EFFECTS OF INSULIN-LIKE GROWTH-FACTOR-I (IGF-I) AND IGF-II ON THE GROWTH OF ANTLER CELLS IN-VITRO

The effects of insulin-like growth factors -I and -II (IGF-I and -II) on the growth of undifferentiated (fibroblast zone) cells from the gro wing tip of red deer velvet antlers and from cells 1.5 cm distal to th e growing tip (cartilage zone) were investigated in primary cell cultu re. The addition of IGF-I or IGF-II to the medium of cultures preincub ated in serum-free medium for 24 h increased the rate of [H-3]thymidin e uptake in a dose-dependent manner in both cell types, with maximal s timulation occurring when 1 nM-30 nM was added. The addition of IGF-II to the incubation medium containing IGF-I did not cause a further inc rease in [H-3]thymidine uptake in either cell type over and above each growth factor alone, indicating that there were unlikely to be synerg istic effects of IGF-II on the mitogenicity of IGF-I. Binding studies were carried out using 3 x 10(5) fibroblast zone cells and cartilage z one cells after they had been incubated in serum-free medium for 24 h. I-125-Labelled IGF-I (10(-9) M) in a final volume of 200 mu l was add ed to each culture and incubation carried out at 4 degrees C for a fur ther hour. I-125-Labelled IGF-I bound specifically to both fibroblasts and cartilage zone cells; binding was displaced by both unlabelled IG F-I and by IGF-I antibody. These findings indicate that IGF-I and IGF- II are important mediators for antler growth in vitro and suggest that in view of correlations between IGF-I and antler growth, IGF is funct ionally significant in controlling velvet antler growth in vivo.