اثرات ميدان هاي مغناطيسي ثابت كوتاه مدت و بلند مدت بر محور هيپوتالاموس- هيپوفيز- تيروئيد در موشهاي صحرايي نر

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

Objectives: The aim of this study was to evaluate the effects of static magnetic fields (SMF) on hypothalamic-pituitary-thyroid (HPT) hormonal disturbances. Materials and Methods: 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 -20°C until use. TSH and thyroid hormones were measured by IRMA and RIA methods using y-counter equipment. The results were analyzed by ANOVA statistical method, followed by Tukey posthoc test. Results: 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. Conclusion: 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).