Abstract
A clinical study was performed in seven patients with insulinoma in order to clarify the correlation between the morphological character of the tumors and the biochemical nature of insulin in the plasma or tumors. “Insulin releasability” of each tumor was estimated on the basis of the numbers of the beta-cells and the capillaries in the tumor tissue. The beta-cells of the tumors were classified into three groups by ultrastructural findings: typical, atypical and mixed types. Four tumors showed typical beta-granules, while the atypical granules were observed in two tumors and the mixed in one tumor. The “insulin releasability” was greater in tumors with the atypical or mixed granules than those with typical granules. An increased response of plasma insulin to tolbutamide or glucagon was observed in tumors with the atypical or mixed granules. However, there were no correlations between the granule types and the insulin response to glucose or arginine. The levels of fasting blood glucose and plasma insulin or the ratio of insulin to blood glucose were correlated with the development of the Golgi apparatus and the granular endoplsmic reticulum. The percentage of “big insulin” was higher in the tumors with atypical granules than those with typical granules. Insulin extracted from the tumors with typical granules rendered a higher immunoreactivity for biological activity compared with that from tumors with atypical granules.
It is concluded that some relationships were observed between the biochemical nature of insulin and the morphological findings of insulinomas. Furthermore, this study also presented various suggestions in the mechanism of insulin secretion.
