Respective role of lipoxygenase and nitric oxide-synthase pathways in plasma histamine-induced macromolecular leakage in conscious hamsters.

1. Intravital microscopy technique was used to determine the distribution of a fluorescent plasma marker (fluorescein-isothiocyanate-dextran, 150 kD; FD-150) into venular and interstitial compartments of dorsal skin fold preparations in conscious hamsters. 2. One mg kg(-1) histamine (i.v.) caused a biphasic decrease in venular fluorescence due to FD-150 extravasation in all organs (general extravasation). Immediately after injection, the venular fluorescence decreased and plateaued in 60 min. Ninety minutes after histamine injection, venular fluorescence further decreased until 180 min. Prior treatment with indomethacin (0.1 mg kg(-1), i.v.) did not modify the time-course of general extravasation but prevented histamine-induced venule dilatation. 3. Prior treatment with the 5-lipoxygenase activating protein (FLAP) inhibitor, 3-[1-(p-chlorobenzyl)-5-(isopropyl)-3-t-butylthioindol-2-yl]-2,2-d imethyl-propanoic acid sodium (MK-886)(10 microg kg(-1), i.v.), the leukotriene receptor antagonist, benzenemethanol a-pentyl-3-(2-quinolinylmethoxy) (REV-5901)(1 mg kg(-1), i.v.), or the glutathione-S-transferase inhibitor, ethacrynic acid (1 mg kg(-1), i.v.), delayed by 60 min the onset of general extravasation caused by 1 mg kg(-1) histamine. 4. Prior treatment with lipoxygenase pathway inhibitors and N(G)-nitro-L-arginine-methylester (L-NAME)(100 mg kg(-1), i.v.) abolished the general extravasation and venule dilatation induced by 1 mg kg(-1) histamine. 5. Injection of 1 microg kg(-1) (i.v.), of leukotriene-C4 (LTC4) or -D4 (LTD4) induced immediate and sustained general extravasation and reduction in venule diameter, these effects being blocked by REV-5901. 6. Histamine (1 mg kg(-1), i.v.) induced biphasic decline in mean arterial blood pressure (MAP). An initial phase (from 0 to 60 min) was followed by a late phase beginning 90 min after histamine injection. L-NAME (100 mg kg(-1), i.v.) and aminoguanidine (1 mg kg(-1), i.v.) prevented the late phase of histamine-induced hypotension. 7. Thus, plasma histamine can trigger both an immediate cysteinyl-leukotriene (Cys-LT)-dependent and a late nitric oxide (NO)-mediated inflammatory cascade. Although the cyclo-oxygenase (COX) pathway might account for histamine-induced venule dilatation, it would not influence histamine-induced extravasation.