CHANGES IN LIPID PEROXIDE LEVELS AND THE ACTIVITY OF REACTIVE OXYGEN SCAVENGING SYSTEMS IN THYROID-TISSUE AFTER EXPOSURE TO RADIOACTIVE IODINE IN RATS

Exposure to ionizing radiation causes radiolysis of water in tissues l eading to generation of reactive oxygen species (ROS), which are known to affect the antioxidant defense systems and induce lipid peroxidati on (LP). Use of radioactive iodine (I-131) for diagnosis and therapy o f thyroid disorders may also generate ROS in the thyroid. Early (24 an d 48 hours) and late (18 days) effects of subablation doses of I-131 ( 370/555/1110 kBq) on the antioxidant defense and LP in the thyroid tis sues have been studied. LP was elevated in all I-131 treated groups by 10% to 41%. Although there was no change in catalase (CAT), the super oxide dismutase (SOD) and glutathione peroxidase (GPx) activities show ed evidence of change from 48 hours onwards-SOD decreased by 32% to 56 % and GPx increased by 15% to 43%. Nonprotein thiols (reduced glutathi one, GSH) showed an elevation of 16% at 24 hours, but later declined b y 15% by day 18 after 370 KBq of I-131. Thus, the increase in LP obser ved may be due to beta irradiation induced ROS by I-131. The parallel decrease in SOD could be due to inactivation by ROS. The increase in G Px may be a consequence of induction due to elevated LP and/or ROS, wh ich may be inadequate to lower the LP. In spite of elevated LP, the th yroid function appears to be normal.