INHIBITION OF NITRIC-OXIDE SYNTHESIS IN VASCULAR SMOOTH-MUSCLE BY RETINOIDS

1 These studies examine the effect of retinoids on interleukin 1 beta (IL-1 beta)-induced nitric oxide synthase (NOS) activity in cultured rat aortic vascular smooth muscle (VSM) cells and isolated rat aortic rings. 2 All-trans-retinoic acid (all-trans-RA, 0.1-10 mu M) and its active analogues produced concentration-dependent inhibition of IL-1 beta (0.1-10 ng ml(-1))-induced nitrite production in cultured VSM cells. In contrast, the inactive retinoid, Ro 14-6113 (0.1-10 mu M), had no effect on IL-1 beta-induced nitrite production. 3 Since some of the actions of retinoids are mediated by induction of transforming growth factor beta (TGF-beta), its effect on inducible NOS activity in VSM cells was examined. TGF-beta produced concentration-dependent (0.1-10 ng ml(-1)) inhibition of IL-1 beta-induced nitrite production and the maximum effect (approximately 90% inhibition) was significantly greater than that seen with all-trans-RA (approximately 70% with 10 mu M). However, an anti-TGF-beta antibody (50 mu g ml(-1)) which blocked the effect of exogenous TGF-beta (5 ng ml(-1)) did not significantly reverse the inhibitory action of all-trans-RA (10 mu M). 4 In addition to inhibiting IL-1 beta-induced nitrite production, all-trans-RA (10 mu M) reduced substantially inducible NOS mRNA and protein levels in IL-1 beta-induced VSM cells (P<0.01). 5 Incubation of isolated rat aortic rings with IL-1 beta (10 ng ml(-1)) caused a progressive resistance of the rings to the vasoconstrictor action of phenylephrine (10 nM to 10 mu M). This effect was abolished by the addition of the nitric oxide synthase inhibitor L-N-G-monomethyl-L-arginine (L-NMMA, 1 mM). All-trans-RA (10 mu M) also markedly and significantly reversed this IL-1 beta-induced vascular hyporeactivity (P<0.01). 6 These data show that all-trans-RA and other active retinoids are able to block cytokine-stimulated expression of inducible NOS in cultured VSM cells and isolated aortic rings.