Enhancement of collecting duct renin in angiotensin II-dependent hypertensive rats

Distal nephron renin may provide a possible pathway for angiotensin (Ang) I generation from proximally delivered angiotensinogen. To examine the effects of Ang II on distal nephron renin, we compared renin protein and mRNA expression in control and Ang II-infused rats. Kidneys from sham (n = 9) and Ang II-infused (80 ng/kg per minute, 13 days, n = 10) Sprague-Dawley rats were processed by immunohistochemistry, Western blot, reverse transcriptase-polymerase chain reaction (RT-PCR), and quantitative real-time RT-PCR. Ang II infusion increased systolic blood pressure (181 +/- 4 versus 115 +/- 5 mm Hg) and suppressed plasma and kidney cortex renin activity. Renin immunoreactivity was suppressed in juxtaglomerular apparatus (JGA) cells in Ang II-infused rats compared with sham (0.1 +/- 0.1 versus 1.0 +/- 0.1 relative ratio) but increased in distal nephron segments (6.4 +/- 1.4 versus 1.0 +/- 0.1 cortex; 2.5 +/- 0.3 versus 1.0 +/- 0.2 medulla). Tubular renin immunostaining was apically distributed in principal cells colocalizing with aquaporin-2 in connecting tubules and cortical and medullary collecting ducts. Renin protein levels were decreased in the kidney cortex of Ang II-infused rats compared with that of sham (0.4 +/- 0.2 versus 1.0 +/- 0.4) rats but higher in the kidney medulla (1.2 +/- 0.4 versus 1.0 +/- 0.1). In kidney medulla, RT-PCR and quantitative real-time PCR showed similar levels of renin transcript in both groups. In summary, the detection of renin mRNA in the renal medulla, which is devoid of JGA, indicates local synthesis rather than an uptake of JGA renin. In contrast to the inhibitory effect of Ang II on JGA renin, Ang II infusion stimulates renin protein expression in collecting ducts and maintains renin transcriptional levels in the medulla, which may contribute to the increased intrarenal Ang II levels in Ang II-dependent hypertension.