1 We investigated the eects of the phospholipase A 2 (PLA 2 ) activators calcium ionophore A 23187, hydrogen peroxide (H 2 O 2 ), bradykinin (BK), histamine and noradrenaline (NA) on the 8-isoprostaglandin (PG)F 2a formation in the isolated human umbilical vein and the isolated rabbit ear. For comparison, the in¯uence of these substances on the thromboxane A 2 (TXA 2 ) release was also investigated. The release of total (esteri®ed as well as free) 8-iso-PGF 2a , free 8-iso-PGF 2a and TXB 2 , the stable metabolite of TXA 2 , was determined by speci®c enzyme immunoassays. 2 The results show that bolus injections of 5.4 mmol H 2 O 2 , 30 nmol A 23187, 10 nmol BK, 50 nmol histamine and 20 nmol NA caused an increased release of total 8-iso-PGF 2a in the umbilical vein and the rabbit ear. A perfusion with H 2 O 2 at a ®nal concentration of 0.3 mM also increased the release of this isoprostane. Increased formation of free 8-iso-PGF 2a was induced by A 23187 injection and by both modes of H 2 O 2 administration, but not by the other treatments. 3 Bolus injections of A 23187, BK and histamine induced an increased release of TXB 2 in both organs. Both modes of H 2 O 2 administration and NA showed no releasing eects. 4 In conclusion, our results show that the substances used are able to stimulate the formation of 8-iso-PGF 2a concurrently with the release of PGs. This eect might be of pathophysiological relevance in in¯ammatory and cardiovascular diseases in which an enhanced release of free radicals, BK, histamine or NA play an important role.

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