Thermoregulatory responses of febrile monkeys during microwave exposure

We have examined experimentally the question of increased vulnerability to the thermalizing effects of MW exposure during febrile illness. In a controlled ambient temperature of 26 degrees C, autonomic mechanisms of heat production and heat loss were measured in febrile squirrel monkeys during 30-min exposures to 450 or 2450 MHz CW MW fields at different phases of the fever cycle (induction, plateau, defervescence). We have shown that MW energy absorbed during a febrile episode spares endogenous energy production, but may augment the fever if deposited deep in the body, as is the case during exposure at the resonant frequency. The fever may also be exacerbated if the MW exposure occurs late in the febrile episode, a condition that may put an organism at some risk, especially if the field strength exceeds safety guidelines.

Indomethacin attenuation of radiation-induced hyperthermia does not modify radiation-induced motor hypoactivity

Exposure of rats to 5-10 Gy of ionizing radiation produces hyperthermia and reduces motor activity. Previous studies suggested that radiation-induced hyperthermia results from a relatively direct action on the brain and is mediated by prostaglandins. To test the hypothesis that hypoactivity may be, in part, a thermoregulatory response to this elevation in body temperature, adult male rats were given indomethacin (0.0, 0.5, 1.0, and 3.0 mg/kg, intraperitoneally), a blocker of prostaglandin synthesis, and were either irradiated (LINAC 18.6 MeV (nominal) high-energy electrons, 10 Gy at 10 Gy/min, 2.8 microseconds pulses at 2 Hz) or sham-irradiated. The locomotor activity of all rats was then measured for 30 min in a photocell monitor for distance traveled and number of vertical movements. Rectal temperatures of irradiated rats administered vehicle only were elevated by 0.9 +/- 0.2 degree C at the beginning and the end of the activity session. Although indomethacin, at the two higher doses tested, attenuated the hyperthermia in irradiated rats by 52-75%, it did not attenuate radiation-induced reductions in motor activity. These results indicate that motor hypoactivity after exposure to 10 Gy of high-energy electrons is not due to elevated body temperature or to the increased synthesis of prostaglandins.

[Changes in heat production in experimental animals during irradiation and administration of radiation-protective agents]

Due to the improvement of field method of oxygen consumption measuring, the instrument to realize simultaneous determination of micromammals heat production has been elaborated. These investigations estimated that the irradiation of mice at the dose of 3 mGy/hour caused the increase of heat production for 11.4%. Injection of radioprotectors increases the animals' heat production with the simultaneous decrease of oxygen consumption.

[The temperature reaction of rabbits to local microwave exposures]

A rapid increase of skin temperature after discontinuation of local microwave (MW) exposure of the heart and thyroid indicates a vasomotor response in the exposed and adjacent zones. The infrared radiation (IR) of the particular parts of skin surface before and after local MW exposures (460 MHz, current density 10, 120 and 230 mW/cm2) of the rabbit heart and thyroid regions was registered by IR thermograph. The investigations were performed on un-narcotized, narcotized (nembutal 40 mg/kg) animals, on rabbits with anaesthetized skin receptors (lidocaine 100 mg) and on carcasses. The changes observed depended on the exposure site, functional status of the rabbits and MW current density. The energy-depending reactions are attributed to direct myocardial reactions and extracardiac vegetative responses in the cardiac and thyroid exposures, respectively.

Exposure to heavy charged particles affects thermoregulation in rats

Rats exposed to 0.1-5 Gy of heavy particles (56Fe, 40Ar, 20Ne or 4He) showed dose-dependent changes in body temperature. Lower doses of all particles produced hyperthermia, and higher doses of 20Ne and 56Fe produced hypothermia. Of the four HZE particles, 56Fe particles were the most potent and 4He particles were the least potent in producing changes in thermoregulation. The 20Ne and 40Ar particles produced an intermediate level of change in body temperature. Significantly greater hyperthermia was produced by exposure to 1 Gy of 20Ne, 40Ar and 56Fe particles than by exposure to 1 Gy of 60Co gamma rays. Pretreating rats with the cyclo-oxygenase inhibitor indomethacin attenuated the hyperthermia produced by exposure to 1 Gy of 56Fe particles, indicating that prostaglandins mediate 56Fe-particle-induced hyperthermia. The hypothermia produced by exposure to 5 Gy of 56Fe particles is mediated by histamine and can be attenuated by treatment with the antihistamines mepyramine and cimetidine.

Athermal alterations in the structure of the canalicular membrane and ATPase activity induced by thermal levels of microwave radiation

Sprague-Dawley rats (200-250 g) were exposed 30 min/day for 4 days to thermogenic levels (rectal temperature increase of 2.2 degrees C) of microwave radiation [2.45 GHz, 80 mW/cm2, continuous-wave mode (CW)] or to a radiant heat source resulting in an equivalent increase in body temperature of 2.2 degrees C. On the fifth day after the 4 days of exposure to microwave radiation, the animals were sacrificed and their livers removed. The canalicular membranes were isolated and evaluated for adenosinetriphosphatase (ATPase) activity, total fatty acid composition and membrane fluidity characteristics. Mg(++)-ATPase activity (Vmax) decreased by 48.5% in the group exposed to microwave radiation, with no significant change in the group exposed to radiant heat. The decrease in Mg(++)-ATPase was partially compensated by a concomitant increase in Na+/K(+)-ATPase activity (170% increase in Vmax over control) in animals exposed to microwave radiation, while no change occurred in the group exposed to radiant heat. This alteration in ATPase activity in the group exposed to microwave radiation is associated with a large decrease in the ratio of saturated to unsaturated fatty acids. Conversely, the group exposed to radiant heat had an increase in the ratio of saturated to unsaturated fatty acids. The most dramatic changes were found in the levels of arachidonic acid. Finally, the electron paramagnetic resonance (EPR) spin label technique used to measure the fluidity of the canalicular membranes of the animals in the three groups (sham, microwave radiation and radiant heat) indicated that the results were different in the three groups, reflecting the changes found in their fatty acid composition. The physiological response to "equivalent" thermal loads in rats is expressed differently for different types of energy sources. Possible mechanisms producing these divergent thermogenic responses are discussed.

In vivo effect of visible light on feline cortical microcirculation

The present study was designed to test the hypothesis that prolonged illumination of the cerebral cortex, for instance during neurosurgical interventions, may affect the pial microcirculation. Experiments were performed with the closed window technique in cats. The cortical surface below the window was exposed to visible, cold light of 61,000 lumens/m2 (lux) over a period of 1 to 5 hours. Pial arterioles reacted with a slight initial dilatation to 106.8 +/- 2.6% of their resting diameter after switching to the high intensity light. Measurements of the cortical surface temperature showed an average temperature increase of 1.5 +/- 0.34 degrees C within the first 10 minutes of illumination. For assessment of pial vascular function, the responses to topical application of acetylcholine (ACh) were tested before and during the illumination period. The effect of sustained illumination on the cortical microcirculation consisted of abolition of the endothelium dependent relaxation due to ACh, and of intravascular thrombus formation, the latter, however, only in the presence of topically applied ACh. The suspected mechanism responsible for these functional alterations is light-induced generation of free oxygen radicals which are known to inactivate or destroy the endothelium-derived relaxing factor (EDRF). Further studies are recommended to elucidate the practical and clinical relevance of these findings to neurosurgical procedures.

Immediate effects of different light intensities on body temperature and alertness

The effects of different light intensities on temperature and alertness were investigated. It was hypothesized that temperature and alertness would be affected by certain light intensities but only during the melatonin release period (after 2100 h). Fifteen subjects were tested under three levels of light known to suppress melatonin (500, 1000, and 5000 lx) and a level known not to affect melatonin (50 lx). Subjects were tested on four occasions from 1700 until 2300 h. Tympanic temperature and measures of alertness (EEG power and frequency and self-reports) were obtained before and after melatonin onset. There were no differences in any measure prior to the melatonin onset, increases in temperature and alertness occurred only after melatonin onset. Temperatures and self-reported alertness scores obtained under light intensities of 500, 1000, and 5000 lx were elevated relative to those obtained under 50 lx but were not significantly different from each other. The results suggest that melatonin may be involved in mediating the effects of light on temperature and alertness and that 500 lx may be near the threshold for significant melatonin suppression, temperature enhancement, and increases in alertness.

[Eye heating caused by microwave ovens]

To clarify the question as to whether microwave ovens represent a risk for the eyes, a worst-case situation was investigated in which it was assumed that a child observes the internal heating process with its eyes as close to the door of a microwave oven as it is possible to get. As expected, heating of the eyes was observed, which, however, was caused mainly by the conventional heating process rather than by microwave radiation. Significant microwave heating was observed only when increased scattered radiation was simulated by inactivating the safety contacts and opening the door of the microwave oven. When the door is opened to a clearly visible gap width (2.3 cm), the contribution of the microwave component to the overall temperature increase of 5 degrees C after one hour of continuous exposure did not exceed 16%. Even at the maximum possible door gap width which just did not cause the oven to switch off automatically (2.6 cm), 15 minutes of continuous exposure contributed only 50% to the 2 degrees C temperature increase. On the basis of these results, damage to the eye through the use of microwave ovens can be excluded.

Physiological interaction processes and radio-frequency energy absorption

Because exposure to microwave fields at the resonant frequency may generate heat deep in the body, hyperthermia may result. This problem has been examined in an animal model to determine both the thresholds for response change and the steady-state thermoregulatory compensation for body heating during exposure at resonant (450 MHz) and supra-resonant (2,450 MHz) frequencies. Adult male squirrel monkeys, held in the far field of an antenna within an anechoic chamber, were exposed (10 min or 90 min) to either 450-MHz or 2,450-MHz CW fields (E polarization) in cool environments. Whole-body SARs ranged from 0-6 W/kg (450 MHz) and 0-9 W/kg (2,450 MHz). Colonic and several skin temperatures, metabolic heat production, and evaporative heat loss were monitored continuously. During brief RF exposures in the cold, the reduction of metabolic heat production was directly proportional to the SAR, but 2,450-MHz energy was a more efficient stimulus than was the resonant frequency. In the steady state, a regulated increase in deep body temperature accompanied exposure at resonance, not unlike that which occurs during exercise. Detailed analyses of the data indicate that temperature changes in the skin are the primary source of the neural signal for a change in physiological interaction processes during RF exposure in the cold.

Heart rate and blood pressure changes during radiofrequency irradiation and environmental heating

1. Whole-body exposure of animals to radiofrequency radiation (RFR) can cause an increase in body temperature. 2. Responses to heating, whether due to RFR or to more conventional means, include changes in heart rate and blood pressure. 3. Although cardiovascular responses to various types of heating are similar, differences in the magnitude of changes may result from different thermal gradients within the body. 4. This review compares the effects of RFR and conventional environmental heating on heart rate and blood pressure.

Thermal and physiologic responses to 1200-MHz radiofrequency radiation: differences between exposure in E and H orientation

Ketamine-anesthetized Sprague-Dawley rats were exposed to far-field 1200-MHz continuous wave radiofrequency radiation in both E and H orientations (long axis of animal parallel to electric or magnetic field, respectively). Power densities were used that resulted in equivalent whole-body specific absorption rates of approximately 8 W/kg in both orientations (20 mW/cm2 for E and 45 mW/cm2 for H). Exposure was conducted to repeatedly increase colonic temperature from 38.5 to 39.5 degrees C in both orientations in the same animal. Irradiation in E orientation resulted in greater colonic, tympanic, left subcutaneous (side toward antenna), and tail heating. The results indicated a more uniform distribution of heat than that which occurred in previous experiments of 2450-MHz irradiation in E and H orientation. A lack of significant differences in blood pressure and heart rate responses between exposures in the two orientations in this study suggest that greater peripheral heating, as was seen in the earlier study of 2450 MHz, is necessary for these differences to occur.

Involvement of prostaglandins and histamine in radiation-induced temperature responses in rats

Exposure of rats to 1-15 Gy of gamma radiation induced hyperthermia, whereas exposure to 20-150 Gy produced hypothermia. Since radiation exposure induced the release of prostaglandins (PGs) and histamine, the role of PGs and histamine in radiation-induced temperature changes was examined. Radiation-induced hyper- and hypothermia were antagonized by pretreatment with indomethacin, a cyclooxygenase inhibitor. Intracerebroventricular administration of PGE2 and PGD2 induced hyper- and hypothermia, respectively. Administration of SC-19220, a specific PGE2 antagonist, attenuated PGE2- and radiation-induced hyperthermia, but it did not antagonize PGD2- or radiation-induced hypothermia. Consistent with an apparent role of histamine in hypothermia, administration of disodium cromoglycate (a mast cell stabilizer), mepyramine (H1-receptor antagonist), or cimetidine (H2-receptor antagonist) attenuated PGD2- and radiation-induced hypothermia. These results suggest that radiation-induced hyperthermia is mediated via PGE2 and that radiation-induced hypothermia is mediated by another PG, possibly PGD2, via histamine.

Acute thermoregulatory responses of the immature rat to warming by low-level 2,450-MHz microwave radiation

Rats were tested at 6-7 days of age to determine thermoregulatory responses to microwave exposure (2,450-MHz; continuous wave). Each animal was partially restrained in a cylindrical holder and irradiated at a power density of either 5 or 20 mW/cm2 [specific absorption rate = 0.60 (W/kg)/(mW/cm2)] at a cold ambient temperature (Ta). Following a 1-hour thermal equilibration period, each rat was monitored at 1-min intervals during 1-hour microwave exposure and 1-hour recovery periods. Colonic temperature (Tco), determined with a Vitek probe, and metabolic heat production (M), derived from measures of oxygen consumption, were sampled and recorded during these periods. Tco increased significantly above initial level at both power densities and reached a plateau after 45 min of microwave exposure. Tco doubled with a four-fold increase in microwave intensity. Prior to exposure, M was elevated in response to cold Ta and remained unchanged during exposure at 5 mW/cm2, but decreased 7.2 W/kg during exposure at 20 mW/cm2. The results indicate that the hypothermic rat pup can be effectively warmed by low-level microwave irradiation and is capable of altering metabolism in response to such heating.

Mechanisms of biological effects of radiofrequency electromagnetic fields: an overview

Manmade sources of electromagnetic (EM) fields, and therefore human exposures to them, continue to increase. Public concerns stem from the effects reported in the literature, the visibility of the sources, and somewhat from confusion between EM fields and ionizing radiation. Protecting humans from the real hazards and allaying groundless fears requires a self-consistent body of scientific data concerning effects of the fields, levels of exposures which cause those effects, and which effects are deleterious (or beneficial or neutral). With that knowledge, appropriate guidelines for safety can be devised, while preserving the beneficial uses of radiofrequency radiation (RFR) energy for military or civilian purposes. The task is monumental because of the large and growing number of biological endpoints and the infinite array of RFR exposure conditions under which those endpoints might be examined. The only way to reach this goal is to understand the mechanisms by which EM fields interact with tissues. As in other fields of science, a mechanistic understanding of RFR effects will enable scientists to generalize from a selected few experiments to derive the "laws" of RFR bioeffects. This article gives an overview of present knowledge of those mechanisms and the part that the USAF School of Aerospace Medicine has played in expanding that knowledge.

Implication of prostaglandins and histamine H1 and H2 receptors in radiation-induced temperature responses of rats

Exposure of rats to 1-15 Gy gamma radiation (60Co) induced hyperthermia, whereas 20-200 Gy induced hypothermia. Exposure either to the head or to the whole body to 10 Gy induced hyperthermia, while body-only exposure produced hypothermia. This observation indicates that radiation-induced fever is a result of a direct effect on the brain. The hyperthermia due to 10 Gy was significantly attenuated by the pre- or post-treatment with a cyclooxygenase inhibitor, indomethacin. Hyperthermia was also altered by the central administration of a mu-receptor antagonist naloxone but only at low doses of radiation. These findings suggest that radiation-induced hyperthermia may be mediated through the synthesis and release of prostaglandins in the brain and to a lesser extent to the release of endogenous opioid peptides. The release of histamine acting on H1 and H2 receptors may be involved in radiation-induced hypothermia, since both the H1 receptor antagonist, mepyramine, and H2 receptor antagonist, cimetidine, antagonized the hypothermia. The results of these studies suggest that the release of neurohumoral substances induced by exposure to ionizing radiation is dose dependent and has different consequences on physiological processes such as the regulation of body temperature. Furthermore, the antagonism of radiation-induced hyperthermia by indomethacin may have potential therapeutic implications in the treatment of fever resulting from accidental irradiations.

Consequences of skin color and fur properties for solar heat gain and ultraviolet irradiance in two mammals

In animals with fur or feather coats, heat gain from solar radiation is a function of coat optical, structural, and insulative characteristics, as well as skin color and the optical properties of individual hairs or feathers. In this analysis, I explore the roles of these factors in determining solar heat gain in two desert rodents (the Harris antelope squirrel, Ammospermophilus harrisi, and the round-tailed ground squirrel, Spermophilus tereticaudus). Both species are characterized by black dorsal skin, though they contrast markedly in their general coat thickness and structure. Results demonstrate that changes in coat structure and hair optics can produce differences of up to 40% in solar heat gain between animals of similar color. This analysis also confirms that the model of Walsberg et al. (1978) accurately predicts radiative heat loads within about 5% in most cases. Simulations using this model indicate that dark skin coloration increases solar heat gain by less than or equal to 5%. However, dark skin significantly reduces ultraviolet transmission to levels about one-sixth of those of the lighter ventral skin.

Bright artificial light produces subsensitivity to nicotine

Bright artificial light is a treatment for seasonal depression. Eleven (11) rats were exposed to bright artificial light (11,500 lux) for two consecutive weeks. The thermic response to nicotine was measured prior to light exposure and after one and two weeks of treatment. The thermic response to nicotine at baseline was -1.69 +/- 0.25 degrees C (mean +/- SEM). The thermic response to nicotine was -0.66 +/- 0.12 degrees C (p less than 0.002) after one and +0.31 +/- 0.14 degrees C (p less than 0.000025) after two weeks of light exposure. The change in temperature was different between weeks one and two (p less than 0.000025). The exposure of animals to constant light at an intensity of 300 lux did not blunt the hypothermic response to nicotine. These findings suggest that bright artificial light, like other antidepressant treatments, produces subsensitivity of a nicotinic mechanism involved in the regulation of core temperature.

Behavioral effects of microwave reinforcement schedules and variations in microwave intensity on albino rats

The objective of this exploratory investigation was to determine the interactive effects of fixed-ratio scheduling of microwave reinforcement in tandem with changes in microwave intensity. Nine albino rats were conditioned to regulate their thermal environment with microwave radiation while living in a Skinner (operant conditioning) Box in which the ambient temperature was about 27.13 degrees F at the beginning of the session. Each rat obtained a 6-sec. exposure of microwave radiation on a fixed-ratio schedule of MW reinforcement, the values of which varied from FR-1 to FR-30. Intensities of MW radiation were 62.5 W, 125 W, 250 W, and 437.5 W. Sessions lasted for 8 to 9 hr. over an approximate 13-mo. period. The effects of the intensity of microwave reinforcement varied as a function of the ratio value of the schedule used. Continuous reinforcement (FR-1) produced the lowest over-all rates, whereas FR-15, and FR-25 produced the highest over-all rates. Relatively higher thermal-behavior rates occurred under 62.5 W than under any of the other MW intensities for FR-1, FR-15, and FR-25, whereas FR-10 and FR-30 ratios produced intermediate rates of thermal responding which were constant for all values of MW intensity. These data are explained in terms of interactive effects between the "local" satiation or deprivation properties of the MW intensity and the ratio requirements of the schedule of MW reinforcement.

[Risks from magnetic fields and radiowaves in equipment for magnetic resonance tomography]

The use of Nuclear Magnetic Resonance Imaging for diagnostic purposes requires a careful analysis of potential risks for workers, patients and public. Aim of this work is a review of the most important biological effects produced by static magnetic fields, radiofrequency fields and field gradients. It's common opinion in fact that the use of magnetic and radiofrequency fields instead of ionizing radiations fields is a safety warranty for patients and workers. Biological experiments in small animals and microorganisms show that also in this case some risks may be expected, due to the trend to employ as much high as possible magnetic fields (and therefore radiofrequency fields). The available data show that the normally used magnetic and radiofrequency fields are below the threshold for somatic effects but denote the necessity of a careful risks/benefit analysis for some patients groups (pacemakers and small surgical metallic implants carriers) and the need of extended and deep studies to specify a possible synergy of different physical agents and incidental oncogenic and teratogenic consequence on the patient.