Effect Of Exogenous Growth Hormone Injection On Skeletal Muscle Growth And GH-IGFs Axis Genes Expression Of Nile Tilapia, Oreochromis Niloticus

Skeletal muscle is a major component of the fish torso, and the basic unit of theskeletal muscle is a muscle fiber. The muscle fibers increase in size (hypertrophygrowth) and the new muscle fibers generate (hyperplasia growth) constitute the totalskeletal muscle growth. The muscle growth of fish is co-regulated by genetics, nutrition,environment and a variety of hormones.GH-IGFs growth axis is the critical path of fishgrowth regulation. The path begins with the secretion of growth hormone (GH) bypituitary, and then GH binds to its receptor in blood circulation to stimulate thesynthesis and secretion of insulin-like growth factor (IGFs).The IGFs start theintracellular signal transduction mechanism in target cells, so as to promote the growthand differentiation of tissues and cells. GH is one of the most important hormones thatregulate animal growth. GH has the effects of promoting growth, accelerating proteinsynthesis, improving food conversion efficiency, and enhancing fish immunity andeuryhaline fish osmoregulation capacity.In order to understand the molecular promoting mechanism of exogenous growthhormone, the same batch of Nile tilapia Oreochromis niloticus was grouped into twogroups: the experimantal group was injected with exogenous recombinant humangrowth hormone in muscle once a week, whereas the control group was injected withPBS only. The body length, weight of the fish were measured weekly, skeletal musclefibers number and area in the first dosal myomere was analysed by means of paraffintissue sections once every two weeks. The results showed that body length and weight of the experimental group were bigger than that of the control group since the firstinjection, significant variation were observed at the5thand7thweek for body weightand body length, respectively. Fibers number and area in the experimantal group werealso bigger than that in the control group since the first week. Significant exogenoushyperplasia and hypertrophy were detected in the experimental group since the5thweek.These results suggested that injection of exogenous growth hormone can promote bodygrowth in body length, body weight, as well as in skeletal muscle. Hypertrophy growthwas more dominant than hyperplasia growth in accounting for skeletal muscle growthof Nile tilapia. And the GH-IGFs growth axis and skeletal muscle MyoDs geneexpression of experimental group and control group were detected by quantitative PCRmethod during1-7weeeks. The results show that GHR1mRNA expression wassignificantly up-regulated in liver and skeletal muscle, however, GHR2mRNAexpression was significantly reduced. IGF-1mRNA and IGF-2mRNA weresignificantly increased in liver and skeletal muscle; MyoD1mRNA, MyoD2mRNAlevels were significantly elevated of skeletal muscle. We can inferred that theexogenous GH accelerates growth and skeletal muscle fiber hyperplasia andhypertrophy of Nile tilapia by up-regulating GHR1, IGF-1, IGF-2and MyoDs geneexpression.