Platelets-induced stimulation of endothelin-1 production and inhibition by phosphoramidon

The effects of platelets on endothelin-1 (ET-1) production were examined by using cultured bovine pulmonary artery endothelial cells (ECs). Platelets (6 x 10(6) to 2 x 10(9) platelets/ml) prepared from rat peripheral arterial blood markedly stimulated immunoreactive (IR)-ET release from ECs into the culture medium, in a time-and platelet number-dependent manner. High-performance liquid chromatography analysis of the culture supernatant following exposure to platelets revealed one major IR-ET component corresponding to the elution position of synthetic ET-1. Northern blot analysis showed that platelets enhanced prepro ET-1 mRNA expression in the ECs. Increased IR-ET release was observed with the supernatant obtained after incubation of platelets, and this increment was significantly inhibited by transforming growth factor-beta 1 neutralizing antibody. Phosphoramidon, an ET converting enzyme inhibitor, significantly decreased the amount of IR-ET accumulating in the culture medium of ECs, incubated with or without platelets, and the decreasing effect of phosphoramidon in the presence of platelets was greater than that in their absence. A similar effectiveness of phosphoramidon was seen when transforming growth factor-beta 1 was used instead of platelets. Thus, platelets appear to stimulate the endothelial production of ET-1 in vitro, probably through a release of transforming growth factor-beta 1. We also suggest that the inhibition of ET converting enzyme by phosphoramidon is more effective in the augmented condition of ET-1 production than in the basal condition.