The effect of iodothyronines on the conversion of thyroxine into 3,3'-5-tri-iodothyronine in isolated rat renal tubules.

Isolated rat renal tubules prepared by collagenase digestion were used to study the effects of 3,3',5'-tri-iodothyronine ('reverse T3', rT3) and other iodothyronines on the formation of 3,3',5-tri-iodothyronine (T3) from thyroxine (T4). rT3 inhibited the conversion with a dose response over the concentration range 1.5nM-1.5microM. The inhibition was competitive in nature. Both 3,3'-di-iodothyronine and 3',5'-di-iodothyronine also inhibited the production of T3 and T4 in isolated rat renal tubules, but tetraiodothyroacetic acid and 3,5-di-iodothyronine were found to have no effect. These experiments demonstrate in an intact cell system that some naturally occurring iodothyronines have significant effects on T4 deiodination.