Chronic Ang II infusion enhances proximal angiotensinogen (AGT) synthesis, secretion as well as urinary excretion. Increased luminal AGT may lead to increased intraluminal Ang II formation if renin and angiotensin converting enzyme are available. Because renin has been localized in cortical collecting duct cells, the present study was designed to determine if renin exists in medullary nephron segments of normal rat kidneys and is regulated in Ang II-dependent hypertension. Renal renin protein and mRNA expressions in sham operated and chronically Ang II-infused (80ng/kg/min, 13 days) rats were evaluated with immunohistochemistry, Western blot, RT-PCR and real time qRT-PCR techniques. Ang II infusion increased SBP (183.6 +/- 3 vs 120.8 +/- 4 mmHg) and led to marked suppression of plasma renin activity (0.9 +/- 0.3 vs 7.5 +/- 0.5 ngAngl·mL·h-1 ) compared to Sham-operated rats. No significant difference was observed in plasma Ang II concentration between Ang II-infused and Sham-operated rats (90.8 +/- 31.9 versus 77.6 +/- 18 fmol/mL) after 13 days of Ang II infusion. However, kidney Ang II contents were significantly higher than plasma levels in Sham-operated rats (111.8 +/- 9.3 versus 77.6 +/- 18; P < 0.05) and even further in Ang II-infused rats (221.7 +/- 15.3 versus 90.7 +/- 31.9, P < 0.01). In addition, Ang II kidney levels were significantly higher in Ang II-infused than Sham-operated rats (221.7 +/- 15.3 versus 111.8 +/- 9.3; P < 0.001). Immunohistochemical evaluation of renin showed marked suppression in juxtaglomerular (JG) cells in Ang II-infused rats compared to sham (0.14 +/- 0.05 vs 1.0 +/- 0.11DU P < 0.001). Renin was colocalized with aquaporin 2 on the apical side of principal cells. Spatial density of collecting duct segment renin immunoreactivity was higher in Ang II-infused than sham (6.40 +/- 1.4 vs 1.0 +/- 0.1 cortex; 2.5 +/- 0.3 vs 1.0 +/- 0.2DU medulla; P < 0.001) rats. Western blot analysis of kidney medulla protein showed an enhancement of renin protein expression in Ang II-infused rats in comparison to the Sham-operated rats (1.22 +/- 0.4 vs 1.0 +/- 0.1; P < 0.05). In contrast, Ang II infusion significantly decreased renin expression in kidney cortex (0.43 +/- 0.2 compared to 1.0 +/- 0.4 densitometric ratio in Sham rats; P < 0.001). Renin 1c mRNA detected in kidney medulla by RT-PCR was not inhibited by Ang II infusions as observed in kidney cortex using real time qRT-PCR (0.31 +/- .05 vs 0.28 +/- 0.04, medulla; 0.26 +/- 0.01 vs 1.00 +/- 0.31, cortex). Additional immunohistochemistry and Western blot experiments performed on isolated cortical collecting duct (M-1) cells confirmed the presence of renin. Ang II treatment (10-7M) applied on M-1 cells by the apical side showed a tendency to enhance the protein renin levels. In conclusion, this study demonstrates that Ang II infusion stimulates renin protein expression in principal cells of cortical and medullary collecting ducts. Detection of renin transcript in renal medulla which is devoid of JG apparatus indicates that renin is synthesized in this region. The enhancement in collecting duct renin provides a mechanism by which Ang I can be generated from proximally delivered AGT and thus contribute to the increased intratubular Ang II levels in Ang II-dependent hypertension / acase@tulane.edu
| Identifer | oai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_24536 |
| Date | January 2004 |
| Contributors | Prieto-Carrasquero, Minolfa (Author), Navar, L. Gabriel (Thesis advisor) |
| Publisher | Tulane University |
| Source Sets | Tulane University |
| Language | English |
| Detected Language | English |
| Rights | Access requires a license to the Dissertations and Theses (ProQuest) database., Copyright is in accordance with U.S. Copyright law |
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