Lack of inhibition of DNA synthesis by prostaglandin I2 in cultured intimal smooth muscle cells from rabbits.

The negative control system for proliferation by prostaglandin I2 (PGI2) was studied in the smooth muscle cells (SMC) cultured from the thickened intima (intimal SMC) of rabbit aortas. Indomethacin was found to enhance DNA synthesis of medial SMC but not that of intimal SMC. Exogenously added PGI2 or its stable analogue, CS-570, was observed to inhibit DNA synthesis of medial SMC enhanced by indomethacin but not that of intimal SMC. These results indicate that medial SMC are negatively controlled by endogenous PGI2 and that intimal SMC have no such negative control system for cell proliferation. This lack of negative control may be one of the mechanisms underlying the rapid growth behavior of intimal SMC as compared to medial SMC.