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Urinary C‐Peptide Excretion: A Novel Alternate Measure of Insulin Sensitivity in Physiological Conditions
Author(s) -
Galgani Jose E.,
Jonge Lilian,
Rood Jennifer C.,
Smith Steven R.,
Young Andrew A.,
Ravussin Eric
Publication year - 2010
Publication title -
obesity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.438
H-Index - 199
eISSN - 1930-739X
pISSN - 1930-7381
DOI - 10.1038/oby.2010.70
Subject(s) - endocrinology , medicine , insulin , excretion , c peptide , ingestion , glucose clamp technique , chemistry , pancreatic hormone , insulin resistance , glycolysis , carbohydrate metabolism , hyperinsulinemia , metabolism
Insulin sensitivity (IS) is measured by the euglycemic–hyperinsulinemic clamp under a nonphysiological condition. Daily C‐peptide urinary excretion may be a physiological index of IS, because C‐peptide is co‐secreted with insulin as a function of nutrient intake and IS. The amount of 2 H 2 O released from glycolytic glucose metabolism after [6,6‐ 2 H 2 ]‐glucose ingestion was recently proposed as a physiological measure of IS. We compared these IS surrogates to the gold standard (euglycemic–hyperinsulinemic clamp). Thirty (15 male/15 female) sedentary, nondiabetic participants (27.2 ± 4.0 (s.d.) kg/m 2 , 35 ± 12 years) were admitted for 3 days to our in‐patient unit. After a 10‐h fast, they received 60 g of glucose and 15 g of [6,6‐ 2 H 2 ]‐glucose. Before glucose ingestion and hourly thereafter for 4 h, plasma glucose and insulin concentrations, and plasma deuterium enrichment were determined. Plasma 2 H 2 O production divided by insulin response was used as the glycolytic index. On day 2, subjects spent 23 h in a metabolic chamber (eucaloric diet, 50% carbohydrate, 30% fat). Urinary C‐peptide excretion was divided by energy intake yielding the C‐peptide to energy intake ratio (CPEP/EI). After leaving the chamber (day 3, 10‐h fast), IS was measured by a 2‐h clamp (120 mU/m 2 /min). Average IS (clamp) was 7.3 ± 2.6 mg glucose/kg estimated metabolic body size/min (range: 3.6–13.2). These values were inversely correlated with CPEP/EI ( r = −0.62; P < 0.01) and positively with the glycolytic rate ( r = 0.60; P < 0.01). In nondiabetic subjects, two novel estimates of IS—daily urinary C‐peptide urinary excretion and glycolytic rate during an oral glucose tolerance test —were related to IS by a clamp.