The effect of glimepiride on pancreatic beta-cell function under hyperglycaemic clamp and hyperinsulinaemic, euglycaemic clamp conditions in non-insulin-dependent diabetes mellitus

The comparative effects of glimepiride (Amaryl; HOE 490) and glibenclamide on insulin and glucose metabolism under hyperglycaemic and hyperinsulinaemic, euglycaemic clamp conditions were studied in a double-blind, placebo-controlled, crossover trial. Patients with sulfonylurea-controlled non-insulin-dependent diabetes were allocated in random order to placebo, glimepiride (5 mg) or glibenclamide (5 mg) and received one week treatment of each with no wash-out period. At the end of each treatment week a clamp study was performed. Two protocols were used. Protocol I used a 5 h hyperglycaemic clamp at 10.9 mmol/l whole blood glucose concentration and Protocol II used a 3 h hyperinsulinaemic, euglycaemic damp at 3.5 mmol/l whole blood glucose concentration. Both glimepiride and glibenclamide exhibited a hypoglycaemic effect. A significant redution in fasting whole blood glucose concentration was observed after one-week treatment of each active agent (fasting glucose: glimepiride v. placebo, 9.3 +/- 0.7 v. 10.7 +/- 0.8 mmol/l, p < 0.02; glibenclamide v. placebo, 8.9 +/- 0.9 v. 10.7 +/- 0.8 mmol/l, p < 0.005). This hypoglycaemic action of both preparations administered in equivalent daily dose appeared comparable. Glimepiride and glibenclamide stimulated beta-cell secretion and in the basal state both beta-cell secretory products insulin and C-peptide, were elevated in the plasma (basal C-peptide concentration: glimepiride v. placebo, 0.79 +/- 0.08 v. 0.68 +/- 0.07 nmol/l, p < 0.01; glibenclamide v. placebo, 0.79 +/- 0.07 v. 0.68 +/- 0.07 nmol/l, p < 0.004). This insulinotropic effect appeared to be comparable with no demonstrable difference in the efficacy of the two preparations. Under steady-state hyperglycaemic conditions both agents promoted insulin release (stimulated C-peptide concentration; glimepiride v. placebo, 1.39 +/- 0.16 v. 1.11 +/- 0.20 nmol/l, p < 0.006; glibenclamide v. placebo, 1.60 +/- 0.18 v. 1.11 +/- 0.20 nmol/l, p < 0.001) and there was no statistically significant difference between active treatments. Under steady-state euglycaemia both preparations continued to stimulate insulin release as evidenced by the mean plasma C-peptide concentrations (glimepiride v. placebo, 0.69 +/- 0.10 v. 0.28 +/- 0.06 nmol/l, p < 0.01; glibenclamide v. placebo, 0.76 +/- 0.12 v. 0.28 +/- 0.06 nmol/l, p(0.01). Both glimepiride and glibenclamide had a comparable and signifiant enhancing effect on glucose metabolism (Protocol II: M: glimepiride v. placebo 4.4 +/- 1.3 v. 1.3 +/- 0.7 mg/kg min, p < 0.05; glibenclamide v. placebo 4.7 +/- 1.3 v. 1.3 +/- 0.7 mg/kg min, p<0.03) and improved tissue sensitivity to the action of insulin as determined by the quantity of glucose metabolised per unit insulin (Protocol II: MII ratio: glimepiride v. placebo, 0.09 +/- 0.03 v. 0.03 +/- 0.01 kg . min per mU/l, p < 0.02; glibenclamide v. placebo, 0.1 +/- 0.03 v. 0.03 +/- 0.01 kg min per mU/l, p < 0.01). In conclusion, glimepiride is a ''second-generation'' sulfonylurea agent which stimulates pancreatic beta-cell insulin secretion, lowers blood glucose and improves tissue insulin sensitivity in non-insulin-dependent diabetic subjects. Its insulinotropic effect is comparable with that of glibenclamide but may diminish in the presence of normoglycaemia. The magnitude and hence, the clinical relevance of a selective beta-cytotropic action, determined by blood glucose concentration, remains to be demonstrated.