Nitric oxide synthase inhibitors inhibit interleukin-1 beta-induced depression of vascular smooth muscle

Interleukin-1 beta (IL-1) reduces vascular smooth muscle contractility. The purpose of the present study was to investigate the role of nitric oxide synthesis in mediating this effect of IL-1. We studied the influence of inhibitors of nitric oxide synthesis on the depression of norepinephrine-induced contractions of rat aortic rings by IL-1. Also, we examined the ability of IL-1 to increase the production of nitric oxide by rat aortic smooth muscle cells in culture as determined indirectly by measuring nitrite concentrations. NG-amino-L-arginine blocked the effect of IL-1 on norepinephrine-induced contractions of rat aortic rings whereas NG-monomethyl-L-arginine and NG-nitro-L-arginine were considerably less effective. In addition, this effect of IL-1 was prevented by coincubation of the rings with cycloheximide. IL-1 greatly elevated nitrite production by rat aortic smooth muscle cells, and this effect could also be blocked completely by the arginine analogs. NG-amino-L-arginine was the most potent inhibitor of nitrite synthesis (IC50 = 1.7 microM) whereas NG-monomethyl-L-arginine and NG-nitro-L-arginine were about 10-fold less potent (IC50 = 16 and 22 microM, respectively). These results suggest that IL-1-induced depression of norepinephrine-induced vascular contraction is mediated by the increased synthesis of nitric oxide synthase by vascular smooth muscle cells. The relative potency of the arginine analogs for the inhibition of nitrite synthesis suggests that the synthase in vascular smooth muscle is similar to the synthase in macrophages.