Effect of growth hormone, insulin‐like growth factor I, basic fibroblast growth factor, and transforming growth factor β on cell proliferation and proteoglycan synthesis by avian postembryonic growth plate chondrocytes

We examined the in vitro effects of pituitary‐derived chicken growth hormone (cGH), recombinant human insulin‐like growth factor‐I (rhIGF‐I), recombinant human basic fibroblast growth factor (rhbFGF), and porcine transforming growth factor β (pTGF‐β) on proliferation ([³H]thymidine uptake) and matrix proteoglycan synthesis (³⁵SO₄ incorporation) by chicken epiphyseal growth plate chondrocytes. Factorial experiments were used to study the effect of these substances in a serum‐free culture system. Basic FGF had to be present in the culture medium for mitogenesis to take place. In the presence of this peptide, TGF‐β, TGF‐β + IGF‐I, and newborn calf serum (NCS) stimulated mitogenesis. The mitogenic activity of NCS could be duplicated by adding platelet‐derived growth factor (PDGF) to the culture medium. For matrix synthesis, IGF‐I was the key factor, with the addition of TGF‐β, TGF‐β + bFGF, or serum producing further stimulation in matrix synthesis. Using this culturing system, homologous cGH did not stimulate cell proliferation or proteoglycan synthesis. The lack of stimulatory activity of cGH was consistent, regardless of the age of the birds from which the chondrocytes were isolated, the zone of the growth plate, or the level of cGH used. None of the growth factors used in this study or several other systemic hormones were found to be permissive factors for GH to be active. Either other factors must be present for a direct effect of GH on growth plate chondrocytes, or the avian species differ from their mammalian counterpart.