Triiodothyronine production by isolated rat hepatocytes: characterization and lack of glucoregulatory hormone effects.

Triiodothyronine (T3) production from thyroxine (T4) was studied in isolated rat hepatocytes. With an initial T4 concentration of 0.56 microM, hepatocyte T3 production was 0.029 +/- 0.003 (SEM) pmoles/min/mg protein. T3 production was greater in hepatocytes than in homogenates from the same liver prepared either before or after liver perfusion with collagenase. Most T3 produced remained within the cells under the conditions employed. Hepatocyte T3 production was dependent on cell number, medium bovine serum albumin concentration and temperature. It was stimulated by dithiothreitol, and inhibited by propylthiouracil, 3,3',5'-triiodothyronine and dinitrophenol; glutathione and ouabain had no effect. Alterations in medium glucose concentration and exposure to insulin or glucagon at several glucose concentrations in vitro did not alter T3 production. These results indicate that in hepatic tissue T3 production is enhanced when intact cellular organization is present and that insulin and glucagon do not acutely influence cell production of T3 in vitro.