Diisopropanolnitrosamine (DIPN) induced rat thyroid lesions. II. An electron microscopic study.

An ultrastructural study was carried out on DIPN induced lesions of rat thyroid glands, in order to characterize in detail each type or subtype as classified by light microscopy in our previous report. Organelles closely related to the endocrine function of the thyroid epithelium such as apical or subapical vesicles, lysosomal granules, colloid droplets, Golgi apparatus, rER, and microvilli on the apical surface, were found to decrease in parallel with structural and cellular atypism of the thyroid lesion under examination, suggesting impairment of their function in the malignant lesions. On the other hand, observations of transitional forms among the lesions in term of the subcellular structure were considered to support the possibility that transformation from one type to another could occur.