Effect of Fasting on Islet Lysosomal Enzyme Activities and the In Vivo Insulin Response to Different Secretagogues

The effect of a 24 hr starvation period on islet lysosomal enzyme activities and the in vivo insulin response to glucose, glibenclamide and L-isopropyl-noradrenaline (L-IPNA) was studied in mice. It was observed that fasting induced a significant decrease of islet acid amyloglucosidase activity, whereas the activities of acid phosphatase, beta-N-acetyl-glucosaminidase, and beta-glucuronidase in islet tissue were unaffected by the fasting period studied. Starvation markedly reduced the acute insulin response to a maximal dose of glucose or glibenclamide. However, the insulin response to a maximal dose of L-IPNA was of similar magnitude in both fed and fasted animals. Pretreatment of fasted mice with purified fungal acid amyloglucosidase could restore the impaired insulin response to glucose to the normal level seen in fed mice. It is suggested that islet acid amyloglucosidase activity is of importance for glucose-stimulated insulin secretion, and that reduced levels of islet amyloglucosidase may contribute to the impairment of glucose-induced insulin release seen after fasting.