Ingestion of a Mixed Meal Does Not Affect the Metabolic Clearance Rate of Biosynthetic Human C-Peptide*

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Abstract
The validity of C-peptide as a peripheral marker of insulin secretion during different physiological conditions depends on the demonstration that C-peptide clearance is constant under these circumstances. Recently biosynthetic human C-peptide, identical in structure to pancreatic human C-peptide, became available for use in human subjects. The present study was undertaken to determine if the metabolic clearance of C-peptide was altered by ingestion of a mixed meal. Eight insulindependent diabetic patients received constant iv infusions of biosynthetic human C-peptide which raised the plasma C-peptide concentration to a level of 3.8 ± 0.2 (±SEM) pmol/ml. The MCR of C-peptide was 4.5 ± 0.3 ml/kg -min. After steady state levels of C-peptide had been reached, each patient consumed a 530 calorie mixed meal. The plasma glucose concentration increased from a baseline value of 104.5 ± 4.8 mg/dl to a 336 ± 10 mg/dl 150 min later. This change in plasma glucose was not associated with a significant alteration in the plasma C-peptide concentration and the MCR of the infused C-peptide was not affected by meal ingestion (4.5 ± 0.3 vs. 4.3 ± 0.3 ml/kg.min). These results therefore support the validity of using C-peptide as a marker for changes in insulin secretion after mixed meals.