Increased insulin secretion in subjects with impaired glucose tolerance.

ABSTRACT

In order to assess the relative roles of insulin deficiency and insulin resistance in the pathogenesis of impaired glucose tolerance (IGT), simultaneous measurement of serum immunoreactive insulin (IRI) and serum immunoreactive C-peptide (IRC) responses during 75 g oral glucose tolerance test were performed in 44 normal-weight adults with IGT (27 men, mean age +/- SEM = 46.1 +/- 1.9 year; 17 women, aged 49.1 +/- 3.3 year) and 44 control subjects (27 men, aged 45.5 +/- 2.1 year; 17 women, aged 47.9 +/- 3.0 year). Subjects with IGT had consistently higher 120-m IRI levels in comparison to corresponding age, sex, and BMI-matched control subjects, i.e. mean +/- SEM = 118.8 +/- 13.7 vs 57.0 +/- 6.9 microU/ml (male, P = 0.0002), and 116.3 +/- 11.8 vs 43.3 +/- 5.8 microU/ml (female, P = 0.0000). Similarly, 120-m IRC levels were higher in subjects with IGT, i.e. 2.12 +/- 0.26 vs 1.35 +/- 0.15 pmol/ml (male, P = 0.0262), and 3.13 +/- 1.01 vs 1.54 +/- 0.19 pmol/ml (female, P = 0.0080). Our findings indicate that increased insulin secretion is present in subjects with IGT, suggesting that insulin resistance is the predominant factor in the pathogenesis of IGT.