Beta cell response to the hyperglycaemic clamp in three patients with insulinoma: a study using a hyperglycaemic glucose clamp.

To determine the mechanism responsible for deficient carbohydrate metabolism in patients with insulinoma, we studied three affected patients and seven normal controls using the hyperglycaemic clamp method (8.4 mmol/l) with the BIOSTATOR (GCIIS). In insulinoma patients, the amount of glucose necessary to reach the hyperglycaemic clamp was less than that required in normal controls (6.19 +/- 1.19 mg/min/kg vs. 9.95 +/- 0.53 mg/min/kg) (p less than 0.05). There was no significant difference in metabolized glucose (M) in the stable phase of the hyperglycaemic clamp; however, the M/IRI in this phase was less in those with insulinoma (7.9 +/- 0.50) than in controls (22.26 +/- 4.14) (p less than 0.05). There was no difference in beta cell secretory response to hyperglycaemic stimulus (defined as the increase in the concentration of C-peptide from the basal state to the stable phase of the hyperglycaemic clamp) between the two groups. Hepatic insulin extraction was significantly lower in patients with insulinoma than in normal controls (+0.72 +/- 0.07 vs. +0.85 +/- 0.01). Finally, the ratios of fractional turnover of glucose (K/IRI); glucose clearance/IRI and total rate of elimination of glucose from the extracellular pool/IRI were also all lower in patients with insulinoma than in controls (p less than 0.05). These data support the conclusion that deficient glucose metabolism seen in these patients is not related to a lack of response to glucose on the part of normal or neoplastic islet tissue.(ABSTRACT TRUNCATED AT 250 WORDS)