INHIBITION OF NO-SYNTHASE AND DEGRANULATION OF RAT OMENTAL MAST-CELLSIN-VITRO

MAST cell amines, platelet-activating factor (PAF), thromboxanes and l eukotrienes have been shown to be released during nitric oxide-synthas e inhibition in the rat intestine. Mast cells in rat isolated omentum (OMCs) or isolated from the rat peritoneal cavity (PMCs) have been use d here to investigate the relationship(s) between these agents. N-nitr o-L-arginine methyl ester (L-NAME, 100 mu M) caused some degranulation of OMCs, but no enhancement of histamine release from PMCs. PAF (5 mu M) and U46619 (1 mu M) degranulated and enhanced histamine release fr om Pre-treatment of the omentum with BN52021 (10 mu M) inhibited degra nulation of OMCs in response to L-NAME, PAF or U46619. Pretreatment wi th 1-benzylimidazole (5 or 50 mu M) inhibited the effect of L-NAME but not that of PAF. Indomethacin (1 mu M) or sodium nitroprusside (10 mu M) also inhibited the effects of L-NAME, but nordihydroguaiaretic aci d (30 mu M) did not. In PMCs BN52021 inhibited PAF-induced, but not U4 6619-induced, release of histamine. These results suggest that inhibit ion of nitric oxide-synthase in the omentum by L-NAME allows thromboxa nes to release PAF, which in tuna degranulates and releases histamine from OMCs.