Local hindlimb antioxidant infusion does not affect muscle glucose uptake during in situ contractions in rat

Abstract

There is evidence that reactive oxygen species (ROS) contribute to the regulation of skeletal muscle glucose uptake during highly fatiguing ex vivo contraction conditions via AMP-activated protein kinase (AMPK). In this study we investigated the role of ROS in the regulation of glucose uptake and AMPK signaling during low-moderate intensity in situ hindlimb muscle contractions in rats, which is a more physiological protocol and preparation. Male hooded Wistar rats were anesthetized, and then N-acetylcysteine (NAC) was infused into the epigastric artery (125 mg.kg(-1).h(-1)) of one hindlimb (contracted leg) for 15 min before this leg was electrically stimulated (0.1-ms impulse at 2 Hz and 35 V) to contract at a low-moderate intensity for 15 min. The contralateral leg did not receive stimulation or local NAC infusion (rest leg). NAC infusion increased (P<0.05) plasma cysteine and cystine (by approximately 360- and 1.4-fold, respectively) and muscle cysteine (by 1.5-fold, P=0.001). Although contraction did not significantly alter muscle tyrosine nitration, reduced (GSH) or oxidized glutathione (GSSG) content, S-glutathionylation of protein bands at approximately 250 and 150 kDa was increased (P<0.05) approximately 1.7-fold by contraction, and this increase was prevented by NAC. Contraction increased (P<0.05) skeletal muscle glucose uptake 20-fold, AMPK phosphorylation 6-fold, ACCbeta phosphorylation 10-fold, and p38 MAPK phosphorylation 60-fold, and the muscle fatigued by approximately 30% during contraction and NAC infusion had no significant effect on any of these responses. This was despite NAC preventing increases in S-glutathionylation with contraction. In conclusion, unlike during highly fatiguing ex vivo contractions, local NAC infusion during in situ low-moderate intensity hindlimb contractions in rats, a more physiological preparation, does not attenuate increases in skeletal muscle glucose uptake or AMPK signaling.

The Janus Head of Oxidative Stress in Metabolic Diseases and During Physical Exercise

“…Treatment with ebselen, an antioxidant reducing H 2 O 2 , similarly reduces glucose uptake, indicating a role of H 2 O 2 generation [107]. Interestingly, these results could not be confirmed during in situ studies of NAC infusion in rats [108] and humans [109], possibly due to different NAC concentrations. Alternatively, ROS may only influence contraction-mediated glucose uptake during higher-intensity exercises with greatest ROS production [110].…”

Effect of N-acetylcysteine infusion on exercise-induced modulation of insulin sensitivity and signaling pathways in human skeletal muscle

“…Although investigations using antioxidant infusion during exercise found no differences in rates of contraction-mediated glucose uptake in humans (28) or during in situ contraction in rats (27), a study by Loh et al (20) used glutathione peroxidase knockout (Gpx1 Ϫ/Ϫ ) mice (which produce elevated basal levels of ROS) to mechanistically link ROS to the potentiation of IS after exercise. Interestingly, IS in the Gpx1 Ϫ/Ϫ mice was not different immediately postexercise but was enhanced 1 hr postexercise compared with WT mice.…”

Mitochondrial antioxidative capacity regulates muscle glucose uptake in the conscious mouse: effect of exercise and diet

“…The role of ROS in contraction-stimulated MGU has been studied ex vivo (48), in situ (34), and in humans (37). These different models have yielded different conclusions (35).…”