Effect of nutrition on the gene expression of insulin like growth factor-II Insulin like growth factor-II as an paracrine factor

雄性去势羔羊被给予对照或低蛋白饮食。在给予低蛋白饲料的绵羊血清尿素氮浓度低于正常范围后，采集部分肝脏和生长板软骨。从这些组织中提取总RNA。实验一采用逆转录-聚合酶链式反应检测胰岛素样生长因子(IGF-I和IGF-II)的mRNAs。虽然肝脏中IGF-I的mRNA因蛋白质缺乏而减少，但饮食处理并不影响软骨中的IGF-I的mRNA。虽然肝脏中IGF-II的mRNA因蛋白质缺乏而降低，但饮食处理不影响软骨中的IGF-II的mRNA。这些结果表明，作为内分泌因子的IGFS在肝脏中的表达受到蛋白质缺乏的抑制，而作为旁分泌因子的IGFS在笼子中的表达不受蛋白质缺乏诱导的营养胁迫的影响。每个IGF都有一些转录本，因为这些基因有几个转录起始点。实验二采用逆转录-聚合酶链式反应检测各IGF基因的转录本。蛋白质缺乏并不能引起两种组织中IGF-I或IGF-II转录产物的变化趋势一致，这表明这两种转录产物的产生受到不同的调控。受蛋白质缺乏影响的转录本在肝脏中不明显。在第三个实验中，我们研究了卵巢切除对育肥牛血浆IGFS浓度的影响。卵巢切除对血浆IGFS浓度无影响。育肥过程中血浆IGF-I水平降低。实验期间血浆IGF-I水平与体重增加呈正相关。而血浆IGF-II浓度无明显变化。这些结果表明，IGF-I是肥育牛体重增加的重要内分泌因子，但IGF-II的作用尚不清楚。

Male castrated lambs were given control or a low protein diet. After serum concentration of urea nitrogen became less than normal range in sheep given the low protein diet, a part of liver and growth plate cartilage of the lib were collected. Total RNA was extracted from these tissues. In the first experiment, mRNAs of insulin like growth factors (IGF-I and II) were determined by reverse transcription PCR. Although the mRNA of IGF-I was decreased by protein deficiency in the liver, dietary treatment did not affect the mRNA of IGF-I in the cartilage. Although the mRNA of IGF-II was decreased by protein deficiency in the liver, dietary treatment did not affect the mRNA of IGF-II in the cartilage. These results suggested that the expression of IGFs as endocrine factors (in the liver) was suppressed by protein deficiency but the expression of IGFs as paracrine factors in the catilage was not affected by nutritional stress induced by protein deficiency. There are some transcripts of each IGF because these genes possess several transcription initiation sites. In the second experiment, the transcripts of each IGF gene were determined by reverse transcription PCR. Protein deficiency did not induce consistent tendency of changes in the transcripts of IGF-I or IGF-II in the both tissues, which suggests that the production of these transcripts was differently regulated. And the transcript affected by protein deficiency was not clear in the liver. In the third experiment, we studied the effect of ovariectomy on plasma IGFs concentrations in fattening cattle. Ovariectomy did not affect plasma IGFs concentrations. Plasma IGF-I level was decreased during fattening. There was a positive correlation between plasma IGF-I level and body weight gain during the experiment. On the other hand, plasma IGF-II concentrations were not changed. These results suggest that IGF-I is important endocrine factor on body weight gain in fattening cattle but the effect of IGF-II is not clear.