| Summary: | Orexins are neuropeptides involved in energy homeostasis. In fish, the function of orexin-A in glucose metabolism is less reported. The present study aims to identify the potential role of orexin-A in the glucose absorption and metabolism in common carp. The full length of orexin cDNA was cloned using RT-PCR and RACE method. The prepro-orexin cDNA was 513 bp containing an open reading frame of 474 bp and encoded 157 amino acids which including 47 amino acids of orexin-A and 28 amino acids of orexin-B. The tissue distribution results showed that orexin was expressed in multiple tissues, especially with high-level expression in hypothalamus. The exogenous orexin-A protein was chemical synthesized. Intraperitoneal injection of orexin-A alleviated the increase of plasma glucose level at 1 h and 2 h after OGTT (Oral glucose tolerance test). Orexin-A also decreased glucose uptake activity and the expression of sglt1 and glut2 mRNA in intestine. However, orexin-A significantly increased the mRNA expression of glut2 in liver and glut4 in muscle. Moreover, the gluconeogenesis-related gene fbpase mRNA was significantly down-regulated, while glycolysis-related genes gk and hk were significantly up-regulated after treatment with orexin-A in vivo and vitro. These results implied that hyperglycemia could be alleviated in common carp after the injection of orexin-A and suggest a role of this peptide as a plasma glucose regulator by inhibition glucose absorption in intestine, promotion glucose transport to liver and muscle. Furthermore, hepatic gluconeogenesis was inhibited. Taken together, this study helped to understand the characterization of prepro-orexin and the function of orexin-A in fish glucose homeostasis.
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