| As a product of the obese gene(ob), leptin has a variety of physiological function. Due to its a pivotal role in the regulation of food intake and energy balance in mammals and potential for treating obesity, many leptin studies have been performed all over the world. However, as a kind of heterothermic animal in water, the fish is quite different from homothermal animal in energy metabolism. Therefore, it is important to study leptin physiological functions in fish. 1. High-lipid and low-lipid adaption metabolism in juvenile grass carpAs a kind of typical herbivorous fish in China, Grass carp(Ctenopharyngodon idellus) has good appetite for aquatic plants in the wild and can be fed with artificial diets in aquaculture, making it a qualified fish variety with potential high feed conversion. This study was conducted to examine the systemic metabolic strategies of grass carp to maintain lipid homeostasis when fed with low- or high-fat diets. The nitrogenous diets with different fat levels(9.3 g/kg, 48.7 g/kg and 107.9 g/kg) were fed to grass carp for 8 weeks. After the feeding trial, the growth rate and feed intake of grass carp fed with low-lipid(LL) diet or high-lipid(HL) diet were lower than fish fed with medium-lipid(ML) diet. Serum triglyceride(TG) and total body fat contents were significantly increased in grass carp with increasing lipid intake. The expressions of genes(gk and pk) involved in glycolysis and the expressions of genes(acc and fas) involved in lipid synthesis were significantly higher in LL group than those in ML group(P < 0.05), meanwhile, the lipolysis gene(cpt1) mRNA abundance was significantly reduced in LL group than ML group(P < 0.05). The expressions of genes(g6pase and pepck) involved in gluconeogenesis and the gene expression of pparα involved in β-oxidation of fatty acids were significantly higher in HL group than those in ML group(P < 0.05), the gene expressions of acc and fas were significantly lower in HL group than ML group(P < 0.05). Furthermore, the expressions of leptin mRNA abundance was highest in HL group(P < 0.05), suggesting that increased β-oxidative-induced FA or gluconeogenesis-induced serum glucose might induce the appetite suppression by high dietary fat through modulation of leptin expression. This study could be a reference in the systemic adaptation of lipid metabolism responding to dietary fat in fish. 2. Leptin function preliminary research in mandarin fishMandarin fish(Siniperca chuatsi) is a special species in China, as a carnivorous benthic ferocious fish, only feeding the living fry in the wild. Found in almost all the rivers and lakes. It is one of the chief economic freshwater fishes in China due to its large size, fast growth and delicious flesh. As we all know that leptins play an important role in the mandarin fish energy regulation, in order to understand mandarin fish leptin physiological function, we study gene expression of leptin in the brain and liver under postprandial and short-term fasting treatment. The expressions of brain leptinA and leptinB were observed to increase after a meal. During the short-term fasting, the expressions of leptins in mandarin fish brain were decreased significantly(P < 0.05). A persistent and significant increase in hepatic leptinA expression(P < 0.05) supported a relationship between leptin and food intake in mandarin fish. These results suggest that leptinA plays an important role in the regulation of energy homeostasis in this carnivorous fish, and leptinB is probably a specialized gene responsible for the central nervous system(CNS) control of energy regulation. |
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