Abstract
A transplantable thyrotropic pituitary tumor (TtT 97) in mice and its responsiveness to thyroxine were studied by electron microscopy.
The secretory granules in the tumor cells of the dependent variant were usually more abundant than those in the autonomous tumor cells. In a response to thyroxine, the secretory granules in the dependent tumor cells were initially increased but subsequently decreased in number. In the autonomous tumor cells, no changes were observed after thyroxine treatment.
A few cells containing larger secretory granules were incidentally found in the dependent variant which showed a marked gonadotropic activity. It is therefore suggested that the thyrotropic pituitary tumor of mice might be another example of a mixed tumor, leaving many questions to be answered.
