Endothelin immunoreactivity in medium from cultured porcine aortic endothelial cells correlates with the biological activity

Using the radioimmunoassay (RIA) of endothelin (ET), we measured immunoreactive ET (IR-ET) in culture medium of porcine aortic endothelial cells. The immunoreactivity in the medium was compared with the biological activity. The amount of IR-ET released into the medium was calculated at 250–350 pg/10 6 cells/hr. The amount of IR-ET released into the culture medium increased progressively with 3–24 hr of incubation and corresponded to the increase in medium-induced vasoconstriction of rat isolated aorta. When the vasoconstrictor activities in the culture medium were plotted against the IR-ET concentration determined by RIA, the concentration-response curve showed similarity to that obtained with synthetic porcine ET. This RIA system will be a useful for investigating mechanisms of ET secretion from endothelial cells.