THE PHYSIOLOGICAL DISPOSITION IN THE RAT OF THE ACETIC AND PROPIONIC ACID ANALOGUES OF THYROXINE AND TRIIODOTHYRONINE1

Abstract

The distribution and excretion in the rat of tetraiodothyroacetic acid and tetraiodothyropropionic acid were compared with that of L-thyroxinc; in addition, the distribution and excretion of 3,5,3′-triiodothyroacetic acid and 3,5,3′-triiodothyropropionic acid were compared with that of 3,5,3′L-triiodo-thyronine. Thyroxine and triiodothyronine disappeared from the blood more rapidly and were concentrated in the peripheral tissues to a greater extent than were their respective acetic- and propionic-acid analogues. The ratio of concentration in tissue to the concentration in plasma was lower with those analogues than with the parent compounds in all tissues examined and at all time intervals studied. The differences observed were of such magnitude as to suggest a possible basis for the diminished physiological potency of the acetic and propionic acid analogues in the rat.