Investigating the impact of hyperglycemia on pancreatic endocrine function promotes our understanding of the pathophysiology of hyperglycemia-related disease.

The objective of the study was to test the hypothesis that experimental hyperglycemia impairs insulin and glucagon secretion.

A randomized, crossover in healthy controls, compared with type 2 diabetic patients.

The study was conducted at a university hospital.

Normal glucose-tolerant subjects (n = 10) and patients with type 2 diabetes (n = 10), individually matched by age, sex, and body mass index.

Normal glucose-tolerant subjects underwent 24 h of experimental hyperglycemia (+5.4 mm above basal). Subjects with type 2 diabetes did not undergo an intervention.

Insulin secretion, glucagon secretion, insulin sensitivity, disposition index, and endogenous glucose production (via [6,6-²H₂]glucose infusion) were measured during hyperglycemic clamps combined with infusion of glucagon-like peptide (GLP)-1_7–36 (0.5 pmol/kg · min) and injection of arginine (5 g).

Insulin secretion was correlated with glucagon suppression in subjects with normal glucose tolerance only. Individuals with type 2 diabetes had lower insulin sensitivity (−33 ± 11%) and insulin secretory responses to glucose, GLP-1, and arginine (−40 ± 11, −58 ± 7, and −36 ± 13%, respectively) and higher plasma glucagon and endogenous glucose production compared with normal glucose-tolerant subjects (all P < 0.05). After 24 h of experimental hyperglycemia, insulin sensitivity (−29 ± 10%), disposition index (−24 ± 16%), and GLP-1- (−19 ± 7%) and arginine-stimulated (−15 ± 10%) insulin secretion were decreased in normal glucose-tolerant subjects (all P < 0.05). However, plasma glucagon responses were not affected. Furthermore, experimental hyperglycemia abolished the correlation between insulin secretion and glucagon suppression.

Experimental hyperglycemia impaired pancreatic β-cell function but did not acutely impair α-cell glucagon secretion in normal glucose-tolerant subjects.