ACE and non-ACE mediated effect of angiotensin I on intracellular calcium mobilization in rat glomerular arterioles

Genetically increased angiotensin I-converting enzyme alters peripheral and renal vascular reactivity to angiotensin II and bradykinin in mice

Angiotensin I-converting enzyme (ACE) levels in humans are under strong genetic influence. Genetic variation in ACE has been linked to risk for and progression of cardiovascular and renal diseases. Causality has been documented in genetically modified mice, but the mechanisms underlying causality are not completely elucidated. To further document the vascular and renal consequences of a moderate genetic increase in ACE synthesis, we studied genetically modified mice carrying three copies of the ACE gene (three-copy mice) and littermate wild-type animals (two-copy mice). We investigated peripheral and renal vascular reactivity to angiotensin II and bradykinin in vivo by measuring blood pressure and renal blood flow after intravenous administration and also reactivity of isolated glomerular arterioles by following intracellular Ca2+ mobilization. Carrying three copies of the ACE gene potentiated the systemic and renal vascular responses to angiotensin II over the whole range of peptide concentration tested. Consistently, the response of isolated glomerular afferent arterioles to angiotensin II was enhanced in three-copy mice. In these mice, signaling pathways triggered by endothelial activation by bradykinin or carbachol in glomerular arterioles were also altered. Although the nitric oxide (NO) synthase (NOS)/NO pathway was not functional in arterioles of two-copy mice, in muscular efferent arterioles of three-copy mice NOS3 gene expression was induced and NO mediated the effect of bradykinin or carbachol. These data document new and unexpected vascular consequences of a genetic increase in ACE synthesis. Enhanced vasoconstrictor effect of angiotensin II may contribute to the risk for cardiovascular and renal diseases linked to genetically high ACE levels.

NEW & NOTEWORTHY A moderate genetic increase in angiotensin I-converting enzyme (ACE) in mice similar to the effect of the ACE gene D allele in humans unexpectedly potentiates the systemic and renal vasoconstrictor responses to angiotensin II. It also alters the endothelial signaling pathways triggered by bradykinin or carbachol in glomerular efferent arterioles.

Direct evidence for intrarenal chymase-dependent angiotensin II formation on the diabetic renal microvasculature

Our previous work supports a major role for angiotensin-converting enzyme (ACE)-independent intrarenal angiotensin (ANG) II formation on microvascular function in type 2 diabetes mellitus. We tested the hypothesis that there is a switch from renal vascular ACE-dependent to chymase-dependent ANGII formation in diabetes mellitus. The in vitro juxtamedullary afferent arteriole (AA) contractile responses to the intrarenal conversion of the ACE-specific, chymase-resistant ANGI peptide ([Pro(10)]ANGI) to ANGII were significantly reduced in kidneys of diabetic (db/db) compared with control (db/m) mice. AA responses to the intrarenal conversion of the chymase-specific, ACE-resistant ANGI peptide ([Pro(11), D-Ala(12)]ANGI) to ANGII were significantly enhanced in kidneys of diabetic compared with control mice. AA diameters were significantly reduced by 9 ± 2, 15 ± 3, and 24 ± 3% of baseline in diabetic kidneys in response to 10, 100, and 1000 nmol/L [Pro(11), D-Ala(12)]ANGI, respectively, and the responses were significantly attenuated by angiotensin type 1 receptor or chymase-specific (JNJ-18054478) inhibition. [Pro(11), D-Ala(12)]ANGI did not produce a significant AA vasoconstriction in control kidneys. Chymase inhibition significantly attenuated ANGI-induced AA vasoconstriction in diabetic, but not control kidneys. Renal vascular mouse mast cell protease-4 or chymase/β-actin mRNA expression was significantly augmented by 5.1 ± 1.4 fold; while ACE/β-actin mRNA expression was significantly attenuated by 0.42 ± 0.08 fold in diabetic compared with control tissues. In summary, intrarenal formation of ANGII occurs primarily via ACE in the control, but via chymase in the diabetic vasculature. In conclusion, chymase-dependent mechanisms may contribute to the progression of diabetic kidney disease.

Effect of chronic inhibition of converting enzyme on proximal tubule acidification

The acute effect of angiotensin-converting enzyme inhibition (ACEi) on proximal convoluted tubule (PCT) function is well documented. However, the effect of chronic treatment is less known. The aim of this work was to evaluate the effect of chronic ACEi on PCT acidification (J(HCO(3)(-))). Rats received enalapril (10 mg.kg(-1).day(-1), added to the drinking water) during 3 mo. Micropuncture experiments were performed to measure the effect of chronic ACEi on J(HCO(3)(-)). Nitric oxide (NO.) synthesis in kidney cortex homogenates was assessed by quantifying the conversion of [(14)C]-L-arginine to [(14)C]-L-citrulline. Western blot analysis was performed to determine the abundances of V-H(+)ATPase and NHE3 isoform of the Na(+)/H(+) exchanger in proximal brush-border membrane vesicles (BBMV). Enalapril treatment induced an approximately 50% increase in J(HCO(3)(-)). Luminal perfusion with ethyl-isopropyl amiloride (EIPA) 10(-4)M or bafilomycin 10(-6)M decreased J(HCO(3)(-)) by approximately 60% and approximately 30%, respectively, in both control and enalapril-treated rats. The effect of EIPA and bafilomycin on absolute J(HCO(3)(-)) was larger in enalapril-treated than in control rats. Acute inhibition of NO. synthesis with N(G)-nitro-L-arginine methyl ester abolished the enalapril-induced increase in J(HCO(3)(-)). Cortex homogenates from enalapril-treated rats displayed a 46% increase in nitric oxide synthase (NOS) activity compared with those from untreated animals. Enalapril treatment did not affect the abundances of NHE3 and V-H(+)ATPase in BBMV. Our results suggest that PCT acidification is increased during chronic ACEi probably due to an increase in NO. synthesis, which would stimulate Na(+)/H(+) exchange and electrogenic proton transport.