Modified hyperinsulinaemic, eu- and hypoglycaemic clamp technique using lispro-insulin for insulinoma diagnostic

Abstract

Characterization of metabolically inadequate insulin secretion is essential for insulinoma diagnostics. Hyperinsulinaemic, eu- and hypoglycaemic clamp procedures have been used to suppress endogenous insulin secretion in healthy subjects. The use of exogenous insulin precluded the use of insulin as a parameter to be measured. We now suggest to use exogenous insulin lispro and an insulin-specific ELISA not cross reacting with insulin lispro. Thus, determination of insulin by ELISA in this experimental setting reflects endogenous insulin. A 39-year-old man with a surgically confirmed pancreatic insulinoma was studied under hyperinsulinaemic [lispro insulin 40 mU x m(-2) body surface x min(-1)] clamp conditions. Euglycaemia was achieved (3.8 +/- 0.5 mmol/L) for 1 h and hypoglycaemia (2.36 +/- 0.49 mmol/L) was achieved for another 30 min. Insulin was evaluated by ELISA (cross-reaction with lispro insulin < 0.006%, C-peptide < 0.01%, proinsulin < 0.001%) and by a nonselective RIA (cross-reaction with proinsulin 40%). In control subjects the euglycaemic hyperinsulinaemia suppressed C-peptide to 0.36 +/- 0.03 ng/ml and hypoglycaemic hyperinsulinaemia to 0.29 +/- 0.03 ng/ml. Endogenous insulin was suppressed to 2.8 +/- 0.03 mU/L under euglycaemia and to 2.6 +/- 0.03 mU/L under hypoglycaemia in control subjects. In the insulinoma patient apparently irregular but small changes in both C-peptide (1.43 +/- 0.1 ng/ml) and more pronounced changes in endogenous insulin concentrations 4.41 +/- 0.1 mU/l under euglycaemia and 5.35 +/- 0.3 mU/l under hypoglycaemic conditions, were observed. The basal level of insulin (ELISA insulin 4.6 mU/L) and C-peptide (1.7 ng/ml) were not markedly elevated. Determination of insulin allowed better characterization of irregular pulses because of the shorter half-life of insulin relative to C-peptide. The new modification of sequential eu- and hypoglycaemic clamp procedures should also be useful in pharmacological studies of insulinotropic substances. Direct measurement of peripheral insulin may be more sensitive than C-peptide to detect low levels of autonomous insulin secretion in small insulinomas.

Insulin Responses to Selective Arterial Calcium Infusion under Hyperinsulinemic Euglycemic Glucose Clamps: Case Studies in Adult Nesidioblastosis and Childhood Insulinoma

“…Normal insulin secretion is suppressed not only by hypoglycemia but also by hyperinsulinemia itself. These negative feedback systems are disrupted in patients with insulinoma, and the lack of inhibition of insulin secretion under hyperinsulinemic glucose clamps with euglycemia [1][2][3][4][5] as well as hypoglycemia [12,14] is used for the biochemical diagnosis of insulinomas. Although the ASVS technique was developed for the localization of insulinomas, the detection of insulinomas or nesidioblastosis by ASVS is essentially biochemical; a positive test implies that pathological beta-cells "paradoxically" responding to in vivo calcium infusion exist downstream of the artery, although the mechanism remains unknown [18].…”

“…Following a 10-min priming period, the insulin analogue lispro (Humalog, Eli Lilly, Indianapolis, IN) was infused continuously at a rate of 1.12 mU/kg/min and glucose concentrations in arterialized venous blood were maintained at a target level of 90 mg/dl by glucose infusion via the artificial pancreas. In a hyperinsulinemic, sequentially euglycemic and hypoglycemic clamp test [12,14], the target glucose level was switched from 90 to 45 mg/dl after a 60-min clamped euglycemic period. An artificial endocrine pancreas was also employed, without insulin infusion, to maintain blood glucose levels during surgery with the target glucose level set at 100 mg/dl.…”

“…Insulin antibodies were absent. A hyperinsulinemic, sequentially euglycemic and hypoglycemic clamp test using lispro-insulin [12] was performed. Computerized tomography and magnetic resonance imaging revealed a tumor of 3.5 cm in diameter in the pancreatic head.…”

“…In the present study, we successfully performed ASVS tests under hyperinsulinemic euglycemic glucose clamps in two cases of hypoglycemia: adult nesidioblastosis and childhood insulinoma. To distinguish endogenous from exogenous insulin, an insulin analogue was utilized for glucose clamps [12]. This is the first report showing that the glucose clamp technique can be useful in the ASVS test for the safety of patients who frequently suffer from hypoglycemic attacks.…”

Diagnosis and Localization of Insulinoma after Negative Laparotomy by Hyperinsulinemic, Hypoglycemic Clamp and Intra-Aterial Calcium Stimulation

“…The hyperinsulinemic, hypoglycemic clamp procedure [2,6,7] suppresses endogenous insulin secretion by hyperinsulinemia-and hypoglycemia-mediated feedback inhibition of beta-cells. The pattern of C-peptide concentrations indicated that the glucose dependence of insulin secretion (C-peptide increments) was qualitatively preserved but quantitatively offset, proving autonomous insulin secretion (Figure 1).…”