SPECIFIC NUCLEAR TRIIODOTHYRONINE BINDING SITES IN RAT LIVER AND KIDNEY¹

Injection of increasing quantities of L-triiodothyronine (T3) resulted in a progressive decrease in the proportion of T3 bound to the nuclear fraction of rat liver and kidney cells. A similar dose-response relationship could not be demonstrated for other ultracentrifugal fractions. Only a modest reduction in nuclear binding of thyroxine was observed after injection of large amounts of this iodothyronine. The results indicate the presence of relatively specific binding sites for T3 in the nuclei of rat liver and kidney.