摘要
GH和IGF 1可作用于垂体或 /和下丘脑负反馈性地调节垂体GH的分泌 ,而这种负反馈作用必须通过下丘脑或垂体的GHR和IGF 1R来实现。为研究猪垂体GH分泌负反馈调节的发育性变化和品种特点 ,分别在 0、3、2 0、30、90、12 0和 180日龄随机选取纯种雄性二花脸猪和大白猪各 4头 ,屠宰并取下丘脑及垂体 ,用相对定量RT PCR分析下丘脑和垂体GHR和IGF 1RmRNA水平。结果表明 :下丘脑GHRmRNA表达呈明显的时序性变化 ,在 0到 12 0日龄期间呈逐渐上升趋势 ,180日龄时显著下降 (P <0 0 5 ) ,提示在快速生长期 ,GH负反馈调控机制逐渐加强。下丘脑GHRmRNA表达还表现明显的品种间差异 ,在 0到 180日龄期间大白猪均显著高于二花脸猪 (P <0 0 5 ) ;而垂体GHRmRNA表达相对稳定 ,品种和年龄间差异不显著 ,提示GH的负反馈作用位点可能主要在下丘脑。IGF 1R与GHR的表达发育模式不同。下丘脑IGF 1RmRNA的表达相对稳定 ,无显著的年龄、品种间差异 ;而在垂体 ,大白猪和二花脸猪IGF 1RmRNA水平在出生时均较高 ,随后显著下降 (P <0 0 5 ) ,2 0日龄后逐渐上升至 90日龄的较高水平 ,随后再次下降。大白猪垂体IGF 1mRNA表达在 30日龄和 90日龄时显著高于二花脸猪 (P <0 0 5 ) ,而 180日龄时二花脸猪垂体IGF 1RmRNA水平却显著高于大白?
GH and IGF-1 may serve as negative feedback factors to regulate GH secretion from pituitary by binding to their respective receptors in hypothalamus and/or pituitary.In order to evaluate the line-specific developmental patterns of negative feedback regulation of GH secretion,Erhualian (EHL) and Large White (LW) pigs with significant difference in growth rate were employed in present study to investigate the developmental changes of GH receptor (GHR) mRNA and type-1 IGF receptor (IGF-1R) mRNA in hypothalamus and pituitary from birth till 180 days of age by relative quantitative RT-PCR.Pigs were sampled at birth,3,20,30,90,120 and 180 days of age respectively.Hypothalamic GHR mRNA was expressed according to an age-dependent manner,being low at birth,then increased steadily till day 120,followed by a decrease (P<0.05) at the age of 180 days,suggesting that the sensitivity of hypothalamus to the GH negative feedback influence increase steadily during fast-growing period.LW boars expressed higher level of GHR mRNA than EHL boars (P<0.05) in hypothalamus.In pituitary,however,the GHR mRNA level was not significantly correlated with the breeds and age.The results suggested that GH might act mainly at the level of hypothalamus to regulate GH secretion.In contrast,the expression of IGF-1R mRNA exhibited line-specific developmental patterns in pituitary but not in hypothalamus.Hypothalamic expression of IGF-1R mRNA was abundant but did not show significant differences between ages,groups or lines.In pituitary,however,the IGF-1R mRNA expression was found to be high at birth both in EHL and LW pigs,subsequently declined till day 20,then followed by a slow rise reaching the second peak at the age of 90 days.At the age of 180 days,the pituitary IGF-1R mRNA level was higher in EHL pigs than that in LW pigs (P<0.05),but the opposite was true at the age of 30 and 90 days.These results suggest that the site for receiving the feedback signal of IGF-1 is more likely in pituitary rather than in hypothalamus in the pig.
基金
国家自然科学基金重点项目 (编号 :3 983 0 2 90 )~~
