Alterations in ornithine decarboxylase activity in the rat mammary gland after different periods of 50 Hz magnetic field exposure.

In a series of experiments with the chemical carcinogen DMBA (7, 12-dimethyl[a]anthracene), we recently found that exposure of female Sprague-Dawley rats in 50 Hz magnetic fields (MF) in the microtesla range significantly facilitates the development and growth of mammary tumors. One possible explanation for this finding would be enhanced proliferation of breast epithelial stem cells by MF exposure, thereby increasing the sensitivity of these cells to chemical carcinogens. In line with this possibility, we previously determined that 50 Hz, 50 microT MF exposure induces increases in ornithine decarboxylase (ODC), i.e., a key enzyme in cell proliferation, in the mammary gland of female Sprague-Dawley rats. In the present study, we examined the time course of this effect, by using different periods of exposure to a 50 Hz, 100 microT MF. Furthermore, we determined ODC in different mammary complexes of the rat mammary gland to evaluate whether differences in response to MF exist over the anterior-posterior extension of this organ. Exposure of young female Sprague-Dawley rats induced marked increases in ODC in the mammary gland that were similar to ODC increases seen in "positive control" experiments with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). However, this effect of MF critically depended on the duration of MF exposure, with no effect, or at least no consistent effect, for short (<1 week) or long (8 weeks and above) exposure periods, but a robust and reproducible enhancing effect on ODC activity after 2 weeks of exposure. Furthermore, we found that the effect of MF exposure depends on the part of the mammary complexes examined, the cranial thoracic (or cervical) complexes being particularly sensitive to ODC alterations in response to MF. This is in line with recent DMBA experiments of our group in which MF-induced increases in tumor development and growth were predominantly seen in this large cranial/cervical part of the mammary gland. The most likely explanation for the observed ODC changes after MF exposure is the "melatonin hypothesis," although other cellular and molecular effects of MF might be involved as well.     

Absence of daytime 50 Hz, 100 microT(rms) magnetic field or bright light exposure effect on human performance and psychophysiological parameters

The purpose of this study was to reproduce and extend two earlier studies of the effects of human exposure to 50 Hz magnetic fields (MF). In a recent paper, we described results of two double-blind investigations performed to examine effects of 100 microT(rms) 50 Hz MF exposure on psychological parameters in the same group of healthy human volunteers. In each exposure session, at 1 week intervals, with sham, continuous, and intermittent (15 s ON/OFF cycles) MF conditions, mood ratings, performance measures, and electrophysiological measures were taken. In the first study, significant amplitude changes were observed in the event-related brain potentials (ERP) recorded during a dichotic listening task. In the second study, latency and reaction time (RT) slowing were seen on a visual discrimination task (P(300) paradigm). Although these results were little related to the number of parameters analysed, they indicate that low level 50 Hz MF might have a slight influence on ERP and RT under specific circumstances of sustained attention. Before concluding that moderately strong MF exposure can influence cognitive function, previous results should be replicated, using the same paradigms with another group of healthy volunteers. In the present study, 18 healthy subjects were exposed to three experimental sessions of 30 min each, given at 1 week intervals. The sessions consisted of continuous 100 microT(rms) 50 Hz MF exposure, sham condition, and bright light (5000 lux) exposure. The study was performed double-blind, with the exposure order counter-balanced. The data on mood, ERP, RT, and other performance measures did not show any differences among the sham exposure, light exposure, and MF exposure conditions. The results of this study do not support the hypothesis that extremely low frequency (ELF) MF exposure affects the brain's electrical activity or cognitive function at field strength (100 microT(rms)) similar to that found in very close proximity of some household and industrial electrical appliances and well in excess of the average MF strength (c. 0.1 microT) found in homes. The sensitivity of the experiment was possibly not sufficient to detect an effect at this relatively low MF, and larger sample sizes would be required in further studies.     

Use of spot measurements for assessing residential ELF magnetic field exposure: a validity study

The purpose of this study was to evaluate residential short term "spot" measurements as surrogates for long term personal magnetic field (MF) exposure. In an epidemiological study on birth weight and pregnancy delay, MF exposure was assessed by taking five spot measurements in each room. For a subsample of 30 subjects 24 h personal MF measurements were made, and the following exposure metrics were calculated: 24 h arithmetic mean, 24 h median, percentage of time above 0.15 microT, and percentage of time above 0.29 microT. The 24 h exposure metrics were used as gold standards, when evaluating the validity of various summary measures calculated from spot measurements for assessing personal exposure. Based on Spearman correlation coefficient (r), specificity and sensitivity, the average of the spot measurements of a residence resulted in least exposure measurement error (misclassification). Also the above bed spot value correlated better with the 24 h metrics than any room average. Spot measurements performed about equally well in predicting different types of exposure metrics.     

One week of exposure to 50 Hz, vertical magnetic field does not reduce urinary 6-sulphatoxymelatonin excretion of male wistar rats

The effect of exposure to 100 or 50 microT, 50 Hz, vertical magnetic field on the excretion of 6-sulphatoxymelatonin (6SM) in the nocturnal urine of rats was studied. Twelve male Wistar rats were kept under 12:12 hr light:dark conditions. The nocturnal urine of animals was collected in metabolic cages over 4 consecutive weeks. The concentration of 6SM in the rat urine was measured by 125I radioimmunoassay and normalized to creatinine concentration. After the first week of urine collection, 6 rats were exposed to 100 microT or 50 microT flux density magnetic fields (MF) for 8 hr daily for 1 week. It was found that the excretion of the primary metabolite of melatonin in the urine, 6SM, did not show statistically significant changes during and after magnetic field exposure.     

Exposure of rats to a 50-Hz, 100 muTesla magnetic field does not affect the ex vivo production of interleukins by activated T or B lymphocytes.

Two separate, independent experiments were conducted to evaluate the effects of exposure of rats to a 50-Hz linearly polarized, 100 microT magnetic field (MF) on the ex vivo production of interleukins (ILs) by mitogen-stimulated splenic lymphocytes. IL-1 and IL-2 were determined by proliferation assays, using IL-dependent murine T cell lines. In the first experiment, female Sprague-Dawley rats were treated with 7,12-dimethylbenz[a]anthracene (DMBA] at a dose of 20 mg per rat (four weekly gavage doses of 5 mg), and were either MF-exposed or sham-exposed for 14 weeks. This experimental protocol has previously been shown to result in a significant increase in breast cancer growth in response to MF exposure. Furthermore, MF exposure at 50-100 microT for 3 months was recently found to induce a suppressed ex vivo proliferation of splenic T cells in response to mitogen stimulation, which could be a result of reduced IL production of spleen lymphocytes. However, the present experiments failed to demonstrate any significant difference between MF- and sham-exposed groups in production of IL-1 by mitogen-activated splenic B cells. In a second experiment, shorter MF exposure periods were studied with respect to IL production from mitogen-stimulated B and T cells. Groups of rats were MF- or sham-exposed for 1 day, 1 week, or 2 weeks, followed by preparation and activation of spleen lymphocytes. No significant difference in IL-1 or IL-2 production from stimulated B or T cells was seen. The data indicate that in vivo MF exposure of rats does not affect the ex vivo IL production of B or T lymphocytes, suggesting that the recently reported changes in T cell proliferation in response to MF exposure may not be mediated via alterations in B or T cell IL production.     

Acute exposure to 50 Hz magnetic fields with harmonics and transient components: lack of effects on nighttime hormonal secretion in men

The purpose of this study was to examine whether low frequency magnetic field (MF) influences nighttime secretion of hormones, particularly melatonin. Ten healthy males stayed in the experimental room (2.7 m cube with 3 axis Merritt coils) on two separate nights. On one night, subjects were exposed to linearly polarized 50 Hz, 20 microT sinusoidal MF with the third (30%) and the fifth (10%) harmonics and repetitive transient waves (1 burst/s of 1 kHz waves, exponentially attenuated with a duration of 50 ms; initially 100 microT peak), and the other night was for blind control. During the nights (2000-0800 h, including sleeping time, 2300-0700 h), blood samples were collected from the subjects at 1 h intervals for determining the levels of plasma hormones (melatonin, growth hormone (GH), cortisol, prolactin) and at 10 min intervals from 2200 to 0200 h for observing the GH surge induced by sleep. Statistical analyses revealed no significant difference between the 2 nights in the profiles of the four hormones, and the result suggested that extremely low frequency (ELF) or intermediate frequency (IF) MF to which humans are exposed residentially has no acute effect on nighttime secretion of hormones, particularly melatonin.     

Occupational 50 Hz magnetic field exposure measurements among female sewing machine operators in Hungary

Occupational magnetic field (MF) exposure is less thoroughly characterized in occupations typically held by women. Our objective was to characterize occupational 50 Hz MF personal exposure (PE) among female sewing machine operators. We measured the full shift PE of 51 seamstresses, who worked in two shifts (6-14 and 14-22 h) according to their normal work routine. Measurements were conducted using EMDEX PAL meters at chest level. The average duration of the measurement periods was 449 min (range 420-470). The average arithmetic mean exposure for all women was 0.76 microT (range 0.06-4.27). The average of maximum values was 4.30 microT (range 0.55-14.80). Women working with older sewing machines experienced higher exposure than women working on newer sewing machines. For women (n = 10) who operated sewing machines produced in 1990 or earlier, the average arithmetic mean exposure was 2.09 microT, and for women (n = 41) who operated sewing machines produced after 1990, the average arithmetic mean was 0.43 microT. We conclude that women working as sewing machine operators experience higher than average occupational MF exposure compared to other working women. Most important determinant of the women's personal MF exposure was the age of the sewing machine the women operated.     

Developmental toxicity evaluation of ELF magnetic fields in Sprague-Dawley rats

To identify possible effects of horizontally polarized magnetic field (MF) exposure on maintenance of pregnancy and embryo-fetal development, an MF exposure system was designed and constructed and 96 time-mated female Sprague-Dawley (SD) rats (24/group) received continuous exposure to 60 Hz MF at field strengths of 0 (sham control) and 5, 83.3, or 500 microT (50, 833, or 5000 mG). Dams received MF or sham exposures for 22 h/day on gestational day 6-20. MF was monitored continuously throughout the study. There were no evidences of maternal toxicity or developmental toxicity in any MF exposed groups. Mean maternal body weight, organ weights, and hematological and serum biochemical parameters in groups exposed to MF did not differ from those in sham control. No exposure related differences in fetal deaths, fetal body weight, and placental weight were observed between MF exposed groups and sham control. External, visceral, and skeletal examination of fetuses demonstrated no significant differences in the incidence of fetal malformations between MF exposed and sham control groups. In conclusion, exposure of pregnant rats to 60 Hz at MF strengths up to 500 microT during gestation day 6-20 did not produce any biologically significant effect in either dams or fetuses.     

Effects of exposure to 30 kV/m, 60-Hz electric fields on the social behavior of baboons

We tested the hypothesis that exposure to a 30-kV/m, 60-Hz electric field produces significant change (stress) in the social behavior of adult male baboons (Papio cynocephalus anubis). One group of eight baboons was exposed to an electric field (12 hours per day, 7 days per week for 6 weeks) while a second group of eight baboons was maintained in a sham-exposure (control) condition. Exposed subjects and control subjects were compared over three, six-week experimental periods (pre-exposure, exposure, and post-exposure). Performance rates of six categories of social behaviors (passive affinity, active affinity, approach, tension, threat, and attack) and four categories of nonsocial behaviors (forage, manipulate, posture, and stereotypy) were used to compare the two groups. The results of our study indicate that 1) there were no significant differences between the two groups during the pre-exposure or post-exposure periods; 2) during the exposure period, experimental and control groups exhibited statistically significant differences in the mean performance rates of three behavior categories; 3) within-group comparisons across periods indicate that the experimentally exposed group exhibited statistically significant changes in passive affinity, tension, and stereotypy; and 4) changes in behavior performance among the exposed subjects reflect a stress response to the electric field.     

Exposure of pregnant dairy heifer to magnetic fields at 60 Hz and 30 microT

Thirty-two pregnant Holstein heifers weighing 499 +/- 45 kg, at 3.1 +/- .7 months of gestation and 21 +/- 2.0 months of age were confined and exposed to 30 microT magnetic fields (MFs) and a 12 h light/12 h dark light cycle. The heifers were divided into two replicates of 16 animals. Each replicate was divided into two groups of eight animals each, one group the non-exposed and the second, the exposed group. The animals were subjected to the different treatments for 4 weeks. After 4 weeks, the animals switched treatment, the exposed group becoming the non-exposed group and vice versa. Then the treatment continued for 4 more weeks. Catheters were inserted into the jugular vein, and blood samples were collected twice a week to estimate the concentration of progesterone (P4), melatonin (MLT), prolactin (PRL), and insulin-like growth factor 1 (IGF-1). Feed consumption was measured daily. The results indicated that exposure of pregnant heifers to MF similar to those encountered underneath a 735 kV high tension electrical power line for 20 h/day during a period of 4 weeks produces slight effects. This is evidenced by statistically significant higher body weight (1.2%), higher weekly body weight gain (30%), and decreases in the concentration of PRL (15%) and IGF-1 (4%) in blood serum. The absence of abnormal clinical signs and the absolute magnitude of the significant changes detected during MF exposure, make it plausible to preclude any major animal health hazard.     

Survey of residential 50 Hz EMF exposure from transformer stations

In Hungary it is typical that 10/04 kV transformer stations are being installed in multistory residential and office buildings. Magnetic fields (MFs) up to several tens of microT have been measured in apartments close to transformers. The aim of the present study was to provide systematic assessment of MF exposure of residents living above transformer stations. Out of 41 addresses provided by the electricity supplier, current load of 21 transformers and MF in 21 apartments was measured. Spot MFs at 1 m height and time weighted average 24 h MF exposure at bed height was measured. All-day personal MF exposure was measured at waist and HOME exposure was calculated. BED exposure was measured at bed height. Participants kept a time-activity diary. The time-weighted average 24 h MF exposure (3.03 microT) exceeded the usual residential exposure (<0.2 microT). The mean HOME and BED personal exposure above transformers was 0.825 and 1.033 microT, respectively. Our study provides exposure assessment of a cohort with a wider exposure range, compared to power-line epidemiological studies.     

Influence of 50 Hz magnetic field on human heart rate variability: linear and nonlinear analysis

This study investigated the problem of the influence of 50 Hz magnetic field (MF) on human heart rate variability (HRV). The exposure system was a commercial device for magnetotherapy, generating field of the strength of 500 microT at the center of the coil, 150-200 microT at the position of human subjects' heart and 20-30 microT at the position of subjects' head. The exposure protocols, applied randomly, were either "half hour MF-off/half hour MF-on" or "half hour MF-off/half hour MF-off." The phonocardiographic (PhCG) signal of 15 volunteers were obtained during exposure and used for calculation of time-domain HRV parameters (mean time between heart beats (N-N), standard deviation of time between heart beats (SDNN), and the number of differences of successive beat-to-beat intervals greater than 50 ms, divided by the total number of beat-to-beat intervals (pNN50)) and nonlinear HRV measures (approximate entropy (ApEn), detrended fluctuation scaling exponents). The protocol MF-off/MF-on was applied in nine subjects. Repeated measures ANOVA (RMANOVA) performed for Mf-off/MF-off protocol indicated no statistical difference among four 15 min intervals of HRV data (P value >20% for all parameters except for N-N, where P = 3.7%). RMANOVA followed by the post hoc Tukey test performed for Mf-off/MF-on protocol indicated a statistically significant difference during MF on for N-N (8% increase, P <.1%), SDNN (40% increase, P = 1.1%), and pNN50 (110% increase, P <.1%). The results of the analysis indicate that the changes of these parameters could be associated with the influence of MF.     

Effects of 60 Hz magnetic field exposure on the pineal and hypothalamic-pituitary-gonadal axis in the Siberian hamster (Phodopus sungorus)

Experiments using the dwarf Siberian hamster Phodopus sungorus were carried out to determine possible neuroendocrine consequences of one-time and repeated exposures to 60 Hz magnetic fields (MF). Animals were maintained in either a short-light (SL, 8 h light:16 h dark) or long-light (LL, 16 h light:8 h dark) photoperiod. Acute (one-time, 15 min) exposure of male SL animals to a linearly polarized, horizontally oriented, 60 Hz MF (0.1 mT) gave rise to a statistically significant (P < .005) reduction in pineal melatonin content as determined 3 and 5 h after onset of darkness. In LL animals, acute exposure to 0.10 mT resulted in a significant decrease in pineal melatonin as measured 4 h after onset of darkness, whereas acute exposure to 50 microT showed no effect compared with sham exposure. In SL animals, an increase in norepinephrine was observed in the medial basal hypothalamus (including the suprachiasmatic nucleus) after acute exposure (P < .01). Daily MF exposure of SL animals to a combination of steady-state and on/off 60 Hz magnetic fields (intermittent exposure) at 0.1 mT for 1 h per day for 16 days was associated with a reduction in melatonin concentrations at 4 h after onset of darkness and an increase in blood prolactin concentrations (P < .05). Exposure of SL animals to a steady state 60 Hz MF for 3 h/day for 42 days resulted in a statistically significant reduction in body weight (ANOVA: P > .05), compared with sham-exposed SL animals. At 42 days, however, no significant changes in overnight melatonin or prolactin levels were detected. In both repeated exposure experiments, gonadal weights were lowest in the MF-exposed groups. This difference was statistically significant (P < .05) after 42 days of exposure. These data indicate that both one-time and repeated exposure to a 0.1 mT, 60 Hz MF can give rise to neuroendocrine responses in Phodopus.     

Lack of adverse effects in pregnant/lactating female rats and their offspring following pre- and postnatal exposure to ELF magnetic fields

We have recently reported that exposure of pregnant rats to 60 Hz at field strengths up to 0.5 mT during the entire period of pregnancy did not induce any biologically significant effects on both pregnant dams and embryo-fetal development. The present study was carried out to investigate the potential effects of gestational and lactational MF exposure on pregnancy, delivery, and lactation of dams and growth, behavior, and mating performance of their offspring in rats. Timed-pregnant female Sprague-Dawley (SD) rats (24/group) received continuous exposure to 60 Hz magnetic field (MF) at field strengths of 0 (sham control), 5 microT, 83.3 microT, or 0.5 mT. Dams received MF or sham exposures for 21 h/day from gestational day 6 through lactational day 21. Experimentally generated MF was monitored continuously throughout the study. No exposure-related changes in clinical signs, body weight, food consumption, pregnancy length, and necropsy findings were observed in dams. Parameters of growth, behavior, and reproductive performance of offspring showed no changes related to MF exposure. There were no adverse effects on embryo-fetal development of F2 offspring from dams exposed to MF. In conclusion, exposure of pregnant SD rats to 60 Hz at field strengths up to 0.5 mT from gestational day 6 to lactational day 21 did not produce biologically significant effects in dams, F1 offspring, or F2 fetuses.     

Lymphocyte subset analyses in blood, spleen and lymph nodes of female Sprague-Dawley rats after short or prolonged exposure to a 50 Hz 100-microT magnetic field.

Based primarily on the results of in vitro studies, it has been suggested that power-line (50 or 60 Hz) magnetic fields (MFs) may reduce immune function, which could lower resistance to infection or cancer. This study was conducted to evaluate the influence of acute and chronic in vivo exposure to a linearly polarized 50 Hz MF on immune function in female Sprague-Dawley rats. Groups of rats were exposed continuously to the MF at a flux density of 100 microT for periods of 3 days, 14 days or 13 weeks. For each exposure period, one control group of rats was sham-exposed together with each MF-exposed group. Experimental end points included analyses of T-lymphocyte subsets as well as other immune cells involved in cell-mediated immune responses, i.e. natural killer (NK) cells, B lymphocytes, macrophages, and granulocytes in blood, spleen and mesenteric lymph nodes. In addition, immunohistochemical methods were used to detect proliferating and apoptotic cells in the various compartments of spleen tissue. The results obtained failed to demonstrate a significant effect of short or prolonged MF exposure on different types of leukocytes, including lymphocyte subsets. Furthermore, the experiments on the in vivo proliferation activity of lymphocytes and the extent of apoptosis in spleen samples did not indicate a difference between the MF-exposed and sham-exposed groups, indicating that MF exposure does not affect the mechanisms involved in the control of lymphocyte homeostasis. The lack of MF effects in the immune tests used in the present in vivo study makes it highly unlikely that MF exposure induces immunotoxicity, at least under the experimental conditions used. However, the data do not exclude the possibility that functional alterations in T-cell responses to mitogens and in NK cell activity as recently described for MF-exposed rodents may be one mechanism involved in the carcinogenic effects of MF exposure observed in some models of co-carcinogenesis.     

Magnetic fields and the melatonin hypothesis: a study of workers chronically exposed to 50-Hz magnetic fields

Because epidemiological studies report clinical disorders (mainly neurobehavioral alterations and/or cancer) that may be related to diminished melatonin secretion or to changes in its circadian rhythm in subjects living or working in environments exposed to magnetic fields, research on the effects of these fields in humans is particularly important. In this study, we examine the circadian rhythm of melatonin in 15 men exposed chronically and daily for a period of 1-20 yr, in the workplace and at home, to a 50-Hz magnetic field in search of any cumulative effect from those chronic conditions of exposure. The weekly geometric mean of individual exposures ranged from 0.1 to 2.6 microT. The results are compared with those for 15 unexposed men who served as controls (individual exposures ranged from 0.004 to 0.092 microT). Blood samples were taken hourly from 2000 to 0800. Nighttime urine was also collected and analyzed. This work shows that subjects exposed over a long period (up to 20 yr) and on a daily basis to magnetic fields experienced no changes in their plasma melatonin level, their urinary 6-sulfatoxymelatonin level, or the circadian rhythm of melatonin. Our data strongly suggest that magnetic fields do not have cumulative effects on melatonin secretion in humans and thus clearly rebut the "melatonin hypothesis" that a decrease in plasma melatonin concentration (or a disruption in its secretion) explains the occurrence of clinical disorders or cancers possibly related to magnetic fields.     

Indoor transformer stations as predictors of residential ELF magnetic field exposure

Transformer stations in apartment buildings may offer a possibility to conduct epidemiological studies that involve high exposure to extremely low frequency magnetic fields (MF), avoid selection bias and minimize confounding factors. To validate exposure assessment based on transformer stations, measurements were performed in thirty buildings in three Finnish cities. In each building, spot measurements in all rooms and a 24-h recording in a bedroom were performed in one apartment above a transformer station (AAT), in one first floor (FF) reference apartment, and one reference apartment on upper floors (UF). The apartment mean of spot measurements was 0.62 microT in the AATs, 0.21 microT in the FF and 0.11 microT in the UF reference apartments The 24-h apartment mean (estimated from the spot measurements and the bedroom 24-h recording) was 0.2 microT or higher in 29 (97%) AATs, in 7 (25%) FF and in 3 (10 %) UF reference apartments. The corresponding numbers for the 0.4 microT cut-off point were 19 (63%), 4 (14%), and 1 (3.3%). The higher MF level in the FF reference apartments indicates that they should not be considered "unexposed" in epidemiological studies. If such apartments are excluded, a transformer station under the floor predicts 24-h apartment mean MF with a sensitivity of 0.41 (or 0.58) and a specificity of 0.997 (or 0.97), depending on the MF cut-off point (0.2 or 0.4 microT). The results indicate that apartments can be reliably classified as high and low MF field categories based on the known location of transformer stations.     

Effects of a 60 Hz magnetic field on photosynthetic CO2 uptake and early growth of radish seedlings

Photosynthetic CO2 uptake rate and early growth parameters of radish Raphanus sativus L. seedlings exposed to an extremely low frequency magnetic field (ELF MF) were investigated. Radish seedlings were exposed to a 60 Hz, 50 microT(rms) (root mean square) sinusoidal magnetic field (MF) and a parallel 48 microT static MF for 6 or 15 d immediately after germination. Control seedlings were exposed to the ambient MF but not the ELF MF. The CO2 uptake rate of ELF MF exposed seedlings on day 5 and later was lower than that of the control seedlings. The dry weight and the cotyledon area of ELF MF exposed seedlings on day 6 and the fresh weight, the dry weight and the leaf area of ELF MF exposed seedlings on day 15 were significantly lower than those of the control seedlings, respectively. In another experiment, radish seedlings were grown without ELF MF exposure for 14 d immediately after germination, and then exposed to the ELF MF for about 2 h, and the photosynthetic CO2 uptake rate was measured during the short-term ELF MF exposure. The CO2 uptake rate of the same seedlings was subsequently measured in the ambient MF (control) without the ELF MF. There was no difference in the CO2 uptake rate of seedlings exposed to the ELF MF or the ambient MF. These results indicate that continuous exposure to 60 Hz, 50 microT(rms) sinusoidal MF with a parallel 48 microT static MF affects the early growth of radish seedlings, but the effect is not so severe that modification of photosynthetic CO2 uptake can observed during short-term MF exposure.     

Effects of pre-exposure to hyperbaric hyperoxia on high-intensity exercise performance

This study comprised 2 main experiments: one was to determine the oxidative DNA damage under hyperbaric hyperoxia (HBO), and the other was to evaluate the effects of pre-exposure to HBO on high-intensity exercise performance. Healthy subjects (n = 8) inspired 100% O2 in an experimental chamber at a pressure of 1.3 atmospheres absolute (ATA) for 50 minutes once per week for 2 weeks. Urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) was measured as a marker of DNA oxidative damage on day 0 and on days 1, 3, and 5 after each HBO exposure. To investigate the effects of pre-exposure to HBO on high-intensity exercise performance, subjects (n = 6) performed maximal isometric knee extensor exercise (30 repetitions x 2 sets) with and without HBO pre-exposure (100% O2 at 1.3 ATA for 50 minutes). Urinary 8-OHdG did not show any significant change after HBO exposure. Isometric knee extensor torque was significantly lower during the first half of the first set of exercises after HBO pre-exposure compared with the normobaric normoxia (NBO) trial. The decreased torque was associated with the lower integrated electromyography with respect to time. Changes in the degree of ischemia-reperfusion in the vastus lateralis muscle during exercise were larger in the HBO pre-exposure trial than in the NBO trial. Muscle fatigue index, serum lactate concentration, heart rate, and systolic blood pressure showed no differences between the 2 trials. These results indicated that HBO exposure was harmless to DNA, and HBO pre-exposure did not enhance high-intensity exercise performance. As a practical application, athletes who require maximal muscle strength should not inspire high-concentration of O2 just before their competitions because it might, as the case may be, impair their performance.