Studies on intimal smooth muscle cells in rabbits: decreased growth response to the tumor promoter.

The growth behavior of intimal smooth muscle cells (SMC) prepared from atheromatous plaques of the thoracic aorta in hyperlipidemic rabbits was studied in a culture system. Specimens of intimal and normal medial SMC were examined in terms of their proliferative response to various growth factors, polypeptide hormones or 12-O-teradecanoylphorbol-13-acetate (TPA). Intimal SMC showed lower rates of growth and DNA synthesis when the cells were exposed to TPA, but there was no difference in growth response between intimal and medial SMC to the other growth-promoting stimuli such as fibroblast growth factor (FGF), epidermal growth factor (EGF), insulin or serotonin. 3H-phorbol-12,13-dibutyrate (3H-PDBu) binding assays showed the number of binding sites to phorbol esters in intimal SMC to be decreased by 65% as compared with that in medial SMC. These results suggested that intimal SMC have different growing characteristics, which seemed to be acquired during the process of intimal thickening.