Urinary excretion rate of C-peptide in fed and fasted obese humans.
The aim of the study was to evaluate the reliability of urinary excretion rate of C-peptide as a marker of B-cell function during fasting. Ten obese subjects of both sexes fasted for 5 days. Diurnal serum C-peptide was collected before and on the 5th day; morning serum samples (for glucose, insulin and C-peptide) and 12-h urine samples (7.00 to 19.00 h) were collected daily. Body weight decreased from 138.7 +/- 15.9 to 132.9 +/- 15.6 kg. Morning glucose, insulin (-40%) and C-peptide (-50%) fell significantly throughout the study. Mean diurnal C-peptide values were 2.19 +/- 0.69 nmol/l before and 0.60 +/- 0.19 nmol/l after fasting (P less than 0.0001) and its secretion rate was 909.4 +/- 297.9 and 244.4 +/- 83.9 nmol/12 h (P less than 0.005), respectively. Excretion rate of C-peptide fell progressively from basal (11.2 +/- 4.2 nmol/12 h) to a nadir value of 1.3 +/- 0.8 nmol/12 h (P less than 0.0005); similarly, the C-peptide to creatinine clearance ratio fell from 0.062 +/- 0.035 to 0.028 +/- 0.015 (P less than 0.05). These results indicate that fasting modifies renal metabolism of C-peptide thus creating several complications in the quantitative interpretation of urinary levels as an index of its secretion rate from the B-cell.
Pasquali
R
R
1st Institute of Clinical Medicine, Orsola Hospital, University of Bologna, Italy.
Buratti
P
P
Casimirri
F
F
Patrono
D
D
Capelli
M
M
Melchionda
N
N
Barbara
L
L
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D002096:C-Peptide / Q000097:blood / Q000652:urine*; D003404:Creatinine / Q000378:metabolism; D004435:Eating; D005215:Fasting; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000178:diet therapy / Q000652:urine*
D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin; D003404:Creatinine