Adenosine 3′:5′-cyclic monophosphate induces regulated secretion of tissue-type plasminogen activator and von Willebrand factor from cultured human endothelial cells

The effect of compounds increasing intracellular adenosine 3':5'-cyclic monophosphate [cAMP](i) levels (prostacyclin, isoproterenol, forskolin, cholera toxin), and of the cAMP analogs 8-bromo-cAMP and dibutyryl-cAMP, on the regulated secretion (acute release) of tissue type plasminogen activator (tPA) and von Willebrand factor (vWF) was studied in cultured human umbilical vein endothelial cells (HUVEC). Prostacyclin, isoproterenol and forskolin, which increased [cAMP](i) in HUVEC, and the cell-permeant cAMP analog 8-bromo-cAMP induced dose-and time-dependent secretion of tPA and vWF. The extent of vWF and tPA release correlated with [cAMP](i), and was increased by the phosphodiesterase inhibitor isobutylmethylxanthine. In contrast to thrombin, the cAMP-elevating agents did not increase the intracellular calcium concentration [Ca2+](i) in HUVEC. At submaximal concentrations, the effects of thrombin and prostacyclin were additive. Our results show that an increase in [cAMP](i) resulted in regulated secretion(acute release) of tPA and vWF from HUVEC, without the concomitant increase in [Ca2+](i) which is, in HUVEC, essential for thrombin-induced regulated secretion to occur. cAMP-induced secretion represents a novel mechanism for causing regulated secretion of tPA and vWF from endothelial cells.