Aims/hypothesis  

The study evaluated whether glucagon secretion is regulated by changes in insulin sensitivity under normal conditions.

Materials and methods  

A total of 155 healthy women with NGT (aged 53–70 years) underwent a glucose-dependent arginine-stimulation test for evaluation of glucagon secretion. Arginine (5 g) was injected i.v. under fasting conditions (plasma glucose 4.8±0.1 mmol/l) and after raising blood glucose concentrations to 14.8±0.1 and 29.8±0.2 mmol/l. The acute glucagon response (AGR) to arginine during the three glucose levels (AGR₁, AGR₂, AGR₃) was estimated, as was the suppression of baseline glucagon by the increased glucose. All women also underwent a 2-h euglycaemic–hyperinsulinaemic clamp study for estimation of insulin sensitivity.

Results  

Insulin sensitivity was normally distributed, with a mean of 73.2±29.3 (SD) nmol glucose kg⁻¹ min⁻¹/pmol insulin l⁻¹. When relating the variables obtained from the arginine test to insulin sensitivity, insulin resistance was associated with increased AGR and with increased suppression of glucagon levels by glucose. For example, the regression between insulin sensitivity and AGR₂ was r=−0.38 (p<0.001) and between insulin sensitivity and suppression of glucagon levels by 14.8 mmol/l glucose r=0.36 (p<0.001). Insulin sensitivity also correlated negatively with insulin secretion; multivariate analysis revealed that changes in insulin sensitivity and insulin secretion were independently related to changes in glucagon secretion.

Conclusions/interpretation  

The body adapts to insulin resistance by increasing the glucagon response to arginine and by increasing the suppression of glucagon levels by glucose. Hence, not only the islet beta cells but also the alpha cells seem to undergo compensatory changes during the development of insulin resistance.