Studies on the essential role of ascorbic acid in the energy dependent release of insulin from pancreatic islets

Pancreatic islets from young normal and scorbutic male guinea pigs were examined for their ability to release insulin when stimulated with depolarizing levels of KCI (45 mM) and by 20 mM n-glyceraldehyde, Islets from normal guinea pigs released insulin in a K+ and D-glyceraldehyde dependent maturer showing a rapid initial secretion phase followed by secondary waves of insulin release during a 120 min period. Islets from scorbutic guinea pigs were able to respond to elevated K+ in a manner identical to that of the control islets, In contrast, insulin release from ascorbic acid deficient islets in response to the secretagogue, D-glyceraldehyde, was significantly delayed and decreased responses were observed during the 120 min period after D-glyceraldehyde stimulation. The results are consistent with the site of action of ascorbic acid on energy-dependent insulin release lying between the triose-phosphate level of glycolysis and the generation of ATP by oxidative phosphorylation. (C) 1997 Academic Press.