Dynamic hormonal changes in the thyroid axis following acute irradiation of rats with different gamma rays doses

Male sexually mature Wistar rats were exposed to gamma-radiation from cesium source Igur-1 with emissive power 1,26 Gy/min. Dose of 0,5, 1,0, 2,0 and 4,0 Gy were applied. Ten aminals from each irradiation dose (total 40 for all doses) were killed by blood letting and the content of the thyroid axis hormones TSH, T3 and T4 was determined by radioimmunoassay. The normal levels of these hormones were determined in 10 animals. It was found that the content of TSH, T3 and T4 was altered as early as the first few post-irradiation days: T3 and T4 incretion by the tyhroid was inhibited, while TSH produced by the anterior hypophysis was essentially increased in the first 5 or 6 days. After the sixth and especially after the twelfth day there occurred total hypothyroidism of central and peripheral nature; the effect was strongest on TSH and T4 and to a lesser degree on T3. The changes in the plasma content of thyroid axis hormones were influenced by the irradiation dose: hypothyroidism was most pronounced with the use of the highest irradiation doses of 2,0 and 4,0 Gy