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Abstract
With the progressive development of the electrical industry, there has been a surge of interest concerning the possible harmful biological effects of the extremely low frequency EMFs with a frequency of 50-60 Hz on the human body. This interest was associated with the phenomenal growth of the use of man-made sources of ELF-EMFs from home electric appliances to the high-power transmission lines, electric grounding systems at work places. Many researchers suggested that environmental exposure to ELF-EMFs potentially affect the cell function in different ways such as chromosomal damage and interference with DNA synthesis and RNA transcription. Exposure to EMFs also has potentially deleterious effects on the proliferating and differentiating embryonic cells causing delayed differentiation, delayed mitotic activities, and inhibition of cell migration. Animal studies can be very helpful in determining the mechanisms of teratogenesis.
The aim of the present study was to evaluate of the effects of prenatal exposure of pregnant albino rats to low frequency electric and magnetic fields during the early (from day 6 to day 10 of gestation) and late (from day 11 to day 15 of gestation) periods of embryogenesis on the growth and development of 16, 18 and 20-day albino rat fetuses and on the structure of the placenta.
Once pregnancy was confirmed, animals were randomly assigned to 9 groups 8 dams for each:
Seventy-two pregnant albino rats were used throughout this study. They were classified into 3 age groups: 16, 18 and 20-day of gestation. Each age group was subdivided into 3 groups: (1) control group, (2) early exposed group were exposed to 50 Hz magnetic field of intensity 1.5G and a strong electric field of intensity 10KV/m (The exposure was started from the gestational day 6 through day10) and (3) late exposed group (were exposed to 50 Hz magnetic field of intensity 1.5G and a strong electric field of intensity 10KV/m. The exposure was started from the gestational day 11 through day15).
The field of exposure was designed in Biophysics laboratory, physics department, faculty of science. The field consisted of sources for magnetic and electric fields. The source of magnetic field was Helmholtz coils. The source of electric field was two plates between which the required potential difference. The exposure system was supplied by an additional cooling system (to avoid any thermal effect) consisting of tube of continuos (in-out) water current connected to the tap.
The pregnant rats were sacrificed at 9 o’ clock on gestational days 16, 18 and 20 by ether. All placentas were examined and their weights were recorded. General fetal morphology was observed and recorded including head size and shape, orofacial development, limb development, abdomen, umbilicus and external genitalia. Approximately half of the fetuses were fixed in Bouin’s solution for external and visceral examination. The other half were preserved in 95% alcohol for skeletal staining using Alizarin red stain. The 16 days fetuses were stained with the double stain (alcian blue & alizarin red) instead of alizarin red stain for skeletal assessment.
Fetuses were evaluated through anthropometric measurements including fetal weight, placental weight, Crown-rump length (CRL), Head length (HL), bipareital diameter (BPD), Chest and abdomen circumferences and the length of ossified parts of long bone.
Samples of Placentae including the abnormal ones selected from each group were thoroughly examined histologically through light microscopy using hematoxylin and eosin stains (H&E).
In the present study it was observed that during EMFs exposure the pregnant albino rats showed abnormal behavioral changes such as increased the aggressiveness behavior toward themselves, toward other animals and toward the surroundings and irritability either in early or late exposure groups.
The present study showed that exposure of pregnant rats to 50 Hz EMFs either in early or late periods of embryogenesis cause increased resorptions and intrauterine growth retardation indicated by decreased growth parameters in all age groups. Also the exposure to EMFs in early period of embryogenesis decreased all fetal growth parameters more than the exposure in the late period.
The present study also indicated that 50 Hz EMFs exposure decreased the fetal bone development either in the early or late period of embryogenesis. Some of the craniofacial bones were significantly affected in early exposed groups more than late exposed groups. Also the coxal bones (ilium, ischium and pubis), metacarpal and metatarsal bones and the vertebral column development was more delayed in early than late exposed groups.
The present study showed that prenatal exposure to low frequency EMFs cause external fetal malformations such as macerated skin, subcutaneous hematomas, forelimb and hindlimb deformities, abnormal head shape, head swelling and umbilical hernias. These abnormalities were more obvious in early exposed groups than late exposed groups, in all age groups. Craniofacial abnormalities presented only in 16 and 18-day early exposed fetuses.
Also EMFs exposure in the present study increased the incidence of internal fetal abnormalities such as internal hemorrhage in the thoracic and head regions, dilated brain ventricles and unilateral renal agenesis in early exposed groups more than late exposed groups. Also brain and kidney abnormalities presented only in the 18-day exposed groups
It was observed in the present study that bone, blood, skin, kidney and nervous system were the most sensitive systems in developing albino rat fetuses to 50 Hz EMFs exposure either in the early period (6-10 day p.c) or the late period (11-15 day p.c) of organogenesis.
In the present study, the exposure in the early period of embryogenesis lead to a marked decrease in placental weight and umbilical cord length when compared with the exposure in the late period in all gestational age.
Also both early and late exposed group placentae showed abnormalities and significant changes in the thickness of their layers. It was obvious that early period of exposure affected some layers of placenta more than the late exposure. But it seems that most critical period of exposure that affect the decidual layer of placenta was the late period of embryogenesis.
It was obvious in the present study EMFs early and late exposure lead to vasoconstriction either in the fetal or maternal blood vessels but there was no change in the thickness of their walls. Also EMFs exposure in both periods of embryogenesis decrease the maturation of the RBCs.