DECREASED PERFUSION-PRESSURE MODULATES RENIN AND ANG-II TYPE-1 RECEPTOR GENE-EXPRESSION IN THE RAT-KIDNEY

To determine whether decreased perfusion pressure affects the abundanc e and distribution of renin and its mRNA and the expression of the ang iotensin II type 1 (AT1) receptor gene within the kidney, adult male S prague-Dawley rats were subjected to aortic coarctation proximal to th e renal arteries (Coarc, n = 8) and compared with sham-operated rats ( Sham, n = 6). Renal renin distribution was determined by immunocytoche mistry using a specific polyclonal antibody against rat renin. Renin m RNA was assessed by in situ hybridization to a S-35-labeled oligonucle otide complementary to rat renin mRNA. Kidney AT1 mRNA levels were det ermined by Northern analysis using a 1,133-base pair rat AT1 cDNA. Fem oral arterial blood pressure, measured 24 h after surgery, was lower i n Coarc than in Sham rats (75 +/- 5.4 vs. 122 +/- 2.3 mmHg, P < 0.05). Aortic coarctation increased the percent of juxtaglomerular apparatus es (%JGA) containing renin and its mRNA (85 +/- 2.5 and 66 +/- 2.8 vs. 49 +/- 5.3 and 36 +/- 1.7%, Coarc vs. Sham, P < 0.05) and the intensi ty of hybridization signals (497 +/- 89 vs. 71 +/- 12 grains/JGA, Coar c vs. Sham, P < 0.05). In addition, recruitment of renin gene expressi ng cells was observed along afferent arterioles in Coarc rats, whereas renin and its mRNA were limited to the JGAs in Sham rats. Renal AT1 r eceptor gene expression was threefold lower in Coarc than in Sham rats . We conclude that reduction of perfusion pressure after abdominal aor tic coarctation acutely enhances renin gene expression and downregulat es AT1 receptor gene expression. We speculate that downregulation of A T1 receptor mRNA in the presence of recruitment of renin gene expressi ng cells within the kidney may represent a local homeostatic mechanism to maintain renal perfusion pressure.