Associations of serum adiponectin with skeletal muscle morphology and insulin sensitivity.
BACKGROUND
Skeletal muscle morphology and function are strongly associated with insulin sensitivity.


OBJECTIVE
The objective of the study was to test the hypothesis that circulating adiponectin is associated with skeletal muscle morphology and that adiponectin mediates the relation of muscle morphology to insulin sensitivity.


METHODS
This was a cross-sectional investigation of 461 men aged 71 yr, participants of the community-based Uppsala Longitudinal Study of Adult Men study.


METHODS
Measures included serum adiponectin, insulin sensitivity measured with euglycemic insulin clamp technique, and capillary density and muscle fiber composition determined from vastus lateralis muscle biopsies.


RESULTS
In multivariable linear regression models (adjusting for age, physical activity, fasting glucose, and pharmacological treatment for diabetes), serum adiponectin levels rose with increasing capillary density (beta, 0.30 per 50 capillaries per square millimeter increase; P = 0.041) and higher proportion of type I muscle fibers (beta, 0.27 per 10% increase; P = 0.036) but declined with a higher proportion of type IIb fibers (beta, -0.39 per 10% increase; P = 0.014). Using bootstrap methods to examine the potential role of adiponectin in associations between muscle morphology and insulin sensitivity and the associations of capillary density (beta difference, 0.041; 95% confidence interval 0.001, 0.085) and proportion of type IIb muscle fibers (beta difference, -0.053; 95% confidence interval -0.107, -0.002) with insulin sensitivity were significantly attenuated when adiponectin was included in the models.


CONCLUSIONS
Circulating adiponectin concentrations were higher with increasing skeletal muscle capillary density and in individuals with higher proportion of slow oxidative muscle fibers. Furthermore, our results indicate that adiponectin could be a partial mediator of the relations between skeletal muscle morphology and insulin sensitivity.
Ingelsson
Erik
E
Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Box 281, SE-171 77 Stockholm, Sweden. erik.ingelsson@ki.se
Arnlöv
Johan
J
Zethelius
Björn
B
Vasan
Ramachandran S
RS
Flyvbjerg
Allan
A
Frystyk
Jan
J
Berne
Christian
C
Hänni
Arvo
A
Lind
Lars
L
Sundström
Johan
J
D052242:Adiponectin / Q000097:blood* / Q000502:physiology; D000368:Aged; D003430:Cross-Sectional Studies; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000166:cytology; D018482:Muscle, Skeletal / Q000098:blood supply / Q000166:cytology*
D052242:Adiponectin; D007328:Insulin