Differential effects of body weight, hyperinsulinemia and oral glucose load on serum C-peptide/insulin molar ratio.
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 g-oral 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] < or = 25) subjects; Group B, young and overweight (BMI > 25) subjects; Group C, aged (> or = 55 years) and normal body weight (BMI < or = 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.
Okada
N
N
Department of Geriatrics, Endocrinology and Metabolism, School of Medicine, Shinshu University, Nagano-ken, Japan.
Kobayashi
M
M
Ohtsuka
H
H
Shigematsu
S
S
Nagasawa
Y
Y
Komatsu
M
M
Aizawa
T
T
Yamada
T
T
D000368:Aged; D001786:Blood Glucose / Q000378:metabolism*; D001835:Body Weight / Q000502:physiology*; D002096:C-Peptide / Q000097:blood* / Q000276:immunology; D005260:Female; D006801:Humans; D006946:Hyperinsulinism / Q000097:blood*; D007328:Insulin / Q000097:blood; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000097:blood
D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin