W e have developed chimeric mice carrying 'regional' null mutation of the angiotensin type 1A (AT1A) receptor, the AT1 receptor subtype exclusively present in mouse juxtaglomerular (JG) cells. The chimeric mouse (Agtr1a -/- <--> +/+) is made up of wild-type (Agtr1a +/+) cells or cells homozygous for Agtr1a deletion (Agtr1a -/-). In the latter, the AT1A coding exon was replaced with a reporter gene, lacZ. In Agtr1a -/- <--> +/+ mice, these two clones of cells are found to be clustered and display patchy distributions in the kidney and heart. Tracking of lacZ activities in hetero- (Agtr1a +/-) and homozygous (Agtr1a -/-) deletion mutant offspring from Agtr1a -/- <--> +/+ mice revealed that the promoter activity of Agtr1a is localized in JG cells, afferent arteriolar walls, glomerular mesangial region and endothelial cells, and apical and basolateral proximal tubule membranes. The JG apparatuses of Agtr1a -/- mice are markedly enlarged with intense expression of renin mRNA and protein. In Agtr1a -/- <--> +/+ mice, these changes were proportional to the degree of chimerism. Within a given Agtr1a -/- <--> +/+ mouse, however, the degree of JG hypertrophy/hyperplasia and the expression of renin mRNA and protein were identical between Agtr1a +/+ and Agtr1a -/- cells. Thus, in the in vivo condition tested, the local interaction between angiotensin and the AT1 receptor on the JG cells has little functional contribution to the feedback regulation of JG renin synthesis.