THE NEURONAL ISOFORM OF CONSTITUTIVE NITRIC-OXIDE SYNTHASE IS UP-REGULATED IN THE MACULA DENSA OF ANGIOTENSINOGEN GENE-KNOCKOUT MICE

Angiotensinogen gene-knockout (Atg(-/-)) mice lacking angiotensin II e xhibit chronic hypotension and an increase in renal renin gene express ion. The present study was designed to provide evidence for the possib le involvement of neuronal type nitric oxide synthase (N-NOS) at the m acula densa in the increased renin production in Atg(-/-) mice. The en zyme activity of N-NOS was histochemically detected by NADPH diaphoras e (NADPHd) reaction combined with N-NOS immunohistochemistry. N-NOS mR NA expression in the renal cortical tissue was determined using revers e transcription-PCR in a semiquantitative manner. The levels of renal renin mRNA were evaluated by Northern blot analysis. In the kidneys of wild-type (Atg(+/+)) mice, N-NOS activity was localized to the macula densa as reported previously. On the other hand, N-NOS-positive macul a densa cells of Atg(-/-) mice were distributed beyond the original lo cation of the macula densa. They often occupy the entire cross-section al profiles of the tubules. In addition, Atg(-/-) mice showed a strong er signal intensity for the enzyme reaction than Atg(+/+) mice. The me an total number of N-NOS-positive cells per 100 glomeruli was 6 times higher in Atg(-/-) mice than in Atg(+/+) mice. Semiquantitative revers e transcription-PCR revealed an increase in the N-NOS mRNA level in re nal cortical tissue of Atg(-/-) mice compared with Atg(+/+) mice. Furt hermore, the selective inhibition of N-NOS activity by 7-nitroindazole significantly decreased the level of renal renin mRNA in Atg(-/-) mic e. These results suggest that increased N-NOS activity at the macula d ensa is involved in renal renin overproduction in Atg(-/-) mice.