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L. F. Zyubanova, L. N. Menshikova, N. N. Goncharova

EFFECT OF A LOW-FREQUENCY ELECTRIC FIELD ON THE REPRODUCTIVE FUNCTION OF ANIMALS

Kharkov Research Institute of Occupational Hygiene and Occupational Diseases

Despite the large number of studies devoted to the biological effects of electromagnetic radiation (EMR) at various frequencies on humans and animals [2, 6, 12], including its effects on reproductive processes [1, 4, 7, 11], the literature has given insufficient attention to the effects of low-frequency EMR. This is especially true of its effects on reproductive function [3].

In light of the above, we conducted experimental studies to investigate changes in the reproductive function of animals exposed to an electric field (EF) at a frequency of 5 kHz, widely used at coal industry enterprises. We determined the sensitivity of the reproductive system of albino rats exposed to low-frequency electric fields (LFEF) of different strengths (10,000, 4,000, and 1,000 V/m).

The experiments were conducted on 676 sexually mature albino rats (404 females and 272 males), including 324 pregnant females; in addition, 1,605 embryos obtained from them were analyzed. The animals were divided into two groups: an experimental group (399 rats) and a control group (277 rats). Animals in the first group were housed in dielectric Plexiglas cages (10 in each), with freedom of movement, and were acclimated to the experimental conditions for 7 days. The experimental rats were exposed continuously for 3 hours each day, corresponding to the average level of occupational EF exposure (according to time-and-motion observations). Control animals were subjected to “sham exposure.”

The LFEF source was a capacitor consisting of four duralumin plates measuring \(1 \times 1.5\) m, with distances of 20, 20, and 60 cm between them. The exposure system was powered by a broadcast amplifier and a G3-56/1 generator. The maximum field strength in the working volume of the system was 10,000 V/m. Field strength in the capacitor gap was monitored by measuring the voltage across the plates with a kilovoltmeter.

In males, we determined sperm motility time, total sperm count, testicular weight coefficients (an indicator of testicular atrophy), osmotic and acid resistance, and the presence of pathologically altered germ cells [10]; in females, the state of the estrous cycle was determined by vaginal smears [5].

To determine the ability of animals of both sexes to reproduce, at each experimental time point (3 and 6 months of exposure and 2 months after exposure), intact rats were cross-mated with exposed rats at a ratio of one male to three females. We studied the fertilizing capacity of males, the ability of females to conceive, and their fertility. After mating, embryonic material was examined on day 20 of pregnancy: the numbers of corpora lutea of pregnancy in the ovaries, live, dead, and resorbed embryos (those that had died at early stages of development), and implantation sites were counted…

…tions. The percentages of preimplantation, postimplantation, and total embryonic mortality were calculated. Fetal and placental weights and crown–rump lengths were also recorded [9]. The experimental data were analyzed statistically on an M-6000 computer using Student’s significance test.

The results demonstrated a damaging effect of the low-frequency electric field on reproductive processes in exposed animals, depending on field strength, exposure duration, and the sex of the animals.

In the exposed males, certain changes in sperm functional status were observed: osmotic resistance decreased to \(1.87\pm0.03\%\) NaCl by the end of exposure (10,000 and 4,000 V/m) and to \(1.78\pm0.05\%\) NaCl 2 months after exposure ceased (10,000 V/m), compared with \(2.08\pm0.05\%\) NaCl in controls. The relative testicular weight also decreased during the post-exposure period following exposure to fields of 10,000 and 4,000 V/m, to \(7.7\pm0.3\) and \(6.8\pm0.2\) g/kg, respectively, compared with \(8.8\pm0.4\) g/kg in controls.*

The observed changes did not permit a definitive assessment of the males’ fertilizing capacity or the viability of their offspring. Accordingly, after 3 and 6 months of exposure and after 2 months of post-exposure observation, exposed males were mated with intact females. The males’ fertilizing capacity was found to be preserved at the indicated times. However, a statistically significant reduction in the number of offspring was observed in healthy females mated with exposed males (10,000 V/m). The number of live embryos per female was \(6.5\pm0.5\) at the end of exposure and \(4.2\pm0.95\) during the post-exposure period, compared with \(8.8\pm1.1\) and \(7.0\pm1.11\), respectively, in controls. This was accompanied by an increase in total embryonic mortality (\(64.0\pm8.6\) versus \(43.2\pm9.2\) in controls), attributable to preimplantation mortality. Similar but less pronounced changes in the measured parameters were observed in animals exposed to a 4,000 V/m electric field. No changes in male reproductive capacity were detected at a field strength of 1,000 V/m, which occurs under workplace conditions.

External examination of fetuses from females mated with the experimental males revealed a small number of embryos with hematomas at various sites at all observation periods (\(20\pm0.95\) in the experimental group; none in controls), but no developmental abnormalities were observed.

Thus, these data indicate that the male gonads are sensitive to low-frequency electric-field exposure.

No changes in indicators of female gonadal function were detected either during exposure or in the post-exposure period at the specified field parameters: the mean duration of the estrous cycle and the number of cycles per female per month remained within the range of physiological variation.

In studying the reproductive function of experimental females chronically exposed to the electric field and mated with intact males, their ability to conceive and their fertility were assessed. The fields studied did not suppress the ability to conceive. However, after 3 months of exposure to a 10,000 V/m field, the number of live embryos per female was \(7.3\pm1.3\), compared with \(10.0\pm1.0\) in controls; when exposure was extended to 6 months, it was \(4.3\pm1.4\), compared with \(8.8\pm1.1\) in controls. The number of corpora lutea of pregnancy in the ovaries of experimental females was virtually indistinguishable from that in controls. The reduction in fertility can therefore apparently be attributed to increased total embryonic mortality (\(63.8\pm10.2\%\) versus \(43.0\pm9.2\%\) in controls). The most pronounced changes in the exposed females’ ability to reproduce were observed during the post-exposure period: the number of live embryos per female fell to \(1.3\pm0.83\), and the number of implantation sites to \(2.0\pm0.83\), compared with \(8.6\pm1.1\) and \(9.3\pm1.1\), respectively, in controls. Total intrauterine mortality rose to \(85.5\%\), owing to preimplantation mortality (\(67.0\%\)). These changes apparently reflect impaired ovarian reproductive function [8].

Placental and embryonic development, as assessed by weight and crown–rump length, in exposed females did not differ from that in the control group.

The deviations observed in the reproductive-function measures studied in females exposed to a 4,000 V/m electric field followed the same pattern but were less pronounced. A field of 1,000 V/m had no effect on the fertility of exposed animals throughout the experiment.

Thus, the results established for the first time an adverse effect of a low-frequency electric field (5 kHz) on reproductive processes in animals and demonstrated the need to study generative function as one of the most sensitive methods in setting hygiene standards for electromagnetic radiation.

* Only statistically significant values are reported. Changes were considered significant at \(p<0.05\).

References

1. Bereznitskaya A. N., Kazbekov M. I., Rysina T. Z. In: Occupational Hygiene and the Biological Effects of Radiofrequency Electromagnetic Waves. Moscow, 1972. pp. 36–36.
2. Davydov B. I., Karpov V. N. Kosmicheskaya biologiya. 1982. No. 5. pp. 18–23.
3. Dumanskii Yu. D., Andrienko L. G. Gigiena i sanitariya. 1982. No. 7. pp. 27–30.
4. Dyshlovoi V. D., Kachura V. S., Panchuk A. S., et al. In: Protection of Humans from Certain Physical Environmental Factors. Kiev, 1977. pp. 10–11.
5. Kabak Ya. M. Practical Exercises in Endocrinology. Moscow, 1968.
6. Kalyada T. V. In: Protection of Humans from Certain Physical Environmental Factors. Kiev, 1977. pp. 22–23.
7. Lobanova E. A., Sokolova I. P., et al. Gigiena truda. 1983. No. 1. pp. 30–35.
8. Makotchenko V. M., Sonkin I. S., Tsyukhno Z. I. The Endocrine System in Occupational Diseases. Kiev, 1985.
9. Experimental Methods for Establishing Thresholds for the Effects of Industrial Poisons on Generative Function for Hygiene Standard-Setting: Methodological Recommendations. Sanotskii I. V., Fomenko V. N., Salnikova L. S., et al. Moscow, 1978.
10. Milovanov V. P. Methods of Operation of Artificial Insemination Stations for Farm Animals. Moscow, 1966.
11. Shandala M. G., Dumanskii Yu. D., Tomashevskaya L. A., et al. Gigiena i sanitariya. 1985. No. 4. pp. 11–13.
12. Narayan P. V., Subrahmanyam S., Satyanarayana M., et al. Current Science (India). 1984. Vol. 53, No. 18. pp. 959–965.

Received December 29, 1986.