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Relationship between insulin sensitivity and in vivo mitochondrial function in skeletal muscle

¹Departments of Human Studies and Nutrition Sciences; ²Department of Diagnostic and Therapeutic Sciences, University of Alabama at Birmingham, Birmingham, Alabama; and ³Department of Family and Consumer Sciences (Human Nutrition), University of Wyoming, Laramie, Wyoming

Submitted 4 August 2005 ; accepted in final form 9 May 2006

Recent data have shown that individuals with low insulin sensitivity (S_I) also have reduced whole body maximal oxygen uptake. The objectives of this study were to determine 1) whether muscle mitochondrial function was independently related to S_I after being adjusted for known determinants of S_I and 2) whether lower S_I among African-American (AA) vs. Caucasian-American (CA) women was due to lower muscle mitochondrial function among AA women. Subjects were 37 CA and 22 AA premenopausal women (age: 33.6 ± 6.3 yr). Mitochondrial function [time constant of ADP (ADP_tc)] was assessed during a 90-s unilateral isometric contraction using ³¹P magnetic resonance spectroscopy, S_I with an intravenous glucose tolerance test, body composition by dual-energy X-ray absorptiometry, and visceral adipose tissue (VAT) with computed tomography. ANOVA was used to compare AA and CA groups, and multiple linear regression modeling was used to identify independent predictors of S_I. Between-race comparisons indicated that muscle oxidative capacity was lower among AAs vs. CAs (ADP_tc: 25.6 ± 9.8 vs. 21.4 ± 9.9 s). Multiple linear regression models for the dependent variable S_I contained 1) VAT and race and 2) VAT, race, and ADP_tc. Significant independent effects for all predictor variables were observed in both the first (r² = 0.345) and second (r² = 0.410) models. The partial correlation for race was lower in the second model (–0.404 vs. –0.300), suggesting that muscle mitochondrial function contributed to the racial difference in S_I. Lower muscle mitochondrial function among AAs may in part explain lower S_I among them.

oxidative capacity; magnetic resonance spectroscopy; visceral adipose tissue; African Americans; premenopausal women

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