RELATIONSHIP BETWEEN NITRIC-OXIDE AND PLATELET-ACTIVATING-FACTOR IN CASTOR-OIL INDUCED MUCOSAL INJURY IN THE RAT DUODENUM

The modualtion of platelet activating factor (PAF) formation in duoden al tissue by nitric oxide (NO) released in response to castor oil was studied in rats pretreated with N-G-nitro-L-arginine methyl ester (L-N AME, 6.25-25 mg/kg, i.p.), an inhibitor of NO synthase, N-G-nitro-D-ar ginine methyl ester (D-NAME, 25 mg/kg, i.p.), the inactive enantiomer of L-NAME or isosorbide-5-mononitrate (IMN, 30-90 mg/kg, p.o.), a NO d onating compound. Castor oil (2 ml/rat orally) increased PAF productio n in the rat duodenum 3 h after challenge. L-NAME, but not D-NAME, enh anced the amount of PAF formed by duodenal tissue, while IMN (30-90 mg /kg) counteracted the effects of L-NAME (12.5 mg/kg) and also reduced PAF release in the tissue of rats treated with castor oil. L-NAME 12.5 mg/kg, but not D-NAME, enhanced both macroscopic damage and acid phos phatase release induced by castor oil. These effects were reduced by a PAF antagonist BN 52021 (3-t-Butyl-hexahydro-4, 7b, 11-trihydroxy-8-m ethyl-9H-1, 7a-epoxymethano-1H, 6aH-cyclopenta [c] furo [2,3b] furo [3 '2':3,4] cyclopenta [1,2-d] furan-5,9,12(4H) trione) 10 and 20 mg/kg i .p. Such findings suggest that endogenous nitric oxide could reduce PA F biosynthesis in castor oil-treated rats.