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At least 811 records · Page 45Linked to original sources
PubMed2004

Strength training increases insulin-mediated glucose uptake, GLUT4 content, and insulin signaling in skeletal muscle in patients with type 2 diabetes.

Strength training represents an alternative to endurance training for patients with type 2 diabetes. Little is known about the effect on insulin action and key proteins in skeletal muscle, and the necessary volume of strength training is unknown. A total of 10 type 2 diabetic subjects and 7 healthy men (control subjects) strength-trained one leg three times per week for 6 weeks while the other leg remained untrained. Each session lasted no more than 30 min. After strength training, muscle biopsies were obtained, and an isoglycemic-hyperinsulinemic clamp combined with arterio-femoral venous catheterization of both legs was carried out. In general, qualitatively similar responses were obtained in both groups. During the clamp, leg blood flow was higher (P < 0.05) in trained versus untrained legs, but despite this, arterio-venous extraction glucose did not decrease in trained legs. Thus, leg glucose clearance was increased in trained legs (P < 0.05) and more than explained by increases in muscle mass. Strength training increased protein content of GLUT4, insulin receptor, protein kinase B-alpha/beta, glycogen synthase (GS), and GS total activity. In conclusion, we found that strength training for 30 min three times per week increases insulin action in skeletal muscle in both groups. The adaptation is attributable to local contraction-mediated mechanisms involving key proteins in the insulin signaling cascade.

Biological Transport↗
PubMed1994

Glucose transport activity in skeletal muscles from transgenic mice overexpressing GLUT1. Increased basal transport is associated with a defective response to diverse stimuli that activate GLUT4.

Glucose transport activity was examined in transgenic mice overexpressing the human GLUT1 glucose transporter in skeletal muscles. Basal transport activity measured in vitro with the glucose analog 2-deoxy-D-glucose (1 mM) was increased 2-8-fold in four different muscle preparations. Incubation of muscles from control nontransgenic littermates with a maximally effective concentration of insulin or with insulin-like growth factor-1 resulted in glucose transport rates that were 2-3-fold higher than basal. In contrast, insulin did not stimulate glucose transport activity in three different muscle preparations from transgenic animals; insulin-like growth factor-1 was similarly ineffective. Activation of System A amino acid transport activity (measured with the nonmetabolizable analog alpha-methylaminoisobutyrate) by insulin was not impaired in muscles from transgenic mice, indicating that the defect does not involve the insulin receptor. In skeletal muscle, glucose transport can be activated by muscle contractions or hypoxia via a pathway separate from that activated by insulin. Incubation of muscles under hypoxic conditions or stimulation of muscles to contract in situ did not increase glucose transport activity in muscles from GLUT1-overexpressing mice, in contrast to the stimulatory effects measured in muscles from control animals. These data suggest that increased glucose flux per se into skeletal muscle results in resistance of GLUT4 to activation by insulin and various other stimuli that activate glucose transport by mechanisms distinct from that of insulin. GLUT1-overexpressing mice thus provide a new model system for studying the effects of glucose-induced resistance to activation of glucose transport.

Amino Acids↗
PubMed1994

Expression of human GLUT4 in mice results in increased insulin action.

Glucose metabolism was evaluated in transgenic mice expressing the human GLUT 4 glucose transporter. Fed GLUT 4 transgenic mice exhibited a 32% and 56% reduction in serum glucose and insulin and a 69% and 33% increase in non-esterified fatty acid and lactate levels, respectively. Transgenic mice exhibited a significant increase in whole-body glucose disposal during a euglycaemic-hyperinsulinaemic clamp. Insulin-stimulated glucose uptake in isolated soleus muscles and adipocytes was greater in transgenic compared to control mice due to increased basal glucose uptake. Transgenic mice displayed increased glycogen levels in liver and gastrocnemius muscle, and increased insulin-stimulated 14C-glycogen accumulation in isolated soleus muscle. We conclude that over-expression of the GLUT 4 glucose transporter in mice results in 1) an increase in whole-body glucose disposal and storage, and 2) an increase in both basal and insulin-stimulated glucose uptake and disposal in vitro. These changes resulted in the reduction of serum glucose and insulin levels. These results provide direct evidence that glucose transport (and GLUT 4 per se) plays a significant role in regulating whole-body glucose homeostasis. Additionally, these data support the idea that pharmacological strategies directed at increasing the expression of GLUT 4 protein may have beneficial (hypoglycaemic) effects in the diabetic state.

Adipocytes↗
PubMed1990

Increased glucose transporter (GLUT4) protein expression in hyperthyroidism.

We have studied skeletal muscle glucose uptake by perfused hindquarter preparations from rats treated with thyroxine. Basal glucose uptake (in the absence of insulin) was approximately 2 fold higher in muscle of hyperthyroid rats compared to controls. Insulin (10(-7) M) stimulated glucose uptake 4.0 and 6.8 fold in the 10 day and 30 day controls rats, respectively. Maximal glucose uptake (10(-7) M insulin) was not different in control and hyperthyroid rats and thus insulin responsiveness in the hyperthyroid animals was reduced to 2.5 fold stimulation. The abundance of the insulin-sensitive glucose transporter protein (muscle/fat, GLUT-4), measured by Western blot analysis using polyclonal antisera, was higher in skeletal muscle from both groups of hyperthyroid rats. These studies indicate that thyroid hormones increase basal glucose uptake in skeletal muscle and this is due, at least in part, to an increment of GLUT-4 isoform. Increased expression of muscle glucose transporter proteins may be responsible for the increased peripheral glucose utilization seen in hyperthyroidism.

Animals↗