Abnormal Glucagon Secretion Contributes to a Longitudinal Decline in Glucose Tolerance.

CONTEXT

Defects in insulin secretion and action contribute to the progression of prediabetes to diabetes. However, the contribution of α-cell dysfunction to this process has been unclear.

OBJECTIVE

This work aimed to understand the relative contributions of α-cell and β-cell dysfunction to declining glucose tolerance.

METHODS

A longitudinal, community-based observational study was conducted at a clinical research unit at an academic medical center. We studied 96 individuals without diabetes (age 55 ± 1 years; body mass index 27.7 ± 0.4) on 2 occasions, 3 years apart using an oral 75-g glucose challenge. Indices for insulin secretion and action were estimated using the oral minimal model. Glucagon secretion rate (GSR) was estimated by deconvolution from peripheral glucagon concentrations. Main outcome measures included glucose tolerance status (categorical variable) and then symmetrical percentage change in peak and 120-minute glucose (post oral glucose tolerance test) concentrations (continuous variables).

RESULTS

A total of 32 individuals progressed from normal to impaired glucose tolerance (IGT) or from IGT to type 2 diabetes. The disposition index (DI) declined in the progressors (568 ± 98 vs 403 ± 65 10-4 dL/kg/min per μU/mL, baseline vs 3 years; P = .04). α-Cell suppression by glucose (δGSR/δglucose) did not change in the nonprogressors (1.5 ± 0.1 vs 1.3 ± 0.1 nmol/min/L; P = .37) but decreased (1.0 ± 0.2 vs 0.8 ± 0.2 nmol/min/L; P < .01) in those who progressed. Analysis of the entire cohort showed that DI and δGSR/δglucose were independently and inversely correlated with an increase in glycemic excursion.

CONCLUSION

These data show that α-cell dysfunction accompanies a decline in β-cell function as IGT or overt type 2 diabetes develops.