Endocrine Abstracts

Aims: Increasing evidence supports the role of glycated insulin in the insulin resistant state of type 2 diabetes. We measured 24-hour profiles of plasma glycated insulin, using a novel radioimmunoassay, to evaluate the effects of meal stimulated insulin secretion and the fasting state on production of plasma glycated insulin in type 2 diabetes. Methods: Patients (n=6, HbA1c 7.2±0.6%, fasting plasma glucose 7.4±0.7 mmol l^-1, BMI 35.7±3.5 kg m^-2, age 56.3±4.4 years) were admitted for 24 hours and received a standardised meal regimen. Half-hourly venous samples were taken for plasma glycated insulin, glucose, insulin and c-peptide concentrations between 0800-2400hrs and 2-hourly overnight. Results: The mean plasma glycated insulin concentration over 24 hours was 26.71±1.1 pmol l^-1 with a mean percentage of glycated insulin of 16.9±1.7%. Serum insulin concentrations followed a basal and meal-related pattern with increments of 560% (P=0.01), 70% (NS), and 205% (NS) and corresponding increments of total plasma glycated insulin of 125%, 191% and 123% following breakfast, lunch and tea respectively. The mean concentration of total glycated insulin during the morning, afternoon, evening and night-time periods were 22.7±1.7, 28.7±2.3, 29.1±1.6 and 26.2±1.5 pmol l^-1 respectively (ANOVA P=0.70). Corresponding mean percentages of glycated insulin were 10.1±1.9% (P < 0.001), 18.2±3.0% (P = 0.0061), and 13.2±1.8% (P < 0.0001) compared to 32.0±2.3 %.pmol.l^-1 at night. Conclusions: We have demonstrated diurnal variation of glycated insulin in type 2 diabetes with a pattern of basal and meal stimulated release. It is apparent that glycated insulin is readily released following a meal, and that a particularly high proportion of plasma glycated insulin circulates during the night.