Failure of somatostatin to inhibit tolbutamide-induced insulin secretion in patients with insulinomas: a possible diagnostic tool.

The effects of somatostatin on tolbutamide-stimulated insulin release were studied in 4 patients with insulin-producing tumors of the pancreas and in 6 normal subjects. In contrast to its effective inhibition of insulin release in normal subjects, somatostatin, without exception, failed to inhibit tolbutamide-induced insulin release in the patients with pancreatic beta-cell tumors. This differential effect of somatostatin may prove useful in the diagnosis of insulin-producing tumors of the pancreas.