Unresponsiveness of insulinoma cells to secretin: significance of the secretin test in patients with insulinoma.

It is well known that B cells in the pancreas release insulin when stimulated by secretin, but there have been few reports on the response of insulinoma cells to secretin. In five patients with insulinoma, changes in serum immunoreactive insulin (IRI) concentration were measured after the intravenous injection of secretin into the peripheral vein before and after extirpation of the insulinoma. The extirpated insulinomas were cultured and tested for their response to secretin. The rise in serum IRI in response to secretin in patients with insulinoma was significantly slower and smaller than in normal volunteers. After removal of the insulinoma, the response to secretin became prompt and increased with time. Cultured insulinoma cells did not release insulin when stimulated by secretin. Therefore, it is concluded that the response of insulinoma cells to secretin is quite different from that of normal beta cells, and that the function of beta cells in the insulinoma-bearing pancreas is suppressed by the autonomous hypersecretion of insulin by the insulinoma. The extent of the decrease in function of the beta cells in patients with insulinoma can be estimated by the intravenous secretin test. Thus, the secretin test is sometimes useful in the differentiation of hypoglycemia due to insulinoma from that due to beta cell hyperplasia or alimentary hyperinsulinemia.