Endothelin is a potent vasoconstrictor peptide and a smooth muscle mitogen produced in large amounts by endothelial cells in culture. To determine whether other cellular elements of the vessel wall modify the release or clearance of endothelin, we studied the effect of coculture of endothelial cells with vascular smooth muscle cells or fibroblasts on endothelin release. Endothelial cells were grown to confluence on microcarrier beads and transferred to dishes containing confluent cultures of smooth muscle cells or fibroblasts or control media only. In parallel experiments, endothelial cells on microcarrier beads were incubated in media conditioned by 48-h exposure to smooth muscle cells or fibroblasts. Endothelin concentration was determined by radioimmunoassay (rabbit anti-endothelin-1 serum). Endothelial cells alone released large amounts of endothelin: 169 +/- 60 and 982 +/- 237 pg/10(6) endothelial cells at 4 and 24 h, respectively. Endothelin accumulation was markedly reduced in coculture with smooth muscle cells or fibroblasts by 81 +/- 10 and 49 +/- 5% (P less than 0.05), respectively, at 24 h. This difference could not be explained by smooth muscle cell binding or degradation of endothelin. Furthermore, smooth muscle cell- or fibroblast-conditioned media significantly reduced endothelin release, and twofold concentration of smooth muscle cell-conditioned media fully reproduced the inhibition of endothelin release found in coculture, confirming the presence of a transferable inhibitor. Therefore, we propose that endothelin secretion from endothelial cells may be regulated by an inhibitory factor produced by the vascular media. This mechanism might limit the production of endothelin in intact vessels and thereby protect against excessive vasoconstriction or proliferation of vascular target cells.