Expression of immunoreactive nitric oxide synthase isoforms in rat kidney. Effects of dietary salt and losartan.

Immunohistochemical studies have shown expression of two different isoforms of NOS in the juxtaglomerular apparatus (JGA). Antibodies to a Ca(++)-calmodulin dependent isoform purified from rat brain (B-NOS) label the macula densa cells whereas antibodies to an isoform purified from rat aortic smooth muscle cells in culture (VSM-NOS) induced with lipopolysaccharide and interferon gamma label the afferent arteriole. Since dietary salt intake and angiotensin II (Ang II) are determinants of renal NO generation, we have tested the hypothesis that salt intake can regulate the immunohistochemical expression of these NOS isoforms through an effect of Ang II. In 4 of 5 paired studies, the immunostaining for both B-NOS and VSM-NOS was more intense in rats that had received a low salt (LS), compared to a high salt (HS), diet. Infusion of the Ang II type 1 (AT1) receptor antagonist, losartan, enhanced the intensity of immunoreactive staining for both isoforms. In conclusion, the immunohistochemical expression of NOS isoforms in the JGA is increased by dietary salt restriction; this effect cannot be ascribed to Ang II acting on type 1 receptors.