Comparative studies of EGF, TGF-alpha, and TGF-beta 1 action on the synthesis of DNA and cellular proteins in rat L6 myogenic cells and fetal bovine myoblasts demonstrated considerable differences between particular growth factors, dependent on dose and target cells. 2. Among examined growth factors only EGF exerted mitostimulatory action, more pronounced at lower concentrations. EGF, progressively with dose, stimulated protein synthesis much more effectively in fetal bovine myoblasts than in L6 cells. 3. The dynamics of stimulation of protein synthesis by TGF-alpha was greater than by EGF in both examined types of cell cultures. 4. The maximal response of fetal bovine myoblasts to TGF-alpha in a concentration of 100 ng/ml reached 370%, whereas EGF in a 10 times higher concentration stimulated protein synthesis only to 123% of control. 5. In contrast to EGF, TGF-alpha significantly inhibits DNA synthesis. Inhibition of the mitogenic response with simultaneous stimulation of protein synthesis by TGF-alpha may indicate changes toward cell differentiation. 6. TGF-beta 1 in smallest concentration inhibits both DNA and protein synthesis. The suppressive action of TGF-beta 1 was more distinct in fetal bovine myoblasts than in the L6 cell line. 7. Increasing concentrations of TGF-beta 1 diminished its inhibitory effect, even leading to stimulation of protein synthesis at higher doses in L6 myoblasts.
