Angiotensin II regulates vascular smooth muscle cell pH, contraction, and growth via tyrosine kinase-dependent signaling pathways

Dysregulation of the renin-angiotensin system in vascular dementia

The renin-angiotensin system (RAS) regulates systemic and cerebral blood flow and is dysregulated in dementia. The major aim of this study was to determine if RAS signalling is dysregulated in vascular dementia. We measured markers of RAS signalling in white matter underlying the frontal and occipital cortex in neuropathologically confirmed cases of vascular dementia (n = 42), Alzheimer's disease (n = 50), mixed AD/VaD (n = 50) and age-matched controls (n = 50). All cases were stratified according to small vessel disease (SVD) severity across both regions. ACE-1 and ACE-2 protein and activity was measured by ELISA and fluorogenic peptide assays respectively, and angiotensin peptide (Ang-II, Ang-III and Ang-(1-7)) levels were measured by ELISA. ACE-1 protein level and enzyme activity, and Ang-II and Ang-III, were elevated in the white matter in vascular dementia in relation to SVD severity. ACE-1 and Ang-II protein levels were inversely related to MAG:PLP1 ratio, a biochemical marker of brain tissue oxygenation that when reduced indicates cerebral hypoperfusion, in a subset of cases. ACE-2 level was elevated in frontal white matter in vascular dementia. Ang-(1-7) level was elevated across all dementia groups compared to age-matched controls but was not related to SVD severity. RAS signalling was not altered in the white matter in Alzheimer's disease. In the overlying frontal cortex, ACE-1 protein was reduced and ACE-2 protein increased in vascular dementia, whereas angiotensin peptide levels were unchanged. These data indicate that RAS signalling is dysregulated in the white matter in vascular dementia and may contribute to the pathogenesis of small vessel disease.

Aging- and gender-related modulation of RAAS: potential implications in COVID-19 disease

Coronavirus disease 2019 (COVID-19) is a new infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 is frequently characterized by a marked inflammatory response with severe pneumonia and respiratory failure associated with multiorgan involvement. Some risk factors predispose patients to develop a more severe infection and to an increased mortality; among them, advanced age and male gender have been identified as major and independent risk factors for COVID-19 poor outcome. The renin-angiotensin-aldosterone system (RAAS) is strictly involved in COVID-19 because angiotensin converting enzyme 2 (ACE2) is the host receptor for SARS-CoV-2 and also converts pro-inflammatory angiotensin (Ang) II into anti-inflammatory Ang(1–7). In this review, we have addressed the effect of aging and gender on RAAS with emphasis on ACE2, pro-inflammatory Ang II/Ang II receptor 1 axis and anti-inflammatory Ang(1–7)/Mas receptor axis.

Aortic "Disease-in-a-Dish": Mechanistic Insights and Drug Development Using iPSC-Based Disease Modeling

Thoracic aortic diseases, whether sporadic or due to a genetic disorder such as Marfan syndrome, lack effective medical therapies, with limited translation of treatments that are highly successful in mouse models into the clinic. Patient-derived induced pluripotent stem cells (iPSCs) offer the opportunity to establish new human models of aortic diseases. Here we review the power and potential of these systems to identify cellular and molecular mechanisms underlying disease and discuss recent advances, such as gene editing, and smooth muscle cell embryonic lineage. In particular, we discuss the practical aspects of vascular smooth muscle cell derivation and characterization, and provide our personal insights into the challenges and limitations of this approach. Future applications, such as genotype-phenotype association, drug screening, and precision medicine are discussed. We propose that iPSC-derived aortic disease models could guide future clinical trials via “clinical-trials-in-a-dish”, thus paving the way for new and improved therapies for patients.

Angiotensin II, a unique vasoactive agent dissociates myosin light chain phosphorylation from contraction

Angiotensin II (100 nM) induced bi-phasic increases in cytosolic Ca²⁺ level ([Ca²⁺]_i) through the activation of angiotensin II type 1 receptor. Pharmacological examinations using 10 µM verapamil, 30 µM La³⁺, and 1 µM thapsigargin indicated that the first phase of the [Ca²⁺]_i-increase was mediated by Ca²⁺ release from sarcoplasmic reticulum (SR) and Ca²⁺ influx independently of voltage dependent Ca²⁺ channel (VDC). In contrast, the second phase of [Ca²⁺]_i-increase was mediated by Ca²⁺ influx through VDC. Although both [Ca²⁺]_i and myosin light chain (MLC)-phosphorylation at the first phase was apparently exceeded the threshold for contraction as estimated by high K⁺-induced responses, there was no appreciable contraction, indicating the dissociation between MLC phosphorylation and force during this phase. In contrast, the second phase of [Ca²⁺]_i was associated with the increases in both MLC phosphorylation and force. These results suggest that angiotensin II is a unique agonist which dissociates MLC-phosphorylation from muscle force during the Ca²⁺ releases from SR.

A reappraisal of loop diuretic choice in heart failure patients

The health and economic burden of heart failure is significant and continues to grow each year. Loop diuretics are an integral part of symptom management in heart failure. Furosemide is used disproportionately compared with other loop diuretics, and there is currently no guidance for physicians regarding which agent to choose. However, there exist pharmacologic differences as well as other mechanistic differences that appear to favor torsemide use over furosemide. Compared with furosemide, torsemide improves surrogate markers of heart failure severity such as left ventricular function, plasma brain natriuretic peptide levels, and New York Heart Association functional class and may also reduce hospitalizations, readmissions, and mortality. Data suggest that these benefits could be mediated through torsemide's ability to positively affect the renin-angiotensin-aldosterone system. Specifically, torsemide has been shown to inhibit aldosterone secretion, synthesis, and receptor binding in vitro, as well as decrease transcardiac extraction of aldosterone, myocardial collagen production, and cardiac fibrosis in patients with heart failure. We identified pertinent literature using keyword MEDLINE searches and cross-referencing prior bibliographies. We summarize the available data suggesting potential benefits with torsemide over furosemide, and call attention to the need for a reappraisal of diuretic use in heart failure patients and also for a well-powered, randomized control trial assessing torsemide versus furosemide use.

Type 2 Diabetes: Endothelial dysfunction and Exercise

PURPOSE

Vascular endothelial dysfunction is an early marker of atherosclerosis characterized by decreased nitric oxide bioavailability in the vascular endothelium and smooth muscle cells. Recently, some animal models and in vitro trials demonstrated that excessive superoxide production from mitochondria within vascular endothelial cells played a role in the pathogenesis of atherosclerosis in type 2 diabetes. This review provides a systematic assessment of the effectiveness of exercise to identify effective approaches to recognize diabetes risk and prevent progression to heart disease.

METHODS

A systematic literature search was conducted to retrieve articles from 1979 to 2013 using the following databases: the MEDLINE, PubMed. Articles had to describe an intervention that physical activity and exercise to identify effective approaches to heart and vascular endothelium.

RESULTS

Currently, physical activity and exercise guidelines aimed to improve cardiovascular health in patients with type 2 diabetes are nonspecific. Benefit of aerobic exercise training on vascular endothelial function in type 2 diabetic patients is still controversial.

CONCLUSION

it is necessary to demonstrate the mechanism of endothelial dysfunction from live human tissues so that we can provide more specific exercise training regimens to enhance cardiovascular health in type 2 diabetic patients.

The angiotensin II type 1 receptor (AT1R) closely interacts with large conductance voltage- and Ca2+-activated K+ (BK) channels and inhibits their activity independent of G-protein activation

Angiotensin II (ANG-II) and BK channels play important roles in the regulation of blood pressure. In arterial smooth muscle, ANG-II inhibits BK channels, but the underlying molecular mechanisms are unknown. Here, we first investigated whether ANG-II utilizes its type 1 receptor (AT1R) to modulate BK activity. Pharmacological, biochemical, and molecular evidence supports a role for AT1R. In renal arterial myocytes, the AT1R antagonist losartan (10 μM) abolished the ANG-II (1 μM)-induced reduction of whole cell BK currents, and BK channels and ANG-II receptors were found to co-localize at the cell periphery. We also found that BK inhibition via ANG-II-activated AT1R was independent of G-protein activation (assessed with 500 μM GDPβS). In BK-expressing HEK293T cells, ANG-II (1 μM) also induced a reduction of BK currents, which was contingent on AT1R expression. The molecular mechanisms of AT1R and BK channel coupling were investigated in co-transfected cells. Co-immunoprecipitation showed formation of a macromolecular complex, and live immunolabeling demonstrated that both proteins co-localized at the plasma membrane with high proximity indexes as in arterial myocytes. Consistent with a close association, we discovered that the sole AT1R expression could decrease BK channel voltage sensitivity. Truncated BK proteins revealed that the voltage-sensing conduction cassette is sufficient for BK-AT1R association. Finally, C-terminal yellow and cyan fluorescent fusion proteins, AT1R-YFP and BK-CFP, displayed robust co-localized Förster resonance energy transfer, demonstrating intermolecular interactions at their C termini. Overall, our results strongly suggest that AT1R regulates BK channels through a close protein-protein interaction involving multiple BK regions and independent of G-protein activation.

Elevated transcriptional co-activator p102 mediates angiotensin II type 1 receptor up-regulation and extracellular matrix overproduction in the high glucose-treated rat glomerular mesangial cells and isolated glomeruli

P102 is a multifunctional transcriptional co-activator. This experiment is designed to investigate the role of p102 in the activation of renin-angiotensin system (RAS) and sequentially extracellular matrix (ECM) over synthesis in diabetic nephropathy. Rat glomerular mesangial cells (MCs) or isolated glomeruli were cultured in normal glucose (NG, 5.5mM) or high glucose (HG, 25 mM) DMEM. The generation of reactive oxygen species was measured by 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) fluorescent probe assay. The protein levels were analyzed by Western blot and the mRNA levels were evaluated by real-time PCR. HG treatment induced an increase in reactive oxygen species production. Culturing the cells in HG for 48 h, p102 mRNA and protein, angiotensin II type 1 receptor (AT1 receptor) mRNA, transforming growth factor-β1 (TGF-β1) and fibronectin proteins were significantly increased. NADPH oxidase inhibitor DPI blocked the HG-induced p102, TGF-β1 and fibronetcin elevations. Knockdown on p102 expression by siRNA depressed the HG-induced AT1 receptor up-regulation as well as the increases in TGF-β1 and fibronectin. In contrast, AT1 receptor antagonist candesartan did not influence p102 levels under either NG or HG condition, but blocked the HG-induced TGF-β1 and fibronectin increases. The results from isolated glomeruli were consistent with that of MCs, which showed that HG exposure stimulated the expression of p102. These results suggest that the overproduction of reactive oxygen species at the early stage of HG incubation stimulates p102 synthesis, which in turn up-regulates AT1 receptor expression. The activation of RAS stimulates TGF-β1 and fibronectin production, which further results in ECM accumulation.

[Ca2+]i and PKC-alpha are involved in the inhibitory effects of Ib, a novel nonpeptide AngiotensinII subtype AT1 receptor antagonist, on AngiotensinII-induced vascular contraction in vitro

The vasoactive peptide AngiotensinII (AngII) is an important factor in the cardiovascular system, exerting most of its effects through AngII receptor type 1 (AT1). Ib, a new nonpeptide AT1 receptor antagonist, has been observed to play a positive role in the treatment of hypertension in preclinical tests. In this study, the inhibitory effects of Ib on AngII-induced vascular contraction in vitro were investigated, and its molecular mechanisms were further explored. In endothelium-denuded aortic rings from rabbits, Ib produced a rightward shift in the concentration-response curve for AngII with a decrease in the maximal contractile response and the pD2' was 7.29. In vascular smooth muscle cells (VSMCs), the specific binding of [125I]AngII to AT1 receptors was inhibited by Ib in a concentration-dependent manner with IC50 value of 0.96nM. Ib could inhibit both AngII-induced Ca2+ mobilization from internal stores and Ca2+ influx. Moreover, the translocation of PKC-alpha stimulated by AngII was inhibited by Ib. Thus, the inhibitory effects of Ib might be related with the depression on AngII-induced increase in [Ca2+]i and translocation of PKC-alpha through blocking AT1 receptors.

Saga of Renin-Angiotensin System and Calcium Channels in Hypertensive Diabetics: Does it Have a Therapeutic Edge?

Current understanding of the genesis of diabetic vascular disease suggests that vascular complications, such as atherosclerosis and hypertension, are associated with changes in structural and functional parameters. Experimental and epidemiological data suggest that activation of the renin-angiotensin-aldosterone system plays an important role in the development of micro- and macro-vascular complications. Most of the negative cardiovascular actions of angiotensin II are mediated through AT1 receptors, whereas the AT2 receptors mediate largely beneficial effects. Hence, compared to angiotensin converting enzyme inhibitors (ACEIs), selective AT1 receptor blockers (ARBs) should provide additional end organ protection via AT2 receptors activation. Although ACEIs are useful therapeutically, they are being currently displaced by ARBs. Enhanced calcium ion channel activity is reported in vascular smooth muscles from diabetic animal models. Clinical benefits of calcium channel blockers (CCBs) in diabetic hypertensive patients are controversial, but there is increasing experimental evidence for the beneficial effects of dihydropyridine-type CCBs. Although the treatment of hypertension in diabetics reduces cardiovascular and microvascular complications, the ideal strategy for treating hypertension in diabetics has not been well defined and warrants a combination approach. Only limited clinical data regarding the use of ARBs in combination with CCBs in diabetics are available. The experimental data suggest that combination of a CCB and an AT1 receptor blocker, or a hypothetical dual blocker of AT1 receptors as well as of calcium channels would be an ideal regimen. There is, however, no conclusive clinical evidence to support the combined use of these drugs. This review highlights the available experimental data that support the therapeutic benefits of this combination.

Cardiac fibrogenesis in magnesium deficiency: a role for circulating angiotensin II and aldosterone

Mechanisms underlying cardiac fibrogenesis in magnesium deficiency are unclear. It was reported earlier from this laboratory that serum from magnesium-deficient rats has a more pronounced stimulatory effect on cell proliferation, net collagen production, and superoxide generation in adult rat cardiac fibroblasts than serum from rats on the control diet. The profibrotic serum factors were, however, not identified. This study tested the hypothesis that circulating angiotensin II may modulate cardiac fibroblast activity in hypomagnesemic rats. Male Sprague-Dawley rats were pair-fed a magnesium-deficient (0.0008% Mg) or -sufficient (0.05%) diet for 6 days, and the effects of serum from these rats on [3H]thymidine and [3H]proline incorporation into cardiac fibroblasts from young adult rats were evaluated in the presence of losartan, an angiotensin II type 1 (AT1) receptor antagonist, and spironolactone, an aldosterone antagonist. Losartan and spironolactone markedly attenuated the stimulatory effects in vitro of serum from the magnesium-deficient and control groups, but the inhibitory effects were considerably higher in cells exposed to serum from magnesium-deficient animals. Circulating and cardiac tissue levels of angiotensin II were significantly elevated in magnesium-deficient animals (67.6% and 93.1%, respectively, vs. control). Plasma renin activity was 61.9% higher in magnesium-deficient rats, but serum angiotensin-converting enzyme activity was comparable in the two groups. Furthermore, preliminary experiments in vivo using enalapril supported a role for angiotensin II in magnesium deficiency. There was no significant difference between the groups in serum aldosterone levels. The findings suggest that circulating angiotensin II and aldosterone may stimulate fibroblast activity and contribute to a fibrogenic response in the heart in magnesium deficiency.

Src family kinase involvement in rat preglomerular microvascular contractile and [Ca2+]i responses to ANG II

Experiments were performed to investigate the potential role of Src family kinase(s) in the rat afferent arteriolar contractile response to ANG II. The in vitro blood-perfused juxtamedullary nephron technique was employed to monitor afferent arteriolar lumen diameter responses to 1-100 nM ANG II before and during Src family kinase inhibition (10 microM PP2). PP2 did not alter baseline diameter but attenuated ANG II-induced contractile responses by 33 +/- 6%. An inactive analog of PP2 (PP3) had no effect on ANG II-induced afferent arteriolar contraction. The effect of Src kinase inhibition on ANG II-induced intracellular free Ca(2+) concentration ([Ca(2+)](i)) responses was probed in fura 2-loaded preglomerular microvascular smooth muscle cells (PVSMCs) obtained from explants and studied after 3-5 days in culture. In untreated PVSMCs, ANG II evoked peak (Delta = 293 +/- 66 nM) and plateau (Delta = 23 +/- 8 nM) increases in [Ca(2+)](i). In PVSMCs pretreated with PP2, baseline [Ca(2+)](i) was unaltered, but both the peak (Delta = 140 +/- 22 nM) and plateau (Delta = 3 +/- 2 nM) phases of the ANG II response were significantly reduced compared with untreated cells. PP3 did not alter [Ca(2+)](i) responses to ANG II. Immunoprecipitation and Western blot analysis confirmed that 100 nM ANG II increased phosphorylation of c-Src (at Y(416)) in PVSMCs. The phosphorylation response was maximal 1 min after ANG II exposure and was prevented by PP2. We conclude that the preglomerular vasoconstriction evoked by ANG II involves rapid c-Src activation with subsequent effects that contribute to the [Ca(2+)](i) response to the peptide.

ANG II type 2 receptor regulates smooth muscle growth and force generation in late fetal mouse development

Although evidence from culture studies implicates the angiotensin II (ANG II) type 2 receptor (AT(2)R) in the regulation of growth and differentiation of arterial smooth muscle (SM) cells (SMC), the lack of its expression in adult arteries has precluded direct investigation of its role in vivo. The goal of the present study was to determine the role of AT(2)R in the control of fetal SMC growth, contractility, and differentiation during vascular development. Determination of isometric tension in fetal aortas showed potentiated ANG II-induced contraction by treatment with the selective AT(2)R antagonist PD-123319, demonstrating the presence of functional AT(2)Rs that mediate reduced force development in vascular SMC. In direct contrast to numerous cell culture studies, proliferation indexes were decreased rather than increased in aortic SMC of fetal homozygous AT(2)R knockout compared with wild-type or heterozygous knockout mice. Experiments using SMC tissues from heterozygous female AT(2)R knockout mice, which are naturally occurring chimeras for AT(2)R expression, showed that AT(2)R mRNA expression was exactly 50% of that of wild type. This indicated that loss of AT(2)R expression did not confer a selective advantage or disadvantage for SMC lineage determination and expansion. Real time RT-PCR analyses showed no significant difference in expression of SM-alpha-actin, SM myosin heavy chain, and myocardin in various SM tissues from all three genotypes, suggesting that knockout of AT(2)R had no effect on subsequent SMC differentiation. Taken together, results indicate that functional AT(2)R are expressed in fetal aorta and mediate reduced force development but do not significantly contribute to regulation of SMC differentiation.

Angiotensin receptors: signaling, vascular pathophysiology, and interactions with ceramide

Angiotensin II (ANG II) is a pleiotropic vasoactive peptide that binds to two distinct receptors: the ANG II type 1 (AT(1)) and type 2 (AT(2)) receptors. Activation of the renin-angiotensin system (RAS) results in vascular hypertrophy, vasoconstriction, salt and water retention, and hypertension. These effects are mediated predominantly by AT(1) receptors. Paradoxically, other ANG II-mediated effects, including cell death, vasodilation, and natriuresis, are mediated by AT(2) receptor activation. Our understanding of ANG II signaling mechanisms remains incomplete. AT(1) receptor activation triggers a variety of intracellular systems, including tyrosine kinase-induced protein phosphorylation, production of arachidonic acid metabolites, alteration of reactive oxidant species activities, and fluxes in intracellular Ca(2+) concentrations. AT(2) receptor activation leads to stimulation of bradykinin, nitric oxide production, and prostaglandin metabolism, which are, in large part, opposite to the effects of the AT(1) receptor. The signaling pathways of ANG II receptor activation are a focus of intense investigative effort. We critically appraise the literature on the signaling mechanisms whereby AT(1) and AT(2) receptors elicit their respective actions. We also consider the recently reported interaction between ANG II and ceramide, a lipid second messenger that mediates cytokine receptor activation. Finally, we discuss the potential physiological cross talk that may be operative between the angiotensin receptor subtypes in relation to health and cardiovascular disease. This may be clinically relevant, inasmuch as inhibitors of the RAS are increasingly used in treatment of hypertension and coronary heart disease, where activation of the RAS is recognized.

Regulation of prostacyclin synthesis by angiotensin II and TNF-alpha in vascular smooth muscle

We had previously established that in a model of Ang II-induced hypertension, administration of an anti-TNF-alpha antibody caused additional increases in mean arterial pressure. Production of vasodilator prostanoids (i.e. PGI2 and PGE2) is increased by Ang II in vascular smooth muscle and is part of a counter-regulatory mechanism that opposes increases in vascular tone. We, therefore, examined the effects of TNF-alpha on Ang II-induced increases in PGI2 production in vascular smooth muscle cells (VSMC). Addition of Ang II caused an increase in the production of PGI2, while addition of TNF-alpha had no effect. However, pretreatment with TNF-alpha potentiated the stimulatory effects of Ang II. The potentiating effect of TNF-alpha was neither at the level of prostacyclin synthetase nor at the level of acyl hydrolase activity. This potentiation was dependent on tyrosine kinase activity, as preincubation with genistein completely abolished the effect of TNF-alpha. TNF-alpha upregulated AA-induced PGI2 synthesis, indicating that the effect of TNF-alpha is at the level of cyclooxygenase (COX). These data suggest that TNF-alpha potentiates Ang II-induced synthesis of PGI2 and PGE2 in a tyrosine kinase-dependent manner, an effect that may contribute to the counter-regulatory influence of prostaglandins on the pressor effects of Ang II in the vasculature.

Role of c-Src in the regulation of vascular contraction and Ca2+ signaling by angiotensin II in human vascular smooth muscle cells

OBJECTIVE

Tyrosine kinases, typically associated with growth-signaling pathways, also play a role in Ang II-stimulated vascular contraction. However the specific kinases involved are unclear. We hypothesize here that c-Src, a non-receptor tyrosine kinase, is an important upstream regulator of vascular smooth muscle cell (VSMC) Ca2+ signaling and associated vascular contraction induced by Ang II.

METHODS

Cultured VSMCs from resistance arteries of healthy subjects were studied. Human VSMCs electroporated with anti-c-Src antibody and c-Src-deficient VSMCs from small arteries of c-Src knockout mice (Src-/-mVSMCs) were also investigated. Intracellular free Ca2+ concentration ([Ca2+]i), c-Src activity and IP3 production were measured by fura 2, immunoblot and radioimmunoassay respectively. Contraction was examined in intact rat small arteries.

RESULTS

Ang II rapidly increased VSMC c-Src activity, with peak responses obtained at 1 min. Ang II induced a biphasic [Ca2+]i response (Emax = 636 +/- 123 nmol/l). The initial [Ca2+]i transient, mediated primarily by Ca2+mobilization, was dose-dependently attenuated by the selective Src inhibitor, PP2, but not by PP3 (inactive analogue). Ang II-elicited [Ca2+]i responses were blunted in cells electroporated with anti-c-Src antibodies and in c-Src-/-mVSMCs. Src inhibition decreased Ang II-induced generation of IP3 in human VSMCs. Ang II dose-dependently increased vascular contraction (Emax = 40 +/- 6.5%). These responses were attenuated by PP2 (Emax = 7.8 +/- 0.08%) but not by PP3 (Emax = 35 +/- 4.5%).

CONCLUSIONS

Our findings identify c-Src as an important regulator of VSMC [Ca2+]i signaling and implicate a novel contractile role for this non-receptor tyrosine kinase in Ang II-stimulated vascular smooth muscle.

Model of cardiovascular injury in magnesium deficiency

Magnesium deficiency is known to produce cardiovascular lesions. It is, however, not clear as to what constitutes magnesium deficiency - reduced serum levels, reduced tissue levels or reduced intracellular levels of the ionic form of the element. This article cites evidence in support of a hypothesis that a fall in serum magnesium levels may trigger a temporal sequence of events involving vasoconstriction, hemodynamic alterations and vascular endothelial injury to produce pro-inflammatory, pro-oxidant and pro-fibrogenic effects, resulting in initial perivascular myocardial fibrosis which, in turn, would cause myocardial damage and replacement fibrosis. Further, angiotensin II may be the prime mover of the pathogenetic cascade in magnesium deficiency. Importantly, such a mechanism of cardiovascular injury would be independent of a reduction in myocardial or vascular tissue levels of magnesium.

Effect of genistein on cardiovascular responses to angiotensin II in conscious unrestrained rats

Soybeans contain genistein, a phytoestrogen that may have beneficial effects in coronary artery disease, osteoporosis, and breast cancer. In vitro studies demonstrated that genistein reduced vascular smooth muscle contractions to angiotensin II. We tested the hypothesis that genistein attenuates the overall cardiovascular responses to angiotensin II via nongenomic mechanisms in conscious rats. Mean arterial blood pressure (MAP) was recorded from conscious unrestrained Sprague-Dawley rats (n = 26) approximately 48 hours after surgery. Cumulative dose response curves to angiotensin II (10-200 ng/kg/min) were constructed before and after i.v. treatment with genistein given as a single bolus dose of 160 microg/kg or 1500 microg/kg, or as a loading dose of 160 microg/kg followed by an infusion at a rate of 20 microg/kg. Angiotensin II infusions were associated with graded increases in arterial pressure ranging between 0+/-1 and 35+/-4 mm Hg. These pressor responses were accompanied by significant dose-dependent decreases in heart rate. None of the genistein treatment regimens significantly affected the pressor responses to angiotensin II. Accordingly, we conclude that short-term i.v. treatment with genistein does not depress pressor responsiveness to angiotensin II.

Rationale for angiotensin II receptor blockers in patients with low-renin hypertension

African Americans outrank other ethnic groups in the United States in prevalence, early onset, and severity of hypertension. Furthermore, African Americans suffer the highest rates of mortality from cardiovascular, cerebrovascular, and end-stage renal disease. The recently concluded Heart Outcomes Prevention Evaluation (HOPE) study reports that the angiotensin-converting enzyme (ACE) inhibitor ramipril significantly reduced morbidity and mortality in a broad range of patients at high risk for cardiovascular events. These results strengthen the case for increasing the use of ACE inhibitor therapy. In accord with the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC VI) guidelines, antihypertensive monotherapy for African Americans is based on the known ability of diuretics and calcium channel blockers to produce greater reductions in blood pressure in this population than those attainable with beta blockers and ACE inhibitors. The national guidelines also suggest ACE inhibitors for all hypertensive patients with left ventricular dysfunction or nephropathy, which implies that African Americans must cross a clinical threshold to become candidates for these agents. The rationale for delaying ACE inhibitor therapy is due in part to a perceived unique pathobiology in hypertensive African Americans: an excess prevalence of salt sensitivity, hypervolemia, and low plasma renin activity (PRA). At first glance, it would seem intuitive to avoid agents that further depress the renin-angiotensin system (RAS) and choose agents that reduce plasma volume. However, most hypertensive African Americans are not hypovolemic. Furthermore, dietary sodium restriction and diuretic therapy raise PRA and improve the response to ACE inhibitors. The overall aim of this article is to explain the rationale for expanded use of drugs that block the RAS in African Americans and low-renin populations.

Acetazolamide and enalapril combination offers complete protection from nitric oxide-deficient stroke in stroke-prone spontaneously hypertensive rats

Chronic oral administration of l -NAME precipitates stroke in stroke-prone spontaneously hypertensive rats (SHRSP). The present study investigated whether acetazolamide (an acidotic agent) given alone or in combination with an angiotensin blocker (enalapril maleate) offers any protection from NO-deficient stroke in SHRSP. We also examined whether protection from NO-deficient stroke involves activation of K(+)channels. Five-week-old SHRSP drank saline (group I), l -NAME (group II), l -NAME+enalapril (group III), l -NAME+acetazolamide (group IV), and l -NAME+enalapril+acetazolamide (group V). Within a few hours following onset of stroke, rats were attached to a blood pressure recorder. In subsequent experiments, to investigate the involvement of K(+)channels, glibenclamide and BaCl(2)(K(+)channel blockers) were included in the drinking solutions that were given to the SHRSP groups receiving l -NAME, acetazolamide and enalapril. Group I of SHRSP did not develop stroke. Group II, III and IV developed stroke in 12+/-2, 29+/-2 and 20+/-2 days, respectively. SHRSP from group V did not develop stroke. However, they died in 70+/-2 days. The glibenclamide and BaCl(2)administration failed to prevent this protection from stroke. In conclusion, concurrent administration of acetazolamide and enalapril prevents onset of NO-deficient stroke in SHRSP. These stroke-protective effects are independent of reductions in mean or systolic blood pressures and do not involve an activation of K(+)channels.

AT(1)-signalling in vascular smooth muscle

Angiotensin II activates multiple signalling pathways in vascular smooth muscle. The precise pattern of signals and their relative importance to a particular functional response depends on both cell type and differentiation state. Although the contractile and trophic effects of Ang II are often thought of as distinct responses it is increasingly difficult to differentiate them in terms of signalling pathways. Since vasoconstriction and abnormal growth are both features of circulatory diseases such as hypertension and atherosclerosis a better understanding of the signalling pathways responsible for the vasoconstrictor and trophic actions of this peptide may help define novel therapeutic targets in cardiovascular disease.

Homocyst(e)ine induces calcium second messenger in vascular smooth muscle cells

Homocysteine found in the plasma of patients with coronary heart disease, induces vascular smooth muscle cell (VSMC) proliferation and increases deposition of extracellular matrix (ECM) components. Yet, the mechanism by which homocysteine mediates this effect and its role in vascular disease is largely unknown. We hypothesized that homocysteine induces ECM production via intracellular calcium release in VSMC. To test this hypothesis, aortic VSMC from Sprague-Dawley rats were isolated and characterized by positive labeling for vascular smooth muscle alpha-actin. Early passage cells (p2-3) were grown in monolayer on coverslips. Calcium transients were quantified with fura2/AM spectrofluorometry. Homocysteine induced intracellular calcium [Ca(2+)](i) transients with an EC(50) of 60 +/- 5 nM. The EC(50) for glutathione and cysteine were 10 and 100-fold lower, respectively. Depleting extracellular calcium did not alter the homocysteine effect on intracellular calcium; however, thapsigargin pretreatment, which depletes intracellular Ca(2+) stores, abolished the homocysteine effect, demonstrating its dependence on intracellular Ca(2+) stores. Extracellular sodium depletion significantly (P < 0.05) increased [Ca(2+)](i) also suggesting a possible role of sodium-calcium exchange in the process. To begin to elucidate the intracellular pathways by which homocysteine might act, VSMC were pretreated with specific inhibitors and stimulators prior to homocysteine stimulation. Staurosporine and phorbol myrisate acetate (PMA), potent simulators of protein kinase C, augmented the release of Ca(2+) by homocysteine. Interestingly, pretreatment with the nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME) greatly exacerbated the sensitivity of VSMC to homocysteine. In contrast, pretreatment with either the phospholipase A(2) activator neomycin, the antioxidant and hepatic hydroxymethyl glutaryl coenzyme A (HMG CoA) reductase inhibitor, pravastatin, the tyrosine kinase inhibitor genestein, or the calcium channel blocker, felodipine completely inhibited the homocysteine-induced Ca(2+) signal in VSMC. This suggests the role of multiple signaling pathways in the homocysteine effect on VSMC Ca(2+). Effects of homocysteine on collagen production, as ascertained by immunoblot analysis, correlated with its effect in intracellular calcium. Regardless of the signaling pathways involved, homocysteine, by virtue of its role on VSMC proliferation and ECM deposition, has the potential to affect vascular reactivity. To determine the effect of homocysteine on the ability of VSMC to react to potent agonist such as angiotensin II, VSMC were pretreated with homocysteine and exposed to a range of angiotensin II concentrations which normally have no effect on intracellular Ca(2+). After homocysteine pretreatment, VSMC were extremely responsive to angiotensin II at concentrations well below the physiologic range. These data taken together suggested that an initial effect of homocysteine is to induce release of intracellular Ca(2+) in VSMC and may induce vascular reactivity. The transient in Ca(2+) correlates with the effect on ECM associated with homocysteine.

Angiotensin II receptor blockers: review of the binding characteristics

Several angiotensin II receptor blockers (ARBs), including candesartan cilexetil, irbesartan, losartan, telmisartan, and valsartan, are currently approved by the US Food and Drug Administration (FDA) for the treatment of patients with hypertension. These agents share a common mechanism of action-antagonism of the angiotensin type 1 (AT1) receptor-and as a result, they block a number of angiotensin II effects that are relevant to the pathophysiology of cardiovascular disease, including vasoconstriction, renal sodium reabsorption, aldosterone and vasopressin secretion, sympathetic activation, and vascular and cardiac hyperplasia and hypertrophy. Unlike the angiotensin converting enzyme (ACE) inhibitors, these new drugs block the effects of angiotensin II regardless of whether it is produced systemically in the circulation or locally via ACE- or non-ACE-dependent pathways in tissues. ARBs also block the angiotensin II-induced feedback regulation of renin release, resulting in an increase in angiotensin II levels. With the AT1 receptor blocked, angiotensin II is available to activate the angiotensin type 2 (AT2) receptor, which mediates several potentially beneficial effects in the cardiovascular system, including vasodilation, antiproliferation, and apoptosis. Thus, ARBs provide a highly selective approach for regulating the effects of angiotensin II.

Activation of the Na(+)-H+ exchanger modulates angiotensin II-stimulated Na(+)-dependent Mg2+ transport in vascular smooth muscle cells in genetic hypertension

This study investigated the role of the Na(+)-H+ exchanger (NHE) on angiotensin II (Ang II)-induced activation of Na(+)-dependent Mg2+ transport in vascular smooth muscle cells (VSMCs) from Wistar-Kyoto rats (WKY; n=20) and spontaneously hypertensive rats (SHR; n=20). Intracellular free concentrations of Mg2+ ([Mg2+]i) and Na+ ([Na+]i) and intracellular pH (pHi) were measured with the specific fluorescent probes mag-fura 2-AM, SBFI-AM, and BCECF-AM, respectively. Na+ dependency of Mg2+ transport was assessed in Na(+)-free buffer, and the role of the NHE was determined with the highly selective NHE blocker 5-(N-methyl-N-isobutyl) amiloride (MIA). Basal [Mg2+]i was lower in SHR than WKY (0.59+/-0.01 versus 0.71+/-0.01 mmol/L, P<0.05). Basal pHi and [Na+]i were not different between the 2 groups. Ang II dose dependently increased [Na+]i and pHi and decreased [Mg2+]i. Responses were significantly greater (P<0.05) in SHR versus WKY ([Na+]i E(max)=37.5+/-1.1 versus 33.7+/-1.9 mmol/L; pHi E(max)=7.35+/-0.04 versus 7.20+/-0.01; [Mg2+]i E(min)=0. 28+/-0.09 versus 0.53+/-0.02 mmol/L, SHR versus WKY). In Na(+)-free buffer, Ang II-elicited [Mg2+]i responses were inhibited. MIA (1 micromol/L) inhibited Ang II-stimulated responses in WKY and normalized responses in SHR ([Mg2+]i E(min)=0.49+/-0.02). Ang II-stimulated activation of NHE was significantly increased (P<0.05) in SHR (0.07+/-0.002 DeltapH(i)/s) compared with WKY (0.05+/-0.004 DeltapH(i)/s). These data demonstrate that in VSMCs [Mg2+]i regulation is Na+ dependent, that activation of NHE modulates Na(+)-Mg2+ transport, and that increased activity of NHE may play a role in altered Na(+)-dependent regulation of [Mg2+]i in SHR.

Oxybutynin chloride inhibits proliferation and suppresses gene expression in bladder smooth muscle cells

PURPOSE

We test the hypothesis that oxybutynin chloride inhibits bladder smooth muscle cell proliferation.

MATERIALS AND METHODS

Cultured rat bladder smooth muscle cells were grown in Medium 199 supplemented with 10% fetal bovine serum in the presence of 0, 1, 10 and 100 microM. oxybutynin. Cell proliferation was assessed by counting cell numbers 48 and 96 hours after plating. To investigate the role of oxybutynin in bladder smooth muscle cell proliferation after mechanical stretch, cells were grown on silicone elastomer bottomed culture plates and subjected to cyclical stretch-relaxation for 48 hours in the presence of 10 microM. oxybutynin. Deoxyribonucleic acid synthesis was assessed by tritiated thymidine incorporation assay. To examine the effect of oxybutynin on stretch activated gene expression, bladder smooth muscle cells were subjected to stretch-relaxation for 2 hours with and without 10 microM. oxybutynin, and relative c-jun messenger (m) ribonucleic acid (RNA) levels were assessed by semiquantitative reverse transcriptase-polymerase chain reaction with normalization to glyceraldehyde-3-phosphate dehydrogenase mRNA levels.

RESULTS

The serum stimulated increase in bladder smooth muscle cell growth was inhibited by oxybutynin in a dose dependent manner. In bladder smooth muscle cells there was a 4.7-fold increase in deoxyribonucleic acid synthesis after mechanical stretch, which decreased by 40% (p <0.01) when cells were stretched in the presence of oxybutynin. Stretch stimulated significant increase in c-jun mNRA levels, which was significantly decreased by oxybutynin.

CONCLUSIONS

Oxybutynin chloride inhibits bladder smooth muscle cell proliferation induced by serum and mechanical stretch. A potential mechanism by which oxybutynin inhibits proliferation may be the down regulation of growth promoting genes, such as c-jun. We speculate that oxybutynin may be useful for preventing permanent hypertrophic bladder changes in addition to decreasing intravesical pressure.

Oxybutynin chloride inhibits proliferation and suppresses gene expression in bladder smooth muscle cells

PURPOSE

We test the hypothesis that oxybutynin chloride inhibits bladder smooth muscle cell proliferation.

MATERIALS AND METHODS

Cultured rat bladder smooth muscle cells were grown in Medium 199 supplemented with 10% fetal bovine serum in the presence of 0, 1, 10 and 100 microM. oxybutynin. Cell proliferation was assessed by counting cell numbers 48 and 96 hours after plating. To investigate the role of oxybutynin in bladder smooth muscle cell proliferation after mechanical stretch, cells were grown on silicone elastomer bottomed culture plates and subjected to cyclical stretch-relaxation for 48 hours in the presence of 10 microM. oxybutynin. Deoxyribonucleic acid synthesis was assessed by tritiated thymidine incorporation assay. To examine the effect of oxybutynin on stretch activated gene expression, bladder smooth muscle cells were subjected to stretch-relaxation for 2 hours with and without 10 microM. oxybutynin, and relative c-jun messenger (m) ribonucleic acid (RNA) levels were assessed by semiquantitative reverse transcriptase-polymerase chain reaction with normalization to glyceraldehyde-3-phosphate dehydrogenase mRNA levels.

RESULTS

The serum stimulated increase in bladder smooth muscle cell growth was inhibited by oxybutynin in a dose dependent manner. In bladder smooth muscle cells there was a 4.7-fold increase in deoxyribonucleic acid synthesis after mechanical stretch, which decreased by 40% (p <0.01) when cells were stretched in the presence of oxybutynin. Stretch stimulated significant increase in c-jun mNRA levels, which was significantly decreased by oxybutynin.

CONCLUSIONS

Oxybutynin chloride inhibits bladder smooth muscle cell proliferation induced by serum and mechanical stretch. A potential mechanism by which oxybutynin inhibits proliferation may be the down regulation of growth promoting genes, such as c-jun. We speculate that oxybutynin may be useful for preventing permanent hypertrophic bladder changes in addition to decreasing intravesical pressure.

Angiotensin II stimulates DNA and protein synthesis in vascular smooth muscle cells from human arteries: role of extracellular signal-regulated kinases

OBJECTIVE

This study investigates the growth effects and associated signaling pathways of angiotensin II (Ang II) in human vascular smooth muscle cells.

METHODS

Cultured vascular smooth muscle cells derived from resistance arteries (< 300 microm diameter) from subcutaneous gluteal biopsies of healthy subjects (n = 6) and human aortic vascular smooth muscle cells were used. Cells were studied between passages 3 and 6. Both 3H-thymidine and 3H-leucine incorporation were measured as indices of vascular smooth muscle cell hyperplasia (DNA synthesis) and cell hypertrophy (protein synthesis), respectively. Growth effects of Ang II (10(-12) - 10(-6) mol/l), in the absence and presence of 10(-5) mol/l losartan (AT1 antagonist) and PD123319 (AT2 antagonist), were determined. Ang II-induced effects were compared to those of endothelin-1. To determine whether extracellular signal-regulated kinase (ERK)-dependent pathways play a role in Ang II-mediated growth, cells were pretreated with the selective ERK kinase (MEK) inhibitor, PD98059 (10(-5) mol/l). ERK activation was determined by Western blot in the absence and presence of PD98059.

RESULTS

Ang II dose-dependently increased 3H-thymidine incorporation in cells from aorta (Emax = 276 +/- 10.4% of control) and resistance arteries (Emax = 284 +/- 5.1% of control). Ang II also stimulated 3H-leucine incorporation in cells from aorta (Emax = 162 +/- 11.6 of control) and resistance arteries (Emax 175 +/- 10% of control). Unlike Ang II, endothelin-1 failed to significantly alter cellular growth, except at high concentrations (> 10(-7) mol/l), where it had a weak stimulatory effect Losartan, but not PD123319, blocked Ang II-stimulated growth responses. Ang II significantly increased phosphorylation of ERK-1 and ERK-2, with maximum responses obtained at 5 min. PD98059 inhibited Ang II-stimulated ERK activity and abrogated agonist-induced DNA and protein synthesis. Losartan, but not PD123319 inhibited Ang II-induced phosphorylation of ERK-1 and ERK-2.

CONCLUSIONS

Ang II stimulates both hyperplasia and hypertrophy in vascular smooth muscle cells from human arteries. These growth effects are mediated via Ang II receptors of the AT1 subtype that are linked to ERK-dependent signaling pathways.

Mitogen-activated protein/extracellular signal-regulated kinase inhibition attenuates angiotensin II-mediated signaling and contraction in spontaneously hypertensive rat vascular smooth muscle cells

This study investigates the role of extracellular signal-regulated kinases (ERKs) in angiotensin II (Ang II)-generated intracellular second messengers (cytosolic free Ca2+ concentration, ie, [Ca2+]i, and pHi) and in contraction in isolated vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) and control Wistar Kyoto rats (WKY) using the selective mitogen-activated protein (MAP)/ERK inhibitor, PD98059. VSMCs from mesenteric arteries were cultured on Matrigel basement membrane matrix. These cells, which exhibit a contractile phenotype, were used to measure [Ca2+]i, pHi, and contractile responses to Ang II (10(-12) to 10(-6) mol/L) in the absence and presence of PD98059 (10(-5) mol/L). [Ca2+]i and pHi were measured by fura-2 and BCECF methodology, respectively, and contraction was determined by photomicroscopy. Ang II-stimulated ERK activity was measured by Western blot analysis using a phospho-specific ERK-1/ERK-2 antibody and by an MAPK enzyme assay. Ang II increased [Ca2+]i and pHi and contracted cells in a dose-dependent manner. Maximum Ang II-elicited contraction was greater (P<0.05) in SHR (41.9+/-5.1% reduction in cell length relative to basal length) than in WKY (28.1+/-3.0% reduction in cell length relative to basal length). Basal [Ca2+]i, but not basal pHi, was higher in SHR compared with WKY. [Ca2+]i and pHi effects of Ang II were enhanced (P<0.05) in SHR compared with WKY (maximum Ang II-induced response [Emax] of [Ca2+]i, 576+/-24 versus 413+/-43 nmol/L; Emax of pHi, 7.33+/-0.01 versus 7.27+/-0.03, SHR versus WKY). PD98059 decreased the magnitude of contraction and attenuated the augmented Ang II-elicited contractile responses in SHR (Emax,19. 3+/-3% reduction in cell length relative to basal length). Ang II-stimulated [Ca2+]i (Emax, 294+/-55 nmol/L) and pHi (Emax, 7. 27+/-0.04) effects were significantly reduced by PD98059 in SHR. Ang II-induced ERK activity was significantly greater (P<0.05) in SHR than in WKY. In conclusion, Ang II-stimulated signal transduction and associated VSMC contraction are enhanced in SHR. MAP/ERK inhibition abrogated sustained contraction and normalized Ang II effects in SHR. These data suggest that ERK-dependent signaling pathways influence contraction and that they play a role in vascular hyperresponsiveness in SHR.

Role of AT2 receptors in angiotensin II-stimulated contraction of small mesenteric arteries in young SHR

This study assesses the receptor subtype (AT1 and AT2) through which angiotensin II (Ang II) mediates contraction in small arteries of young and adult spontaneously hypertensive rats (SHR). Segments of third-order mesenteric arteries ( approximately 200 microm in lumen diameter) were mounted in a pressurized system. Systolic blood pressure and media:lumen ratio of small arteries were significantly greater (P<0.001) in young SHR and adult SHR than in age-matched Wistar-Kyoto rats (WKY). Ang II-induced contractile effects were significantly increased (P<0.05) in young SHR compared with age-matched WKY. AT1 blockade with losartan, and combined AT1 and AT2 blockade with losartan and PD123319, abolished Ang II-stimulated contraction in young and adult rats. AT2 blockade (PD123319) significantly reduced (P<0.01) Ang II-elicited contraction in young SHR but had no effect in WKY or adult SHR, indicating that AT2 receptors may contribute to Ang II-induced contraction in young SHR. To determine the Ang receptor status in rat mesenteric vessels, AT1 and AT2 receptor mRNA expression was determined by reverse transcription-polymerase chain reaction. AT1 and AT2 receptor protein expression were detected by Western blot analysis. AT1 receptor mRNA was equally expressed in age-matched rats, but expression was significantly lower in young rats compared with adult rats. AT2 receptor mRNA was weakly expressed in WKY and adult SHR. In vessels from young SHR, AT2 receptor mRNA expression was significantly increased compared with the other groups. AT1 receptor protein was equally expressed in adult rats of both strains but was undetectable in young rats. AT2 receptor protein was only detectable in young rats, with the magnitude of expression greater in SHR than WKY. In conclusion, Ang II-stimulated contractile responses are augmented in vessels from young SHR. These effects are reduced by selective AT2 blockade and abolished by AT1 blockade, indicating that both Ang receptor subtypes are involved in contraction in young SHR. In WKY and adult SHR, losartan, but not PD123319, inhibited Ang II-induced contraction, indicating the exclusive involvement of AT1 receptors. Thus, in SHR, in the phase of developing hypertension, enhanced Ang II-stimulated vascular contraction may be associated with changes in Ang II receptor status, as evidenced pharmacologically and by increased vascular AT2 receptor mRNA and protein expression.

Role of tyrosine phosphorylation in excitation-contraction coupling in vascular smooth muscle

Increasingly it is recognized that tyrosine phosphorylation plays an important part in the regulation of function in differentiated contractile vascular smooth muscle. Tyrosine kinases and phosphatases are present in large amounts in vascular smooth muscle and have been reported to influence a number of processes crucial to contraction, including ion channel gating, calcium homeostasis and sensitization of the contractile process to [Ca2+]i. This review summarizes current understanding regarding the role of tyrosine phosphorylation in excitation-contraction coupling in blood vessels.

Angiotensin II induces superoxide anion production by mesangial cells

BACKGROUND

The recognized role of angiotensin II (Ang II) in the pathogenesis of the progression of renal disease cannot be solely attributed to Ang II's hemodynamic effects. Indeed, growth stimulating signals driven by Ang II promote mesangial cell (MC) hypertrophy and extracellular matrix production, prominent features of progressive glomerular injury. Superoxide anion (O2-) avidly interacts with nitric oxide, an endogenous vasodilator that inhibits growth factor stimulated MC growth and matrix production. In addition, O2- acting as an intracellular signal is linked to growth related responses such as activation of mitogen activated protein (MAP) kinases. The studies reported herein were designed to investigate: (a) whether Ang II induces MC O2-production and (b) if increased O2- production elicits growth responses in MC.

METHODS

MC were exposed to Ang II for 24 or 48 hours. In some experiments, in addition to Ang II, MC were exposed to: diphenylenieodonium (DPI), an inhibitor of the flavin containing NADH/NADPH oxidase; losartan (LOS), an Ang II type 1 (AT1) receptor blocker; PD 98059, a MAP kinases inhibitor; the protein kinase C inhibitors Calphostin C or H-7; and the tyrosine kinase inhibitors, herbymycin A or genistein.

RESULTS

Ang II (10(-5) M to 10(-8) M) dose dependently increased MC O2- production up to 125% above control (ED 50 5 x 10(-7) M). LOS as well as DPI, and the PKC inhibitors blocked Ang II stimulated MC O2- production. Ang II dose dependently increased MC 3H-leucine incorporation, and MC protein content, two markers of MC hypertrophy, as well as 3H-thymidine incorporation, a marker of MC hyperplasia. PD98059, a specific inhibitor of MAP kinases prevented Ang II induced MC hypertrophy. Moreover, LOS, DPI, and the PKC inhibitors each independently inhibited MC 3H-leucine incorporation, thereby establishing the specificity of Ang II induced O2- in driving MC hypertrophy.

CONCLUSIONS

The current studies demonstrate a previously unrecognized link between Ang II and MC O2- production that may participate in the pathophysiology of progressive renal disease by concomitantly affecting the hemodynamics of the glomerular microcirculation as well as growth related responses of MC to injury.