Expression of angiotensinogen mRNA and protein in angiotensin II-dependent hypertension.

Abstract

Chronic elevations in circulating angiotensin II (AngII) levels produce sustained hypertension and increased intrarenal AngII contents through multiple mechanisms, which may include sustained or increased local production of AngII. This study was designed to test the hypothesis that chronic AngII infusion increases renal angiotensinogen mRNA and protein levels, thus contributing to the increase in intrarenal AngII levels. AngII (80 ng/min) was infused subcutaneously for 13 d into Sprague-Dawley rats, using osmotic minipumps. Control rats underwent sham operations. By day 12, systolic arterial BP increased to 184 +/- 3 mmHg in AngII-treated rats, whereas values for sham-treated rats remained at control levels (125 +/- 1 mmHg). Plasma renin activity was markedly suppressed (0.2 +/- 0.1 versus 5.3 +/- 1.2 ng AngI/ml per h); however, renal AngII contents were significantly increased in AngII-treated rats (273 +/- 29 versus 99 +/- 18 fmol/g). Western blot analyses of plasma and liver protein using a polyclonal anti-angiotensinogen antibody demonstrated two specific immunoreactive bands, at 52 and 64 kD, whereas kidney tissue exhibited one band, at 52 kD. Densitometric analyses demonstrated that AngII infusion did not alter plasma (52- or 64-kD), renal (52-kD), or hepatic (52-kD) angiotensinogen protein levels; however, there was a significant increase in hepatic expression of the highly glycosylated 64-kD angiotensinogen protein, of almost fourfold (densitometric value/control value ratios of 3.79 +/- 1.16 versus 1.00 +/- 0.35). Renal and hepatic expression of angiotensinogen mRNA, which was examined by semiquantitative reverse transcription-PCR, was significantly increased in AngII-treated rats, compared with shamtreated rats (kidney, densitometric value/glyceraldehyde-3-phosphate dehydrogenase mRNA value ratios of 0.82 +/- 0.11 versus 0.58 +/- 0.04; liver, densitometric value/glyceraldehyde-3-phosphate dehydrogenase mRNA value ratios of 2.34 +/- 0.07 versus 1.32 +/- 0.15). These results indicate that increases in circulating AngII levels increase intrarenal angiotensinogen mRNA levels, which may contribute to the sustained renal AngII-generating capacity that paradoxically occurs in AngII-treated hypertensive rats.