The Pancreatic Glucagon and C-Peptide Secretion During Hyperinsulinemia in Euglycemic Glucose Clamp With or Without Somatostatin Infusion in Normal Man

Summary

6 normal subjects received two times of 2 hr euglycemic glucose clamp studies (insulin infusion rate 40 mU/M²/min) one with and the other without somatostatin (SRIF) infusion (500 ug/hr). Serum C-peptide and glucagon levels were measured during clamp to study the sensitivity of pancreatic alpha and beta cells to the suppressive effects of exogenous hyperinsulinemia during normoglycemia in normal subjects and to find whether SRIF had any modulative effects on endocrine pancreas secretion at the status of hyperinsulinemia.

The results showed that in normal man the degree of suppression of pancreatic glucagon secretion by hyperinsulinemia (˜100 uU/ml) during euglycemic glucose clamp without SRIF infusion was less than that of C-peptide with mean value of 62±4% of basal glucagon remained at the end of clamp study; while only about 30±2% of basal C-peptide concentrations remained. But during SRIF infused glucose clamp studies (SRIF was infused from 60 to 120 min), 32±2% of mean basal C-peptide concentrations and 38±6% of mean basal glucagon concentrations left at the end of 2 hr clamp studies when serum insulin level was about 100 uU/ml. For the glucose infusion rate (M value), it was significantly greater in our normal subjects in response to insulin + SRIF as compared to insulin alone (12.0+0.9 vs 8.8±1.4; P < 0.01). We concluded: (1) during hyperinsulinemia (100 uU/ml), the sensitivity of pancreatic alpha cells to insulin seems less than that of beta cells in normal man at normoglycemia. (2) in normal man, adding SRIF did not further bring down the pancreatic beta cell's secretion when it was maximally suppressed by insulin whereas more pancreatic alpha cell's secretion was inhibited. (3) SRIF may potentiate glucose infusion rate during euglycemic clamp in normal man.

Key-Words

Glucose Clamp - Somatostatin - Pancreatic Suppression - Normal Subjects