CELL-BIOLOGICAL STUDIES ON AMINO ACID NUTRITION AND BONE GROWTH IN SHEEP

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The expressed classes of messenger RNA of Insulin-like growth factor (IGF) -I and -II were determined in the growth cartilage and the liver of 10 days old lambs using RT-PCR.Three classes of IGF-I mRNA were found in either tissues. In the cartilage, all the classes of IGF-II mRNA other than class 1 were expressed. On the other hand, all the classes including class 1 were expressed in the liver. IGF-I and -II mRNAs were quantitatively determined by RT-PCR in the cartilage when PCR of 20 to 40 cycle was adopted. In addition, it was clear that the expression of IGF-I mRNA was less than that of IGF-II in the cartilage, which suggested that IGF-II is an important paracrine factor in the growth cartilage.Isolated chondrocytes from the growth plate of lambs were placed into the diffusion chambers then the chambers were subcutaneously implanted into lambs. The cells were proliferated in the chamber till 10 days of implantation then the cells were morphologically changed and accumulation of uronic acid, which is an index of cartilage activity, was stimulated. On 60 days of implantation, these differentiated chondrocytes were largely occupied the inside of chamber.Then lambs were fed a high protein diet or low protein diet with or without by-passed methionine. Then the chambers placed isolated chondrocytes were subcutaneously implanted into these lambs. The cellular proliferation was stimulated by addition of the methionine when sheep were fed the high protein diet. The contents of uronic acid was increased in all of the group by 60 days but there was not clear difference among the groups. When lambs were fed the low protein diet without the methionine, IGF-I mRNA content was increased. However, IGF-I mRNA was decreased in the other groups. IGF-II mRNA content was not changed during the in vivo incubation and was not affected by the difference of nutritional plane of protein.