Expression of glut2 in response to glucose load, insulin and glucagon in grass carp (Ctenophcuyngodon idellus)

Generally, fish are thought to have a limited ability to utilize carbohydrate. Postprandial blood glucose is cleared sluggishly in fish, resulting in prolonged hyperglycemia. Facilitative glucose transporters (GLUTs) play an important role in glucose utilization. In the present study, the expression levels of glut2 in different tissues were detected in grass carp. Furthermore, the effects of oral glucose administration on glut2 mRNA expression in the liver, intestine and kidney were investigated, and we also evaluated the response of glut2 mRNA to insulin and glucagon in the primary hepatocytes of grass carp. The expression level of glut2 mRNA was highest in the liver, followed by the intestine and kidney, but lower in other tissues. The result of glucose tolerance test (GTT) showed that serum glucose reached the highest level at 3 h after GTT and recovered to the basic level at 6 h. The glut2 mRNA in the intestine was up-regulated at 1 h after GTT. However, the glut2 mRNA expression in the liver of grass carp was unchanged after GTT for 1, 3, 6 h, and even decreased at 12 h after GTT. In addition, the expression of glut2 mRNA in the primary hepatocytes was enhanced by insulin and glucagon at 3 h post treatment. These results suggested that glut2 expression in the liver of grass carp was sensitive to insulin and glucagon, but not blood glucose. The up-regulation of glut2 by these hormones might be involved in the bi-directional transportation of glucose in the liver.