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At least 469 records · Page 26Linked to original sources
PubMed1998

Free amino acid concentrations in milk: effects of microwave versus conventional heating.

Microwave effects on free amino acid concentrations in milk versus a water bath heating were investigated in view of their importance for infant growth. Concentrations of few amino acids, such as aspartate, serine or lysine, are unchanged whatever the way and the temperature of heating. In contrast, tryptophan concentrations decreased similarly whatever the way of heating (110 +/- 3 mumol/l before heating vs 84 +/- 4 mumol/l after 30 degrees C microwave heating, p < 0.05). On the contrary, concentrations of glutamate and glycine increased more after water bath heating at 90 degrees C (325 +/- 4 and 101 +/- 1 mumol/1, respectively) than after microwave heating (312 +/- 4 and 95 +/- 1 mumol/l, respectively, p < 0.05) suggesting milk proteolysis. Moreover, the accumulation of ammonia observed at 90 degrees C with the water bath together with increase Glu levels might reflect a degradation of glutamine. An ornithine enrichment, more evident with microwave heating, was shown and could be of interest as it is a polyamine precursor. Also, considering few variations of free amino acid concentrations and the time saved, microwave heating appears to be an appropriate method to heat milk.

Amino Acids↗
PubMed1980

Microwave irradiation and in vitro release of enzymes from hepatic lysosomes.

An exposure system for examining in vitro effects of microwave irradiation on cellular and subcellular components has been developed. The system was used to test the effect of 2.45-GHz CW microwaves on the release of two lysosomal enzymes. At a specific absorption rat (SAR) of 10, 50 or 100 mW/g (90 min) no effects were noted at 37 degrees C (pH of 7.3) on lysosomal fragility as determined by the release of the lysosomal enzymes cathepsin D and beta-glucuronidase. When the medium was adjusted to pH 5.0, microwave irradiation of the lysosomal suspension had no effect on the acid-induced enhancement of release of lysosomal enzymes. The data indicate that microwave irradiation had no labilizing effect on the lysosomal membrane, although other microwave-membrane interactions not associated with enzyme release may occur.

Animals↗
PubMed1996

Keratin antigen retrieval in oral mucosal biopsies using microwave processing.

In immunohistochemistry, it is well known that the majority of monoclonal antibodies to keratins work best on fresh frozen tissue specimens, yet in clinical practice most biopsies are routinely fixed in formaldehyde. This seriously limits the range of keratins that can be reliably assessed in retrospective studies (particularly where only rare archival material exists) and where subtle changes during tissue differentiation may be important. Antigen retrieval using exposure to microwave radiation is one technique that has been applied successfully to other tumour markers (e.g., p53). However, few papers have used this method when immunolabelling for keratins, in spite of the widespread use of antikeratin antibodies as markers of differentiation. The effect of keratin antigen retrieval using microwave processing was assessed on a range of oral mucosal biopsies, since the oral cavity displays a wide range of keratins. A panel of six well characterized antibodies was chosen: LP34 (Ck1, 5, 6, 18), LH1 (Ck10), LL025 (Ck16), A53 BA2 (Ck19), AE8 (Ck13), and E3 (Ck17). For each specimen, one piece was stored in liquid nitrogen and another piece fixed in formalin. Tissue sections were cut from each and, using the peroxidase avidin biotin technique, keratin expression was recorded for a frozen section, a dewaxed section, and a microwave-heated dewaxed section. Although overall there was a 25% improvement in identification of keratins after microwaving, some antibodies performed better than others. Given that keratins have been shown to be of value in tumour diagnosis, this study suggests that microwave processing of archival material can be a valuable adjunct to such analysis.

Antibodies↗
PubMed1981

A circular dichroism study of human erythrocyte ghost proteins during exposure to 2450 MHz microwave radiation.

The effect of 2450 MHz microwave radiation on the proteins of human erythrocyte ghosts has been investigated using circular dichroism spectroscopy. A specially constructed waveguide inserted into the spectropolarimeter allowed the continuous recording of optical activity before, during and after microwave irradiation. The data indicate that high levels of microwave radiation (600 mW/g, specific absorption rate) induce decreases in alpha-helical conformation that may result from both thermal vibrations and increased strain on the intramolecular hydrogen bonds that maintain secondary structure. The latter effect may result from differential intramolecular interactions with the oscillating electric field. Spectrin (bands 1 and 2) isolated from the ghosts was more sensitive to microwave irradiation than intact ghosts, and spectrin-depleted vesicles were the least sensitive. The data, therefore, indicate that the alpha-helical conformation of spectrin is altered by high levels of microwave radiation.

Circular Dichroism↗
PubMed1980

The effect of 2450 MHz microwave radiation on histamine secretion by rat peritoneal mast cells.

Isolated rat peritoneal mast cells actively secrete histamine in response to reaginic or chemical stimulation. Mast cells were irradiated in a waveguide microwave exposure chamber at 2450 MHz with power absorptions of 8.2 and 41.0 mW/g for periods up to 3 h. These levels of microwave absorption caused no change in the morphological characteristics or viability of the cells. Irradiated mast cells were stimulated with compound 48/80, a potent, noncytotoxic histamine releasing agent. The dose response curves showed that neither prior nor simultaneous irradiation of mast cells at 37 degrees C affected 48/80-induced secretion. However, microwave power absorptions of 41.0 mW/g inhibited secretion at 44.0 degrees C. Precise measurements of the effect of heat on secretion indicated that this level of inhibition could have been produced by a radiation induced increase in cell temperature between 0.4 and 0.9 degrees C above ambient levels. Alternatively, the heat stress produced at 44 degrees C may have sensitized the cells to the electromagnetic effects of the microwave radiation. Rat peritoneal mast cells can therefore be useful as a model for the study of functioning secretory cells during microwave irradiation and can also be used to monitor the synergistic effects of cell heating during in vitro exposure.

Animals↗
PubMed2002

Microwave extraction of heavy metals from wet rhizosphere soils and its application to evaluation of bioavailability.

Single microwave extraction of heavy metals Cr, Ni, Zn, Cu, Cd, and Pb by the extractants CaCl(2), EDTA, CH(3)COOH and HCl has been established. The experimental conditions were optimized. A microwave power of 60% and an extraction time of 25 min were adopted. Comparison of microwave extraction and conventional extraction methods revealed that results obtained by microwave techniques were generally in a good agreement with those obtained by use of extraction methods; use of the former resulted in substantial time saving and a better precision, however. Microwave extraction was used to evaluate the bioavailability of heavy metals in soils. Single correlation analysis was performed to establish the relationship between the concentrations of the extractable heavy metals in wet rhizosphere soils and their concentrations in wheat ( Troticum aestivum L.) grown on the soils under greenhouse conditions. The correlation coefficients between the extractable metals in soils and their concentrations in wheat roots were found to be 0.5398-0.7819, 0.6425-0.8073, 0.5568-0.8276, 0.5851-0.6087 for the extractants CaCl(2), EDTA, CH(3)COOH, and HCl, respectively.

Biological Availability↗
PubMed1998

Case selection for high-energy transurethral microwave thermotherapy.

Transurethral microwave thermotherapy (TUMT) is a minimally invasive outpatient procedure for the treatment of benign prostatic hyperplasia (BPH). Different devices and operating software have been used in various clinical trials. The objective of this study was to identify the possible baseline parameters that could be used to identify the best responders to different microwave devices and treatment programs. Data on three different high-energy thermotherapy devices (Urowave, Prostalund, and Prostatron) were collected and analyzed. At 1 year of follow-up, 166 patients were available for the Prostatron system. In all, 52 had a > or = 50% change in both symptom score and peak flow rate, whereas 114 patients were considered nonresponders. Responders were characterized at baseline by a lower peak flow rate (8.80 versus 10.48 ml/s, P < or = 0.0001) and a larger degree of outlet obstruction as measured by the URA parameter (45.33 versus 36.70 cmH2O, P < or = 0.0300); a larger energy dose was delivered to this group during treatment (173.36 versus 156.40 kJ, P < or = 0.0258). A total of 19 patients were available from the Prostalund cohort. No significant difference was found in the values recorded for baseline parameters between responders (5 patients) and nonresponders (14 patients). Stratification of 143 patients treated with the Urowave resulted in 29 responders (> or = 50% improvement in both Qmax and AUA score) at 6 months of follow-up, with a significant difference being found in the baseline value recorded for peak flow rate (7.0 versus 8.0 ml/s, P < or = 0.026). At 12 months, however, this significance difference could no longer be found. In conclusion, baseline parameters with significant predictive value for a clinical response could be identified for the Prostatron device only. The results of this study further confirm the importance of an extensive laboratory and clinical research program for a fuller understanding of the clinical response obtained with a certain microwave device and a particular treatment software and for provision of the greatest possible advantage from these new alternative treatments. Further exploratory work is required for a better understanding of the role of other parameters such as prostate tissue architecture and vascularity, the microwave frequency, the applicator design, the intraprostatic temperature, and the treatment duration in the clinical response to microwave thermotherapy.

Diathermy↗
PubMed1997

Effect of global system for mobile communication (GSM) microwave exposure on blood-brain barrier permeability in rat.

We investigated the effects of global system for mobile communication (GSM) microwave exposure on the permeability of the blood-brain barrier using a calibrated microwave exposure system in the 900 MHz band. Rats were restrained in a carousel of circularly arranged plastic tubes and sham-exposed or microwave irradiated for a duration of 4 h at specific brain absorption rates (SAR) ranging from 0.3 to 7.5 W/kg. The extravasation of proteins was assessed either at the end of exposure or 7 days later in three to five coronal brain slices by immunohistochemical staining of serum albumin. As a positive control two rats were subjected to cold injury. In the brains of freely moving control rats (n = 20) only one spot of extravasated serum albumin could be detected in one animal. In the sham-exposed control group (n = 20) three animals exhibited a total of 4 extravasations. In animals irradiated for 4 h at SAR of 0.3, 1.5 and 7.5 W/kg (n = 20 in each group) five out of the ten animals of each group killed at the end of the exposure showed 7, 6 and 14 extravasations, respectively. In the ten animals of each group killed 7 days after exposure, the total number of extravasations was 2, 0 and 1, respectively. The increase in serum albumin extravasations after microwave exposure reached significance only in the group exposed to the highest SAR of 7.5 W/kg but not at the lower intensities. Histological injury was not observed in any of the examined brains. Compared to other pathological conditions with increased blood-brain barrier permeability such as cold injury, the here observed serum albumin extravasations are very modest and, moreover, reversible. Microwave exposure in the frequency and intensity range of mobile telephony is unlikely to produce pathologically significant changes of the blood-brain barrier permeability.

Animals↗
PubMed2000

Comparison of the effects of in-vivo thermal ablation of pig liver by microwave and radiofrequency coagulation.

Microwave and radiofrequency coagulation is frequently used for the treatment of hepatic tumors. However, differences between these types of therapy have not been clearly demonstrated so far. We performed both types of thermal ablative treatment on pig liver, and compared the size and shape of the coagulated areas produced. The effects of combining both treatments and interrupting hepatic blood flow were also evaluated. The liver of an anesthetized pig was thermally coagulated, with or without interruption of hepatic blood flow, using a needle electrode at 40 W for 150 s with 2450-MHz microwaves and/or with a 460-kHz radiofrequency current. The diameters of the coagulated areas in the liver were 20 +/- 3 mm (mean +/- SD; n = 4) after microwave coagulation and 28 +/- 3 mm following radiofrequency coagulation when blood flow was not interrupted, whereas they were 31 +/- 2 mm and 37 +/- 3 mm, respectively, when blood flow was interrupted. When these treatments were combined sequentially, the diameters of the lesions were 43 +/- 3 mm and 29 +/- 2 mm with and without blood flow interruption, respectively. The ellipticity of the coagulated area, as measured by the largest-to-smallest ratio of its diameters, was 2.3 +/- 0.4 after microwave coagulation and 1.1 +/- 0.1 following radiofrequency coagulation. We conclude that radiofrequency coagulation produces a larger and more spherical coagulated area in the liver (P < 0.01) than does microwave coagulation. The lesion becomes larger (P < 0.05) with both treatments when hepatic blood flow is interrupted during the treatment. The sequential combination of these treatments produces a much larger lesion (P < 0.05) than that produced by either treatment alone.

Animals↗
PubMed2006

Determination of the mineral fraction and rheological properties of microwave modified starch from Canna edulis.

The goal of this study was to evaluate the effect of the physical modification by microwave irradiation on the mineral fraction and rheological properties of starch isolated from Canna edulis rhizomes. Phosphorus, sodium, potassium, magnesium, iron, calcium and zinc were evaluated using atomic absorption spectrophotometry. Rheological properties were determined using both the Brabender amylograph and Brookfield viscosimeter. Except for the calcium concentration, mineral contents decreased significantly (p < 0.05) after microwave treatment. The amylographic profile was also modified, showing increased pasting temperature range and breakdown index, whereas the viscosity peak, viscosity at holding (95 degrees C) and cooling periods (50 degrees C), setback and consistency decreased as compared to the native starch counterpart. Although viscosity decreased in the microwaved sample, presumably due to starch changes at molecular level, it retained the general pseudo plastic behavior of native starch. It is concluded that canna starch may be modified by microwave irradiation in order to change its functional properties. This information should be considered when using microwave irradiation for food processing. Furthermore, the altered functional attributes of canna modified starch could be advantageous in new product development.

Food Irradiation↗
PubMed1991

Effect of 2.45 GHz microwave radiation on permeability of unilamellar liposomes to 5(6)-carboxyfluorescein. Evidence of non-thermal leakage.

The influence of 2.45 GHz microwave radiation on the membrane permeability of unilamellar liposomes was studied using the marker 5(6)-carboxyfluorescein trapped in phosphatidylcholine liposomes. The release of the fluorescent marker was followed by spectrofluorimetry after an exposure of 10 minutes to either microwave radiation or to heat alone of the liposome solutions. A significant increase of the permeability of carboxyfluorescein through the membrane was observed for the microwave-exposed samples compared to those exposed to normal heating only. Exposure to 2.45 GHz microwave radiation of liposomes has been previously found to produce increased membrane permeability as compared with heating. However, in contrast to previous studies, the observations reported here were made above the phase transition temperature of the lipid membrane. The experimental setup included monitoring of the temperature during microwave exposure simultaneously at several points in the solution volume using a fiberoptic thermometer. Possible mechanisms to explain the observations are discussed.

Fiber Optic Technology↗
PubMed1977

Microwave alteration of the blood-brain barrier system of rats.

Rats were exposed to 1.3 gHz microwave energy to assess the uptake of several neutral polar substances in certain areas of the brain. A quantitative, radioactive isotope method, which uses an internal standard, was employed to measure the loss of test substances to brain tissue. Single, 20 min exposure, to either pulsed or continuous wave (CW) microwave energy induced an increase in the uptake of D-mannitol at average power densities of less than 3.0 mW/sp. cm. The permeability change was greatest in the medulla, followed, in decreasing order, by the cerebellum and hypothalamus, with small or negligible changes in the hippocampus and cortex. Permeability increases were observed for mannitol and inulin but not for dextran. Increased permeability was observed both immediately and 4 h after exposure, but not 24 h after exposure. After an initial rise, the permeability of cerebral vessels to saccharides decreased with increasing microwave power. Differences in the level of uptake occurred between CW energy and pulsed energy of the same average power. Microwaves of the same average power but different pulse characteristics also produced different uptake levels. Our findings suggest that microwaves induce a temporary change in the permeability for small molecular weight saccharides in the blood-brain barrier system of rats.

Animals↗
PubMed1989

The use of microwave energy for processing acrylic resins.

Test strips of five different resins were processed with (1) microwaves by using a kitchen-type microwave oven, and (2) a conventional water bath. The strips were tested for hardness, porosity, and transverse strength. The results showed no significant difference between resin strips cured by either method. Maxillary dentures were waxed on stone casts of an aluminum model in another study. The dentures were processed with the same five resins, half by using microwave energy and the remainder with the water bath. The adaptation of the processed dentures to the aluminum cast was measured with feeler gauges. The results showed no statistically significant differences between dentures cured by either method. These studies demonstrated that the important physical characteristics of microwave-cured resin are approximately the same as resin cured in a conventional water bath. Curing dentures by microwave energy has the advantages of reduced curing time, ease, and cleanliness.

Acrylic Resins↗
PubMed1983

The effect of microwave irradiation on vasopressin in plasma and hypothalamo-neurohypophyseal system.

Radioimmunoreactive vasopressin was measured in plasma, neurohypophysis and hypothalamus of the rats after different procedures of killing: a) microwave irradiation; b) decapitation; c) decapitation following a stress induced by immobilization in a restrainer. Vasopressin content in the neurohypophysis and hypothalamus was much lower in microwave irradiated than in both decapitated and stressed decapitated rats. In addition, the data from microwave technique were inconsistent with a large scatter. Plasma vasopressin concentration was elevated in both the microwave irradiated and stressed decapitated rats, demonstrating that restraining of the animals induced an excessive stress. Microwave irradiation technique including the necessary manipulation of the animal proved to be less suitable than decapitation technique for the measurement of vasopressin. It is likely that vasopressin in the hypothalamus and neurohypophysis is relatively resistant against post-mortem proteolysis.

Animals↗
PubMed1985

Microwave sterilization of nitrous oxide nasal hoods contaminated with virus.

Although there exists a desire to eliminate the possibility of cross-infection from microbial contaminated nitrous oxide nasal hoods, effective and practical methods of sterilization in a dental office are unsatisfactory. Microwaves have been used to sterilize certain contaminated dental instruments without damage. In this study nasal hoods contaminated with rhinovirus, parainfluenza virus, adenovirus, and herpes simplex virus were sterilized in a modified microwave oven. Ninety-five percent of the virus activity was destroyed after 1 minute of exposure of the contaminated nasal hoods to microwaves. By the end of 4 minutes, complete inactivation of all four viruses was found. Repeated exposure of the nasal hoods to microwaves resulted in no damage to their texture and flexibility. Microwave sterilization may potentially provide a simple and practical method of sterilizing nitrous oxide anesthesia equipment in a dental or medical practice.

Adenoviruses, Human↗
PubMed1984

Ventilatory frequency of mouse and hamster during microwave-induced heat exposure.

Ventilatory frequency was recorded in unrestrained mice and hamsters using microwave radiation. The microwave exposure system was also used to impact varying heat loads to the rodents at ambient temperatures of 10, 20 and 30 degrees C. The absorbed heat load accrued from microwave exposure was measured as the time-averaged rate of energy absorption per unit body weight or specific absorption rate (SAR, W/kg). In both species there was an inverse relationship between ambient temperature (Ta) and threshold SAR to invoke an increase in ventilatory frequency. However, the threshold SAR's for mice were 270 to 450% higher than for hamsters depending on Ta. Above threshold SAR the increase in ventilatory frequency per unit elevation in SAR increased directly with Ta in mice but not with hamsters. On the basis of rate of absorbed energy normalized to body weight (i.e., W/kg), mice can tolerate much more heat from microwave exposure than hamsters. The differences in sensitivity to microwave exposure in the mouse and hamster are probably attributable to species-specific characteristics, and especially differences in body mass and, consequently, passive heat loss.

Absorption↗
PubMed1994

Influence of microwave exposure on chlordiazepoxide effects in the mouse staircase test.

To ascertain whether behavioral effects of benzodiazepines are altered by exposure to microwave radiation, we compared the performance of male, Swiss CD1 mice in the staircase test 30 min after pretreatment with chlordiazepoxide (8, 16, and 32 mg/kg, IP) and immediately following a 5-min exposure to microwave radiation (4, 12, and 36 W/kg, continuous wave, 1.8 or 4.7 GHz). In this paradigm, chlordiazepoxide reduction in the number of rears (NR) and number of steps ascended (NSA) is postulated to reflect anxiolytic and sedative drug effects, respectively. In sham-exposed mice, increasing doses of chlordiazepoxide increased NSA without affecting NR, increased NSA and decreased NR, then decreased both NSA and NR. Microwave exposure generally did not alter NSA or NR in mice pretreated with lower doses of chlordiazepoxide. However, in mice pretreated with 32 mg/kg chlordiazepoxide, exposure to 36 W/kg microwave radiation significantly reversed the reductions in NSA and NR at 4.7 GHz but not at 1.8 GHz. These findings indicate that exposure to microwave radiation can selectively alter effects of chlordiazepoxide in this psychopharmacological paradigm.

Animals↗
PubMed1994

Ultrastructural immunogold localization of tumor necrosis factor-alpha to the cytoplasmic granules of rat peritoneal mast cells with rapid microwave fixation.

Tumor necrosis factor-alpha (TNF-alpha) is a multifunctional, proinflammatory cytokine, which can be produced by mast cells and several other cell types. We used a newly developed microwave energy-assisted aldehyde fixation method to prepare purified rat peritoneal mast cells for the postembedding immunogold ultrastructural localization of TNF-alpha. These fixation methods were superior to chemical fixation alone in preserving both the ultrastructural morphology and immunoreactive TNF-alpha in rat mast cells. The percent of TNF-alpha-positive mast cells in samples prepared with microwave-assisted fixation in low (84%) and standard (81%) glutaraldehyde concentrations exceeded that for low (56%) and standard (15%) glutaraldehyde concentrations without the assistance of microwave energy. TNF-alpha was identified in the large storage granules of rat mast cells. The percent of positive granules in microwave-assisted standard (44%) and low (40%) glutaraldehyde samples was considerably higher than the percent of positive granules in standard (5%) and low (10%) glutaraldehyde-fixed samples without microwave assistance. This location of TNF-alpha in rat peritoneal mast cells suggests that this cytokine can use the regulated secretory route(s) for release from appropriately stimulated rat mast cells into the microenvironment.

Animals↗