Effects of pulsed extremely-low-frequency magnetic fields on skin wounds in the rat

Rats with skin-wounds surgically created on their backs were exposed immediately after surgery and every 12 h thereafter to pulsed, extremely-low-frequency magnetic fields. The shape of the pulse was a positive triangle (50 Hz, 8 mT peak). The rate of healing of skin wounds was evaluated macroscopically and by light and electron microscopy at 6, 12, 21, and 42 days after the operation. A significant increase in the rate of wound contraction was found in rats treated with magnetic fields. Forty-two days after surgery all treated animals show fully closed wounds, while control rats at the same time intervals still lacked a final 6% of the wound surface to be covered. Treated rats showed earlier cellular organization, collagen formation and maturation, and a very early appearance of newly formed vascular network.     

SENSORY TRANSDUCTION AS A PROPOSED MODEL FOR BIOLOGICAL DETECTION OF ELECTROMAGNETIC FIELDS

Laboratory studies of the biological effects of low-frequency electromagnetic fields (EMFs) have demonstrated that the fields can produce or alter a wide range of phenomena. Explaining the diversity of the reported effects is a central problem. Our basic hypothesis is that the effects are generally indirect, and arise as a consequence of sensory transduction of the fields. In this view, EMF detection and its biological consequences occur in different types of cells. Experimental verification of the hypothesis will ultimately require data showing that the interaction of EMFs with tissue results in biological changes that are the same as or similar to changes that occur during sensory transduction. The goal was to identify the specific phenomena that would be expected to occur if the hypothesis were true. We therefore analyzed the presently accepted models of sensory transduction in the somatic and special senses. Many kinds of processes were identified in connection with transduction of different kinds of stimuli, but we found that a change in the conductance of a membrane ion channel in a neuron or a neuroepithelial cell was the earliest process that occurred in all forms of sensory transduction. Evidence from an appropriate model excitable cell or tissue that EMFs affect membrane currents or membrane potential would therefore support the hypothesis that EMF transduction is a species of sensory transduction.     

Circularly polarized,sinusoidal, 50 Hz magnetic field exposure does not influence plasma testosterone levels of rats

We exposed rats to circularly polarized 50 Hz magnetic fields to determine if plasma testosterone concentration was affected. Previous experiments indicate that magnetic fields suppress the nighttime rise in melatonin, suggesting that other neuroendocrine changes might occur as well. Male Wistar-King rats were exposed almost continuously for 6 weeks to magnetic flux densities of 1,5, or 50 μT. Blood samples were obtained by decapitation at 12:00 h and 24:00 h. Plasma testosterone concentration showed a significant day-night difference, with a higher level at 12:00 h when studied in July and December, but the day-night difference disappeared when concentrations were studied in April. In three experiments, magnetic field exposure had no statistically significant effect on plasma testosterone levels compared with the sham-exposed groups. These findings indicate that 6 weeks of nearly continuous exposure to circularly polarized, 50 Hz magnetic fields did not change plasma testosterone concentration in rats. © 1994 Wiley-Liss, Inc.     

Comparison of 60-Hz electric fields and incandescent light as aversive stimuli controlling the behavior of rats

Rats were exposed to two procedures which enabled them to press a lever to turn off a 90 or 100 kV/m 60-Hz electric field or, later in the study, illumination from an incandescent lamp. Under one procedure, a response turned off the stimulus for a fixed duration, after which the stimulus was turned on again. A response during the off-period restarted the fixed duration. None of the rats turned the field off reliably. Next, under an alternative procedure, pressing one lever turned the field off; pressing the other lever turned it back on; responding under those conditions differed little from that seen at 0 kV/m. Under both procedures, when illumination from an incandescent lamp served as the stimulus, each rat did turn the stimulus off, and performances varied with stimulus intensity. The results show that a 100 kV/m 60-Hz electric field is not sufficient to function as an aversive stimulus under two procedures where illumination from a lamp does function as an aversive stimulus.     

Changes in chromogranin A-immunoreactive guinea-pig pulmonary neuroendocrine cells after sensitization and challenge with ovalbumin

Immunohistochemical study with antisera to chromogranin A and neuron-specific enolase, a general marker for nerves and endocrine cells, was used to quantify changes in bronchial neuroendocrine cells in guineapigs sensitized and challenged with ovalbumin. Actively sensitized animals were killed 2, 6, 24, 48, 72, and more than 144 hours after being challenged by an aerosolized solution of ovalbumin. The number of chromogranin A-immunoreactive cells was significantly greater in sensitized but unchallenged animals and in sensitized animals killed 2 and 6 h after challenge when compared to controls; it decreased significantly in animals killed more than 24 h after challenge when compared to sensitized, unchallenged animals. The number of neuron-specific-enolase-immunoreactive cells did not change. We conclude that the peptide content of bronchial neuroendocrine cells increases during sensitization and in the early phase of a hypersensitivity reaction, and that the cells release their granule contents in the late phase of such a reaction. They may therefore play a role in immunoallergic events in the lung.     

Interactive effects in 60-HZ electric-field exposure systems

The level of exposure of laboratory animals to 60-Hz electric fields is commonly specified in terms of the unperturbed field strength present before the introduction of experimental subjects and their cages. In the research reported in this paper, rats were housed in two parallel rows of 12.4 cm × 25.1 cm × 10.2 cm high plastic cages resting on the lower electrode of a parallel-plate exposure system, and the actual perturbed electric fields experienced by an experimental animal were investigated. The most important results are: 1) Reducing the spacing between the exposure electrodes from 8.7 to 1.7 times the height of a singly exposed rat model, while maintaining a constant unperturbed field strength, resulted in a 15% increase in the electric field at the highest point on the surface of the body and a 10% increase in the short-circuit current of the model. 2) For multiple animal exposures, increases of 10% in both the field at the highest point of the body and the short-circuit current were observed when the electrode spacing was reduced from 8.7 to 2.6 times the height of a rat. 3) Plastic cages caused 1 – 6% reductions in the electric field at the surface of the body, except very near the cage walls, where enhancements of more than 20% were observed. 4) When 16 rats were simultaneously exposed, the short-circuit current, I_s, of an individual subject of weight W (in g), that was surrounded on all sides by other rats of weight W, was reduced from the short-circuit current, I_u, measured with the same subject individually exposed as follows: during a 12 h light (sleeping) cycle, I_s/I_u = 1.00 – 0.0173W^1/2; during a 12 h night (awake) cycle, I_s/I_u = 1.00 – 0.0136W^1/2.     

The diffuse endocrine system: from embryogenesis to carcinogenesis

In the present review we will summarise the current knowledge about the cells comprising the Diffuse Endocrine System (DES) in mammalian organs. We will describe the morphological, histochemical and functional traits of these cells in three major systems gastrointestinal, respiratory and prostatic. We will also focus on some aspects of their ontogeny and differentiation, as well as to their relevance in carcinogenesis, especially in neuroendocrine tumors. The first chapter describes the characteristics of DES cells and some of their specific biological and biochemical traits. The second chapter deals with DES in the gastrointestinal organs, with special reference to the new data on the differentiation mechanisms that leads to the appearance of endocrine cells from an undifferentiated stem cell. The third chapter is devoted to DES of the respiratory system and some aspects of its biological role, both, during development and adulthood. Neuroendocrine hyperplasia and neuroendocrine lung tumors are also addressed. Finally, the last chapter deals with the prostatic DES, discussing its probable functional role and its relevance in hormone-resistant prostatic carcinomas.     

Development of young rats and rabbits exposed to a strong electric field

Body growth and circulating levels of hormones were assessed in young rats and rabbits exposed to a 50-Hz electric field of 50 kV/m. Eight-week-old male rats were exposed 8 h/day for 4 weeks and rabbits were exposed 16 h/day from the last 2 weeks of gestation to 6 weeks after birth. The body and the organ growth of exposed rats were not statistically different from those of sham-exposed controls. No important differences from controls were observed in plasma levels of corticosterone, TSH, ACTH, and T4 or in adrenal levels of epinephrine, norepinephrine, and corticosterone although T3 was slightly, but significantly, decreased. No large histological changes in the thyroid or adrenals were noted. In rabbits, organ and body weights of exposed animals were comparable to those of controls. Plasma levels of various hormones (ACTH, GH, T3, T4, corticosterone, cortisol), serum glucose, triglycerides, and cholesterol were not significantly altered. Adrenal content of cortisol was lower, however, in exposed rabbits. No histological changes of the thyroid or adrenal glands were observed.     

Influence of weak static and 50 Hz magnetic fields on the redox activity of cytochrome-C oxidase

The effects of static and 50 Hz magnetic fields on cytochrome-C oxidase activity were investigated in vitro by strictly controlled, simultaneous polarographic measurements of the enzyme's high- and low-affinity redox reaction. Cytochrome-C oxidase was isolated from beef heart. Control experiments were carried out in the ambient geomagnetic and 50 Hz magnetic fields at respective flux densities of 45 and 1.8 μT. The experimentally applied fields, static and time-varying, were generated by Helmholtz coils at flux densities between 50 μT and 100 mT. Exposures were timed to act either on the combined enzyme-substrate interchange or directly on the enzyme's electron and proton translo-cations. Significant changes as high as 90% of the overall cytochrome-C oxidase activity resulted during exposure (1) to a static magnetic field at 300 μT or 10 mT in the high-affinity range, and (2) to a 50 Hz magnetic field at 10 or 50 mT in the low-affinity range. No changes were observed at other flux densities. After exposure to a change-inducing, static or time-varying field, normal activity returned. © 1993 Wiley-Liss. Inc.     

Behavioral studies with mice exposed to DC and 60-Hz magnetic fields

Behavioral measures were evaluated in adult CD-1 and LAF-1 mice continuously exposed for 72 h to a 1.5-Tesla (1 T = 10(4) Gauss) homogeneous DC magnetic field, and in LAF-1 mice continuously exposed for 72 h to a sinusoidal 60-Hz, 1.65-mT (rms) homogeneous AC field. Three types of behavioral tests were employed: (1) Memory of an electroshock-motivated passive avoidance task was assessed in animals that had been trained immediately prior to the field exposure. The strength of memory was varied either by altering the strength of the electric footshock during training, or by administering a cerebral protein synthesis inhibitor, anisomycin, at the time of training. (2) General locomotor activity was measured using a quadrant-crossing test immediately after termination of the magnetic field exposure. (3) Sensitivity of the experimental subjects to the seizure-inducing neuropharmacological agent, pentylenetrazole , was assessed immediately after the field exposure on the basis of three criteria: (a) the percentage of subjects exhibiting a generalized seizure, (b) the mean time to seizure, and (c) the mean seizure level. The results of these studies revealed no behavioral alterations in exposed mice relative to controls in any of the experimental tests with the 1.5-T DC field or the 60-Hz, 1.65-mT (rms) AC field.     

Limitations of Chromogranin A in clinical practice

Context: Usefulness of circulating Chromogranin A (CgA) for the diagnosis of neuroendocrine tumors (NEN) is controversial. The aim of the present study was to assess the actual role of this marker as diagnostic tool. Methods: Serum blood samples were obtained from 42 subjects affected with NEN, 120 subjects affected with non-endocrine neoplasias (non-NEN) and 100 non-neoplastic subjects affected with benign nodular goitre (NNG). Determination of CgA was performed by means of immunoradiometric assay. Results: The CgA levels among NEN-patients were not significantly different from NNG and non-NEN subjects. The Receiver operating characteristic (ROC) curves analysis failed to identify a feasible cut-off value for the differential diagnosis between NEN and the other conditions. Conclusion: Serum CgA is not helpful for the first-line diagnosis of NEN.     

Effects of 60-Hz electric fields on specific humoral and cellular components of the immune system

We evaluated humoral and cellular functions of the immune system of Swiss-Webster mice exposed to 60-Hz electric fields at 100 kV/m. No significant differences were observed in primary antibody response to keyhole limpet hemocyanin (precipitating antibody levels) between exposed (30 or 60 days) and control mice, nor were there significant changes in mitogen-stimulation response of spleen cells from mice similarly exposed for 90 or 150 days when compared to sham-exposed animals.     

General properties of the interaction between animals and ELF electric fields

An analysis is given of the interaction between extremely low-frequency (ELF) electric fields and animals of arbitrary body shape. This analysis is based on three approximations which are valid in the ELF range: In living tissues, capacitive (displacement) currents are negligible compared to conduction currents; effects resulting from the finite velocity of propagation of electromagnetic fields are negligible; skin effect in living tissues is negligible. Major conclusions of the analysis are: (a) The electric field outside the body, the induced charge on the surface of the body, and the total current crossing any section through the body (eg, through the neck or limbs) are completely determined by the characteristics of the applied ELF electric field, the shape of the body, its location relative to ground and other conductors, and any conduction currents from the body to ground or other conductors. (b) All of the quantities in (a) can be measured using conducting animal models. (c) The magnitudes of the electric field outside the body and the induced charge density on the surface of the body are independent of frequency, in the ELF range, when the body is either insulated from or shorted to ground (and any other conductors in the system). (d) The only quantities affected by the electrical properties of the tissues comprising the body are the current density and electric field inside the body. (e) The electric field outside and inside a body will be unchanged by a scaled change in its size.     

Influence of 50 Hz electric and magnetic fields on the human heart

This investigation studied the effect of 50 Hz electric and magnetic fields on the human heart. The electrocardiograms of 27 transmission-line workers and 26 male volunteers were recorded with a Holter recorder both in and outside the fields. The measurements took from half an hour to a few hours. The electric field strength varied from 0.14 to 10.21 kV/m and the magnetic flux density from 1.02 to 15.43 μT. Analysis of the ECG recordings showed that extrasystoles or arrhythmias were as frequent outside the field as in the field. In some cases a small decrease in heart rate was observed after field exposure. © 1993 Wiley-Liss, Inc.     

Studies on prenatal and postnatal development in rats exposed to 60-Hz electric fields

A series of three experiments was performed to determine the effects of 30-day exposures to uniform 60-Hz electric fields (100 kV/m) on reproduction and on growth and development in the fetuses and offspring of rats. In the first experiment, exposure of females for 6 days prior to and during the mating period did not affect their reproductive performance, and continued exposure through 20 days of gestation (dg) did not affect the viability, size, or morphology of their fetuses. In the second experiment, exposure of the pregnant rat was begun on 0 dg and continued until the resulting offspring reached 8 days of age. In the third experiment, exposure began at 17 dg and continued through 25 days of postnatal life. In the second and third experiments, no statistically significant differences suggesting impairment of the growth or survival of exposed offspring were detected. In the second experiment, a significantly greater percentage of the exposed offspring showed movement, standing, and grooming at 14 days of age than among-sham-exposed offspring. There was a significant decrease at 14 days in the percentage of exposed offspring displaying the righting reflex in the second experiment and negative geotropism in the third experiment. These differences were all transient and were not found when the animals were tested again at 21 days of age. Evaluation of the reproductive integrity of the offspring of the second experiment did not disclose any deficits.