| Orange-spotted grouper, Epinephelus coioides,is one of the popular marineaquaculture teleosts in South-east and South China. Because of its importantcommercial value, Many studies of grouper have been carried out. Ghrelin is agastrointestinal hormone, of which the third serine residue is uniquely modified byoctanoylation, and this acylation is essential for both binding to its receptor GHSR1aand eliciting biological activity. Besides ghrelin there are two more differentmolecules that originate from the same precursor molecule, pre-pro-ghrelin.Differentmeans of post-translational processing result in the formation of desacyl ghrelin andobestatin. Until today, there are studies only for ghrelin providing well-establishedand repeatedly validated insights on its regulatory effect on satiety and food intake.The signal transducing pathways of ghrelin however are only in part well identified.Yet the effects of desacyl ghrelin and obestatin on feeding behavior still remainlargely unknown and are being controversially discussed in the recent literature. Inthis thesis, the major results are as follows: 1. In the early study of our laboratory, the orange-spotted grouper cDNA andgene sequences of ghrelin have been cloned.The cDNA fragment encoding themature Desacyl Ghrelin was subclond into the vector pPICZɑA .Aftertransformation and screening ,high expression X-33 engineered strains wasobtained ,which can highly express the recombinant Desacyl Ghrelin with secretaryform.2. The effects of Desacyl Ghrelin in the orange-spotted grouper hypothalamus andpituitary were investigated by in vivo of intraperitoneal injection . For the in vivostudies, the dose of 1μg/g B.W and 2μg/g B.W. Desacyl Ghrelin can increase theexpression of GH mRNA significantly (P<0.05) after injection Desacyl Ghrelin 3hr or6hr. Desacyl Ghrelin caused a significant increase in the levels of GH mRNA ofpituitary in both dose and time-dependent manners (P<0.05). The dose of 1μg/g B.Wand 2μg/g B.W. Desacyl Ghrelin can decrease the expression of NPY mRNAsignificantly (P<0.05) after injection Desacyl Ghrelin 3hr , while Desacyl Ghrelin candecrease the expression of NPY mRNA significantly (P<0.01) after injection DesacylGhrelin 6hr. The dose of 1μg/g B.W and 2μg/g B.W. Desacyl Ghrelin can decreasethe expression of GHSR-1a mRNA significantly (P<0.05) after injection DesacylGhrelin 6hr. The dose of 2μg/g B.W. Desacyl Ghrelin can increase the expression ofPSSI mRNA significantly (P<0.05) after injection Desacyl Ghrelin 6hr.3. The effect of Desacyl Ghrelin in the orange-spotted grouper hypothalamus andpituitary was investigated by in vitro static cultures. The results showed that 1000nMDesacyl Ghrelin led to significant decrease NPY mRNA level at 6hr (P<0.01). Thedose of 1000nM Desacyl Ghrelin significantly decrease the expression of GHSR-1amRNA in hypothalamus (P<0.05) at 6hr .However, The dose of 1000nM DesacylGhrelin showed the significant increase in the expression of the PSSI mRNA inhypothalamus (P<0.05). Desacyl Ghrelin can increase GH mRNA level , while thehigh dose of 1000nM Desacyl Ghrelin showed the significant increase in theexpression of the GH mRNA in pituitary (P<0.01) at 6hr.4. We artificially synthesized the proteins of orange-spotted Grouper Ghrelin andDesacyl Ghrelin, of which the third serine residue has not octanoylation. With mixing and stiring methods, we blended the protein with routine diet, and feeded theorange-spotted groupers at the age of eight months for seven weeks. Desacyl Ghrelinhas impact on body weight and body length but Ghrelin has no this function. However,Ghrelin can increase the GH mRNA, NPY mRNAand GHSR-1a mRNA level, whileDesacyl Ghrelin can only increase the expression of the NPY mRNA inhypothalamus.
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