Evaluation of the potential genotoxic effects of rTMS on the rat brain and current density mapping.

OBJECTIVE: The objectives of this work were: (i) to evaluate the relevance for clinical studies of repetitive transcranial magnetic stimulation (rTMS) investigations on rats, (ii) to investigate the occurrence of DNA damage in rat brain cells following rTMS under conditions similar to those used in clinical treatment of depression. METHODS: Rats were exposed to 2000 magnetic pulses at 100% of motor threshold (MT). Software, written to take detailed anatomical and conductivity data into account, was used to map current density in the rat brain. A method was developed for standardizing magnetic pulse efficacy to facilitate comparison with other rTMS studies. Genotoxicity was explored using the alkaline comet assay on rat brain cells, measuring Olive moment and %DNA in the tail. RESULTS: The current density was ca. 6.6 A/m2 in the motor cortex at MT (Motor Cortex Threshold Densities: MCTDs), 5.2 A/m2 in the brain (range 0-17 A/m2), and 2.0 A/m2 at prefrontal cortex. Similar standard MCTDs were found in rats and humans. Concerning the comet assay, both Olive moment and %DNA in the tail, there was no statistically-significant difference between rTMS-exposed and sham-exposed brain cell samples. In contrast, significant increases in both parameters were detected in positive controls. CONCLUSIONS: Under the assumptions developed in the discussion, these data showed no evidence that the standard current density at motor threshold in human motor cortex would differ from that in rats. Furthermore, there was no evidence of DNA damage in rat brain cells following a single scheme of rTMS, under conditions similar to the clinical treatment of depression. SIGNIFICANCE: This study supports the use of rats as a model for studying the bioeffects of rTMS (molecular targets, action mechanisms, toxicology, etc.) and suggests that a single rTMS scheme, similar to that used daily in the treatment of depression, is not genotoxic.

Effect of GSM-900 and -1800 signals on the skin of hairless rats. I: 2-hour acute exposures.

PURPOSE: The acute influence on the skin of non-ionizing electromagnetic fields in the radiofrequency (RF) range used in mobile telephony has not been widely studied to date. The purpose of this work was to determine whether the cells of hairless rat skin are affected by acute local exposure to Global System for Mobile Communication: GSM-900 or -1800 RadioFrequency Radiation (RFR). MATERIALS AND METHODS: Hairless female rats were exposed or sham-exposed for 2 h to GSM-900 or -1800 signals, using a loop-antenna located on the right part of the rats' back. The local Specific Absorption rate (SAR) at skin level was ca. 5 W/kg (5.8+/-0.4 and 4.8+/-0.4 W/kg at 900 and 1800 MHz, respectively). A skin biopsy was done at the end of the experiment not only at the location of exposure, but also on the symmetrical part of the back. RESULTS: Analysis of skin sections using Hematoxylin Eosin Saffron (HES) coloration showed no difference in skin thickness or apparent cell toxicity (with no sign of cellular necrosis) among the animal groups. Histological analysis of the epidermis showed that the ratio between cells expressing the antigen Ki-67 (cellular proliferation marker) and the total number of cells remained within the range of normal proliferation ratio for the exposed side of the animal. No Ki-67 labelling was observed at the dermis level. Results on filaggrin, collagen and elastin levels also showed an insignificant influence of RFR. CONCLUSIONS: These results do not demonstrate any major physical and histological variations at skin level induced by RFR used in mobile telephony.

Effect of GSM-900 and -1800 signals on the skin of hairless rats. II: 12-week chronic exposures.

PURPOSE: The purpose of this work was to determine whether the cellular components of Hairless-rat skin are affected by a chronic local exposure to non-ionizing radiations of Global Mobile Phone System: GSM-900 or -1800 radiations at specific absorption rate (SAR) 2.5 and 5 W/kg. MATERIALS AND METHODS: A selected part of the right back of five-week old female hairless rats was exposed or sham exposed (n = 8) for 2 h per day, 5 days a week, for 12 weeks to GSM-900 or -1800 signals using a loop-antenna. At the end of the experiment, skin biopsies were taken. RESULTS: Analyses of skin sections using hematoxylin eosin saffron (HES) coloration showed no significant difference in skin thickness among the groups. Immunohistochemical analysis of basal lamella cells in radiofrequency radiation (RFR)-exposed epidermis showed that the ratio of the antigen Ki-67 (cellular proliferation marker) positive cells to total lamella cells remained within the range of the normal proliferation ratio. No significant differences in the level of filaggrin, collagen, and elastin were observed among the different groups. CONCLUSIONS: The results of this 12-week chronic study do not demonstrate major histological variations in the skin of hairless rats exposed to RFR used in mobile telephony (GSM-900 or -1800).

Modulatory role of 1,25 dihydroxyvitamin D3 on pancreatic islet insulin release via the cyclic AMP pathway in the rat.

1. Previous studies have shown that vitamin D3 deficiency impairs the insulin response to glucose via an alteration of signal transduction pathways, such as Ca2+ handling and the phosphoinositide pathway. In the present study the adenylyl cyclase pathway was examined in islets from 3 independent groups: normal rats, 4 weeks-vitamin D3 deficient rats and one week-1,25 dihydroxyvitamin D3 (1,25(OH)2D3) treated rats. 2. We found that the very low rate of insulin release observed in vitamin D3 deficient rats could be restored in vitamin D3 deficient islets only with high concentrations of dioctanoyl-cyclic AMP (DO-cyclic AMP), whereas 1,25(OH)2D3 improved the sensitivity of the islets to this exogenous cyclic AMP analogue. 3. The beneficial effect of 1,25(OH)2D3 observed with or without DO-cyclic AMP was protein kinase A-dependent, since the addition of N-[2-(p-bromocinnamylamino) ethyl]-5-isoquinolinesulphonamide (H-89), a specific inhibitor of cyclic AMP-dependent protein kinases, decreased the insulin release of treated rats back to the level seen in vitamin D3 deficient islets. 4. The low rate of insulin release could not be consistently related to an alteration in cyclic AMP content of the islets. Indeed, low insulin response to a barium+theophylline stimulus observed in vitamin D3 deficient islets was paradoxically associated with a supranormal cyclic AMP content in the islets. 5. This paradoxical increase in cyclic AMP observed in these conditions could not be attributed to a lower total phosphodiesterase (PDE) activity, although the portion of Ca(2+)-calmodulin-independent PDE was predominant in islets from vitamin D3 deficient rats. 6. On the other hand, the higher cyclic AMP content of vitamin D3 deficient islets could be related to an increase in glucagon-induced cyclic AMP synthesis in relation to the hyperglucagonaemia previously observed in vitamin D3 deficient rats. Since higher concentrations of exogenous glucagon and higher endogenous cyclic AMP concentrations were required in vitro to restore insulin release to normal values, the cyclic AMP-dependent pathways that usually potentiate insulin secretion appeared to be less efficient in relation to an alteration in the post cyclic AMP effector system. 7. 1,25(OH)2D3 exerted a stimulating effect on insulin release via protein kinase A activation but reduced the supranormal cyclic AMP synthesis, thus exerting a differential modulatory influence on biochemical disturbances in islets induced by vitamin D3 deficiency.

Immediate in-vivo effect of corticosterone on glucose-induced insulin secretion in the rat.

The effect of infused corticosterone (300 micrograms/h per kg body wt) on the concentrations of insulin in the plasma of the rat was examined (1) when glucose concentration was basal, (2) at standardized glucose levels attained by modulated glucose infusion and (3) in response to a standard or a modulated glucose pulse. There was no effect of corticosterone on the levels of plasma insulin when the glucose concentrations were either basal or raised in response to the standard pulse of glucose. However, when glucose was infused a significantly reduced plasma level of insulin was detected after 60 min when the glucocorticoid was present and this level remained significantly reduced after the modulated pulse of glucose. Thus the infusion of corticosterone leads to an acute depression of the concentrations of insulin in the plasma and of their response to a glucose pulse only when the hormone acts in the presence of a concentration of glucose in the plasma that is insulin-stimulatory.

Influence of vitamin D3 deficiency and 1,25 dihydroxyvitamin D3 on de novo insulin biosynthesis in the islets of the rat endocrine pancreas.

Because 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) is known to activate the biosynthesis of numerous proteins in various tissues, experiments were undertaken to compare the influence of 1,25(OH)2D3 in vitro on both the secretion and biosynthesis of insulin in islets of Langerhans from both 4-week vitamin D3-deficient rats and normal rats. Islets were either incubated or perifused after a 6-h induction period in the presence of various concentrations of 1, 25(OH)2D3 from 10(-12) M, which was inactive in controls, to 10(-6) M. Experiments were performed in the presence of a non-labelled amino acid mixture, to favour protein synthesis. Tritiated tyrosine was added as tracer during glucose stimulation. The newly synthesised proteins, labelled with [3H]tyrosine, were extracted by an acid-alcohol method and separated by gel chromatography adapted for low-molecular-weight proteins. Even in the presence of the amino acid mixture, the insulin response of the islets to 16.7 mM glucose was decreased by vitamin D3 deficiency and improved by 1,25(OH)2D3. This beneficial effect did not occur in basal conditions, but only during glucose stimulation, and was observed in both phases of insulin release. Moreover, these effects disappeared in the presence of 5x10(-4 )M cycloheximide, a protein biosynthesis inhibitor. Islets from vitamin D3-deficient rats exhibited a general decrease in the amount of de novo biosynthesised proteins and of [3H]tyrosine-labelled insulin and proinsulin fractions. A 6-h period of 1,25(OH)2D3 induction significantly improved the amount of de novo biosynthesised proteins, and particularly of newly synthesised insulin in response to a 2-h glucose stimulation. Calculation of the rate of conversion of newly synthesised proinsulin-like material to insulin as the [3H]insulin/[3H]proinsulin-like material ratio provided evidence for a dose-dependent increase, induced by 1, 25(OH)2D3, that could exceed that of normal islets. These data support the hypothesis that 1,25(OH)2D3 in vitro not only facilitated the biosynthetic capacity of the beta cell - which was highly induced during a 16.7-mM glucose stimulation, via a global activation of islets protein biosynthesis - but also produced an acceleration of the conversion of proinsulin to insulin.

The de novo synthesis of numerous proteins is decreased during vitamin D3 deficiency and is gradually restored by 1, 25-dihydroxyvitamin D3 repletion in the islets of langerhans of rats.

Since both the release and de novo biosynthesis of insulin are severely decreased by vitamin D3 deficiency and improved by 1, 25-dihydroxyvitamin D3 (1,25(OH)2D3) repletion following a 6-h delay in the rat, the present experiments investigated the effects of vitamin D3 deficiency on the biosynthesis of heavier molecular weight proteins using electrophoretic separation. Gel protein staining by Coomassie blue showed very different profiles for islets protein production from 4-week vitamin D3-deficient rats compared with normal islets. The pattern was characterised by a decrease in high molecular weight proteins, concomitantly accompanied by an increase in low molecular weight proteins. This tendency was partially reversed in vivo by 1,25(OH)2D3 repletion treatment for 7 days and was evident after only 16 h of treatment. In parallel with these in vivo observations, which represent a static index of islets protein production, a kinetic study was performed in vitro by a double-labelling method allowing us to measure the de novo synthesis of proteins in islets during a strong 16.7 mM glucose stimulation. Comparison of 3H and 14C labelled samples was achieved via coelectrophoresis to avoid experimental artefacts. The study of the ratio of d.p.m. 3H/d.p.m. 14C for each molecular weight protein in islets stimulated by 16.7 mM glucose (versus basal 4.2 mM glucose) showed an increase in the height of certain peaks: 150, 130 and 8.5 kDa. Under the same conditions, islets from 4-week vitamin D3-deficient rats (versus normal islets) presented a large deficit of numerous newly synthesised proteins and particularly those implicated in the response to glucose stimulation. In vitro repletion of 1,25(OH)2D3 tended to reverse, at least in part, the deleterious effect of vitamin D3 deficiency on the de novo protein synthesis of islets but these effects were gradual. Indeed, there was no detectable effect at 2 h incubation, but 1,25(OH)2D3 increased the 60 to 65 kDa, 55 kDa, and 9 to 8 kDa molecular mass proteins at 4 h, and increased the level of most newly synthesised proteins at 6 h. These data support the hypothesis of a beneficial genomic influence of 1,25(OH)2D3 that occurs progressively within the islets of Langerhans and which may prepare the beta cells for an enhanced response to glucose stimulation.

Inhibition by corticosterone of calcium inflow and insulin release in rat pancreatic islets.

Corticosterone (0.6 mumol/l) inhibited both 45Ca outflow and insulin release evoked by glucose, the combination of leucine and glutamine, 2-ketoisocaproate, gliclazide or the association of gliclazide and a tumour-promoting phorbol ester in rat pancreatic islets perifused at normal extracellular Ca2+ concentration (1.0 mmol/l). In all cases, the inhibitory action of corticosterone reached statistical significance within 10-22 min of exposure to this steroid and failed to be rapidly reversible. Corticosterone failed to affect basal 45Ca outflow and insulin release. The steroid also failed to affect the inhibitory action of glucose upon 45Ca outflow, as judged from either the glucose-induced early fall in effluent radioactivity from islets maintained at normal extracellular Ca2+ concentration or the steady-state values for 45Ca outflow from glucose-stimulated but Ca2+-deprived islets. Corticosterone caused a modest increase in 86Rb outflow from islets perifused in the presence of glucose (16.7 mmol/l). It is concluded that corticosterone impairs Ca2+ inflow into the islet cells and, by doing so, causes a progressive inhibition of insulin release. The pancreatic B cell might thus serve as a further model for the study of the rapid biological response to steroids, as presumably mediated by alteration in the biophysical properties of the plasma membrane.

Relationship between calbindin-D28K levels in the A and B cells of the rat endocrine pancreas and the secretion of insulin and glucagon: influence of vitamin D3 deficiency and 1,25-dihydroxyvitamin D3.

The pancreatic B cell is equipped with specific receptors for 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) and contains vitamin D-dependent calcium binding proteins (calbindin-D). Insulin secretion is impaired by vitamin D deficiency and is restored by 1,25-(OH)2D3 (concomitantly with an improved calcium handling within B cells) but the effect of 1,25-(OH)2D3 on the pancreatic B cell via calbindin-D is unclear. Therefore we examined the relationship between calbindin-D28K or calbindin-D9K and the activity of the endocrine pancreas in normal (N), four week vitamin D-deficient (-D) and one week 1,25-(OH)2D3-replete (+D) rats. Calbindin-D9K was not found in the pancreas, neither in the islets nor in the exocrine part, of any of the groups of rats (N, -D, or+D). Surprisingly, total islet calbindin-D28K content was increased by vitamin D deficiency and partly restored by 1,25-(OH)2D3. Calbindin-D28K immunostaining was observed only on A and B cells in the endocrine part of the pancreas, the greatest staining being found in A cells. This difference in staining density was increased by vitamin D deficiency and decreased by 1,25-(OH)2D3 treatment. In vitro, 1,25-(OH)2D3 also produced a negative influence on calbindin-D28K staining in A cells, as demonstrated using pieces of pancreas incubated with the steroid for 2 h. No significant influence on labeling intensity of B cell calbindin-D28K could be shown. Plasma insulin and islet insulin release in response to 10 mM arginine stimulation were decreased in -D rats and enhanced in +D rats towards N values. In contrast, plasma glucagon and the amount of glucagon secretion, stimulated in vitro by 10 mM arginine or by low (1.7 mM) glucose concentration, was increased in -D rats and attenuated by 1,25-(OH)2D3. Thus there appears to be no relationship between the steady state level of B cell calbindin-D28K and the regulation of insulin secretion by 1,25-(OH)2D3 in vitamin D-deficient rats. However there is a correlation between A cell calbindin-D28K and glucagon secretion, which are both negatively regulated by 1,25-(OH)2D3. The predominance of calbindin-D28K in A cells raises the question as to how A and B cells interact and the role of calbindin-D28K in calcium handling.

Facilitation of insulin release by N-p-tosylglycine.

N-p-tosylglycine, which inhibits transglutaminase activity in islet homogenates, was found to cause a rapid and sustained facilitation of insulin release evoked by D-glucose, L-leucine or the association of Ba2+ and theophylline in intact islets. Such a facilitating action could not be attributed to any obvious effect upon either nutrient oxidation or 45Ca net uptake and outflow. It failed to be reproduced by glycine, N alpha-p-tosyl-L-arginine methyl ester or N alpha-p-tosyl-L-lysine methyl ester. N-p-tosylglycine (5.0 mM) slightly enhanced insulin release evoked by a high concentration of glucose (16.7 mM) and failed to affect significantly the secretory response to the association of L-leucine and L-glutamine or that of D-glucose and gliclazide. N-p-tosylglycine failed to affect the incorporation of [2,5-3H]histamine in trichloroacetic acid-precipitable material in intact islets. These results suggest that N-p-tosylglycine interferes with a late event in the secretory sequence, possibly at the level of the cell boundary, rather than inhibiting the crosslinking of intracellular proteins.

Cholinergic stimulation of ion fluxes in pancreatic islets.

Cholinergic agents are known to stimulate the hydrolysis of polyphosphoinositides in pancreatic islets. The effect of carbamylcholine upon ion fluxes in the islet cells was investigated. Carbamylcholine provoked a rapid but poorly sustained increase in 45Ca and 86Rb outflow from perifused islets. Such a cationic response was observed at different glucose concentrations (zero to 16.7 mM), at three concentrations of carbamylcholine (10 microM, 100 microM and 1.0 mM), and in the absence or presence of extracellular Ca2+. It coincided with a biphasic stimulation of insulin release, both the cationic and secretory responses being abolished in the presence of atropine (10 microM). At variance with nutrient secretagogues, carbamylcholine failed to affect the net production of cyclic AMP and caused a transient decrease in 32P outflow from islets prelabelled with [32P]phosphate. It is proposed that cholinergic agents mobilize Ca2+ from intracellular sites, possibly through generation of inositol, 1,4,5-triphosphate from phosphatidylinositol 4,5-bisphosphate. The intracellular redistribution of Ca2+ does not appear sufficient, however, to account fully for the secretory response, which may also involve activation of protein kinase C by diacylglycerol.

Vitamin D3 deficiency and alterations of glucose metabolism in rat endocrine pancreas.

After 5 weeks of vitamin D3 deficiency, rats exhibited signs of rachitism, hypocalcaemia and hypoinsulinaemia. As the glucose-induced insulin release process requires calcium and energy production from glucose metabolism within beta cells of Langerhans islets, several steps in the glycolytic pathway and the tricarboxylic acid cycle within beta cells were investigated in vitro. The sensitivity of islets to glucose was studied during incubations in the presence of crescent concentrations of glucose (4.2 to 16.7 mM). Comparison of 50% maximal insulin response showed no modifications induced by vitamin D3 deficiency despite a large fall in the secretory capacity of beta cells. The use of two secretagogues (D-glucose and D-glyceraldehyde) to stimulate insulin release at two different glycolysis steps gave similar responses during perifusions performed in the presence of crescent concentrations of these nutrients, indicating that vitamin D3 deficiency was not a major influence on the first steps in glycolysis. Glucose utilisation by islets, as determined by 3HOH production from D-[5-3H]glucose, was slightly decreased during glucose stimulation of islets from vitamin D3-deficient rats, whereas glucose oxidation inside the tricarboxylic acid cycle, as measured by 14CO2 production from D-[6-14C]glucose, was severely affected. These data, which suggest that vitamin D3 deficiency affects the glycolytic pathway after the D-glyceraldehyde step and mainly alters oxidative events within the tricarboxylic acid cycle, support the hypothesis of an alteration of mitochondrial metabolism.

Low extracellular calcium enhances beta cell sensitivity to the stimulatory influence of 1,25-dihydroxyvitamin D3 on insulin release by islets from vitamin D3-deficient rats.

The beneficial effect of 1,25-dihydroxyvitamin D3 [1,25 (OH)2 D3] on insulin secretion from beta cells in hypocalcemic vitamin D3-deficient rats is now well established. Moreover, few data concerning the mechanism of 1,25 (OH) 2D3 efficiency as a function of the severity of hypocalcemia. In the present experiment, we submitted islets from vitamin D3-deficient rats to in vitro exposure to a range of decreasing extracellular Ca2+ concentrations ([Ca2+]ex), from 0.5 mM to 0.6 mM, during a 6-h 10-8 M 1,25 (OH) 2D3 induction. Thereafter, we compared the effect of this pretreatment on the islets' insulin response to a given stimulus. Various stimuli were used, and we measured in parallel the variations of 86Rb+ and 45Ca2+ efflux and insulin release into the perifusion medium. In the presence of 1,25 (OH) 2D3, we observed an inverse correlation between the [Ca2+]ex pre-exposure and the amplitude of the insulin response to certain stimuli studied, suggesting that beta cells that were pre-exposed to low [Ca2+]ex became more sensitive to the beneficial effect of 1,25 (OH) 2D3 on insulin release. This effect was observed when beta cells were activated by acetylcholine but only during its second phase of stimulation, and more particularly with the barium plus theophylline stimulus. In contrast, insulin release was not affected by [Ca2+]ex pre-exposure during 1,25 (OH) 2D3 induction in response to acetylcholine during its first phase of stimulation, thus excluding any mechanism mediated via nutrient pathways, membrane depolarization, or inositol triphosphate (IP3)-dependent events. Moreover, the islets that were pre-exposed to a 10-fold [Ca2+]ex exhibited only a 50% lower 45Ca2+ content after 45Ca2+ loading, suggesting a different or relatively more efficient storage capacity in the presence of low extracellular calcium. Studies of 45Ca2+ efflux showed that the mobilization of Ca2+ stores induced by a barium plus theophylline stimulus, in the absence of calcium in the perifusion medium, was more efficient in islets pre-exposed to low [Ca2+]ex, whereas the acetylcholine-IP 3-induced mobilization of Ca2+ from reticular stores was not affected. These results generated the hypothesis that 1,25 (OH)2D3 may prepare the beta cells during their pre-exposure to low [Ca2+]ex to become more efficient as concerns insulin release via a more efficient mobilization of 45Ca2+ stores (mitochondrial?) and by an activation of release potentiating systems via protein kinase C protein kinase A pathways.

Stimulatory effect of 1,25-dihydroxyvitamin D3 on calcium handling and insulin secretion by islets from vitamin D3-deficient rats.

Among the various vitamin D3 metabolites, 1,25-(OH)2D3 is the specific secosteroid hormone that can enhance, in vitro, the weak insulin response to glucose of islets from vitamin D3-deficient rats. Because this potentiating effect is preceded by an increase in Ca2+ handling, several putative sites of action were studied by measuring 45Ca2+ and 86Rb+ (as K+ tracer) efflux during perifusions in the presence of various stimuli known to affect Ca2+ movements in different ways: high glucose without calcium, high calcium without glucose, high potassium, or barium-theophylline without calcium or glucose. The present results show that 1,25-(OH)2D3 may activate Ca2+ handling by at least two mechanisms: (1) an increase of Ca2+ entry via voltage-dependent Ca2+ channels in the experiments in which extracellular Ca2+ was present and where Ca2+ channels were opened; this 1,25-(OH)2D3 influence on Ca2+ channels was not mediated by a possible indirect influence on K+ channels because 86Rb+ fluxes were never observed to be affected by the steroid; (2) an enhancement of 45Ca2+ mobilization from intracellular stores as suggested by barium-theophylline stimulation and probably also via the Ca2+ stimulus. Both of these 1,25-(OH)2D3 influences tended to provide more calcium to the B cell of vitamin D3-deficient rats. But this prerequisite was not sufficient in itself to potentiate the insulin response; indeed, experiments with barium-theophylline suggested that 1,25-(OH)2D3 may also activate a cAMP-dependent exocytosis process.

Effects of ELF and static magnetic fields on calcium oscillations in islets of Langerhans.

Several experimental studies have produced contradictory results on the effects of extremely low frequency (ELF) magnetic fields on cellular processes involving calcium ions. Furthermore, the few positive results have not been independently replicated. In most of these studies, isolated cells were used. Our study used mouse islets of Langerhans, in which very regular oscillations of calcium concentration can be observed at length. These oscillations are sustained by processes that imply energetic and inter-intracellular communication. Various magnetic fields were applied, either sinusoidal at different frequencies (50 Hz or multiples of the natural oscillation frequency) at 0.1 or 1 mT or static at 1 mT. Islets were also exposed to "cyclotron resonance" conditions. There was neither alteration of the fundamental oscillation frequency nor the degree of organisation under all exposure conditions. Using this sensitive model, we could not show new evidence of alterations of calcium processes under exposure to various magnetic fields.

Effects of constant magnetic fields on the B-cells and insulin target cells in the rat.

Young male rats were exposed to constant uniform magnetic fields of 400 and 800 millitesia (mT). No changes were observed in the body and in the pancreas weight, in the pancreatic insulin content and in the in vitro insulin release of Langerhans islets, in glucose and insulin plasma levels. The magnetic fields abolished the insulin effect on glucose uptake of diaphragms, but not on 1-14C-glucose oxidation. In adipocytes 400 mT increased insulin-stimulated 1-14C-glucose oxidation, when expressed as percentage of mean basal oxidation, and 800 mT diminished it.

Effect of exposure to the edge signal on oxidative stress in brain cell models.

In this study we investigated the effect of the Enhanced Data rate for GSM Evolution (EDGE) signal on cells of three human brain cell lines, SH-SY5Y, U87 and CHME5, used as models of neurons, astrocytes and microglia, respectively, as well as on primary cortical neuron cultures. SXC-1800 waveguides (IT'IS-Foundation, Zürich, Switzerland) were modified for in vitro exposure to the EDGE signal radiofrequency (RF) radiation at 1800 MHz. Four exposure conditions were tested: 2 and 10 W/kg for 1 and 24 h. The production of reactive oxygen species (ROS) was measured by flow cytometry using the dichlorofluorescein diacetate (DCFH-DA) probe at the end of the 24-h exposure or 24 h after the 1-h exposure. Rotenone treatment was used as a positive control. All cells tested responded to rotenone treatment by increasing ROS production. These findings indicate that exposure to the EDGE signal does not induce oxidative stress under these test conditions, including 10 W/kg. Our results are in agreement with earlier findings that RF radiation alone does not increase ROS production.

A confirmation study of Russian and Ukrainian data on effects of 2450 MHz microwave exposure on immunological processes and teratology in rats.

In a series of Russian and Ukrainian papers published from 1974-1986, it was reported that 30-day whole-body exposures to continuous-wave (CW) radiofrequency (RF) radiation at 2375 MHz and 5 W/m(2) disrupted the antigenic structure of rat brain tissue. The authors suggested that this action caused an autoimmune response in exposed animals. Moreover, these studies reported that blood serum from exposed rats injected into intact nonexposed female rats on the 10th day of pregnancy led to increased postimplantation embryo mortality and decreased fetus size and body weight. Because the results of these studies served in part as the basis for setting exposure limits in the former USSR, it was deemed necessary to perform confirmation studies, using modern dosimetric and biological methods. In our study, a new system was constructed to expose free-moving rats under far-field conditions. Whole-body and brain-averaged specific absorption rates (SARs) were calculated. All results, using ELISA and classic teratology end points, were negative in our laboratory. On the basis of this investigation, we conclude that, under these exposure conditions (2450 MHz, CW, 7 h/day, 30 days, 0.16 W/kg whole-body SAR), RF-radiation exposure had no influence on several immune and degenerative parameters or on prenatal development.

Simultaneous determination of insulin secretion and glucose oxidation rates during incubation of isolated rat islets of Langerhans.

Insulin secretion being related to glucose metabolism of the B cell, it seemed of interest to develop a suitable system to measure these two parameters on the same islet pool, in order to overcome the great individual differences observed when these are measured in separate experiments. For this reason, we used an incubation system allowing the measurement of insulin secretion concomitantly with the determination of the corresponding oxidation rate. The results obtained agree well with those described by several authors using separate experimental procedures. Thus, our experimental design appears to be a reliable method for simultaneous determination of insulin secretion and glucose oxidation rates.

Direct effect of corticosterone upon insulin secretion studied by three different techniques.

The immediate effect of corticosterone upon insulin secretion rates estimated by three different techniques (perfusior of isolated rat pancreas and perifusion or incubation of isolated islets of Langerhans) was studied for one hour. Three corticosterone concentrations were used: 0.02, 0.2 or 20 mg/l. With 4.2 mmol/l glucose, corticosterone did not affect insulin secretion, whereas, with a stimulating glucose concentration (16.7 mmol/l), insulin secretion was inhibited by the three corticosterone concentrations tested during incubation experiments, and by only the two physiological ones (0.02 and 0.2 mg/l) during islets perifusion and pancreas perfusion experiments. Moreover the inhibitory effect appeared more rapid with perifused islets than perfused pancreas, where only the second insulin secretory phase was disturbed.