Biochemical determination of islet lysosomal enzyme activities following crinophagy-stimulating treatment with diazoxide in mice.

The pattern of islet lysosomal enzyme activities, islet insulin concentration and the plasma levels of insulin and glucose were studied in freely fed mice after the in vivo administration of diazoxide in doses known to induce crinophagy in islet beta-cells. After diazoxide treatment at time 0 and at 18 hr, the plasma glucose levels at 20 hr were markedly enhanced from 6.6 +/- 0.2 mmol/l (controls) to 27.2 +/- 2.7 mmol/l (diazoxide). Inhibition of insulin secretion by diazoxide was reflected in the insulinogenic index, which was reduced by approximately 40% (p less than 0.01) in the diazoxide-treated animals, who also displayed an increased concentration of islet insulin (+50%; p less than 0.01). Moreover, we found that the activities of certain lysosomal enzymes in islet tissue were markedly increased following diazoxide treatment. Thus the activities of the acid phosphatase, (+57%; p less than 0.02) the hexosaminidase N-acetyl-beta-D-glucosaminidase, (+52%; p less than 0.001), and the carboxyl proteinase cathepsin D (+41%; p less than 0.001), were all enhanced after diazoxide, whereas the activity of another lysosomal enzyme, the glycogen hydrolysing acid amyloglucosidase, was not altered by diazoxide treatment. The present data thus indicate that the morphological observation of diazoxide-induced crinophagy in pancreatic beta-cells has a biochemical correlate in enhanced levels of certain islet lysosomal enzyme activities known to participate in degradative processes. The results also suggest that islet lysosomal enzyme activities and/or lysosome populations can be modulated by a relative independence from each other.