Muscle glucose transport, GLUT-4 content, and degree of exercise training in obese Zucker rats

Abstract

The effects of high (HI)- and low (LI)-intensity exercise training were examined on insulin-stimulated 3-O-methyl-D-glucose (3-MG) transport and concentration of insulin-regulatable glucose transporter protein (GLUT-4) in the red (fast-twitch oxidative) and white (fast-twitch glycolytic) quadriceps of the obese Zucker rat. Sedentary obese (SED) and lean (LN) Zucker rats were used as controls. 3-MG transport was determined during hindlimb perfusion in the presence of 8 mM 3-MG, 2 mM mannitol, 0.3 mM pyruvate, and 0.5 mU/ml insulin. HI and LI rats displayed greater rates of red quadriceps 3-MG transport and GLUT-4 concentrations than SED rats. No significant differences in rates of 3-MG transport or GLUT-4 concentrations were observed in the red quadriceps of HI and LI rats. There were no differences found in the rates of 3-MG transport in the white quadriceps of HI, LI, and SED rats although the difference between the HI and SED rats approached significance (P< 0.07). The GLUT-4 concentration and citrate synthase activity of HI rats were significantly greater than SED rats. The 3-MG transport rates of LN rats were twofold greater than SED rats regardless of fiber type, but a difference in GLUT-4 content between the LN and SED rats was observed only in the white quadriceps. GLUT-4 content of the obese rats was significantly correlated with citrate synthase activity (r = 0.93) and 3-MG transport (r = 0.82).(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise and thiazolidinedione therapy normalize insulin action in the obese Zucker fatty rat.

“…Our studies also shed some light on the potential mechanisms underlying amelioration of insulin resistance. Total GLUT4 content measured in skeletal muscle of ZF rats has yielded variable results, with some studies reporting a decrease in specific muscle types and others finding no change (7,(10)(11)(12). In the current investigation, we found a 37% decrement in total skeletal muscle GLUT4 protein content in ZF rats compared with lean rats (P = 0.09, two-tailed test; P = 0.045, one-tailed test).…”

“…Interestingly, whereas significant reductions in glucose transport capacity have been observed, there is no apparent reduction in GLUT4 transporter protein expression in the insulin-resistant obese ZF rat when compared with insulinsensitive lean Zucker littermates (7,(9)(10)(11)(12). Thus, the defect in glucose uptake is thought to be constrained to one or more loci within the insulin-signaling cascade (13)(14)(15).…”

Effect of Mild Exercise Training on Glucose Effectiveness in Healthy Men

“…Some studies have reported that physical training increases the GLUT4 protein concentration in human skeletal muscle (9,23). Interestingly, mild exercise training increases the GLUT4 protein concentration to the same extent as that of intensive exercise training in an animal study (24). Phillips et al (23) reported that the expression of GLUT1 in human skeletal muscle increased after moderate exercise training-training that was somewhat harder than that used in our program (60% VO 2max for 1 month).…”

General aspects of muscle glucose uptake

“…This effect is important to increase expression of GLUT-4 (Kirwan and del Aguila 2003), IRS-1 (Jorge et al 2011) and insulin sensitivity (Kirwan and del Aguila 2003). Beyond the direct benefits in the insulin-dependent glucose uptake pathway, physical training increases maximal aerobic capacity (Cortez et al 1991), and raises the levels of enzymes involved in glucose catabolism (hexokinase and citrate synthase) (Banks et al 1992, Brozinick et al 1993, Cortez et al 1991.…”