EARLY LESIONS OF PANCREATIC-ISLETS IN SMALL-OB MICE (C57BL/6J-OB/OB)

Pancreatic islets of C57BL/6j-ob mice were microscopically examined at the ages of 5,13, and 21 days, to clarify the time of the increase in number of A-cells, which appears to lead to diabetic symptoms in Small-ob mice (C57BL/6j-ob/ob). The findings of islet in 5-day-old C57BL/6J-ob mice were the same as those of C57BL/6j-+/+ mice. At 13 days of age, changes in islet of C57BL/6j-ob mice were classified into 3 groups. They were no significant changes (putative normal), hypertrophic B-cells with clear cytoplasm (Ob mice), and an increase of A-cells (Small-ob mice), respectively. Electron microscopically, a tendency toward dilatation of endoplasmic reticulum was found in the hypertrophic B-cells. In the islets that had an increase in number of A-cells, only a few vacuoles, which were suggestive of degranulation, were found in the cytoplasm of B-cells, and premature secretory granules were seen in the A-cells. In part of the A-cells, development of rough-surfaced endoplasmic reticulum was also seen. Mild hypertrophy of the islets and the B-cells were observed in more non-diabetic Ob mice at the age of 21 days than non-obese mice at the same age, and only 2 of 6 mice had the increase in number of A-cells. In Small-ob mice, the increase in number of A-cells was more obvious than in the diabetic Ob mice, while other islet findings were similar to those of non-obese mice in extent. These observations disclosed that the changes in islet of Small-ob mice appear between 6 and 12 days of age.