Vascular smooth muscle cells (VSMCs) as well as macrophages have been
shown to generate a substantial amount of NO in inflammatory vascular
lesions. Prostaglandin (PG) D-2 (PGD(2)) is produced by inflammatory c
ells, including mast cells and macrophages. We investigated whether PG
D(2) modulates NO metabolism in rat VSMCs. PGD(2) at a concentration o
f 10(-7) mol/L or greater dose-dependently inhibited nitrite accumulat
ion in the medium of cultured VSMCs stimulated with interleukin 1 beta
(IL-1 beta). In a dose-response analysis of IL-1 beta and nitrite acc
umulation, PGD(2) was seen to decrease the maximal ability of VSMCs to
generate NO, arguing against competition by PGD(2) at cytokine recept
ors. Northern analysis showed that PGD(2) suppresses induction of indu
cible NO synthase (iNOS) mRNA in Il-1 beta-stimulated VSMCs, with cons
equent inhibition of iNOS protein expression in Western analysis. A th
romboxane A(2) (TXA(2)) analogue, U46619 (10(-5) mol/L), produced less
inhibition of NO generation than did PGD(2). Neither the PGI(2) analo
g carbaprostacyclin nor PGE(1) showed any inhibition. PGD(2) dose-depe
ndently inhibited NO generation despite the addition of the TXA(2) ant
agonist SQ29548, PGJ(2), Delta(12)-PGJ(2), and 15-deoxy-Delta(12,14)-P
GJ(2), all metabolites of PGD(2) were as potent as or slightly stronge
r than PGD(2) in the inhibition of NO generation. These data suggest t
hat PGD(2) suppresses NO generation in VSMCs by inhibiting iNOS mRNA e
xpression, most likely through the cascade of the PGJ(2) series rather
than through the TX receptor or cAMP upregulation. Such action makes
it likely that PGD(2) regulates NO metabolism in vascular lesions.