Common clinical indices of thyroid hormone action: relationships to serum free 3,5,3'-triiodothyronine concentration and estimated nuclear occupancy.

Abstract

ABSTRACT. In an attempt to develop a model relating several clinical indices of thyroid hormone action to serum free T3 concentration and the estimated occupancy of nuclear T3 receptors, we have performed serial studies in 19 patients with hyperthyroidism and 16 patients with hypothyroidism both before and after the initiation of standard treatment. With increasing serum free T3 concentrations, we observed gradual increases in mean heart rate and sleeping heart rate, reaching, respectively, mean plateau values of 109 and 99 beats/min. As expected, with increasing serum T3 concentrations, a hyperbolic fall in serum cholesterol, serum creatine phosphokinase activity (CPK), and Achilles tendon reflex relaxation time (ATRT) was noted. Nuclear occupancy was calculated from the plasma T3 concentration and the physicochemical characteristics of human nuclear receptor sites, as determined in other studies. Nuclear T3 occupancy was found to be linearly related to mean heart rate (r = 0.81) and to sleeping heart ra...