Efflux of T-4 from the in situ perfused liver of rainbow trout: effect of T-4, dithiothreitol and cysteine in the perfusate

A Cortland saline-perfused rainbow trout (Oncorhynchus mykiss) liver model was used to study aspects of T-4 efflux from the intact organ system. There was a consistent efflux of T-4 in the absence of T-4 in the perfusate, and the T-4 efflux was increased in the presence of T-4 in the perfusate, but the efflux was not T-4-dose dependent. The addition of the thiol-containing compound dithiothreitol (DTT, 2 mM) to the perfusate had no significant ef fect on the flux of T-4 from the liver, whereas the addition of cysteine (2 mM), a thiol-containing amino acid suppressed T-4 efflux. The results are consistent with the known mechanisms of thyroid hormone trafficking across cell membranes, and suggest that organ systems, such as the liver, may act as a major reserve of hormone, thus participating in plasma thyroid hormone homeostasis. (C) 1999 Elsevier Science Inc. All rights reserved.