Angiotensin peptides modulate bradykinin levels in the interstitium of the dog heart in vivo

Kinins and chymase: the forgotten components of the renin-angiotensin system and their implications in COVID-19 disease

The unique clinical features of COVID-19 disease present a formidable challenge in the understanding of its pathogenesis. Within a very short time, our knowledge regarding basic physiological pathways that participate in SARS-CoV-2 invasion and subsequent organ damage have been dramatically expanded. In particular, we now better understand the complexity of the renin-angiotensin-aldosterone system (RAAS) and the important role of angiotensin converting enzyme (ACE)-2 in viral binding. Furthermore, the critical role of its major product, angiotensin (Ang)-(1-7), in maintaining microcirculatory balance and in the control of activated proinflammatory and procoagulant pathways, generated in this disease, have been largely clarified. The kallikrein-bradykinin (BK) system and chymase are intensively interwoven with RAAS through many pathways with complex reciprocal interactions. Yet, so far, very little attention has been paid to a possible role of these physiological pathways in the pathogenesis of COVID-19 disease, even though BK and chymase exert many physiological changes characteristic to this disorder. Herein, we outline the current knowledge regarding the reciprocal interactions of RAAS, BK, and chymase that are probably turned-on in COVID-19 disease and participate in its clinical features. Interventions affecting these systems, such as the inhibition of chymase or blocking BKB1R/BKB2R, might be explored as potential novel therapeutic strategies in this devastating disorder.

Increased myocardial stiffness due to cardiac titin isoform switching in a mouse model of volume overload limits eccentric remodeling

We investigated the cellular and molecular mechanisms of diastolic dysfunction in pure volume overload induced by aortocaval fistula (ACF) surgery in the mouse. Four weeks of volume overload resulted in significant biventricular hypertrophy; protein expression analysis in left ventricular (LV) tissue showed a marked decrease in titin's N2BA/N2B ratio with no change in phosphorylation of titin's spring region. Titin-based passive tensions were significantly increased; a result of the decreased N2BA/N2B ratio. Conscious echocardiography in ACF mice revealed eccentric remodeling and pressure volume analysis revealed systolic dysfunction: reductions in ejection fraction (EF), +dP/dt, and the slope of the end-systolic pressure volume relationships (ESPVR). ACF mice also had diastolic dysfunction: increased LV end-diastolic pressure and reduced relaxation rates. Additionally, a decrease in the slope of the end diastolic pressure volume relationship (EDPVR) was found. However, correcting for altered geometry of the LV normalized the change in EDPVR and revealed, in line with our skinned muscle data, increased myocardial stiffness in vivo. ACF mice also had increased expression of the signaling proteins FHL-1, FHL-2, and CARP that bind to titin's spring region suggesting that titin stiffening is important to the volume overload phenotype. To test this we investigated the effect of volume overload in the RBM20 heterozygous (HET) mouse model, which exhibits reduced titin stiffness. It was found that LV hypertrophy was attenuated and that LV eccentricity was exacerbated. We propose that pure volume overload induces an increase in titin stiffness that is beneficial and limits eccentric remodeling.

Role of the kidney in the fetal programming of adult cardiovascular disease: an update

It is well established that an adverse in utero environment can impinge upon fetal development and place the offspring on a track leading to future cardiovascular disease. Significantly, this may occur in the absence of any outward manifestations at birth. In this brief review, we focus on potential renal mechanisms that lead to adaptations in glomerular and tubular function that initiate hypertension of developmental origin and examine potential therapeutic interventions. This report updates recent data in this field.

Angiotensin-(1-7) attenuates angiotensin II-induced cardiac remodeling associated with upregulation of dual-specificity phosphatase 1

Chronic hypertension induces cardiac remodeling, including left ventricular hypertrophy and fibrosis, through a combination of both hemodynamic and humoral factors. In previous studies, we showed that the heptapeptide ANG-(1-7) prevented mitogen-stimulated growth of cardiac myocytes in vitro, through a reduction in the activity of the MAPKs ERK1 and ERK2. In this study, saline- or ANG II-infused rats were treated with ANG-(1-7) to determine whether the heptapeptide reduces myocyte hypertrophy in vivo and to identify the signaling pathways involved in the process. ANG II infusion into normotensive rats elevated systolic blood pressure >50 mmHg, in association with increased myocyte cross-sectional area, ventricular atrial natriuretic peptide mRNA, and ventricular brain natriuretric peptide mRNA. Although infusion with ANG-(1-7) had no effect on the ANG II-stimulated elevation in blood pressure, the heptapeptide hormone significantly reduced the ANG II-mediated increase in myocyte cross-sectional area, interstitial fibrosis, and natriuretic peptide mRNAs. ANG II increased phospho-ERK1 and phospho-ERK2, whereas cotreatment with ANG-(1-7) reduced the phosphorylation of both MAPKs. Neither ANG II nor ANG-(1-7) altered the ERK1/2 MAPK kinase MEK1/2. However, ANG-(1-7) infusion, with or without ANG II, increased the MAPK phosphatase dual-specificity phosphatase (DUSP)-1; in contrast, treatment with ANG II had no effect on DUSP-1, suggesting that ANG-(1-7) upregulates DUSP-1 to reduce ANG II-stimulated ERK activation. These results indicate that ANG-(1-7) attenuates cardiac remodeling associated with a chronic elevation in blood pressure and upregulation of a MAPK phosphatase and may be cardioprotective in patients with hypertension.

Translational success stories: angiotensin receptor 1 antagonists in heart failure

The title of the proposed series of reviews is Translational Success Stories. The definition of "translation" according to Webster is, "an act, process, or instance of translating as a rendering of one language into another." In the context of this inaugural review, it is the translation of Tigerstedt's and Bergman's(1) discovery in 1898 of the vasoconstrictive effects of an extract of rabbit kidney to the treatment of heart failure. As recounted by Marks and Maxwell,(2) their discovery was heavily influenced by the original experiments of the French physiologist Brown-Séquard, who was the author of the doctrine that "many organs dispense substances into the blood which are not ordinary waste products, but have specific functions." They were also influenced by Bright's(3) original observation that linked kidney disease with hypertension with the observation that patients dying with contracted kidneys often exhibited a hard, full pulse and cardiac hypertrophy. However, from Tigerstedt's initial discovery, there was a long and arduous transformation of ideas and paradigms that eventually translated to clinical applications. Although the role of the renin-angiotensin system in the pathophysiology of hypertension and heart failure was suspected through the years, beneficial effects from its blockade were not realized until the early 1970s. Thus, this story starts with a short historical perspective that provides the reader some insight and appreciation into the long delay in translation.

Alternative pathways for angiotensin II generation in the cardiovascular system

The classical renin-angiotensin system (RAS) consists of enzymes and peptides that regulate blood pressure and electrolyte and fluid homeostasis. Angiotensin II (Ang II) is one of the most important and extensively studied components of the RAS. The beneficial effects of angiotensin converting enzyme (ACE) inhibitors in the treatment of hypertension and heart failure, among other diseases, are well known. However, it has been reported that patients chronically treated with effective doses of these inhibitors do not show suppression of Ang II formation, suggesting the involvement of pathways alternative to ACE in the generation of Ang II. Moreover, the finding that the concentration of Ang II is preserved in the kidney, heart and lungs of mice with an ACE deletion indicates the important role of alternative pathways under basal conditions to maintain the levels of Ang II. Our group has characterized the serine protease elastase-2 as an alternative pathway for Ang II generation from Ang I in rats. A role for elastase-2 in the cardiovascular system was suggested by studies performed in heart and conductance and resistance vessels of normotensive and spontaneously hypertensive rats. This mini-review will highlight the pharmacological aspects of the RAS, emphasizing the role of elastase-2, an alternative pathway for Ang II generation.

Cardioprotective role for angiotensin-(1-7) and angiotensin converting enzyme 2 in the heart

Angiotensin-(1-7), a biologically active peptide of the renin-angiotensin system, is cardioprotective following ischemia/reperfusion and reduces cardiac hypertrophy. A recently discovered homolog of angiotensin converting enzyme (ACE), ACE2, is present in the heart and synthesizes angiotensin-(1-7) from angiotensin II. Cardiac ACE2 is elevated following inhibition of Ang II subtype 1 (AT(1)) receptors or blockade of angiotensin II production, suggesting that angiotensin-(1-7) plays a role in the beneficial effects of AT(1) receptor antagonists and ACE inhibitors in the heart. An increase in ACE2 activity and the production of angiotensin-(1-7) may thus represent a novel therapy for heart failure following myocardial infarction.

The one-two punch: knocking out angiotensin II in the heart

Ang II plays an important role in the pathophysiology of cardiovascular disease. Angiotensin-converting enzyme (ACE) inhibitors lower Ang II levels by inhibiting conversion of Ang I to Ang II, but Ang II levels have been shown to return to normal with chronic ACE inhibitor treatment. In this issue of the JCI, Wei et al. show that ACE inhibition induces an increase in chymase activity in cardiac interstitial fluid, providing an alternate pathway for Ang II generation.

Distinct roles for angiotensin-converting enzyme 2 and carboxypeptidase A in the processing of angiotensins within the murine heart

Angiotensin-converting enzyme 2 (ACE2), a homologue of angiotensin-converting enzyme (ACE), converts angiotensin (Ang) I to Ang(1-9) and Ang II to Ang(1-7), but does not directly process Ang I to Ang II. Cardiac function is compromised in ACE2 null mice; however, the importance of ACE2 in the processing of angiotensin peptides within the murine heart is not known. We determined the metabolism of angiotensins in wild-type (WT), ACE (ACE(-/-)) and ACE2 null mice (ACE2(-/-)). Angiotensin II was converted almost exclusively to Ang(1-7) in the cardiac membranes of WT and ACE(-/-) strains, although generation of Ang(1-7) was greater in the ACE(-/-) mice (27.4 +/- 4.1 versus 17.5 +/- 3.2 nmol(-1) mg h(-1) for WT). The ACE2 inhibitor MLN4760 significantly attenuated Ang II metabolism and the subsequent formation of Ang(1-7) in both strains. In the ACE2(-/-) hearts, Ang II metabolism and the generation of Ang(1-7) were significantly attenuated; however, the ACE2 inhibitor reduced the residual Ang(1-7)-forming activity in this strain. Angiotensin I was primarily converted to Ang(1-9) (WT, 28.9 +/- 3.1 nmol(-1) mg h(-1); ACE(-/-), 49.8 +/- 5.3 nmol(-1) mg h(-1); and ACE2(-/-), 35.9 +/- 5.4 nmol(-1) mg h(-1)) and to smaller quantities of Ang(1-7) and Ang II. Although the ACE2 inhibitor had no effect on Ang(1-9) formation, the carboxypeptidase A inhibitor benzylsuccinate essentially abolished the formation of Ang(1-9) and increased the levels of Ang I in cardiac membranes. In conclusion, our studies in the murine heart suggest that ACE2 is the primary pathway for the metabolism of Ang II and the subsequent formation of Ang(1-7), a peptide that, in contrast to Ang II, exhibits both antifibrotic and antiproliferative actions.

On the mechanism of coronary vasodilation induced by angiotensin-(1-7) in the isolated guinea pig heart

Various mechanisms have been postulated to be involved in angiotensin-(1-7)-induced endothelium-dependent vasodilation. Here, we characterized the vasodilator action of angiotensin-(1-7) in the isolated guinea pig heart. Angiotensin-(1-7) (1-10 nmol, bolus) induced dose-dependent increase in the coronary flow. The coronary vasodilation induced by angiotensin-(1-7) was significantly reduced by the nitric oxide synthase inhibitor, L-N(G)-nitroarginine methyl ester (L-NAME) (100 microM) and abolished by a B(2) receptor antagonist, icatibant (100 nM). Coronary vasodilation induced by bradykinin (3 pmol, bolus) was inhibited by L-NAME and icatibant to similar extent as that induced by angiotensin-(1-7). Neither the selective AT(2) angiotensin receptor antagonist, PD123319 (1 microM), nor the antagonist of a putative angiotensin-(1-7) receptors, [D-alanine-7]-angiotensin-(1-7) (A-779, 1 microM), influenced the response to angiotensin-(1-7). In conclusion, in the isolated guinea pig heart angiotensin-(1-7) induces coronary vasodilation that is mediated by endogenous bradykinin and subsequent stimulation of nitric oxide release through endothelial B(2) receptors. In contrast to other vascular beds, AT(2) angiotensin receptors and specific angiotensin-(1-7) receptors do not appear involved in angiotensin-(1-7)-induced coronary vasodilation in the isolated guinea pig heart.

Angiotensin-(1-7): pharmacology and new perspectives in cardiovascular treatments

Many advances have been made in the cardiovascular field in the last several decades. Among them is the progress completed to date on the heptapeptide member of the renin-angiotensin system (RAS), angiotensin-(1-7) [Ang-(1-7)]. The peptide's beneficial actions against pathophysiological processes, such as cardiac arrhythmia, heart failure, hypertension, renal disease, preeclampsia, and even cancer are continuously being uncovered. This review encompasses the pharmacology of Ang-(1-7) and expounds upon the peptide's potential as a therapeutic agent against pathological processes both within and outside the cardiovascular continuum.

Angiotensin, bradykinin and the endothelium

Angiotensins and kinins are endogenous peptides with diverse biological actions; as such, they represent current and future targets of therapeutic intervention. The field of angiotensin biology has changed significantly over the last 50 years. Our original understanding of the crucial role of angiotensin II in the regulation of vascular tone and electrolyte homeostasis has been expanded to include the discovery of new angiotensins, their important role in cardiovascular inflammation and the development of clinically useful synthesis inhibitors and receptor antagonists. While less applied progress has been achieved in the kinin field, there are continuous discoveries in bradykinin physiology and in the complexity of kinin interactions with other proteins. The present review focuses on mechanisms and interactions of angiotensins and kinins that deal specifically with vascular endothelium.

Regulation of Cardiovascular Control Mechanisms by Angiotensin-(1–7) and Angiotensin-Converting Enzyme 2

Among the molecular forms of angiotensin peptides generated by the action of renin on angiotensinogen (Aogen), both angiotensin II (Ang II) and the amino terminal heptapeptide angiotensin-(1–7) [Ang-(1–7)] are critically involved in the long-term control of tissue perfusion, cell-cell communication, development, and growth. Whereas an impressive body of literature continues to uncover pleiotropic effects of Ang II in the regulation of cell function, research on Ang-(1–7) has a shorter history as it was only 16 yr ago that a biological function for this heptapeptide was first demonstrated in the isolated rat neuro-hypophysial explant preparation (1). On the contrary, the synthesis of angiotonin/ hypertensin (now Ang II) was first obtained in 1957 (2), three decades ahead of the discovery of Ang-(1–7) biological properties.

Role of the kallikrein-kinin system in Ang-(1-7)-induced vasodilation in mesenteric arterioles of Wistar rats studied in vivo-in situ

Angiotensin-(1-7) [Ang-(1-7)], exerts a variety of actions in the cardiovascular system, with an important effect being vasodilation. In this work, we investigated the relationship between the vasodilatory activity of Ang-(1-7) and the kallikrein-kinin system. Intravital microscopy was used to study the vasodilation caused by Ang-(1-7) in the mesenteric vascular bed of anesthetized Wistar rats. The topical application of Ang-(1-7) caused vasodilation of mesenteric arterioles that was reduced by A-779, JE 049 and peptidase inhibitors (aprotinin, SBTI, PKSI 527, E-64, PMSF). These results indicated that the vasodilation induced by Ang-(1-7) in the mesenteric arterioles of Wistar rats was heavily dependent on the activation of kallikrein and subsequent kinin formation.

Advances in biochemical and functional roles of angiotensin-converting enzyme 2 and angiotensin-(1-7) in regulation of cardiovascular function

Angiotensin-converting enzyme 2 (ACE2) is the first human homologue of ACE to be described. ACE2 is a type I integral membrane protein that functions as a carboxypeptidase, cleaving a single hydrophobic/basic residue from the COOH-terminus of its substrates. Because ACE2 efficiently hydrolyzes the potent vasoconstrictor angiotensin II to angiotensin (1-7), this has changed our overall perspective about the classical view of the renin angiotensin system in the regulation of hypertension and heart and renal function, because it represents the first example of a feedforward mechanism directed toward mitigation of the actions of angiotensin II. This paper reviews the new data regarding the biochemistry of angiotensin-(1-7)-forming enzymes and discusses key findings such as the elucidation of the regulatory mechanisms participating in the expression of ACE2 and angiotensin-(1-7) in the control of the circulation.

Angiotensin-(1-7) inhibits growth of cardiac myocytes through activation of the mas receptor

Peptide hormones such as ANG II and endothelin contribute to cardiac remodeling after myocardial infarction by stimulating myocyte hypertrophy and myofibroblast proliferation. In contrast, angiotensin-(1-7) [ANG-(1-7)] infusion after myocardial infarction reduced myocyte size and attenuated ventricular dysfunction and remodeling. We measured the effect of ANG-(1-7) on protein and DNA synthesis in cultured neonatal rat myocytes to assess the role of the heptapeptide in cell growth. ANG-(1-7) significantly attenuated either fetal bovine serum- or endothelin-1-stimulated [(3)H]leucine incorporation into myocytes with no effect on [(3)H]thymidine incorporation. [d-Ala(7)]-ANG-(1-7), the selective ANG type 1-7 (AT(1-7)) receptor antagonist, blocked the ANG-(1-7)-mediated reduction in protein synthesis in cardiac myocytes, whereas the AT(1) and AT(2) angiotensin peptide receptors were ineffective. Serum-stimulated ERK1/ERK2 mitogen-activated protein kinase activity was significantly decreased by ANG-(1-7) in myocytes, a response that was also blocked by [d-Ala(7)]-ANG-(1-7). Both rat heart and cardiac myocytes express the mRNA for the mas receptor, and a 59-kDa immunoreactive protein was identified in both extracts of rat heart and cultured myocytes by Western blot hybridization with the use of an antibody to mas, an ANG-(1-7) receptor. Transfection of cultured myocytes with an antisense oligonucleotide to the mas receptor blocked the ANG-(1-7)-mediated inhibition of serum-stimulated MAPK activation, whereas a sense oligonucleotide was ineffective. These results suggest that ANG-(1-7) reduces the growth of cardiomyocytes through activation of the mas receptor. Because ANG-(1-7) is elevated after treatment with angiotensin-converting enzyme inhibitors or AT(1) receptor blockers, ANG-(1-7) may contribute to their beneficial effects on cardiac dysfunction and ventricular remodeling after myocardial infarction.

Dynamic and differential changes in myocardial and plasma endothelin in patients undergoing cardiopulmonary bypass

OBJECTIVE

The bioactive peptide endothelin modulates left ventricular function by changing afterload, coronary vascular tone, and myocardial contractility. However, whether increased plasma endothelin levels observed in patients during and after coronary revascularization and cardiopulmonary bypass reflect actual myocardial interstitial levels are unknown.

METHODS

A microdialysis probe (outer diameter: 0.77 mm; length: 4 mm) was placed in the left ventricular apical midmyocardium in 20 patients and myocardial interstitial fluid was collected (2.5 microL/min) at baseline and up to 30 minutes after cardiopulmonary bypass. Myocardial interstitial and systemic arterial endothelin were measured by radioimmunoassay.

RESULTS

Baseline myocardial interstitial endothelin was over 6-fold higher than plasma (20.11 +/- 2.07 vs 3.19 +/- 0.25 fmol/mL, P < .05). Plasma endothelin increased by 23% +/- 12% at 60 minutes of cardiopulmonary bypass whereas myocardial interstitial endothelin increased by 105% +/- 24%, P < .05), and this change was higher than in the plasma ( P < .05). Although no further change in plasma endothelin occurred during cardiopulmonary bypass, myocardial interstitial levels increased further after crossclamp removal (400% +/- 75%) and remained significantly higher than plasma at separation from cardiopulmonary bypass.

CONCLUSION

The unique findings of this study were 2-fold: First, significant compartmentalization of endothelin exists within the human myocardium. Second, a significantly higher and temporally disparate change in myocardial interstitial endothelin occurs during and after cardiopulmonary bypass when compared with systemic levels. These dynamic changes in myocardial endothelin likely influence coronary vascular tone and contractility.

Mechanisms of angiotensin II-induced expression of B2 kinin receptors

Although the primary roles of the kallikreinkinin system and the renin-angiotensin system are quite divergent, they are often intertwined under pathophysiological conditions. We examined the effect of ANG II on regulation of B(2) kinin receptors (B2KR) in vascular cells. Vascular smooth muscle cells (VSMC) were treated with ANG II in a concentration (10(-9)-10(-6) M)- and time (0-24 h)-dependent manner, and B2KR protein and mRNA levels were measured by Western blots and PCR, respectively. A threefold increase in B2KR protein levels was observed as early as 6 h, with a peak response at 10(-7) M. ANG II (10(-7) M) also increased B2KR mRNA levels twofold 4 h after stimulation. Actinomycin D suppressed the increase in B2KR mRNA and protein levels induced by ANG II. To elucidate the receptor subtype involved in mediating this regulation, VSMC were pretreated with losartan (AT(1) receptor antagonist) and/or PD-123319 (AT(2) receptor antagonist) at 10 microM for 30 min, followed by ANG II (10(-7) M) stimulation. Losartan completely blocked the ANG II-induced B2KR increase, whereas PD-123319 had no effect. In addition, expression of B2KR mRNA levels was decreased in AT(1A) receptor knockout mice. Finally, to determine whether ANG II stimulates B2KR expression via activation of the MAPK pathway, VSMC were pretreated with an inhibitor of p42/p44(mapk) (PD-98059) and/or an inhibitor of p38(mapk) (SB-202190), followed by ANG II (10(-7) M) for 24 h. Selective inhibition of the p42/p44(mapk) pathway significantly blocked the ANG II-induced increase in B2KR expression. These findings demonstrate that ANG II regulates expression of B2KR in VSMC and provide a rationale for studying the interaction between ANG II and bradykinin in the pathogenesis of vascular dysfunction.

Upregulation of angiotensin-converting enzyme 2 after myocardial infarction by blockade of angiotensin II receptors

We investigated in Lewis normotensive rats the effect of coronary artery ligation on the expression of cardiac angiotensin-converting enzymes (ACE and ACE 2) and angiotensin II type-1 receptors (AT1a-R) 28 days after myocardial infarction. Losartan, olmesartan, or the vehicle (isotonic saline) was administered via osmotic minipumps for 28 days after coronary artery ligation or sham operation. Coronary artery ligation caused left ventricular dysfunction and cardiac hypertrophy. These changes were associated with increased plasma concentrations of angiotensin I, angiotensin II, angiotensin-(1-7), and serum aldosterone, and reduced AT1a-R mRNA. Cardiac ACE and ACE 2 mRNAs did not change. Both angiotensin II antagonists attenuated cardiac hypertrophy; olmesartan improved ventricular contractility. Blockade of the AT1a-R was accompanied by a further increase in plasma concentrations of the angiotensins and reduced serum aldosterone levels. Both losartan and olmesartan completely reversed the reduction in cardiac AT1a-R mRNA observed after coronary artery ligation while augmenting ACE 2 mRNA by approximately 3-fold. Coadministration of PD123319 did not abate the increase in ACE 2 mRNA induced by losartan. ACE 2 mRNA correlated significantly with angiotensin II, angiotensin-(1-7), and angiotensin I levels. These results provide evidence for an effect of angiotensin II blockade on cardiac ACE 2 mRNA that may be due to direct blockade of AT1a receptors or a modulatory effect of increased angiotensin-(1-7).

Cardiac angiotensin-(1-7) in ischemic cardiomyopathy

BACKGROUND

Accumulating evidence suggests that angiotensin-(1-7) (Ang-[1-7]) may play an important role in counteracting the pressor, proliferative, and profibrotic actions of angiotensin II in the heart. Thus, we evaluated whether Ang-(1-7) is expressed in the myocardium of normal rats and those in which myocardial infarction was produced 4 weeks beforehand.

METHODS AND RESULTS

The left coronary artery in 10-week-old Lewis rats was either ligated (n=5) or exposed but not occluded in age-matched controls (sham; n=5). Left ventricular end-diastolic pressures were significantly elevated 4 weeks after myocardial infarction (25+/-1 versus 5+/-1 mm Hg for sham; P<0.001), whereas left ventricular systolic pressures were significantly reduced (ligated 86+/-4 versus sham 110+/-5 mm Hg; P<0.01). Hemodynamic effects of coronary artery ligation were accompanied by significant cardiac hypertrophy (heart weight to body weight: ligated 4.3+/-0.1 versus sham 2.9+/-0.1 mg/g; P<0.001). In both ligated and sham rats, Ang-(1-7) immunoreactivity was limited to cardiac myocytes and absent in interstitial cells and coronary vessels. Ang-(1-7) immunoreactivity was significantly augmented in ventricular tissue surrounding the infarct area in the heart of rats with myocardial infarction.

CONCLUSIONS

Development of heart failure subsequent to coronary artery ligation leads to increased expression of Ang-(1-7),which was restricted to myocytes.

Renal interstitial fluid angiotensin I and angiotensin II concentrations during local angiotensin-converting enzyme inhibition

It was recently demonstrated that angiotensin II (AngII) concentrations in the renal interstitial fluid (RIF) of anesthetized rats were in the nanomolar range and were not reduced by intra-arterial infusion of an angiotensin-converting enzyme (ACE) inhibitor (enalaprilat). This study was performed to determine changes in RIF AngI and AngII concentrations during interstitial administration of ACE inhibitors (enalaprilat and perindoprilat). Studies were also performed to determine the effects of enalaprilat on the de novo formation of RIF AngII elicited by interstitial infusion of AngI. Microdialysis probes (cut-off point, 30,000 D) were implanted in the renal cortex of anesthetized rats and were perfused at 2 micro l/min. The effluent dialysate concentrations of AngI and AngII were measured by RIA, and reported values were corrected for the equilibrium rates at this perfusion rate. Basal RIF AngI (0.74 +/- 0.05 nM) and AngII (3.30 +/- 0.17 nM) concentrations were much higher than plasma AngI and AngII concentrations (0.15 +/- 0.01 and 0.14 +/- 0.01 nM, respectively; n = 27). Interstitial infusion of enalaprilat through the microdialysis probe (1 or 10 mM in the perfusate; n = 5 and 8, respectively) significantly increased RIF AngI concentrations but did not significantly alter AngII concentrations. However, perindoprilat (10 mM in the perfusate, n = 7) significantly decreased RIF AngII concentrations by 22 +/- 4% and increased RIF AngI concentrations. Interstitial infusion of AngI (100 nM in the perfusate, n = 7) significantly increased the RIF AngII concentration to 8.26 +/- 0.75 nM, whereas plasma AngI and AngII levels were not affected (0.15 +/- 0.02 and 0.14 +/- 0.02 nM, respectively). Addition of enalaprilat to the perfusate (10 mM) prevented the conversion of exogenously added AngI. These results indicate that addition of AngI in the interstitial compartment leads to low but significant conversion to AngII via ACE activity (blocked by enalaprilat). However, the addition of ACE inhibitors directly into the renal interstitium, via the microdialysis probe, either did not reduce RIF AngII levels or reduced levels by a small fraction of the total basal level, suggesting that much of the RIF AngII is formed at sites not readily accessible to ACE inhibition or is formed via non-ACE-dependent pathways.