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Angiotensin-induced vasodilation, involving type 2 receptor (AT2R)-induced generation of nitric oxide (NO; by endothelial NO synthase) and endothelium-derived hyperpolarizing factors, may be limited to women. To distinguish the contribution of female sex hormones and chromosomes to AT2R function and endothelium-derived hyperpolarizing factor-mediated vasodilation, we made use of the four-core genotype model, where the testis-determining Sry gene has been deleted (Y(-)) from the Y chromosome, allowing XY(-) mice to develop a female gonadal phenotype. Simultaneously, by incorporating the Sry gene onto an autosome, XY(-)Sry and XXSry transgenic mice develop into gonadal male mice. Four-core genotype mice underwent a sham or gonadectomy (GDX) operation, and after 8 weeks, iliac arteries were collected to assess vascular function. XY(-)Sry male mice responded more strongly to angiotensin than XX female mice, and the AT2R antagonist PD123319 revealed that this was because of a dilator AT2R-mediated effect occurring exclusively in XX female mice. The latter could not be demonstrated in XXSry male and XY(-) female mice nor in XX female mice after GDX, suggesting that it depends on both sex hormones and chromosomes. Indeed, treating C57bl/6 GDX male mice with estrogen could not restore angiotensin-mediated, AT2R-dependent relaxation. To block acetylcholine-induced relaxation of iliac arteries obtained from four-core genotype XX mice, both endothelial NO synthase and endothelium-derived hyperpolarizing factor inhibition were required, whereas in four-core genotype XY animals, endothelial NO synthase inhibition alone was sufficient. These findings were independent of gonadal sex and unaltered after GDX. In conclusion, AT2R-induced relaxation requires both estrogen and the XX chromosome sex complement, whereas only the latter is required for endothelium-derived hyperpolarizing factors. [ABSTRACT FROM AUTHOR]

Common adverse effects of angiogenesis inhibition are hypertension and renal injury. To determine the most optimal way to prevent these adverse effects and to explore their interdependency, the following drugs were investigated in unrestrained Wistar Kyoto rats exposed to the angiogenesis inhibitor sunitinib: the dual endothelin receptor antagonist macitentan; the calcium channel blocker amlodipine; the angiotensin-converting enzyme inhibitor captopril; and the phosphodiesterase type 5 inhibitor sildenafil. Mean arterial pressure was monitored telemetrically. After 8 days, rats were euthanized and blood samples and kidneys were collected. In addition, 24-hour urine samples were collected. After sunitinib start, mean arterial pressure increased rapidly by ≈30 mm Hg. Coadministration of macitentan or amlodipine largely prevented this rise, whereas captopril or sildenafil did not. Macitentan, captopril, and sildenafil diminished the sunitinib-induced proteinuria and endothelinuria and glomerular intraepithelial protein deposition, whereas amlodipine did not. Changes in proteinuria and endothelinuria were unrelated. We conclude that in our experimental model, dual endothelin receptor antagonism and calcium channel blockade are suitable to prevent angiogenesis inhibition-induced hypertension, whereas dual endothelin receptor antagonism, angiotensin-converting enzyme inhibitor, and phosphodiesterase type 5 inhibition can prevent angiogenesis inhibition-induced proteinuria. Moreover, the variable response of hypertension and renal injury to different antihypertensive agents suggests that these side effects are, at least in part, unrelated. [ABSTRACT FROM AUTHOR]

Dual renin-angiotensin system (RAS) blockade in diabetic nephropathy is no longer feasible because of the profit/side effect imbalance. (Pro)renin receptor [(P)RR] blockade with handle region peptide (HRP) has been reported to exert beneficial effects in various diabetic models in a RAS-independent manner. To what degree (P)RR blockade adds benefits on top of RAS blockade is still unknown. In the present study, we treated diabetic TGR(mREN2)27 rats, a well-established nephropathy model with high prorenin levels [allowing continuous (P)RR stimulation in vivo], with HRP on top of renin inhibition with aliskiren. Aliskiren alone lowered blood pressure and exerted renoprotective effects, as evidenced by reduced glomerulosclerosis, diuresis, proteinuria, albuminuria, and urinary aldosterone levels as well as diminished renal (P)RR and ANG II type 1 receptor expression. It also suppressed plasma and tissue RAS activity and suppressed cardiac atrial natriuretic peptide and brain natriuretic peptide expression. HRP, when given on top of aliskiren, did not alter the effects of renin inhibition on blood pressure, RAS activity, or aldosterone. However, it counteracted the beneficial effects of aliskiren in the kidney, induced hyperkalemia, and increased plasma plasminogen activatorinhibitor 1, renal cyclooxygenase-2, and cardiac collagen content. All these effects have been linked to (P)RR stimulation, suggesting that HRP might, in fact, act as a partial agonist. Therefore, the use of HRP on top of RAS blockade in diabetic nephropathy is not advisable. [ABSTRACT FROM AUTHOR]

This article discusses a study which examined the effects of angiotensin II type 2 (AT2) receptor agonist compound 21 (C21) in vitro, using preparations known to display AT2 receptor-mediated responses. Researchers discovered that C21 did not cause AT2 receptor-mediated vasodilation, but it induce vasodilation by blocking calcium transport into cell and constriction via angiotensin II type 1 receptor stimulation.

Medial degeneration is a key feature of aneurysm disease and aortic dissection. In a murine aneurysm model we investigated the structural and functional characteristics of aortic wall degeneration in adult fibulin-4 deficient mice and the potential therapeutic role of the angiotensin (Ang) II type 1 (AT1) receptor antagonist losartan in preventing aortic media degeneration. Adult mice with 2-fold (heterozygous Fibulin-4+/R) and 4-fold (homozygous Fibulin-4R/R) reduced expression of fibulin-4 displayed the histological features of cystic media degeneration as found in patients with aneurysm or dissection, including elastin fiber fragmentation, loss of smooth muscle cells, and deposition of ground substance in the extracellular matrix of the aortic media. The aortic contractile capacity, determined by isometric force measurements, was diminished, and was associated with dysregulation of contractile genes as shown by aortic transcriptome analysis. These structural and functional alterations were accompanied by upregulation of TGF-&bgr; signaling in aortas from fibulin-4 deficient mice, as identified by genome-scaled network analysis as well as by immunohistochemical staining for phosphorylated Smad2, an intracellular mediator of TGF-&bgr;. Tissue levels of Ang II, a regulator of TGF-&bgr; signaling, were increased. Prenatal treatment with the AT1 receptor antagonist losartan, which blunts TGF-&bgr; signaling, prevented elastic fiber fragmentation in the aortic media of newborn Fibulin-4R/R mice. Postnatal losartan treatment reduced haemodynamic stress and improved lifespan of homozygous knockdown fibulin-4 animals, but did not affect aortic vessel wall structure. In conclusion, the AT1 receptor blocker losartan can prevent aortic media degeneration in a non-Marfan syndrome aneurysm mouse model. In established aortic aneurysms, losartan does not affect aortic architecture, but does improve survival. These findings may extend the potential therapeutic application of inhibitors of the renin-angiotensin system to the preventive treatment of aneurysm disease. [ABSTRACT FROM AUTHOR]

To investigate whether the putative (pro)renin receptor blocker, the handle region peptide (HRP), exerts effects on top of the blood pressure-lowering and cardioprotective effects of the renin inhibitor aliskiren, spontaneously hypertensive rats were implanted with telemetry transmitters to monitor heart rate and mean arterial pressure (MAP). After a 2-week recovery period, vehicle, aliskiren, HRP (100 and 1 mg/kg per day, respectively), and HRP+aliskiren were infused for 3 weeks using osmotic minipumps. Subsequently, the heart was removed to study coronary function according to Langendorff. Baseline MAP and heart rate in vehicle-treated rats were 146±3 mm Hg and 326±4 bpm. HRP did not affect MAP, whereas aliskiren and HRP+aliskiren lowered MAP (by maximally 29±2 and 20±1 mm Hg, respectively) without affecting heart rate. Aliskiren significantly reduced MAP throughout the 3-week infusion period, whereas the blood pressure-lowering effect of HRP+aliskiren returned to baseline within 2 weeks of treatment. In comparison with vehicle, aliskiren increased the endothelium-dependent response to bradykinin and decreased the response to angiotensin II in the coronary circulation, whereas these responses were not altered after treatment with HRP or HRP+aliskiren. HRP did not alter plasma renin activity, plasma angiotensin levels, or the renal angiotensin content, either alone or on top of aliskiren, nor did it alter the aliskiren-induced decrease in renal Ang II type 1 receptor expression. Yet, it did reverse the aliskiren-induced reduction in cardiomyocyte area, without affecting this area when given alone. In conclusion, HRP counteracts the beneficial effects of aliskiren on blood pressure, coronary function, and cardiac hypertrophy in an angiotensin-independent manner. [ABSTRACT FROM AUTHOR]

Angiogenesis inhibition with sunitinib, a multitarget tyrosine kinase inhibitor of the vascular endothelial growth factor receptor, is associated with hypertension and cardiac toxicity, of which the underlying pathophysiological mechanism is unknown. We investigated the effects of sunitinib on blood pressure (BP), its circadian rhythm, and potential mechanisms involved, including the endothelin-1 system, in 15 patients with metastatic renal cell carcinoma or gastrointestinal stromal tumors. In addition, we investigated in rats the effect of sunitinib on BP, serum endothelin-1 levels, coronary microvascular function, cardiac structure, and cardiac mitochondrial function. In patients, BP increased by ≈15 mm Hg, whereas heart rate decreased after 4 weeks of treatment. Furthermore, the nocturnal dipping of BP diminished. Plasma endothelin-1 concentration increased 2-fold (P<0.05) and plasma renin decreased (P<0.05), whereas plasma catecholamines and renal function remained unchanged. In rats, 8 days of sunitinib administration induced an ≈30-mm Hg rise in BP, an attenuation of the circadian BP rhythm, and a 3-fold rise in serum endothelin-1 and creatinine, of which all but the rise in creatinine reversed after sunitinib withdrawal. Coronary microvascular function studies after 8 days of sunitinib administration showed decreased responses to bradykinin, angiotensin II, and sodium nitroprusside, all normalizing after sunitinib withdrawal. Cardiac structure and cardiac mitochondrial function did not change. In conclusion, sunitinib induces a reversible rise in BP in patients and in rats associated with activation of the endothelin-1 system, suppression of the renin-angiotensin system, and generalized microvascular dysfunction. [ABSTRACT FROM AUTHOR]

Aims: Our aim was to determine the contribution of the three angiotensin (Ang) II receptor subtypes (AT1a, AT1b, AT2) to coronary responsiveness, cardiac histopathology, and tissue Ang II levels using mice deficient for one, two, or all three Ang II receptors. [ABSTRACT FROM PUBLISHER]

Because angiotensin (Ang) metabolites mediate functions independent of Ang II, we investigated their effects on coronary flow in spontaneously hypertensive rats (SHRs). Results were compared with those in the iliac artery and abdominal aorta and the coronary circulation of the Wistar rat. Ang II, III, and IV decreased coronary flow in SHRs and Wistar rats, with Ang III and IV being approximately 10 and approximately 1000 times less potent than Ang II. Ang-(1-7) decreased coronary flow at concentrations >1 micromol/L in SHRs. The Ang II type 1 receptor antagonist irbesartan blocked the effects of Ang II, III, and IV, whereas the Ang II type 2 receptor antagonist PD123319 blocked the effects of Ang-(1-7). The maximal Ang II- and III-induced decreases in coronary flow in SHRs were twice as large as those in Wistar rats. PD123319 enhanced the constrictor effects of Ang II and III in Wistar rats so that, in the presence of this drug, their effects were comparable to those in SHRs. In contrast, PD123319 did not alter the Ang II- and III-induced responses in SHRs and blocked the constrictor effect of Ang II in iliac arteries. Ang II type 2 receptor-mediated relaxation did not occur in iliac arteries and abdominal aortas, and the constrictor effects of Ang metabolites in these vessels were identical in Wistar rats and SHRs. In conclusion, coronary constriction induced by Ang II, Ang III, and Ang-(1-7) is enhanced in SHRs as compared with Wistar rats. This is attributable to the absence of counterregulatory Ang II type 2 receptor-mediated relaxation and/or a change of the Ang II type 2 receptor phenotype from relaxant to constrictor. [ABSTRACT FROM AUTHOR]

Angiotensin II activates two distinct receptors, the angiotensin II receptors type 1 (AT1) and type 2 (AT2). In rodents, two AT1 subtypes were identified (ATIa and ATlb). To determine receptor-specific functions and possible angiotensin II effects independent of its three known receptors we generated mice deficient in either one of the angiotensin II receptors, in two, or in all three (triple knockouts). Triple knockouts were vital and fertile, but survival was impaired. Hypotension and renal histological abnormalities in triple knockouts were comparable to those in mice lacking both AT1 subtypes. All combinations lacking ATla were distinguished by reduced heart rate. AT1a deletion impaired the in vivo pressor response to angiotensin II bolus injection, whereas deficiency for AT1b and/or AT2 had no effect. However, the additional lack of AT1b in AT1a-deficient mice further impaired the vasoconstrictive capacity of angiotensin II. Although general vasoconstrictor properties were not changed, angiotensin II failed to alter blood pressure in triple knockouts, indicating that there are no other receptors involved in direct angiotensin II pressor effects. Our data identify mice deficient in all three angiotensin II receptors as an ideal tool to better understand the structure and function of the reninangiotensin system and to search for angiotensin II effects independent of AT1 and AT2. [ABSTRACT FROM AUTHOR]

The article offers information that the Betta fish is indigenous to central Thailand and the lower Mekong and is mostly known for its domesticated forms appreciated as an ornamental fish but was originally bred for its use in gambling matches similar to cock fights. It also mentions that researchers have examined the inheritance of body color, fin length, and sex determination in classic crosses in the 1930s to 1940s.

Blockers of the renin-angiotensin-aldosterone system (RAAS), that is, renin inhibitors, angiotensin (Ang)-converting enzyme (ACE) inhibitors, Ang II type 1 receptor antagonists, and mineralocorticoid receptor antagonists, are a cornerstone in the treatment of hypertension. How exactly they exert their effect, in particular in patients with low circulating RAAS activity, also taking into consideration the so-called Ang II/aldosterone escape that often occurs after initial blockade, is still incompletely understood. Multiple studies have tried to find parameters that predict the response to RAAS blockade, allowing a personalized treatment approach. Consequently, the question should now be answered on what basis (eg, sex, ethnicity, age, salt intake, baseline renin, ACE or aldosterone, and genetic variance) a RAAS blocker can be chosen to treat an individual patient. Are all blockers equal? Does optimal blockade imply maximum RAAS blockade, for example, by combining ≥2 RAAS blockers or by simply increasing the dose of 1 blocker? Exciting recent investigations reveal a range of unanticipated extrarenal effects of aldosterone, as well as a detailed insight in the genetic causes of primary aldosteronism, and mineralocorticoid receptor blockers have now become an important treatment option for resistant hypertension. Finally, apart from the deleterious ACE-Ang II-Ang II type 1 receptor arm, animal studies support the existence of protective aminopeptidase A-Ang III-Ang II type 2 receptor and ACE2-Ang-(1 to 7)-Mas receptor arms, paving the way for multiple new treatment options. This review provides an update about all these aspects, critically discussing the many controversies and allowing the reader to obtain a full understanding of what we currently know about RAAS alterations in hypertension., (© 2015 American Heart Association, Inc.)

Significance: Angiogenesis inhibition with humanized antibodies targeting vascular endothelial growth factor (VEGF) or orally active small tyrosine kinase inhibitors targeting VEGF receptors has become an established treatment modality for various forms of cancer. A common side effect of angiogenesis inhibition is the development of sometimes severe hypertension, which simultaneously appears to be predictive for a favorable antitumor response., Recent Advances: Since VEGF increases the expression and activity of endothelial nitric oxide synthase, it has been assumed that the mean blood pressure (MAP) rise during angiogenesis inhibition is caused by a decrease in nitric oxide bioavailability. Yet, the results from experimental and clinical studies exploring this possibility are conflicting. Recent studies provided evidence that the MAP rise during angiogenesis inhibition rather is mediated by activation of the endothelin-1 (ET-1) axis, which, among others, induces oxidative stress. Nevertheless, conclusive evidence for the involvement of reactive oxygen species in the MAP rise could not be obtained so far., Critical Issues: The mechanism underlying activation of the ET-1 axis during angiogenesis inhibition is unclear, and this activation was not anticipated in view of studies showing that VEGF stimulates both the expression and production of ET-1 by endothelial cells., Future Directions: In fact, this activation of the ET-1 axis may support the use of ET receptor antagonists for the treatment of angiogenesis inhibition-induced hypertension, especially because ET receptor stimulation in vascular smooth muscle cells results in VEGF production and mitogenesis in a mitogen-activated protein kinase pathway-dependent manner.

Angiogenesis inhibition by blocking vascular endothelial growth factor (VEGF)-mediated signalling with monoclonal antibodies or tyrosine kinase inhibitors has become an established treatment of various forms of cancer. This treatment is frequently associated with the development of hypertension and proteinuria. As VEGF increases the expression and the activity of nitric oxide synthase in endothelial cells, a decrease in the bioavailability of nitric oxide has been proposed as a key mechanism leading to hypertension during angiogenesis inhibition. However, results of clinical and experimental studies exploring this possibility are conflicting. Rarefaction, that is a structural decrease of microcirculatory vessels, has been reported during antiangiogenic treatment, but evidence that it plays a role in development of hypertension is lacking. Elevated circulating and urinary levels of endothelin-1 have been observed in clinical and experimental studies with angiogenesis inhibitors. Furthermore, the observation that endothelin receptor blockers can prevent or revert the rise in blood pressure during angiogenesis inhibition and attenuate proteinuria provides strong evidence that an activated endothelin-signalling pathway is a final common mediator of angiogenesis inhibition-induced rise in blood pressure and renal toxicity.

Background: Elevated prorenin levels associate with microvascular complications in patients with diabetes mellitus, possibly because prorenin affects vascular function in diabetes mellitus, for example by generating angiotensins following its binding to the (pro)renin receptor [(P)RR]. Here we evaluated whether the renin inhibitor aliskiren, with or without the putative (P)RR antagonist handle region peptide (HRP) improved the disturbed vascular function in diabetic TGR(mREN2)27 rats, a high-prorenin, high-(P)RR hypertensive model., Methods: Telemetry transmitters were implanted to monitor blood pressure. After 3 weeks of treatment, rats were sacrificed, and iliac and mesenteric arteries were removed to evaluate vascular reactivity., Results: Diabetes mellitus enhanced the contractile response to nitric oxide synthase (NOS) blockade, potentiated the response to phenylephrine, diminished the effectiveness of endothelin type A (ETA) receptor blockade and allowed acetylcholine to display constrictor, cyclo-oxygenase-2 mediated, endothelium-dependent responses in the presence of NOS inhibition and blockers of endothelium-derived hyperpolarizing factors. Aliskiren normalized blood pressure, suppressed renin activity, and reversed the above vascular effects, with the exception of the altered effectiveness of ETA receptor blockade. Remarkably, when adding HRP on top of aliskiren, its beneficial vascular effects either disappeared or were greatly diminished, although HRP did not alter the effect of aliskiren on blood pressure and renin activity., Conclusions: Renin inhibition improves vascular dysfunction in diabetic hypertensive rats, and HRP counteracts this effect independently of blood pressure and angiotensin. (P)RR blockade therefore is unlikely to be a new tool to further suppress the renin-angiotensin system (RAS) on top of existing RAS blockers.

Angiogenesis inhibition is an established treatment for several tumor types. Unfortunately, this therapy is associated with adverse effects, including hypertension and renal toxicity, referred to as "preeclampsia." Recently, we demonstrated in patients and in rats that the multitarget tyrosine kinase inhibitor sunitinib induces a rise in blood pressure (BP), renal dysfunction, and proteinuria associated with activation of the endothelin system. In the current study we investigated the effects of sunitinib on rat renal histology, including the resemblance with preeclampsia, as well as the roles of endothelin 1, decreased nitric oxide (NO) bioavailability, and increased oxidative stress in the development of sunitinib-induced hypertension and renal toxicity. In rats on sunitinib, light and electron microscopic examination revealed marked glomerular endotheliosis, a characteristic histological feature of preeclampsia, which was partly reversible after sunitinib discontinuation. The histological abnormalities were accompanied by an increase in urinary excretion of endothelin 1 and diminished NO metabolite excretion. In rats on sunitinib alone, BP increased (ΔBP: 31.6±0.9 mm Hg). This rise could largely be prevented with the endothelin receptor antagonist macitentan (ΔBP: 12.3±1.5 mm Hg) and only mildly with Tempol, a superoxide dismutase mimetic (ΔBP: 25.9±2.3 mm Hg). Both compounds could not prevent the sunitinib-induced rise in serum creatinine or renal histological abnormalities and had no effect on urine nitrates but decreased proteinuria and urinary endothelin 1 excretion. Our findings indicate that both the endothelin system and oxidative stress play important roles in the development of sunitinib-induced proteinuria and that the endothelin system rather than oxidative stress is important for the development of sunitinib-induced hypertension.

Thoracic aortic aneurysms (TAAs) are a potential life-threatening disease with limited pharmacological treatment options. Current treatment options are aimed at lowering aortic hemodynamic stress, predominantly with β-adrenoceptor blockers. Increasing evidence supports a role for the renin-angiotensin system (RAS) in aneurysm development. RAS blockade would not only lower blood pressure, but might also target the molecular pathways involved in aneurysm formation, in particular the transforming growth factor-β and extracellular signal-regulated kinase 1/2 pathways. Indeed, the angiotensin II type 1 (AT₁) receptor blocker losartan was effective in lowering aortic root growth in mice and patients with Marfan's syndrome. RAS inhibition (currently possible at 3 levels, i.e. renin, ACE and the AT₁ receptor) is always accompanied by a rise in renin due to interference with the negative feedback loop between renin and angiotensin II. Only during AT₁ receptor blockade will this result in stimulation of the non-blocked angiotensin II type 2 (AT₂) receptor. This review summarizes the clinical aspects of TAAs, provides an overview of the current mouse models for TAAs, and focuses on the RAS as a new target for TAA treatment, discussing in particular the possibility that AT₂ receptor stimulation might be crucial in this regard. If true, this would imply that AT₁ receptor blockers (and not ACE inhibitors or renin inhibitors) should be the preferred treatment option for TAAs., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Inhibition of angiogenesis with humanized monoclonal antibodies to vascular endothelial growth factor (VEGF) or with tyrosine kinase inhibitors targeting VEGF receptors has become an established treatment for various tumor types. Contrary to expectations, angiogenesis inhibition by blocking VEGF-mediated signaling is associated with serious side effects including hypertension and renal and cardiac toxicity in a substantial proportion of patients. Fortunately, most of these side effects as discussed in this paper seem to be manageable, but likely become more problematic when survival increases. Although several hypotheses regarding the etiology of angiogenesis inhibition-related cardiovascular and renal side effects have been postulated, many of the underlying pathophysiological mechanisms remain to be elucidated. This may lead to the development of more specific angiogenesis inhibitors, better management of their side effects and may potentially provide new insights into the pathogenesis of cardiovascular disease in general.

Aminopeptidases metabolize angiotensin II to angiotensin-(2-8) (=angiotensin III) and angiotensin-(3-8) (=angiotensin IV), and carboxypeptidases generate angiotensin-(1-7) from angiotensin I and II. Angiotensin-converting enzyme (ACE) inhibitors and/or angiotensin II type 1 (AT1) receptor blockers affect the concentrations of these metabolites, and they may thus contribute to the beneficial effects of these drugs, possibly through stimulation of non-classical angiotensin AT receptors. Here, we investigated the effects of angiotensin II, angiotensin III, angiotensin IV and angiotensin-(1-7) in the rat coronary vascular bed, with or without angiotensin AT1 - or angiotensin II type 2 (AT2) receptor blockade. Results were compared to those in rat iliac arteries and abdominal aortas. Angiotensin II, angiotensin III and angiotensin IV constricted coronary arteries via angiotensin AT1 receptor stimulation, angiotensin III and angiotensin IV being approximately 20- and approximately 8000-fold less potent than angiotensin II. The angiotensin AT2 receptor antagonist PD123319 greatly enhanced the constrictor effects of angiotensin III, starting at angiotensin III concentrations in the low nanomolar range. PD123319 enhanced the angiotensin II-induced constriction at submicromolar angiotensin II concentrations only. Angiotensin-(1-7) exerted no effects in the coronary circulation, although, at micromolar concentrations, it blocked angiotensin AT1 receptor-induced constriction. Angiotensin AT2 receptor-mediated relaxation did not occur in iliac arteries and abdominal aortas, and the constrictor effects of the angiotensin metabolites in these vessels were identical to those in the coronary vascular bed. In conclusion, angiotensin AT2 receptor activation in the rat coronary vascular bed results in vasodilation, and angiotensin III rather than angiotensin II is the preferred endogenous agonist of these receptors. Angiotensin II, angiotensin III, angiotensin IV and angiotensin-(1-7) do not exert effects through non-classical angiotensin AT receptors in the rat coronary vascular bed, iliac artery or aorta.

Background: Angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism-related differences in ACE concentration do not result in differences in angiotensin levels., Methods and Results: To investigate whether this relates to differences in the contribution of the ACE C-domain and N-domain, we quantified, using the C-domain-selective inhibitors quinaprilat and RXPA380, and the N-domain-selective inhibitor RXP407, the contribution of both domains to the metabolism of angiotensin I, bradykinin, the C-domain-selective substrate Mca-BK(1-8), and the N-domain-selective substrate Mca-Ala in serum of IIs, DDs, and 'hyperACE' subjects (i.e., subjects with increased ACE due to enhanced shedding). During incubation with angiotensin I, the highest angiotensin II levels were observed in sera with the highest ACE activity. This confirms that ACE is rate-limiting with regard to angiotensin II generation. C-domain-selective concentrations of quinaprilat fully blocked angiotensin I-II conversion in DDs, whereas additional N-domain blockade was required to fully block conversion in IIs. Both domains contributed to bradykinin hydrolysis in all subjects, and the inhibition profile of RXP407 when using Mca-Ala was identical in IIs and DDs. In contrast, the RXPA380 concentrations required to block C-domain activity when using Mca-BK (1-8) were three-fold higher in IIs than DDs., Conclusion: The contributions of the C-domain and N-domain differ between DDs and IIs, and RXPA380 is the first inhibitor capable of distinguishing D-allele ACE from I-allele ACE. The lack of angiotensin II accumulation in DDs in vivo is not because of the often quoted concept that ACE is a nonrate-limiting enzyme. It may relate to the fact that in IIs both the N-domain and C- domain generate angiotensin II, whereas in DDs only the C-domain converts angiotensin I.

Somatic angiotensin-converting enzyme (ACE) contains 2 domains (C-domain and N-domain) capable of hydrolyzing angiotensin I (Ang I) and bradykinin. Here we investigated the effect of the selective C-domain and N-domain inhibitors RXPA380 and RXP407 on Ang I-induced vasoconstriction of porcine femoral arteries (PFAs) and bradykinin-induced vasodilation of preconstricted porcine coronary microarteries (PCMAs). Ang I concentration-dependently constricted PFAs. RXPA380, at concentrations >1 mumol/L, shifted the Ang I concentration-response curve (CRC) 10-fold to the right. This was comparable to the maximal shift observed with the ACE inhibitors (ACEi) quinaprilat and captopril. RXP407 did not affect Ang I at concentrations < or =0.1 mmol/L. Bradykinin concentration-dependently relaxed PCMAs. RXPA380 (10 micromol/L) and RXP407 (0.1 mmol/L) potentiated bradykinin, both inducing a leftward shift of the bradykinin CRC that equaled approximately 50% of the maximal shift observed with quinaprilat. Ang I added to blood plasma disappeared with a half life (t(1/2)) of 42+/-3 minutes. Quinaprilat increased the t(1/2) approximately 4-fold, indicating that 71+/-6% of Ang I metabolism was attributable to ACE. RXPA380 (10 micromol/L) and RXP407 (0.1 mmol/L) increased the t(1/2) approximately 2-fold, thereby suggesting that both domains contribute to conversion in plasma. In conclusion, tissue Ang I-II conversion depends exclusively on the ACE C-domain, whereas both domains contribute to conversion by soluble ACE and to bradykinin degradation at tissue sites. Because tissue ACE (and not plasma ACE) determines the hypertensive effects of Ang I, these data not only explain why N-domain inhibition does not affect Ang I-induced vasoconstriction in vivo but also why ACEi exert blood pressure-independent effects at low (C-domain-blocking) doses.

Airborne exposure to lung-toxic agents may damage the lung surfactant system and epithelial and endothelial cells, resulting in a life-threatening pulmonary edema that is known to be refractory to treatment. The aim of this study was to investigate in rats (1) the respiratory injury caused by nose-only exposure to perfluoroisobutene (PFIB), and (2) the therapeutic efficacy of a treatment at 4 and/or 8 h after exposure consisting of the natural surfactant Curosurf and/or the anti-inflammatory drug N-acetylcysteine (NAC). For that purpose, the following parameters were examined: respiratory frequency (RF), lung compliance (Cdyn), airway resistance (Raw), lung wet weight (LWW), airway histopathology; and in brochoalveolar lavage (BAL) fluid, total protein, total phospholipid, cell count and differentiation, and changes in the surface tension of the BAL fluid. The mean (+/- SEM) surface tension of BAL fluid derived from PFIB-exposed (C . t = 1100-1200 mg min(-1) m(-3), approximately 1LCt50; t = 20 min) animals at 24 h following exposure (11 +/- 3 mN/m) was higher than that of unexposed rats (0.8 +/- 0.4 mN/m), reflecting damage to the surfactant system and justifying treatment with exogenous surfactant. Curosurf treatment (62.5 mg/kg i.t.) decreased pulmonary edema caused by PFIB, reflected by a decreased LWW, and decreased the amount of protein in BAL fluid. NAC treatment (1000 mmol/kg ip) inhibited the interstitial pneumonia reflected by a decreased percentage of neutrophils in the alveolar space. It was concluded that a combined treatment of Curosurf + NAC improved respiration, that is, RF and Cdyn, whereby Curosurf predominantly decreased pulmonary edema and NAC predominantly reduced the inflammatory process. A combined treatment may therefore be considered a promising therapeutic approach in early-stage acute respiratory distress caused by PFIB, although the treatment regimes need further investigation.