EXPERIMENTAL THYROIDITIS IN THE GUINEA PIG. II. ELECTRON MICROSCOPY.

In a study of the cytochemistry of experimental thyroiditis in the guinea pig, changes were observed in the apical aspect, lysosomes, the Golgi apparatus and mitochondria of acinar cells.' The apical plasma membrane of acinar cells in animals with severe thyroiditis occasionally revealed adenosine triphosphatase (ATPase) activity, a feature never observed in controls. An increase in number and size of lysosomes was found in both TSH-stimulated thyroids and in glands with thyroiditis. These organelles were confined to the apical aspect of the cell in TSHstimulated glands and many more and larger lysosomes were scattered throughout the cytoplasm in the glands with thyroiditis. In TSH-stimulated and in glands the seat of inflammation, large complex Golgi bodies were noted. Many Golgi lamellae of acinar cells in severe thyroiditis were curled into small spherical bodies. Large granular clumps exhibiting DPNH-Nitro-BT reductase activity (?swollen, clumped mitochondria) were noted in acinar epithelium in animals with thyroiditis. An increased number of mitochondria appeared in TSH-stimulated acinar epithelium. Changes were not observed in the endoplasmic reticulum or the sinusoids. To facilitate interpretation of the cytochemical alterations, it was necessary to examine the preparations by electron microscopy. Examples of thyroiditis were compared with those reflecting TSH-stimulation, because the acini in these glands resembled each other superficially.