Tumor necrosis factor (TNF) has been shown to induce the phosphorylation of a 27 kDa protein in a time‐ and concentration‐dependent manner in HeLa D98/AH2, ME 180 and bovine aortic endothelial cells. This phosphorylation could be reproduced by the calcium ionophore, A23187. However, this phosphorylation was not observed in L929 cells, for which TNF is highly cytotoxic, suggesting that it might play a role in actions of TNF other than the induction of cell death.

ATP and ATP gamma S(10-100 microM) stimulated the release of prostacyclin (PGI2) from bovine aortic smooth muscle cells. This effect was reproduced by UTP, ITP and partially by GTP. ADP and ADP beta S, the P2X-selective agonist alpha, beta-methylene ATP (APCPP), AMP and adenosine were all inactive. This effect of ATP gamma S was not inhibited by Reactive Blue 2, an antagonist of P2Y receptors. The stimulation of PGI2 production in aortic smooth muscle cells by these nucleotides thus seems to involve receptors distinct from both P2X and P2Y subtypes, which are responsible for smooth muscle contraction and PGI2 release from endothelial cells, respectively.

In bovine aortic endothelial cells, phorbol 12-myristate, 13-acetate induced a smaller stimulation of prostacyclin release than ionophore A23187: the combination of both agents was highly synergistic. The responses of the bovine aortic smooth muscle were very different in the 2 preparations studied. In media explants cultured for short periods, neither phorbol 12-myristate, 13-acetate, nor A23187, alone or in combination, were able to increase prostacyclin release, whereas serotonin was an effective stimulus. In cultured smooth muscle cells, outgrown from the explants, phorbol 12-myristate, 13-acetate increased prostacyclin release to the same levels as A23187 or serotonin. It is concluded that increased cytosolic Ca++ level and protein kinase C activity induce a synergistic stimulation of endothelial prostacyclin. On the other hand, the phenotypic modulation of the arterial smooth muscle, from a contractile to a synthetic state, seems to be associated with a profound change in the control of prostacyclin.

The action of dipyridamole on the vascular production of prostacyclin (PGI2) has been investigated. Dipyridamole (1-100 microM) did not induce a significant stimulation of PGI2 release in any of the following experimental models: rings of rabbit aorta, cultured endothelial cells from bovine aorta or human umbilical vein, cultured explants of bovine aortic smooth muscle. The activity of known stimuli of PGI2 release (ADP, suloctidil, serotonin) and the capacity of dipyridamole to inhibit adenosine uptake into endothelial cells were carefully checked. Pretreatment of the rabbit aorta with dipyridamole (10-100 microM) prolonged the transient stimulation of PGI2 release induced by mechanical deendothelialization: this effect was probably due to a partial protection of the cyclooxygenase against oxidative self-inactivation. Our largely negative results are consistent with the current theory that the antiplatelet action of dipyridamole is mediated by adenosine and not by PGI2.

Clinical Pharmacology & Therapeutics (1999) 65, 189–189; doi: