Reduced glutamate decarboxylase activity in rat islet beta cells which survived streptozotocin-induced cytotoxicity.

Rat pancreatic beta cells exhibit a 16-fold higher glutamate decarboxylase (GAD) activity than islet non-beta cells, but a similar glutamate dehydrogenase (GDH) activity. beta Cells which survive exposure to 2 mM streptozotocin only contain 10 percent of the GAD activity of control cells, but their GDH activity remains unaltered. Culture of streptozotocin-treated beta cell preparations with 2 mM nicotinamide reduces the number of dead cells and prevents in part the decline in GAD activity of surviving beta cells. These data indicate that loss in activity of the beta cell specific enzyme GAD can serve as marker for beta cells which survived a destructive process. It is furthermore demonstrated that nicotinamide increases the percent surviving cells and decreases their loss in GAD activity.