Insulin binding to isolated monocytes and adipocytes in the study of hypoglycemic subjects and in the follow-up of patients with insulinoma.

The present study was performed to see whether insulin receptor evaluation is useful as a diagnostic tool in the differential diagnosis of hypoglycemia. The receptor numbers and affinity constants of insulin binding to adipocytes isolated from subcutaneous tissue were determined in 5 metabolically healthy subjects, undergoing laparatomy for cholecystectomy, and in 4 patients undergoing surgery for insulinoma removal. The specific insulin binding to monocytes at physiological concentrations (1 ng/ml) was also determined in all these subjects, and in 6 patients with functional hypoglycemia. The study was repeated in insulinoma patients 7 days after surgery. Results show that insulinoma patients before tumor removal have greater than 50% fall in binding capacity on both monocytes and fat cells, in keeping with the down-regulation mechanism, whereas the values for patients with functional hypoglycemia are in the normal range. After surgery, the insulin binding to monocytes sharply increased, nearly to the lower level of the normal range when the insulinoma was removed; no change was observed when the tumor was not resected (case 3). Insulin receptor study may therefore be of diagnostic and prognostic assistance in the investigation of hypoglycemic syndromes.