Studies on Thyroid Immunity. VIII Biliary Clearance 1 of Thyroxine in Thyroglobulin Immunized Rats 2

Abstract

Summary

Biliary clearance of radiothy-roxine (¹³¹I-T₄) and its whole body half-time (T _1/2) were determined in rats with actively induced thyroglobulin immunity, as well as in albumin immunized and saline injected controls. Biliary clearance in thyroglobulin immunized rats (0.26 ml/hr) was decreased four-fold in comparison to controls (1.04-1.07 ml/hr), and thin layer chromatography of radioactivity secreted in the bile showed no differences between animals. The decrease in biliary clearance in thyroglobulin immunized rats was seen coexistent with markedly reduced disappearance of ¹³¹I-T₄ tracer as determined by whole body half-time measurements (T_1/2 in thyroglobulin immunized rats = 80.8 hr vs. T_1/2 of 19 hr in controls). The percent of total thyroxine that was dialyzable in thyroglobulin immunized animals (0.016) was reduced ~three-fold in comparison to control rats (0.052). The primacy of effects of plasma binding of thyroid hormone relative to its biliary clearance was further shown in passive transfer experiments where T₄ antibody-containing antithyroglobulin serum when injected into normal rats reduced biliary clearance of T₄ to half that noted in controls. On the other hand injection of thyroglobulin alone in normal rats dramatically accelerated biliary clearance of T₄ (over 400% increase in comparison to the control value of 1.05 ml/hr). The significance of these findings is briefly elaborated.