Glucose uptake in vivo in skeletal muscles of insulin-injected chicks

Glucose uptake across the plasma membrane in animal cells plays a crucial role in whole-body glucose homeostasis. Insulin-stimulated glucose transport activity in vivo in several tissues was estimated using the 2-deoxy-d-[1-3H]glucose ([3H]2DG) uptake determination method. A tracer dose of [3H]2DG was injected intravenously into 8-day-old chicks (Gallus gallus) administered simultaneously or previously with porcine insulin (40 μg/kg BW). After 10 or 20 min, several major tissues, including skeletal and cardiac muscle, were sampled and their 2-deoxy-d-[1-3H]glucose 6-phosphate content analyzed. Plasma glucose concentration and [3H]2DG radioactivity were lowered by insulin within 20 min of [3H]2DG administration, while the plasma [3H]2DG/glucose ratio was not significantly different between chicks injected with insulin and their control counterparts. A marked uptake of 2DG was observed in cardiac tissue and brain, followed by kidney and skeletal muscles. In skeletal muscles, insulin increased the 2DG uptake in soleus, extensor digitorum longus and pectoralis superficialis muscles. On the other hand, no significant increases in insulin-induced 2DG uptake were detected in cardiac muscle or adipose tissue compared to controls. The results show that glucose transport across the plasma membrane in vivo in most skeletal muscles tested, but not cardiac muscle, was increased by insulin administration to chicks. These findings suggest that an insulin-responsive glucose transport mechanism is present in chickens, even though they intrinsically lack GLUT4 homologous gene, the insulin-responsive glucose transporter in mammals.