EXPRESSION OF NEURONAL TYPE NITRIC-OXIDE SYNTHASE AND RENIN IN THE JUXTAGLOMERULAR APPARATUS OF ANGIOTENSIN TYPE-1A RECEPTOR GENE-KNOCKOUT MICE

Angiotensin type-la (AT1a) receptor gene-knockout (ATA1a(-/-)) mice ex hibit chronic hypotension and renin overproduction. In the kidneys of AT1a(-/-) mice. the activity of neuronal type nitric oxide synthase (N -NOS) was histochemically detected by nicotinamide adenine dinucleotid e phosphate (NADPH) diaphorase (NADPHd) reaction combined with N-NOS i mmunohistochemistry. The localization of renin was detected by immunoh istochemistry and the results were analyzed morphometrically. The leve ls of N-NOS and renin mRNA in the renal cortical tissue were determine d by reverse transcription-PCR and Northern blot analysis, respectivel y. In the renal sections from wild-type mice, NADPHd activity and N-NO S immunoreactivity were localized to the discrete region of the macula densa in contact with the parent glomerulus. In contrast, N-NOS-posit ive macula densa cells were distributed beyond the original location o f the macula densa, occasionally extending to the opposite side of the distal tubules. The mean number of N-NOS positive macula densa cells was significantly increased in AT1a(-/-) mice (186 per 100 glomeruli) compared with wild-type mice (65 pel 100 glomeruli). AT1a(-/-) mice sh owed 1.4-times higher N-NOS mRNA levels in the renal cortical tissues than wild-type mice. The plasma renin activity was significantly highe r in AT1a(-/-) mice (205.5 +/- 26.1 ng/ml/hr) than in wild-type mice ( 8.0 +/- 0.2 ng/ml/hr). The renin-positive areas per glomerulus and ren al renin gene expression were 12-times and 2.6-times higher in AT1a(-/ -) mice than in wild-type mise, respectively. These abnormalities, how ever, were less remarkable in ATA1a(-/-) mice compared with angiotensi nogen-knockout mice. When AT1a(-/-) mice were fed a high-salt diet, th e signal intensity of the NADPHd reaction and the number of positively -stained macula densa cells were significantly decreased. The levels o f renal cortical N-NOS mRNA were also suppressed by the treatment. Die tary salt loading produced a parallel decrease in plasma renin activit y, renal renin-immunoreactive areas, and the levels of renin mRNA with out affecting systemic blood pressure. These results provide evidence for the possible involvement of N-NOS at the macula densa in the incre ased renin production in AT1a(-/-) mice.