The influence of cytokines on intracellular calcium concentration ([Ca2+]i) and the production of prostacyclin (prostaglandin l2; PGI2) by cultured human umbilical vein endothelial cells (HUVEC) were examined. HUVEC were incubated for 24 h in media containing interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN gamma), or interleukin-6 (IL-6), and thrombin-stimulated increases in [Ca2+]i and PGI2 production were then examined. Thrombin-stimulated PGI2 production by HUVEC pretreated with 10 U/mL of IL-1 beta or 200 U/mL of TNF-alpha for 24 h was potentiated, while increases in [Ca2+]i were suppressed. In contrast, HUVEC pretreated with 5000 U/mL of IFN-gamma for 24 h had both enhanced PGI2 production and increases in [Ca2+]i. IL-6 affected neither PGI2 production nor [Ca2+]i in HUVEC stimulated with thrombin. The burst increase in thrombin-stimulated PGI2 production by HUVEC pretreated with cytokines did not correlate with the increase in [Ca2+]i. Cytokines have been reported to induce enzymes involved in the arachidonic acid cascade, such as phospholipase A2 (PLA2) and cyclooxygenase-2 (COX-2). Therefore, the increase in [Ca2+]i does not appear to be as important for thrombin-stimulated PGI2 production as does the induction of these enzymes by cytokines.