The insulin secretory responses of tumor tissues (induced by streptozotocin-nicotinamide injections) to glucagon and somatostatin will be estimated in an in vitro perifusion system. The activity of the adenylate cyclase-phosphodiesterase system will be monitored concurrently. The effects of glucagon and somatostatin on insulin biosynthesis will be correlated with known effects on this activity in normal islet tissue. These studies may help elucidate the defect in phasic insulin release patterns exhibited by tumor tissues. Insulinase (insulin-specific protease) of tumor tissues will be determined after exposure to high or low glucose in vitro in order to test the theory that this enzyme may regulate the cellular levels of insulin stores in islet tissue. The ultrastructure, cytoarchitecture, and hormone immunohistochemistry of tumors will be studied in order to better understand their physiology and development.