Localization of Thyroxine 5′-Monodeiodinase Activity in the Renal Proximal Tubules in Rabbits and Rats

Summary

To determine the localization of T₄ 5′-monodeiodinase activity in rabbit and rat nephron segments, the formation of tri-iodothyronine (T₃ ) from thyroxine (T₄) was measured in kidney homogenate and in isolated nephron segments obtained by the microdissection method. In order of decreasing activity, homogenates of rabbit renal cortex, outer medulla and inner medulla were capable of converting T₄ to T₃. In the isolated nephron segments of the rabbit cortex, the activities were noted in both proximal convoluted and proximal straight tubules. On the other hand, the activities were not detected in segments including the cortical thick ascending limb of Henle's loop, the distal convoluted tubule, the connecting tubule, and the cortical collecting tubule. It is concluded that both the convoluted and the straight tubules are the sites of T₃ production in the kidney.

Key-Words:

Thyroxine - 3,5,3′-Triiodothyronine - Renal Tubules