The Application of anin VitroPerfused Liver Preparation to Examine the Effects of Epinephrine and Bovine Thyroid-Stimulating Hormone on Triiodo-l-thyronine Release from the Liver of Rainbow Trout (Oncorhynchus mykiss)

Abstract

An isolated, perfused rainbow trout liver preparation was developed to investigate the action of nonthyroidal hormones on hepatic thyroid hormone metabolism. Several assessments were made of the stability and viability of the preparations under a range of conditions, including measures of lactate dehydrogenase flux and tissue ATP and glycogen content, all of which indicated that the perfused liver was stable for the 60-min perfusion period. Moreover, the liver preparations were responsive to an epinephrine challenge and, throughout the series of experiments, sustained hepatic glucose release. Triiodo-l-thyronine (T3) flux from the liver preparation was significantly increased by the provision of thyroxine (T4) substrate. Epinephrine and bovine thyroid stimulating hormone (TSH) were perfused alone and in combination with T4to evaluate the effect of these hormones on T3flux from the liver. Both epinephrine and TSH significantly enhanced hepatic T3flux in the absence of T3substrate, but neither had an additional effect on T3flux when perfused in combination with T4. The results of the study suggest that a relationship exists between the circulating levels of nonthyroid hormones and peripheral thyroid hormone metabolism that may be receptor-mediated.