SEROTONIN INHIBITS NITRIC-OXIDE SYNTHESIS IN RAT VASCULAR SMOOTH-MUSCLE CELLS STIMULATED WITH INTERLEUKIN-1

We investigated the effects of serotonin (5-hydroxytryptamine; 5-HT) o n nitric oxide (NO) synthesis in vascular smooth muscle cells. We meas ured the production of nitrite, a stable metabolite of NO, and the exp ression of inducible NO synthase protein in cultured rat vascular smoo th muscle cells. Incubation of the cultures with interleukin-1 beta (1 0 ng/ml) caused a significant increase in nitrite production. 5-HT inh ibited nitrite production by interleukin-1 beta-stimulated vascular sm ooth muscle cells in a concentration-dependent manner (10(-8)-10(-5) M ). 5-HT-induced inhibition of nitrite production was accompanied by de creased inducible NO synthase protein accumulation in vascular smooth muscle cells. Addition of the 5-HT2 receptor antagonist ketanserin, bu t not the 5-HT1A receptor antagonist spiroxatrine, inhibited the effec t of 5-HT. On the other hand, the 5-HT2 receptor agonist alpha-methyl- 5-HT, but not the 5-HT1A receptor agonist (+/-)-8-hydroxy-2-(di-n-prop ylamino) tetralin, decreased interleukin-1 beta-induced nitrite produc tion by vascular smooth muscle cells. 5-HT significantly increased pro tein kinase C activity in vascular smooth muscle cells, and the protei n kinase C inhibitor calphostin C dose-dependently abolished the effec t of 5-HT on nitrite production. After protein kinase C activity was f unctionally depleted by treatment of cells with phorbol 12-myristate 1 3-acetate for 24 h, the effect of 5-HT was abolished, These results in dicate that 5-HT acts on 5-HT2 receptors and inhibits NO synthesis in interleukin-1 beta-stimulated vascular smooth muscle cells at least pa rtially through a protein kinase C-dependent pathway. (C) 1997 Elsevie r Science B.V.