Inhibition of glucose-stimulated insulin release in the perfused rat pancreas by parathyroid secretory protein-I (chromogranin-A).

The effect of graded doses (10(-10)-10(8) M) of highly purified bovine parathyroid secretory protein-I (SP-I; chromogranin-A) or synthetic porcine pancreastatin on glucose-stimulated insulin release in the perfused rat pancreas was examined. SP-I (10(-9) M) inhibited the first phase of glucose-stimulated insulin release, and 10(-8) M SP-I inhibited both the first and second phases of glucose-stimulated insulin release; 10(-10) M SP-I was inactive. In comparison, pancreastatin at 10(-10) M inhibited the first phase of insulin release, and at 10(-9) and 10(-8) M, pancreastatin inhibited both phases of insulin release. The inhibition by SP-I was achieved at concentrations that normally exist in the general circulation of man. These and other data suggest that circulating SP-I plays a physiological role in the regulation of insulin secretion.