LHRH-A对尼罗罗非鱼生长及生长轴相关基因表达的影响

促性腺激素释放激素(GnRH)的主要作用是刺激脑垂体促性激素(GtH)的释放, 亦可促进鱼类生长激素(GH)的释放。促黄体素释放激素类似物(LHRH-A)是哺乳类GnRH的类似物, 为了分析LHRH-A对尼罗罗非鱼生长调节的作用, 设计了长期和短期2个实验, 采用腹腔注射(剂量0.1 μg/g体重)方法, 分析LHRH-A对尼罗罗非鱼绝对生长率、特定生长率、肝体系数和肥满度的影响, 并应用荧光实时定量PCR方法检测在注射LHRH-A后不同时段(6h、12h、24h、2周)尼罗罗非鱼垂体GH、肝脏GHR和肝脏IGF-I基因的表达变化。结果表明, LHRH-A组尼罗罗非鱼的绝对生长率、特定生长率、肝体系数、肥满度均显著高于对照组(P<0.05); 注射LHRH-A后12h、24h垂体GH mRNA表达水平均显著升高(P<0.05), 2周后恢复到对照组水平; 注射LHRH-A后24h和2周肝脏GHR mRNA表达水平显著上升(P<0.05); 注射LHRH-A后6h肝脏IGF-I mRNA表达水平显著升高(P<0.05), 12h、24h和2周恢复到对照组水平。以上结果提示, LHRH-A可显著上调尼罗罗非鱼生长轴相关基因的表达, 从而促进鱼类的生长。

EFFECTS OF LHRH-A ON THE GROWTH AND GENE EXPRESSIONS OF THE GROWTH AXIS IN NILE TILAPIA OREOCHROMIS NILOTICUS

Regulations of synthesis and secretion of growth hormone (GH) in teleosts are based on the dual control of hypothalamic stimulators including gonadotropin-releasing hormone (GnRH), dopamine (DA), and growth hormone-releasing hormone (GHRH), and hypothalamic inhibitors including somatostatin (SS) and norepinephrine (NE). Gonadotropin-releasing hormone (GnRH) can stimulate the release of growth hormone (GH). LHRH-A is an analog of mammalian GnRH. Nile tilapia (Oreochromis niloticus), a freshwater fish with sexual dimorphism. The effects of LHRH-A on the growth and expressions of GH, GHR and IGF-I mRNA in Nile tilapia remain unclear. Two experiments, designated as long-term and short-term experiments, were carried out. In the long-term experiment, two hundreds Nile tilapias of similar body weight were randomly assigned to the control group (intraperitoneal injection with phosphate saline) and the LHRH-A group (intraperitoneal injection with LHRH-A, 0.01 μg/g body weight) and fed under the same conditions for 70 days. The absolute growth rates (AGR), specific growth rates (SGR), condition factor (CF) and hepatosomatic index (HSI) were obtained by measuring the body length, body weight and hepatic weight at different stages. AGR_W and AGR_L levels of LHRH-A-treated male and female increased by 15.95%, 14.82% and 5.06%, 25.36%, respectively, compared to control group (P<0.05). During the 0—2, 2—6, and 6—10 weeks, SGR_W and AGR_L levels of LHRH-A-treated male increased by 11.52%, 1.21%, 39.06% and 3.94%, 1.08%, 10.00%, respectively, compared to the control group (P<0.05); similarly, SGR_W and AGR_L levels of LHRH-A-treated female increased by 14.29%, 6.88%, 5.83% and 24.19%, 9.09%, 28.21%, respectively (P<0.05). Furthermore, CF and HIS levels of the LHRH-A group were also significantly higher than those of the control group (P<0.05). In the short-term experiment, 120 Nile tilapias of similar body weight were randomly assigned to the control group (intraperitoneal injection with phosphate saline) and the LHRH-A group (intraperitoneal injection with LHRH-A, 0.01 μg/g body weight) and sampled at 6, 12, 24h, and 2 week. Real-time quantitative PCR was used to detect the expressions of GH in pituitary and GHR and IGF-I in liver at different life stages after injection. The expressions of GH in pituitary increased at 12h (P<0.05), and IGF-I in liver increased quickly at 6h, but soon returned to the level of control group. The expression of GHR in liver increased slowly at 24h (P<0.05) and maintained high at 2 week (P<0.01). The results indicated that LHRH-A could increase the mRNA expressions of GH in pituitary and GHR and IGF-I in liver, and significantly promote growth of Nile tilapia. Moreover, our study suggested that large scale administration of some neruoendocrine factor in diet to accelerate the growth rate of cultured fish has promising potential.