The presence of prostaglandin (PG) H 2 in the supernatant of human umbilical vein endothelial cells (HU-VEC) stimulated by thrombin restores the capacity of aspirin-treated platelets to generate thromboxane (TX) B 2 . Induction of cyclooxygenase-2 (Cox-2) by interleukin (IL)-1␣ or a phorbol ester increases this formation. HU-VEC treated with aspirin lost their capacity to generate PGs but recovery occurred after 3-or 6-h induction of Cox-2 with phorbol ester or IL-1␣. Enzyme activity of the newly synthesized Cox-2 in aspirin-treated cells, evaluated after immunoprecipitation, was similar to untreated cells but after 18 h of cell stimulation only 50 -60% recovery of Cox-1 was observed. The use of SC58125, a selective Cox-2 inhibitor, confirmed these findings in intact cells. Cyclooxygenase activity was related to the amount of Cox proteins present in the cells, but after induction of Cox-2, contribution of the latter to PG production was 6 -8-fold that of Cox-1. Aspirin-treated or untreated cells were incubated in the absence or presence of SC58125 and stimulated by thrombin, the ionophore A23187, or exogenous arachidonic acid. The production of endogenous (6-keto-PGF 1␣ , PGE 2 , PGF 2␣ ) versus transcellular (TXB 2 ) metabolites was independent of the inducer, the source of arachidonic acid and the Cox isozyme. However, in acetylsalicylic acidtreated cells, after 6-h stimulation with IL-1␣, newly synthesized Cox-2 produced less TXB 2 than 6-keto-PGF 1␣ compared to untreated cells. At later times (>18 h), there was no metabolic difference between the cells. These studies suggest that in HUVEC, Cox compartmentalization occurring after short-term activation may selectively affect transcellular metabolism, but not constitutive production, of PGs.

U46619, a thromboxane A2 analogue, and basic fibroblast growth factor (FGF-2) both induced the expression of the inducible cyclo-oxygenase (Cox)-2 in porcine aortic smooth-muscle cells. This induction was dose-dependent (submaximal at 300 nM for U46619 and 1 ng/ml for FGF-2) and time-dependent, with similar intensity and maximal expression at 2 h. Under these conditions, both inducers stimulated rapid activation of extracellular signal-regulated kinase (ERK2) at 5-10 min, a transient and lower intensity being induced by U46619 whereas that induced by FGF-2 was sustained (>1 h). PD98059, an inhibitor of the ERK pathway, inhibited the expression of Cox-2. In contrast, activation of Jun-N-terminal kinase (JNK1) was sustained with U46619 but poorly induced by FGF-2. Cox-2 expression induced by U46619 or FGF-2 was similarly reduced by prostaglandin (PGE2), forskolin or dibutyryl-cAMP, suggesting a regulatory effect of adenylate cyclase on Cox-2 expression. However, activation of ERK2 by FGF-2 was not affected by PGE2 whereas that of JNK1 by U46619 was inhibited, suggesting that inhibition of COX-2 expression by cAMP may be downstream of ERK2. The effects of PGE2 and forskolin on Cox-2 and phosphorylation of JNK1 were reversed with the protein kinase A inhibitor H89. In addition, endogenous PGE2 down-regulated the expression of Cox-2 by the two inducers, as stimulation of the cells in the presence of different Cox inhibitors increased the expression of the protein. Overall, these results suggest that exogenous and endogenous PGE2 exert negative inhibitory effects on Cox-2 expression mediated by stimulation of protein kinase A.

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Die Prostaglandine E2 (I) und F2α (II), deren industrielle Herstellung für das nächste Jahr prognostiziert wird, besitzen eine starke kontrazegtive, abortive und geburtauslösende Wirkung, ohne ‐ so weit bisher feststeht ‐schädliche Nebenwirkungen zu verursachen.