Maturing Sprague-Dawley (S-D) rats develop
obesity and skeletal muscle
insulin resistance. To investigate the relationship between fat mass and
insulin responses, we performed surgical removal of the epididymal and retroperitoneal depots of visceral adipose tissue (VF) or
sham surgery (
SHAM) in male rats aged 4 months. At sacrifice, 30 days later, the mass of visceral fat was 48% lower (p<0.05) in VF- compared to
SHAM, while subcutaneous fat was essentially unchanged. VF- animals displayed increased
insulin responses in isolated strips of skeletal muscle.
Insulin-stimulated
glucose transport was increased 28% in soleus muscle (p<0.05), with a trend toward a 31% increase in extensor digitorum longus muscle (p=0.058).
Glucose tolerance was not significantly affected by surgical fat removal. In VF- animals, serum
resistin was reduced 26% (p<0.05) and serum
adiponectin was reduced 30% (p<0.05), with trends for reductions in
IL-4 (58% reduction, p=0.084) and
IL-6 (56% reduction, p=0.123).
TNF-alpha,
leptin and
free fatty acids (NEFAs) were unchanged. We conclude that in maturing S-D rats, increased visceral adiposity leads to an increase in systemic release in
resistin and possibly
interleukins. Elevation of circulating
cytokines may play a role in the development of muscle
insulin resistance.