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

Abstract

The present study was undertaken to investigate the peripheral iodothyronine 5′-monodeiodination in different human and rat tissues. We studied iodothyronine 5′-monodeiodinase type I (5′-DI) activity in liver, kidney, intestine, right cardiac atrium and skeletal muscle and we compared the results with those in rat tissues. Iodothyronine 5′- monodeiodinase type II (5′-DII) activity was studied in normal and ischemic human heart and in rat normal myocardium 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 in human. However, no significant differences were observed in 5′-DI activity between normal and tumoral human intestine or between intestinal tissue of man and rat. 5′-DI activity in normal human skeletal muscle was significantly higher than that in rat skeletal muscle (p<0.05). The 5′-DI activity was lower in human ischemic myocardium when compared to normal myocardium either 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 activity 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 decreased in tumoral tissues of human liver and kidney and in ischemic myocardium, while no significant difference was found between human and rat cardiac 5′-DII activity.