Functional implications of cAMP and Ca2+ on prostaglandin I2 and thromboxane A2 synthesis by human endothelial cells.

Abstract

Human umbilical vein endothelial cells were incubated with ATP, ADP, thrombin, or ionophore A23187 for as long as 600 seconds. A statistically significant rise in the prostaglandin I2 (prostacyclin; PGI2) and thromboxane A2 (TxA2) release was observed after 45 seconds. The maximum amount of cytosolic free Ca2+ was reached between 20 and 30 seconds. A statistically significant elevation of intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels was observed only in response to ATP and ADP after 120 seconds. Furthermore, adenosine, caffeine, phorbol 12-myristate 13-acetate (PMA), and adenosine 5'-(alpha, beta-methylene)triphosphate were tested alone or in combination with ATP or thrombin. PMA inhibited ATP-stimulated eicosanoid biosynthesis but had no effect on thrombin. Of the agents used to increase cytosolic free Ca2+ concentrations, only PMA failed to provoke eicosanoid release. Similarly, only PMA failed to induce a Ca2+ flux in the absence of extracellular Ca2+. The data presented show that PGI2 and TxA2 release from human umbilical cord endothelial cells is closely associated with Ca2+ mobilized from intracellular sources. Extracellular Ca2+, as well as changes in intracellular cAMP levels, has no influence on endothelial eicosanoid synthesis, at least for short-term regulation (less than or equal to 600 seconds).

Chronic exposure of cultured bovine endothelial cells to oxidized LDL abolishes prostacyclin release.

“…7 Under basal conditions, LDL stimulated phospholipase C activity, an effect that was not mediated by a cell-dependent oxidative process of LDL. The maximum stimulation of IPs production was not affected by LDL, but for a concentration of 100 nmol/L, bradykinin-induced IPs formation remained significantly higher, revealing a dissociation between the release of prostacyclin (which decreased) and the enhanced activity of the phospholipase C. The physiological significance of this dissociation between the signal transduction mechanism and the biological response is difficult to explain.…”

“…18 In contrast to bradykinin-stimulated 6-keto-PGF lCT formation, the facilitatory effect of LDL on ATPinduced 6-keto-PGF, Q formation occurred in the absence of NAC. A recent study shows that, in contrast to thrombin (another agonist inducing prostacyclin release), ATP-induced 6-keto-PGF la formation can be abolished by activation of protein kinase C. 7 Different regulatory mechanisms of the prostacyclin synthetic pathway could account for the difference of effect of LDL observed during different receptor-dependent prostacyclin release mechanisms. 21 Another explanation for this result could be an increase in AA available because of the lipoprotein stimulating the cyclooxygen- ase/prostacyclin synthase pathway.…”

“…6 Its release from cultured endothelial cells, which seems to be dependent on formation of inositol phosphates (IPs), 7 can be stimulated by low concentrations of hydrogen peroxide 8 or short-term exposure to Ox-LDL. 9 Potentially, even the cell's own oxidative metabolism could be a stimulus.…”

Relaxant effects of antidepressants on human isolated mesenteric arteries

“…Under the present experimental conditions, the effect of antidepressants on the release of intracellular Ca 2+ appears to be masked by a marked effect on extracellular Ca 2+ influx and thus vasodilation is observed. However, the increase in intracellular Ca 2+ by protein kinase C is closely associated with prostacyclin production in human endotelial cells [ 27] and aortic smooth muscle cells [ 28]. The attenuation by indomethacin of the relaxant effects of antidepressants is consistent with the release of prostacyclin from the artery wall.…”

Markers of Endothelial Dysfunction

“…The ratio of P G I 2 to TXA 2 formation was 100 at the time of maximum P G I 2 formation and 1.5 at the time of maximum TXA 2 f o rmation. Using physiological stimuli like ATP or thrombin, both eicosanoids were released simultaneously, and ratios of 4 and 5.2 were observed respectively (13). This dissociation of simultaneous PGI 2 and TXA 2 f o r m ation by reactive oxygen species could contribute to the reduction in the protective function of the endothelium in hemostasis and changes in the vascular tone when oxygen radicals are generated.…”