DIETARY-FAT MODIFIES EXERCISE-DEPENDENT GLUCOSE-TRANSPORT IN SKELETAL-MUSCLE

Exercise stimulates muscle glucose uptake both directly and by increas ing the sensitivity of this process to insulin. This study was designe d to investigate whether the level of dietary fat would interact with the action of acute exercise in the presence or absence of insulin. We anling female Sprague-Dawley rats were fed two levels of dietary fat ( 5 vs. 20%; wt/wt) for 6 wk. Rats then remained sedentary or were exerc ised by a single bout of swimming for a total of 2 h with 5-min rest i ntervals each 0.5 h. Basal (insulin-independent) and insulin-stimulate d glucose uptake rates were determined in isolated epitrochlearis musc les by using 3-O-[methyl-H-3]methyl-D-glucose. Muscles of sedentary ra ts fed a high-fat diet showed decreased glucose uptake overall because of a marked decrease in insulin-stimulated uptake. Muscles of rats fe d a high-fat diet also showed considerable impairment of insulin-depen dent glucose uptake measured both immediately and 3.5 h after exercise . Glucose uptake was suppressed by 64% at half-maximal concentrations of insulin (0.8 nM) and by 34% at maximally stimulating (20 nM) insuli n levels. This lowered sensitivity and response to insulin were not al tered by acute exercise. Glucose uptake in response to acute exercise (insulin independent) was quantitatively similar in rats fed high- and low-fat diets; rats on a high-fat diet, however, showed higher insuli n-independent glucose uptake at 3.5 h after exercise.