DIVERGENT SELECTION FOR HIGH OR LOW GROWTH-RATE MODIFIES THE RESPONSEOF MUSCLE-CELLS TO SERUM OR INSULIN-LIKE GROWTH-FACTOR-I IN-VITRO

Genetic differences in growth potential could result from changes in t he levels of growth stimulatory factors or in the response of target t issues, The latter possibility was tested in adult myoblasts prepared from chickens selected for high (HG) or low growth rate (LG). Stimulat ion of [H-3]-thymidine incorporation into DNA by serum was of higher a mplitude in HG than LG muscle cells irrespective of whether the cell p reparations mere enriched in myoblasts or fibroblasts, HG myoblasts we re also more responsive to insulin-like growth factor-I (IGF-I) in ter ms of [H-3]-thymidine incorporation, IGF analogues with a reduced affi nity for IGF binding proteins gave similar results suggesting that act ivity of binding proteins could not explain the difference between cel ls from the HG and LG lines, This difference was restricted to the pro liferative stage because in myotubes, basal or IGF-I stimulated glucos e and amino acid transports, tyrosine incorporation and protein degrad ation were not different,