Normal Inhibition by Somatostatin of Glucose-Stimulated B Cell Secretion in Obese Subjects

Summary

Aim of the present study was to evaluate whether the inhibitory effect of somatostatin on pancreatic B-cell secretion is normal in nondiabetic obese subjects. For this purpose plasma C-peptide concentrations were measured in 10 nondiabetic obese subjects and 10 nonobese healthy controls during a 4-h hyperglycemic (11 mmol/l) glucose clamp. Somatostatin was infused (2.5 nmol/min) during the third hour of the study period in order to inhibit glucose-stimulated B-cell secretion.

Fasting C-peptide averaged 0.46 ± 0.04 nmol/l (mean ± SEM) in nonobese subjects, and 0.85 ± 0.08 nmol/l in obese patients (P < 0.001). In the period 0-120 min the area under the plasma C-peptide curve was significantly higher in obese than in nonobese subjects (292 ± 23 vs. 230 ± 17 nmol/l × 120 min, P < 0.05), however, in the last 20 min of the glucose infusion period without somatostatin (100-120 min) plasma C-peptide was not significantly different in the two groups (2.94 ± 0.32 nmol/l in nonobese subjects and 3.21 ± 0.19 nmol/l in obese patients, p = NS). During somatostatin infusion while maintaining hyperglycemia, plasma C-peptide decreased in both groups, and in the period 160-180 min it averaged 0.89 ± 0.12 nmol/l in control subjects and 0.93 ± 0.08 nmol/l in obese patients (P = NS), with a percent reduction similar in the two groups (70 ± 2% in controls and 71 ± 2% in obese patients). After discontinuing somatostatin infusion, plasma C-peptide increased to concentrations which were higher in obese than in nonobese subjects.

These results suggest that, at least at the dose employed, the inhibitory effect of somatostatin on glucose-stimulated pancreatic B-cell secretion is not different from normal in human obesity.

Key words

Somatostatin - B-Cell Secretion - C-Peptide - Obesity