Increased Mitochondrial Glycerol Phosphate Dehydrogenase Activity in Insulinomas of Two Hypoglycemic Infants*

The activities of flavin-linked, mitochondrial glycerol phosphate dehydrogenase in islet cell adenomas from two infants were 8 and 16 times higher than those in their uninvolved pancreases. The enzyme in the insulinomas, but not that in the nearby pancreases, was inhibited by diazoxide, which is a known inhibitor of insulin secretion in vitro and in vivo. These results provide preliminary evidence that the enzyme may be used as an adjunct to histology for identifying human insulin-secreting tissues. Its sensitivity to diazoxide adds specificity to the test. Taken together with previous work with animal pancreatic islets, the results of the present study suggest that the glycerol phosphate shuttle plays an important role in stimulus-secretion coupling in the pancreatic beta-cell.