Protective role of nitric oxide in a model of thrombotic microangiopathy in rats

A new model of thrombotic microangiopathy (TMA) was previously developed, a nd it was demonstrated that endothelial nitric oxide (NO) synthase (NOS) is upregulated in glomeruli in this model. It was hypothesized that the synth esis of NO, a potent vasodilator and platelet inhibitory factor, is induced as a defense mechanism. The goal of this study was to clarify the role of NO in this model. Ex vivo experiments using Western blotting and functional assays demonstrated upregulation of endothelial NOS in isolated glomeruli from TMA rats. In in vivo experiments, five groups of rats were studied, in cluding rats with TMA treated with vehicle. N-G-nitro-L-arginine methyl est er (L-NAME) (a NOS inhibitor), or L-N-6-(1-iminoethyl)lysine (L-NIL) (a spe cific inducible NOS inhibitor) and normal control rats treated with vehicle or L-NAME. Blood urea nitrogen levels, BP, urinary nitrate/nitrite excreti on, and proteinuria were measured. Histologic assessments using periodic ac id-Schiff staining and immunohistologic studies with markers for endotheliu m, platelets, fibrin, cell proliferation, and apoptosis were also performed . L-NAME inhibition of NO synthesis in rats with TMA resulted in more sever e glomerular and tubulointerstitial injury, which was accompanied by thromb us formation and a marked loss of endothelial cells, with more apoptotic ce lls. These changes were associated with severe renal function deterioration . In contrast, these features were less pronounced in the vehicle- or L-NIL -treated rats with TMA and were absent in the control animals. In conclusio n, inhibition of NO production in this model of TMA markedly exacerbated re nal injury. The absence of effects with L-NIL treatment suggests a minor ro le for inducible NOS in this model. These results suggest that production o f NO, most likely by endothelial cells, is an important protective mechanis m in TMA.