Urinary angiotensinogen as an indicator of intrarenal angiotensin status in hypertension

Abstract

Angiotensin II (AngII) infusions augment renal angiotensinogen mRNA and protein and urinary angiotensinogen excretion (UAGT). Further experiments were performed in 4 groups of rats: normal salt diet with sham operation, NS+Sham, n=6; NS with AngII infusion at 40 ng/min via osmotic minipump, NS+AngII(40) n=9; NS with AngII infusion at 80 ng/min, NS+AngII(80), n=9; high-salt diet with deoxycorticosterone acetate salt pellet (100 mg), HS+DOCA, n=4. These experiments sought to determine whether enhanced UAGT is specifically associated with increased kidney AngII levels or is a nonspecific consequence of the hypertension. Systolic BP (SBP) was significantly increased to 131±2 and 162±2 mm Hg at day 11 in NS+AngII(40) and NS +AngII(80), respectively, compared with NS+Sham (110±1). Regression analysis demonstrated a positive relationship (R=0.49) between SBP and UAGT for NS+Sham (1.1±0.3 nmol AngI/d), NS+AngII(40) (2.5±0.9), and NS+AngII(80) (5.5±1.5). UAGT was also highly correlated (R=0.70) with kidney AngII content for NS+Sham (49±6 fmol/g), NS+AngII(40) (215±49), and NS+AngII(80) (347±47); but not with plasma AngII (R=0.12). HS+DOCA rats also exhibited increased SBP to 134±1 mm Hg, but UAGT(1.4±0.4 nmol AngI/d) and intrarenal AngII content (13±2 fmol/g) were not increased despite the hypertension. Infused human angiotensinogen could not be detected in urine of sham-operated or AngII-infused rats (n=4 each). These data demonstrate that UAGT increases in AngII-dependent hypertension in a dose- and time-dependent manner, but not in hypertension elicited by HS+DOCA. The results support the hypothesis that AngII-dependent hypertension results in elevated intrarenal AngII and angiotensinogen levels, reflected by increased UAGT, which does not occur in an AngII-independent hypertensive model.