DIFFERENTIAL EXPRESSION AND INDUCTION OF MESSENGER-RNAS ENCODING 2 INDUCIBLE NITRIC-OXIDE SYNTHASES IN RAT-KIDNEY

We used quantitative PCR methods and renal microdissection to characte rize the expression of inducible nitric oxide synthase (iNOS) mRNAs in rat kidney and cultured glomerular mesangial cells. A partial cDNA ho mologous to murine macrophage iNOS (macNOS), but distinct from rat vas cular smooth muscle iNOS (vsmNOS), was cloned from normal rat kidney. macNOS was the principal iNOS isoform tonically expressed in microdiss ected glomeruli, proximal tubules, medullary thick ascending limbs (mT AL), cortical and inner medullary collecting ducts (IMCD), and culture d mesangial cells, whereas vsmNOS was the major isoform expressed in a rcuate and interlobular arteries. Basal macNOS expression was greatest in mTALs and IMCDs. Restriction mapping of RT-PCR products indicated that basal expression of macNOS mRNA was comparable to that of vsmNOS in cortex, but greater than vsmNOS in outer and inner medulla. However , compared to controls, lipopolysaccharide (LPS)-treated rats exhibite d a much greater proportion of vsmNOS mRNA and higher levels of total iNOS mRNA in each zone. Similarly, TNF(alpha and IF-gamma preferential ly induced expression of vsmNOS mRNA in cultured mesangial cells. We c onclude that two iNOS isoforms are constitutively and heterogeneously expressed in the normal rat kidney, and that endotoxemia and cytokines differentially induce their expression.