Role of Ca2+ and cyclic AMP in the regulation of the production of prostacyclin by the vascular endothelium.

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Abstract
Incubation of primary monolayer cultures of human umbilical vein endothelial cells with buffer, thrombin (0.5 U/ml), ionophore A23187, calcimycin (calcimycin, 10 .mu.M), arachidonic acid (20 .mu.M), or prostaglandin [PG] H2 (4 .mu.M) resulted in prostacyclin (PGI2) production in nanomolar quantities to the extent of 36 .+-. 2, 276 .+-. 13, 485 .+-. 32, 533 .+-. 22 and 532 .+-. 22, respectively, as measured by radioimmunoassay of 6-keto-PGF1.alpha.. Preincubation of the endothelium with 1 mM 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate, an antagonist of cytoplasmic Ca2+, or with 4 mM 1-methyl-3-isobutylxanthine (MIX), an inhibitor of cyclic nucleotide phosphodiesterase activity, blocked PGI2 release induced by thrombin or A23187, decreased arachidonic acid-induced release by .apprx. 50%, but had no effect on PGH2-induced release. Radioimmunoassay of cAMP in the endothelium showed that the basal level (1.85 .+-. 0.14 pmol of cAMP per 4.5 .times. 105 cells) was increased by an average of 3.9-fold with 4 mM MIX. PGI2 (0.4 .mu.M) had no significant effect on cAMP levels in the absence of MIX, but caused a 2-fold increase with 4 mM MIX. The stimulation of PGI2 biosynthesis apparently is mediated by Ca2+, increased cAMP inhibits PGI2 production and cAMP phosphodiesterase activity modulates PGI2-induced increases in the intracellular concentration of cAMP.