Proportion of proinsulin two minutes after arginine stimulation: a pilot study

Abstract

To seek an easy way to evaluate islet beta cell function. 214 residents of Shanghai, aged 20-70, all of Han nationality, were divided into 3 groups according the 1999 WHO standard: 39 in the normal glucose tolerance (NGT) group, aged 52 years +/- 6 years, with the BMI of 22.3 kg/m(2) +/- 0.4 kg/m(2); 29 in the impaired glucose tolerance (IGT) group, aged 54 years +/- 9 years, with the BMI of 24.4 kg/m(2) +/- 0.6 kg/m(2); and 146 in the T2DM group, that was subdivided into 2 subgroups: 43 in the newly diagnosed T2DM (NT2DM) group, aged 52 years +/- 9 years, with the BMI of 24.4 kg/m(2) +/- 0.5 kg/m(2), and 103 in the previously diagnosed T2DM (PT2DM) group, aged 57 years +/- 9 years, with the BMI of 23.5 kg/m(2) +/- 0.3 kg/m(2). Arginine at the dose of 10% 50 ml was injected intravenously in fasting situation. Two, four, and six minutes after blood samples were collected from a needle indwelling in the contralateral vein to examine the levels of plasma glucose (PG), true insulin (TI), and proinsulin (PI). (1) The TI and TI/PG levels of all groups peaked 2 minutes after arginine stimulation and then gradually decreased, however, the levels 6 minutes after stimulation were still higher than the baseline values. The peak values of TI and TI/PG were arranged from high to low in the order of IGT, NGT, NT2DM and PT2DM. The peak values of NT2DM and PT2DM groups were significantly lower than those of the NGT and IGT groups (all P < 0.01). The peak values of the NT2DM group were significantly higher than those of the PT2DM group (both P < 0.01). (2) The PI value of the IGT, NT2DM and PT2DM groups peaked 2 minutes after the stimulation and then gradually decreased with the peak values significantly higher than that of the NGT group (all P < 0.05). The fasting PI/TI and PI/(TI + PI) of the NGT group were all significantly lower than those of the IGT group (both P < 0.05). (3) The changes of PI/TI in each groups manifested almost the mirror image of TI/PG mentioned above, and the lowest PI/TI levels were observed 2 minutes after stimulation. The similar changes of PI/(TI + PI) were found. The lowest points of groups 2 minutes after stimulation was arranged from low to high in the order of NGT, IGT, NT2DM and PT2DM. The PI/TI and PI/(TI + PI) values 2 minutes after arginine stimulation may be used as predictors for beta cell function in clinical practice.