ABSTRACT We and other investigators obtained evidence that platelets stimulate endothelin-i (ET-i) production at both message and protein levels in vascular endothelial cells (EC5),and that plate let-derived transforming growth factor-f31 (TGF-j3i) is respon sible for this stimulation. In the present study, we examined the effects of acidification or heat treatment, known to activate latent TGF-f31, on the platelet supernatant-induced Er-i pro duction in cultured porcine aortic ECs. Supematant of platelets (6.0 x 1O@ platelets/mI) aggregated by adenosine diphosphate contained large amounts of TGF-pi, but were almost in a latent form, and the proportion of active TGF-j31 in the supematant was increased markedly in the case of acidification or heat treatment. These treatments also significantly potentiated the supematant-induced stimulation of prepro Er-i mRNA expres sion and the Er-i release in ECs. Purified TGF-@i also en hanced Er-i release, dose-dependently, but the enhancement declined at the higher concentrations. Thus, powerful stimula tion of Er-i production by platelet supematant after acidifica tion or heat treatment cannot be explained only by increments in active TGF-131. The supematant-induced stimulation of Er-i synthesis was significantly inhibited by concomitant treatment of TGF-@i neutralizing antibody, but this inhibition was incom plete even at a concentration that abolished TGF-31 -induced maximal stimulation. These resutts suggest that platelet-induced stimulation and subsequent acidification and heat treatment induced potentiation on endothelial Er-i production depend closely on release and activation of TGF-@i derived from plate lets. However, when TGF-fii concentration is increased, this peptide may further stimulate Er-i production, probably through interactions with other platelet-derived substances
