A study of iodothyronine 5 '-monodeiodinase activities in normal and pathological tissues in man and their comparison with activities in rat tissues

The present study was undertaken to investigate the peripheral iodothyronin e 5'-monodeiodination in different human and rat tissues. We studied iodoth yronine 5'-monodeiodinase type I (5'-DI) activity in liver, kidney, intesti ne, right cardiac atrium and skeletal muscle and we compared the results wi th those in rat tissues. Iodothyronine 5'- monodeiodinase type II (5'-DII) activity was studied in normal and ischemic human heart and in rat normal m yocardium and brain. The 5'-DI activity (fmol/min.mg protein) in liver and kidney was significantly higher (p<0.001,ANOVA) in normal rat tissue than i n human. However, no significant differences were observed in 5'-DI activit y between normal and tumoral human intestine or between intestinal tissue o f man and rat. 5'-DI activity in normal human skeletal muscle was significa ntly higher than that in rat skeletal muscle (p<0.05). The 5'-DI activity w as lower in human ischemic myocardium when compared to normal myocardium ei ther in humans (p<0.05) or rat (p<0.001). The Km of 5'-DI was significantly lower in rat than in human kidney and liver (p<0.05). We conclude that 1) 5'-DI is distributed widely among extrathyroidal human and rat tissues and 5'-DII activity is detectable both in human and rat heart; 2) 5'-DI activit y in liver and kidney is lower in man than in rat; 3) 5'-DI activity in the skeletal muscle is higher in man than in the rat; 4) 5'-DI activity is dec reased in tumoral tissues of human liver and kidney and in ischemic myocard ium, while no significant difference was found between human and rat cardia c 5'-DII activity. (C) 2000 Elsevier Science Inc. All rights reserved.