Lysosomes and pancreatic islet function: adaptation of beta-cell lysosomes to various metabolic demands.

The effect of various functional demands on the lysosomes of pancreatic islet beta cells was studied in vivo. To expose pancreatic islets to different metabolic situations, normal syngeneic mouse islets were transplanted to either lean mice, alloxan-diabetic mice, or obese hyperglycemic mice. Two weeks after transplantation, primary and secondary beta-cell lysosomes of the islet grafts were analyzed by morphometry. The beta-cell lysosomes and secretory granules of the endogenous islets of lean and obese hyperglycemic mice were also measured. The beta cells of the islets transplanted to lean normoglycemic mice showed only a moderately developed synthetic apparatus and a great number of secretory granules. They had mainly secondary lysosomes, frequently containing secretory granule material, indicating a high crinophagic activity. The islet beta cells exposed to the high serum glucose concentration of alloxan-diabetic and obese hyperglycemic mice had an extensive synthetic apparatus, but a very small content of secretory granules. In these beta cells, there was a predominance of small primary lysosomes, indicating a low crinophagic activity. It is concluded that crinophagy may provide a mechanism for the pancreatic beta cell to moderate its content of insulin. When its secretory granule stores are diminished due to increased demands on insulin secretion, the beta cell seems able to drastically decrease the crinophagic activity. The detailed morphometric analysis of the endogenous islets of the lean and obese hyperglycemic mice showed that the beta cells of the obese hyperglycemic mice had a smaller number and size of the secretory granules.(ABSTRACT TRUNCATED AT 250 WORDS)