Parallel manifestation of insulin resistance and beta cell decompensation is compatible with a common defect in Type 2 diabetes

We studied 203 men of the same age but with varying degrees of glucose tolerance. These men participated in (i) an oral glucose tolerance test, (ii) a euglycaemic clamp combined with indirect calorimetry and infusion of [3-³H]-glucose and (iii) a stepwise assessment of acute insulin response to arginine (AIR) at three different glucose concentrations (fasting, 14 and 28 mmol/l).

There was a linear increase in NEFA levels (p<0.0005) and WHR (p<0.0005) and decrease in glucose uptake due to a reduction in glucose storage over the entire range of glucose tolerance (r=−0.404; p<0.005). No increase in endogenous glucose production (EGP) was seen until patients had manifest diabetes. However, when EGP was expressed relative to fasting insulin concentrations, there was a linear deterioration of basal hepatic insulin sensitivity (r=−0.514; p<0.005). The AIR followed a bell-shaped curve with an initial rise and subsequent decrease. However, AIR adjusted for insulin sensitivity (disposition index) showed a linear decrease with increasing glucose concentrations (r=−0.563; p<0.001) starting already in subjects with normal glucose tolerance. There was an inverse correlation between increase in WHR and NEFA and peripheral as well as hepatic insulin sensitivity. Subjects with the genotype combination of CAPN10 consisting of SNP44 TT and SNP43 GG genotypes had significantly lower insulin-stimulated glucose uptake than carriers of the other genotype combinations (5.3±0.4 vs 7.2±0.4 mg·ffm kg⁻¹·min⁻¹·mU·l⁻¹; p<0.005).