Search PubMed⌕ Search

Biomedical subjects

S M Michaelson

Publications and source records attributed to S M Michaelson.

At least 37 records · Page 2Linked to original sources
PubMed1984

Effect of 2450 MHz microwave energy on the blood-brain barrier to hydrophilic molecules. C. Effect on the permeability to [14C]sucrose.

Intravenously injected [14C]sucrose was used as a small molecular weight (342 daltons), hydrophilic tracer for determination of 2450 MHz CW microwave and ambient heat effects on rat blood-brain barrier permeability in the cerebral cortex, hypothalamus, cerebellum and medulla. The tracer was injected 4 min following exposure of conscious, unrestrained rats to microwaves at 0 or 65 mW/cm2 for 30 or 90 min (SAR approximately equal to 13.0 W/kg) or to ambient heat (42 +/- 2 degrees C) for 90 min. Comparison of mean permeability-surface area products (PA) and uptake ratios between sham and microwave-exposed animals revealed a statistically significant (P less than 0.05) decrease of both PA and uptake ratios for the hypothalamus, cerebellum and medulla of rats exposed to microwaves for 30 min. This decrease was not apparent for rats exposed to microwaves for 90 min. A pertinent observation, with regard to this latter group of animals, was the increased circulating levels of the tracer when colonic temperature was raised to approximately 41.4 degrees C or higher.

Animals↗
PubMed1984

Effect of 2450 MHz microwave energy on the blood-brain barrier to hydrophilic molecules. D. Brain temperature and blood-brain barrier permeability to hydrophilic tracers.

Measurement of temperature within the cerebral cortex, hypothalamus, cerebellum and medulla of rats sham-, heat- or microwave-exposed revealed the presence of a thermal gradient within the brain. In all groups, cerebral cortex and the cerebellum were cooler than the deeper hypothalamus and medulla. Exposure to 2450 MHz CW microwaves or ambient heat (42 +/- 2 degrees C) resulted in measurable elevation of regional brain temperature, but without alteration of temperature gradients normally observed within the brain. Exposure to 20 mW/cm2 (SAR approximately equal to 4 W/kg) for 30, 90 or 180 min induced a small, but significantly (U = 0, P less than 0.05) increased temperature of the colon, and in each region of the brain studied. Exposure to an incident power density of 65 mW/cm2 (SAR approximately equal to 13.0 W/kg) for 30 or 90 min or to ambient heat (42 +/- 2 degrees C) for 90 min resulted in a substantially greater thermal response as indicated by higher colonic and brain temperatures. Comparison of regional brain temperature with individual colonic temperatures is expressed as delta T = t degrees Cbrain--t degrees Ccolon. In general delta T values for ambient heat or microwave-exposed rats did not differ significantly from those of sham-exposed animals. Exposure to microwaves or ambient heat did not alter the general relationships between regional brain and colonic temperatures, i.e., cortical and cerebellar temperatures were always below and hypothalamic and medullary temperatures always above corresponding colonic temperatures. The plotted temperature data (brain vs colonic temperature) indicate a linear relationship between brain and colonic temperatures. Levels of sodium fluorescein (NAFl), horseradish peroxidase (HRP) and [14C]sucrose (described in preceding papers) within the brain show a high correlation (P less than 0.05) with brain temperature. Suppression of blood-brain barrier permeability to hydrophilic tracers was most pronounced at brain temperatures exceeding approximately 40 degrees C and is demonstrated to be temperature dependent.

Animals↗
PubMed1983

Human leukocyte functions and the U.S. safety standard for exposure to radio-frequency radiation.

Human mononuclear leukocytes were exposed to microwaves at energies relevant to current public safety recommendations. No detectable effects on viability or function of the leukocytes resulted from exposure to microwaves at specific absorption rates up to 4 milliwatts per milliliter. The results were highly reproducible and provided no evidence that current safety standard recommendations are inappropriate insofar as leukocyte function is concerned.

DNA↗
PubMed1983

A dual vial waveguide exposure facility for examining microwave effects in vitro.

A waveguide exposure system operated between 2 and 4 GHz was assembled in a laboratory incubator in order to study potential temperature-dependent and temperature-independent actions of microwaves. Two vials containing cell cultures were exposed simultaneously in a single waveguide in order to reduce the space required, and to allow concurrent study of autologous cell cultures in two different functional states (resting and stimulated) during exposure. Dosimetry was performed using three techniques with different underlying assumptions, as well as the technique of differential power measurement. Each of the four techniques yielded different results, although differences between the two vials using any single technique were negligible. A significant 'hot spot' occurred at the center of each vial. The ratio between maximum and minimum absorption rate within a single vial was 33-fold using a vial of 1.2-cm diameter and 1.6-cm height. With agitation and exposure at specific absorption rate (SAR) equal to 21 mW/ml, the thermal gradient was less than 0.1 degrees C between these two points. The averaged SAR can be determined by steady-state heating analysis. The exposure system can be calibrated readily by calculation for the measured powers, but not by differential power measurement.

Cells, Cultured↗
PubMed1983

Increased serum enzyme activity in microwave-exposed rats.

Heat stable serum enzymes were studied in rats exposed to microwaves (2.45 GHz, 120 Hz amplitude modulated) 24 hr after a single 4-hr exposure or immediately after 3 and 10 exposures to 0.1 to 55 mW/cm2. In addition, stable colonic temperature at 41.5 degrees C for 30 min was maintained by microwave exposure in a group of five rats under barbiturate anesthesia. Alkaline phosphatase and lactic dehydrogenase did not increase as a result of microwave exposure. Increased serum glutamic pyruvic transaminase (GPT) and glutamic oxaloacetic transaminase (GOT) were noted in the 41.5 degrees C group 24 hr after exposure. A threshold body temperature for acute cellular injury after microwave exposure was demonstrated. The acute cellular injury could be in the liver. These mild elevations in the serum enzyme levels (mean +/- SE, GOT = 167 +/- 40 U/liter: GPT = 74 +/- 26 U/liter) indicated that the injuries were not accompanied by any significant sequelae in the rat. From this threshold and colonic temperature (41.5 degrees C for 30 min) in barbiturate-anesthetized, microwave-exposed rats, we derived a tentative threshold for the whole-body average absorption rate at 14 W/kg (70 mW/cm2 at 2.45 GHz for adult rats) for 4 hr. This tentative threshold is subject to changes by duration of exposure and by compounding variables influencing maintenance of body temperature.

Alanine Transaminase↗
PubMed1982

Physiologic regulation in electromagnetic fields.

Electromagnetic fields have been demonstrated to elicit thermoregulatory responses, neuroendocrine, neurochemical modulations, and behavioral reactions. These physiologic regulatory processes are exquisitely tuned, interrelated functions that constitute sensitive indicators of organismic responses to radiofrequency energy absorption (the radiofrequency portion of the electromagnetic spectrum includes as one part microwaves). Assessment of the integration and correlation of these functions relative to the thermal inputs and homeokinetic reactions of the individual subjected to radiofrequency energy should permit differentiation between potential hazards that might compromise the individual's ability to maintain normal physiologic function and effects that are compensated by physiologic redundancy.

Acclimatization↗
PubMed1982

Cell survival as a determinant of tumor cure for rat 9L subcutaneous tumors following microwave-induced hyperthermia.

The relationship of cell survival to tumor cure after local hyperthermia treatment was studied in subcutaneous 9L rat tumors. Tumors weighing 0.2-0.4 g were heated to 42.5, 43.0, 44.0 and 45.0 degrees C by local exposure to 2450 MHz microwaves. Cell survival data was obtained by an in vivo to in vitro colony forming technique and a cell survival curve was constructed for each temperature as a function of exposure duration (0-180 min). Cell survival followed a simple exponential function with an increasingly steeper slope as temperature increased. At 44 degrees C, it was observed that cells from large tumors (1.0-1.4 g) were inactivated at the same rate as those from small tumors. When tumor response was monitored in the small tumors for 90 days following treatment, a direct correlation between the percentage of tumor cures and time at 44 degrees C (0-60 min) was observed; therefore, at 44 degrees C, tumor cure was exponentially related to cell survival in this range. However, when approximately the same cell survival was obtained with 3 other temperature--time regimens, the resulting percentage of tumor cures was not the same. These results indicate that while cell survival is related to tumor cure, it is probably not the primary determinant of tumor response following local hyperthermia in these 9L subcutaneous tumors.

Animals↗
PubMed1982

The influence of radiofrequency/microwave energy absorption on physiological regulation.

Physiological regulation represented by thermoregulation, neuro endocrine function, neurochemical activity, and immune responses is a composite of exquisitely "tuned" interrelated systems that constitute sensitive indicators of body responses to environmental stimuli or absorbed physical energies. Exposure to microwave/radiofrequency fields may affect such physiological regulation. Study of the integration and correlation of many body functions relative to the altered homoeostatic status of the microwave/radiofrequency-exposed subject is thus indicated. Microwave-induced physiological changes cannot be dissociated from increases in tissue temperature. Such responses are considered to be essential in defence against environmental changes as a febrile response is essential for host immune defence. These responses can also be considered to reflect the utilization of physiological function to maintain regulations or adjustments. These are not necessarily adverse reactions to environmental stimuli. These responses can be transient or persistent, beneficial or detrimental. Assessment of the integration and correlation of these functions relative to the thermal inputs and homoeokinetic reactions of the individual subjected to microwave/radiofrequency energy should permit differentiation between potential hazards which might compromise the individual's ability to maintain normal physiological function and effects which are compensated by physiological redundancy.

Animals↗
PubMed1981

Influence of location within a tumor on cell survival as measured by a clonogenic assay.

In order to elucidate the influence of the location of a cell within a tumor on cell survival, 12 to 16 samples from an individual 9L s.c. tumor were assayed for colony formation. These samples (4 to 6 mg) were taken from untreated, heated, or irradiated tumors, and the variances of the mean relative colony-forming efficiency (RCFE) for individual tumors or groups of similarly treated tumors were compared. These comparisons allowed determination of the effect of location and treatment on the intratumor variability in cell survival. Three factors can influence variability of the RCFE's across tumors: (a) inherent differences in clonogenic capacities; (b) unequal dose distribution of the treatment agent, and (c) different sensitivities of cells to the treatment. Considerable variability was found in the cell survival of control tumors, and treatment of tumors in air-breathing or nitrogen-asphyxiated rats with X-rays did not change the magnitude of this variability. However, the variance of the mean RCFE of heated tumors was an order of magnitude greater than that observed in either control or irradiated tumors. Of the three possible factors that could influence cell survival within a tumor, all were shown to contribute to the variances of the mean RCFE measured in 9L s.c. tumors. However, our study demonstrated that the relative contribution of each of these factors to the variance will probably depend on the treatment agent(s).

Animals↗
PubMed1980

Delineating acute neuroendocrine responses in microwave-exposed rats.

One hundred and eighteen male rats (Long-Evans) were acclimated to experimental procedures (i.e., handling, transferring from and back to "home" cage, body weight and colonic temperature determinations) for 2 wk and then subjected to cage confinement for 3 days before microwave (MW) exposure to 2,450 MHz for 1-, h, at 1-70 mW.cm-2 or sham exposure at ambient temperature of 24 +/- 1 degree C. Colonic temperature increased after exposure to power densities greater than or equal to 20 mW.cm-2 and was the most sensitive parameter measured. Inverse relationships between corticosterone and thyrotropin or growth hormone were noted after exposure for 1 h at 50 mW.cm-2 and above. Pituitary-thyroid function was inhibited after exposure to 20 mW.cm-2 for 2-8 h. Changes in other hormones were transient or inconsistent. Corticosterone, thyrotropin, and growth hormone levels could be correlated with power density or colonic temperature in rats exposed to MW for 1 h; corticosterone and thyrotropin levles correlated with colonic temperatures in shams. Body temperature influences adenohypophysial hormones in studies of MW biological effects.

Animals↗
PubMed1979

Microwaves: effect on thermoregulatory behavior in rats.

Rats, with their fur clipped, pressed a lever to turn on an infrared lamp while in a cold chamber. When they were exposed to continuous-wave microwaves at 2450 megahertz for 15-minute periods, the rate at which they turned on the infrared lamp decreased as a function of the microwave power density, which ranged between 5 and 20 milliwatts per square centimeter. This result indicates that behaviorally significant levels of heating may occur at an exposure duration and intensities that do not produce measurable changes in many other behavioral measures or in colonic temperature. Further study of how microwaves affect thermoregulatory behavior may help us understand such phenomena as the reported "nonthermal" behavioral effects of microwaves.

Animals↗
PubMed1979

Effects of hypophysectomy and dexamethasone on rat adrenal response to microwaves.

Circulating corticosterone levels were measured to compare the adrenocortical response to acute microwave exposure of normal, hypophysectomized, or sham-hypophysectomized rats. Plasma corticosterone levels in acutely hypophysectomized rats exposed to 60 mW/cm2 for 60 min were below control levels, indicating that the microwave-induced corticosterone response observed in normal, intact rats is dependent on ACTH secretion by the pituitary. In other groups of rats pretreated with dexamethasone before being exposed to microwaves for 60 min, the corticosterone response to a 50-mW/cm2 exposure was completely suppressed by doses equal to or greater than 3.2 micrograms dexamethasone/100 g body weight. However, the corticosterone response to a 70-mW/cm2 exposure was only partially suppressed by prior administration of 3.2 or 5.6 micrograms dexamethasone/100 g BW. The evidence obtained in these experiments, in conjunction with the results of other experiments previously reported, is consistent with the hypothesis that the stimulation of the adrenal axis in the microwave-exposed rat is a systemic, integrative process due to a general hyperthermia.

Adrenal Glands↗