Studies with Mouse Pituitary Thyrotropic Tumors. X. Formationin Vitroof 3,5,3'-Triiodothyronine from Thyroxine by Dependent but Not Autonomous Strains

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Abstract
Labeled 3, 5, 3[image]-triiodothyronine (T3 ) has been found in appreciable amounts in slices of transplanted dependent mouse pituitary thyrotropic tumors incubated in vitro with labeled thyroxine (T4 ). On the average, T3 constituted 18% of the total radioactivity in the tissue, whereas a maximum of 4% of the radioactivity was present as T3 in slices from a closely related autonomous strain. Tumor T3 concentrations in vivo after parenteral T4 administration, however, are high for both strains. Slices from control tumors and tissues including boiled responsive tumor, incubated under the same conditions, contained 1-4% of the radioactivity as T3 . The difference in metabolic behavior in vitro between dependent and autonomous tumors may have a possible relationship to the mechanism of autonomy.