Immunohistochemical and electron microscope studies of rat islets of Langerhans one month after adult thymectomy.

Ultrastructural and quantitative immunocytochemical studies of rat pancreata were carried out 1 month after adult thymectomy. The proportions of insulin-, glucagon-, and somatostatin-immunoreactive cells in the pancreas were estimated on paraffin sections using the unlabelled peroxidase-antiperoxidase method. Relative islet volume, islet size and number were determined on hematoxylin and eosin stained sections. A moderate increase of the islet volume on account of size was found in the pancreas of the thymectomized rats. The proportion of insulin-immunoreactive cells was also elevated. Ultrastructural studies showed a rich supply of secretory granules in most beta-cells. Mixed beta-endocrine-acinar cells were often observed. Mitotic figures were found in single beta-cells. The blood glucose level was in the normal range. The findings suggest a moderate stimulation of beta-cell secretory activity after thymectomy which is not associated with elevated blood glucose levels.