Studies with mouse pituitary thyrotropic tumors. IV. Presence of 3,5,3'-triiodothyronine in certain mouse pituitary tumors after the injection of labeled L-thyroxine.

Abstract

Labeled 3,5,3′-triiodothyronine (T3*) has been found in large amounts in transplanted dependent and autonomous thyrotropic mouse pituitary tumors, at various time intervals after the intraperitoneal injection of labeled L-thyroxine (T4*). No T3* was identified in serum, in an adrenotropic mouse pituitary tumor, in a fibrosarcoma arising spontaneously in the same strain of mice, in a breast carcinoma in Swiss mice, or in kidney or muscle tissues. The evidence suggests that the presence of T3* probably is due to the deiodination of T4* in the tumor cells. The data raise the possibility that specific thyrotropin-secreting cells may exist in the pituitary and that these cells may metabolize T4* to uniquely large amounts of T3*. It is further suggested that T3* formation may be related to the control of thyrotropin secretion. However, the finding does not appear to relate to the question of autonomy or dependency since, in all the thyrotropic tumor strains, T3* was present in similarly large amounts.