CYTOLOGIC ALTERATIONS IN THE ANTERIOR PITUITARY GLAND FOLLOWING THYROIDECTOMY: AN ELECTRON MICROSCOPE STUDY1

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Abstract
Thin sections of the anterior pituitary gland of thyroidectomized and control male rats were examined with the electron microscope. Examination of early thyroidec-tomy changes established definitive morphologic criteria which allowed recognition of the unstimulated thyrotropic cell in the normal animal. The thyrotrope is seen to be angular and to contain fine, ill defined secretory granules. It is usually not located directly on a sinusoid. These features of the thyrotrope are contrasted with those of the gonadotrope which is more rounded, contains larger, denser granules and is typically located on a sinusoid. Both cell types exhibit rounded nuclei with 1 or 2 nucleoli and show variable numbers of ovoid vesicles in the cytoplasm in addition to the usual cytoplasmic constituents. Following thyroidectomy, changes are seen to occur in the fine structure of the thyrotrope which further distinguish them from normal gonadotropes and gonadotropes stimulated by castration. Thyroidectomy basophils are ordinarily grouped together and contain larger vesicles at earlier periods following operation. Thyroidectomy cells contain few or no secretory granules and those present are small and ill defined. As early as 10 days following thyroidectomy, uniformly dense ovoid or rounded bodies are found within cytoplasmic vesicles. These bodies increase in size and number as the period following operation increases. Castration basophlls show no tendency for grouping, contain more uniform vesicles for a given period following operation and always contain well defined secretory granules. The dense rounded bodies characteristically seen in the vesicles of thyroldectomy cells are not found in castration cells.