Adenosine stimulates nitric oxide synthesis in vascular smooth muscle cells

Objective: The aim was to investigate the effects of adenosine on nitric oxide (NO) synthesis in vascular smooth muscle cells. Methods: NO and cAMP synthesis was measured in confluent rat vascular smooth muscle cells in culture at passage 5-10, using Griess reagent and an enzyme immunoassay kit, respectively. The expression of inducible NO synthase mRNA was assayed by Northern blotting. Results: Incubation of cultures with interleukin-1 beta (10 ng/ml) for 24 h caused a significant increase in nitrite production. The interleukin-1 beta-induced nitrite production by vascular smooth muscle cells was significantly increased by adenosine or its stable analogue, 2-chloroadenosine, in a dose-dependent manner. The adenosine A(2a) receptor antagonist, KF17837, but not the A(1) receptor antagonist; DPCPX, significantly inhibited 2-chloroadenosine-mediated nitrite production. The 2-chloroadenosine-induced nitrite production by interleukin-1 beta-stimulated cells was accompanied by increased inducible NO synthase mRNA accumulation. In the presence of dibutyryl-cAMP(1 mM), interleukin-1 beta-induced nitrite accumulation was further increased, but the effect of 2-chloroadenosine was not additive or synergistic. Addition of 2-chloroadenosine dose-dependently increased intracellular cAMP levels of vascular smooth muscle cells. Conclusions: These results indicate that adenosine acts on A(2) receptors and augments NO synthesis in interleukin-1 beta-stimulated vascular smooth muscle cells, at least partially through a cAMP-dependent pathway.