GROWTH-HORMONE INHIBITS DIFFERENTIATION OF AVIAN EPIPHYSEAL GROWTH-PLATE CHONDROCYTES

The effect of chicken growth hormone (cCH) on the proliferation and di fferentiation of avian growth-plate chondrocyte was evaluated in cultu re. In culture, addition of ascorbic acid to the culture media caused cell differentiation. Treatment of proliferating chondrocytes with cGH caused a time-dependent increase in collagen type II gene expression together with a decrease in the appearance of osteopontin (OPN) in the medium. In addition, the ascorbic acid-dependent increase in alkaline phosphatase (AP) activity was inhibited by cGH. IGF-I, on the other h and, caused an increase in AP activity in the ascorbic acid-treated ch ondrocytes. In the presence of ascorbic acid, cGH did not affect colla gen type II gene expression or the appearance of OPN in the medium. Pr oliferation of avian growth-plate chondrocytes, in contrast to mammali an chondrocytes, was not stimulated by GH alone, although the presence of cGH was essential for chondrocyte survival in long-term culture. c GH in combination with epidermal growth factor (EGF) stimulated cell p roliferation. These results suggest that GH inhibits differentiation i n avian growth-plate chondrocytes, thereby sustaining their proliferat ive state and maintaining their sensitivity to growth factors such as EGF.