 +/- 1.78 and 5.7 +/- 1.60 in bone marrow, respectively. In contrast, the positive controls (7 mice) showed a significantly elevated incidence of micronuclei/1,000 PCEs in peripheral blood and bone marrow, and the mean frequencies were 50.9 +/- 6.18 and 55.2 +/- 4.65, respectively. When the animals with mammary tumors were considered separately, there were no significant differences in the incidence of micronuclei/1,000 PCEs between the group exposed to RF radiation (12 mice) and the sham-exposed group (8 mice), and the mean frequencies were 4.6 +/- 1.03 and 4.1 +/- 0.89 in peripheral blood and 6.1 +/- 1.76 and 5.5 +/- 1.51 in bone marrow, respectively. Thus there was no evidence for genotoxicity in mice prone to mammary tumors that were exposed chronically to 2450 MHz RF radiation compared with sham-exposed controls.

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

These experiments were designed to investigate the effects of sub-resonant microwave (MW) exposure (350 MHz, E orientation, average power density 38 mW/cm2, average whole-body specific absorption rate 13.2 W/kg) on selected physiological parameters. The increase in peripheral body temperature during 350 MHz exposure was greater than that in earlier experiments performed at 700 MHz (resonance). Heart rate and mean arterial blood pressure were significantly elevated during a 1 degree C increase in colonic temperature due to 350 MHz exposure; respiratory rate showed no significant change. The results are consistent with other investigators' reports comparing sub-resonance exposures with those at resonance and above.

Circulatory failure induced by 35 GHz microwave heating: effects of chronic nitric oxide synthesis inhibition.

Sustained exposure to radiofrequency radiation of millimeter wave (MMW) length produces hyperthermia and subsequent circulatory failure. This study sought to determine whether this phenomenon is altered by chronic pretreatment with the nitric oxide (NO) synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME). Rats drank either 1) water, 2) water + L-NAME, or 3) water + L-NAME + L-arginine (at 20 and 50 times the dose of L-NAME) for 14 days. Ketamine-anesthetized rats were exposed to MMW until mean arterial blood pressure (MAP) fell to 75 mmHg, at which point MMW exposure was discontinued. MAP initially increased during exposure in all groups; the pressor response in L-NAME-treated rats was greater than that in water-drinking rats. Subsequently, MAP fell in all groups. The MMW exposure time required to reach MAP = 75 mmHg was significantly reduced in L-NAME-treated rats, although survival times (post-MMW) of L-NAME-treated and control rats were not statistically different. Coadministration of L-arginine abolished the enhanced pressor response produced by L-NAME, but did not completely reverse the shortened MMW exposure time in L-NAME-treated rats. Thus, chronic NO synthesis inhibition with L-NAME reduces the ability of rats to withstand 35 GHz microwave heating, suggesting that NO does not mediate the hypotension produced by this form of hyperthermia.

Does nitric oxide mediate circulatory failure induced by 35-GHz microwave heating?

The purpose of this study was to determine whether nitric oxide (NO) contributes to the hypotensive state induced by exposure to radiofrequency radiation of millimeter-wavelength (MMW). This was accomplished using a synthetic analogue of L-arginine, N omega-nitro-L-arginine methyl ester (L-NAME), to competitively inhibit NO synthesis. Ketamine-anesthetized rats were instrumented for the measurement of arterial blood pressure, ECG, and temperature at five sites. Animals were exposed to 35-GHz radiofrequency radiation until mean arterial pressure (MAP) decreased to 75 mmHg. MMW exposure was then halted and either saline or L-NAME (1, 2.5, 5, or 10 mg/kg) was administered; each rat received only one dose. Following irradiation, L-NAME at each dose produced a peak increase in MAP that was smaller than that produced by the same dose of L-NAME in nonirradiated rats. There was no difference in post-MMW survival times between L-NAME-and saline-treated rats. These results indicate that bolus administration of L-NAME does not reverse hypotension induced by 35-GHz microwave heating, suggesting that excess levels of NO do not mediate this form of circulatory failure.

Tolazoline decreases survival time during microwave-induced lethal heat stress in anesthetized rats.

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.

High-peak-power microwave pulses: effects on heart rate and blood pressure in unanesthetized rats.

INTRODUCTION: Exposure sources capable of generating high-peak-power microwave pulses, with relatively short pulse widths, have recently been developed. Studies of the effect of these sources on the cardiovascular systems of animals have not been reported previously. METHODS: We exposed 14 unanesthetized male Sprague-Dawley rats to 10 high-peak-power microwave pulses generated by a transformer-energized megawatt pulsed output (TEMPO) microwave source, at frequencies ranging from 1.2-1.8 GHz. Peak power densities were as high as 51.6 kW/cm2. At 14 d prior to irradiation, the animals were implanted with chronic aortic cannulae. With appropriate shielding of the transducer, blood pressure recordings were obtained during microwave pulsing. RESULTS: In a preliminary series of exposures at 1.7-1.8 GHz (peak power density 3.3-6.5 kW/cm2), an immediate but transient increase in mean arterial blood pressure (significant) and decrease in heart rate (non-significant) were observed. A loud noise was associated with each pulse produced by the TEMPO; this factor was subsequently attenuated. In a second series of exposures at 1.2-1.4 GHz (peak power density 14.6-51.6 kW/cm2), there were no significant changes in mean arterial blood pressure or heart rate during microwave exposure. CONCLUSIONS: The earlier significant increase in blood pressure that occurred during microwave exposure appeared to be related to the sharp noise produced by the TEMPO source. After appropriate sound attenuation, there were no significant effects of exposure to the microwave pulses.

Sustained 35-GHz radiofrequency irradiation induces circulatory failure.

The objective of this study was to determine the thermal distribution and concomitant cardiovascular changes produced by whole-body exposure of ketamine-anesthetized rats to radiofrequency radiation of millimeter wave (MMW) length. Rats (n = 13) were implanted with a flow probe on the superior mesenteric artery and with a catheter in the carotid artery for the measurement of arterial blood pressure. Temperature was measured at five sites: left (Tsl) and right subcutaneous (sides toward and away From the MMW source, respectively), colonic (Tc), tympanic, and tail. The animals were exposed until death to MMW (35 GHz) at a power density that resulted in a whole-body specific absorption rate of 13 W/kg. During irradiation, the Tsl increase was significantly greater than the Tc increase. Heart rate increased throughout irradiation. Mean arterial pressure (MAP) as well maintained until Tsl reached 42 degrees C, at which point MAP declined until death. Mesenteric vascular resistance tended to increase during the early stages of irradiation but began to decrease at Tsl > or = 41 degrees C. The declines in both mesenteric vascular resistance and MAP began at Tc < 37.5 degrees C; death occurred at Tc = 40.3 +/- .3 degrees C and Tsl = 48.0 +/- .4 degrees C. These data indicate that circulatory failure and subsequent death may occur when skin temperature is rapidly elevated, even in the presence of relatively normal Tc.

Microwave-induced lethal heat stress: effects of phentolamine, prazosin and metoprolol.

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.

Chronic administration of L-NAME in drinking water alters working memory in rats.

To examine the role of nitric oxide (NO) in the maintenance of working memory of rats, the effects of chronic administration (in drinking water) of the NO synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME), on this behavior was examined with a simple test of remembering recently explored objects. Unlike other working memory tasks that require a subject to perform for a reward such as food or water or to avoid shock, our task measured spontaneous exploration of novel and familiar objects and has been described as a "pure" working memory task [9]. Normal subjects spend significantly more time in contact with new environmental components and less time with familiar objects. A subject that extensively reexplores a stimulus with which it has previous experience is presumed to exhibit some memory loss associated with the object. Memory changes were evaluated by measuring the relative time subjects explored familiar versus new stimulus objects. Rats (n = 15) that chronically drank L-NAME (approximately 90 mg/kg/day) for 14 days spent significantly less time exploring a novel object than did rats (n = 13) that drank only tap water (p < .05). This effect of L-NAME was abolished by concurrent administration of L-Arginine (approximately 4.5 g/kg/day). Total object exploration was not affected by our drug treatments, suggesting that our object discrimination task is not activity dependent. These data are consistent with the hypothesis that NO is required for some forms of working memory.