Effects of different durations and intensities exposure of static magnetic fields on the hypothalamic-pituitary-thyroid axis in the male rats

The aim of this study was to evaluate the effects of static magnetic fields (SMF) on hypothalamic-pituitary-thyroid (HPT) hormonal disturbances. One hundred and ninety two male rats were divided into four experimental protocols. Each experimental protocol consisted of four groups and each group contained 12 rats. After one-week adaptation, rats were exposed to SMF (0, 6, 12 and 24 mT, at 50 Hz) for 40 or 120 minutes daily (at 9 a.m.) for 17 or 34 days. At the end of each experiment, the animals were anaesthetized; blood sera were collected and kept frozen under -200C until use. TSH and thyroid hormones were measured by IRMA and RIA methods using -counter equipment. The results were analyzed by ANOVA statistical method, followed by Tukey posthoc test.No change was observed in TSH and thyroid hormones following exposure to SMF of 40 min/day for 17 days. TSH at many SMFs protocols, exposed or sham-exposed animals have not affected, except those rats exposed to 24 mT (120 min/day for 34 days) which was higher than other groups with same protocol (P<0.05), also T3 resin uptake significantly has decreased. There were statistically significant increased in serum free thyroxine index and total thyroxine values at 12 and 24 mT (40 min/day for 34 days) compared with other groups (P<0.01 and P<0.001 respectivel). Serum free thyroxine index and total thyroxin values at 24 mT (120 min /day for 17 days) was significantly lower compare to sham-exposed animals (P<0.05), however TSH and free thyroxin levels did not change significantly (P>0.05) using this SMFs. SMF, with low duration (17 days) and short time exposure (40 min/day) can not alter HPT hormonal axis secretion in male rats. But it can enhances HPT axis disorders with increasing duration (34 days) and long time exposure (120 min/day)