Immunohistochemical and ultrastructural studies on rat islet cell tumours induced by streptozotocin and nicotinamide

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Abstract
Summary Fourteen rat islet tumours induced by Streptozotocin and nicotinamide were examined by light microscopy with indirect immunoperoxidase staining and by electron microscopy. Most tumours consisted predominantly of B cells, but over a half of the tumours examined showed mixed cellularity with considerable numbers of A cells and small numbers of D or PP cells. Only 4 tumours consisted exclusively of B cells. There was no positive reaction for any kind of specific islet hormone antibodies in 2 tumours. Ultrastructurally, most tumours were composed of cells containing numerous secretory granules with B cell properties, with great variation in size, shape and number. We often encountered enterochromaffin-like cells or atypical granular cells or cells containing non-beta secretory granules. We could not identify, however, the ultrastructural counterparts of A or D cells. The results suggested that the multiplicity of the endocrine cells of rat islet cell tumours might be an expression of the cellular dedifferentiation of tumour cells which could re-differentiate into the whole range of components of the endocrine pancreas.