Inhibitory effects of PGD2, PGJ2 and 15-deoxy-Delta(12,14)-PGJ2 on iNOS induction in rat mesenteric artery

PGD2 and its metabolites PGJ2 and 15-deoxy-Delta(12,14)-PGJ2 have been repo rted to inhibit iNOS induction in cultured vascular smooth muscle cells. Th e present study was undertaken to determine whether these prostanoids inhib it iNOS induction in the isolated rat mesenteric artery. The artery without endothelium was incubated with and without lipopolysaccharide (LPS) at 37 degrees C for 6 hrs, then washed and mounted in an organ bath to measure is ometric changes in tension. L-Arginine but not D-arginine (10(-6) - 10(-3) M) induced concentration-dependent relaxations only in the artery preincuba ted with LPS, the relaxations of which were attenuated by L-N-G-nitroargini ne methyl ester (LNAME, 10(-4) M), a non-selective iNOS inhibitor, and 1400 W (10(-5) and 10(-4) M), a selective NOS inhibitor. Go-treatment of cyclohe ximide (10(-5) M), a protein synthesis inhibitor, or actinomycin D (10(-7) M), an RNA synthesis inhibitor with LPS inhibited the development of relaxi ng ability in response to L-arginine, indicating iNOS induction by LPS. PGD 2, PGJ2 and 15-deoxy-Delta(12,14)- PGJ2 but not PGE2, PGI2 or PGF2 alpha al so inhibited the development. of relaxing ability in response to L-arginine when added during incubation with LPS. Incubation of the artery with LPS a t 37 degrees C for 6 hrs markedly increased production of nitric oxide (NO) , which was abolished by 15-deoxy-Delta(12,14) -PGJ2 (10(-5) M). An imunohi stochemical study using antibody against murine iNOS showed that 15-deoxy-D elta(12,14)-PGJ2 (10(-5) M) inhibited the expression of iNOS protein in iso lated rat mesenteric arteries. These results demonstrated that PGD2 and its metabolites inhibit iNOS induction by LPS in isolated rat mesenteric arter ies, resulting in reduced relaxing ability in response to L-arginine.