Halevy, O., Department of Animal Science, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, 76100, Israel
Schindler, D., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, Bet Dagan 50-250, Israel
Hurwitz, S., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, Bet Dagan 50-250, Israel
Pines, M., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, Bet Dagan 50-250, Israel

Avian chondrocytes and fibroblasts, derived from epiphyseal growth-plate and skin, respectively, were cultured in vitro. In chondrocytes, epidermal growth factor (EGF) caused a dose-dependent stimulation of proliferation. EGF receptor mRNA was not detected with the v-erb B probe in chondrocytes cultured in the presence of 5% fetal calf serum (FCS). In the absence of FCS in the medium, a time-dependent increase in the level of EGF receptor mRNA was observed. Parallel changes were also observed in the level of EGF receptor, as demonstrated by immunofluorescence using antibodies directed against avian EGF receptor. In avian fibroblasts, EGF receptor mRNA and EGF receptor levels were not affected by FCS. Furthermore, FCS did not affect the level of thyroid hormone receptor mRNA (using v-erb A as a probe) in either chondrocytes or fibroblasts. Parathyroid hormone (PTH), which acts as a mitogen in avian chondrocytes attenuated - whereas atrial natriuretic peptide (ANP), a suppressor of chondrocyte proliferation, enhanced - EGF receptor mRNA. The present results show that avian growth-plate chondrocytes respond to EGF and bear EGF receptors. The levels of EGF mRNA and EGF receptor are inversely related to cell proliferation. The results also support previous suggestions that PTH and ANP play important roles in chondrocyte proliferation, possibly through their effect on the synthesis of the EGF receptor. © 1991.