GROWTH-HORMONE STIMULATES THE SECRETION OF INSULIN-LIKE GROWTH-FACTORBINDING PROTEIN-2 (IGFBP-2) BY MONOLAYER-CULTURES OF SHEEP COSTAL GROWTH-PLATE CHONDROCYTES

Using monolayer cultures of costal chondrocytes established from four week old Clun Forest lambs, we have demonstrated that, under serum fre e conditions the cells release three IGFBPs (32, 29 and 21 kDa) into t he medium. The most abundant of these -the 32 kDa BP-was shown to be I GFBP-2 by Western blotting. Furthermore we demonstrate that the levels of IGFBP-2 in conditioned medium are acutely increased (6, 12 and 24 h time points) following treatment of cells with bovine GH (1100 ng/ml ). In a parallel set of experiments, using ovine fibroblasts (derived from dermis) we show that IGFBPs of Mr 32, 29 and 21 kDa are also secr eted by this cell type. However the relative abundance of these BPs di ffered from that seen in the chondrocyte cultures, with the 21 kDa spe cies now the most abundant. In addition, prolonged exposure of autorad iographs indicated that fibroblasts secreted a higher Mr IGFBP (most p robably ovine BP-3) that was not detected in any of our chondrocyte cu ltures. Most significant however was the demonstration that bGH did no t dramatically affect the levels of IGFBPs in fibroblast cell cultures , We conclude that GH stimulates BP-2 production from chondrocytes and this is a cell-type specific effect in as much as it is not replicate d in cultures of dermal fibroblasts.