Evidence for the existence of two distinct functions for the inducible NO synthase in the rat kidney:: Effect of aminoguanidine in rats with 5/6 ablation

The functional role of the NO synthase (NOS) isoforms in the normal or diseased kidney is uncertain. This study examined the renal expression of the endothelial (eNOS), neuronal (nNOS), and inducible (iNOS) isoforms by both immunohistochemistry and Western blot analyses in sham-operated rats (S) and in rats subjected to 5/6 nephrectomy (Nx). Primary antibodies from two different sources were used to detect iNOS. Additional S and Nx rats were chronically treated with aminoguanidine (AG), a selective iNOS inhibitor. All three isoforms were clearly expressed in S kidney. Their renal abundance, evaluated by Western blot analysis, fell in Nx rats. With the use of anti-iNOS antibodies from two distinct sources, the immunohistochemical analysis showed the presence of what appeared to be two distinct iNOS fractions: a "tubular" fraction, present in S and with decreased intensity in Nx; and an "interstitial" fraction, observed only in inflamed areas of Nx rats. AG treatment greatly attenuated renal injury in Nx rats by a direct antiinflammatory effect, likely related to iNOS inhibition, rather than to amelioration of renal hemodynamics or to reduced protein glycation. These observations suggest that: (1) the functional role of the renal iNOS isoform may vary dramatically under different physiologic conditions; (2) caution should be taken in the interpretation of immunohistochemical iNOS data, because antibodies from different sources may detect different iNOS fractions; and (3) AG treatment may become useful in the treatment of human progressive nephropathies, even those not associated with diabetes or aging.