Effect of furosemide on radioiodine-131 retention in mice thyroid gland

Retention of iodine in the thyroid gland is the result of renal excretion and transport of iodine to thyroid cells. Both processes are affected by furosemide. The aim of our study was to test whether furosemide influenced radioiodine-131 ((131)I) retention in the thyroid gland of living mice. Our methods were as follows: After 15 days of low-iodine diet, 19 Swiss mice received an intra-peritoneal injection of 0.37+/-0.03 MBq of (131)I. Thereafter, 11 mice were treated with intraperitoneal injections of furosemide (0.3 mg/kg, every 8 h, for 72 h), Group A and 8 mice served as controls, Group B. Seventy-two hours after (131)I administration, the mice were anaesthetized, their thyroids were carefully extirpated, and their radioactivity was measured by a gamma counter. Our results showed that the mean value of (131)I retention after 72 h was 63.09% in Group A and 82.25% in Group B. The difference between these two groups was significant (T=3.0919, P=0.0033). In conclusion, furosemide after the administration of (131)I, decreases retention of (131)I in the thyroid gland in mice. The well known increase of iodine renal excretion by furosemide and consequently decrease of iodine blood pool may be the reason for this decreased (131)I retention by the thyroid gland.