Differential Effects of Body Weight, Hyperinsulinemia and Oral Glucose Load on Serum C-Peptide/ Insulin Molar Ratio

Summary

Serum C-peptide immunoreactivity (CPR)/immunoreactive insulin (IRI) molar ratio was determined in 136 subjects without renal, hepatic and thyroid disorders, at fasting, and during the initial period of 75 goral glucose tolerance test. The subjects were divided into 4 groups based on their body weight and age; Group A, young (< 55 years) and normal body weight (body mass index [BMI, kg/m²] ≤ 25) subjects; Group B, young and overweight (BMI > 25) subjects; Group C, aged (≥ 55 years) and normal body weight (BMI ≤ 25) subjects; Group D, aged and overweight subjects. Fasting CPR/IRI ratio and absolute CPR level negatively correlated in Groups B and D but not in A and C. After oral glucose load with elevation of insulin, CPR/IRI ratio invariably declined in all groups and significant negative correlation between CPR/IRI and CPR was found in Groups A, B and D but not in C. Slope of the regression lines obtained for correlation between CPR/IRI ratio and CPR were significantly steeper at fasting compared to the post-stimulation phase.

CPR/IRI ratio is affected by hyperinsulinemia and oral glucose load but not by obesity alone. Assuming that CPR/IRI ratio reflects hepatic extraction of insulin, the insulin clearance at fasting is progressively reduced with increasing insulin secretion in overweight subjects: failure to detect such phenomenon in normal body weight subjects may be due to a narrower CPR range in this population. Insulin metabolism at fasting and during glucose stimulation is likely to be regulated by distinct factors.

Key words

CPR/IRI Ratio - Insulin Metabolism - Obesity - Aging