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

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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.