Islet Amyloglucosidase and Sulphonylurea-Stimulated Insulin Release in Three Different Strains of Mice

Abstract

The activities of the lysosomal enzymes acid amyloglucosidase and β-glucuronidase were assayed in isolated pancreatic islets and liver tissue from three different strains of mice. It was observed that acid amyloglucosidase activity in islets isolated from the CBA-strain and the C-57 strain was only 44% and 36% respectively of the activity recorded in the NMRI-strain. β-Glucuronidase activity displayed a similar pattern. In liver tissue the activities of the two lysosomal enzymes displayed a different pattern. The highest activities of acid amyloglucosidase and β--glucuronidase in the liver were observed in the C-57 strain while the other two strains showed slightly lower activities. There was no difference between the three strains with regard to basal plasma insulin levels and thus no apparent relation to the activities of the lysosomal enzymes in the islets. However, the insulin releasing capacity in the three different strains following an intravenous injection of a maximal dose of the sulphonylurea compound, glibenclamide, roughly correlated with islet amyloglucosidase activity while a similar stimulation by the β-adrenergic agonist L-isopropylnoradrenaline (L-IPNA) elicited an insulin response of equal magnitude in all three strains. It is suggested that acute sulphonylureastimulated insulin release is dependent on islet amyloglucosidase activity while β-adrenergic stimulation of insulin release is independent of the activity of this enzyme.