Cyclic nucleotides in pancreatic islets. Tolbutamide- and arginine-induced insulin release

With the use of isolated rat islet perfusion, levels of the islet cyclic adenosine 3' ,5' -monophosphate (cAMP) were compared with dynamic insulin secretion induced by tolbutamide and arginine. Tolbutamide elevated islet cAMP rapidly and augmented both glucose-induced islet cAMP levels and insulin secretion; arginine, however, did not elevate islet cAMP but did enhance glucose-induced insulin secretion. Since the latter result could have been modulated by cyclic guanosine 3' ,5' -monophosphate, this cyclic nucleotide was also measured and found to remain unchanged during stimulation of insulin secretion by arginine and a combination or arginine and glucose. Thus, the action of tolbutamide appears to be modulated in part by cAMP, whereas arginine appears to augment insulin secretion independently of cyclic nucleotides.