Studies with mouse pituitary thyrotropic tumors. Viii. 'inclusions' In liver and tumor cell nuclei of mice bearing somatotropic variants.

Somatotropic variants of mouse pituitary thyrotropic tumor strains have been induced by prolonged suppression of implants of the parent tumor through thyroid hormone feeding. Markedly enlarged livers developed in host mice implanted with these variant tumors. Histologically, there were unique changes in the nuclei of such liver cells, suggesting inclusion bodies. Similar ““inclusions” were present in the tumor cell nuclei. Electron microscopic examination suggested that the hepatic and tumor “inclusions” might be infoldings of the cell cytoplasm into the nuclei. The changes in the liver cell nuclei were shown to be hormonally dependent, since they appeared only after the tumor implant was well established and disappeared subsequent to surgical removal of the tumor. The question of viral origin of the nuclear changes was raised by the presence of particles within vacuoles in the cytoplasm of the tumor cells, suggesting virus particles. (Endocrinology 75: 66, 1964)