Angiotensin-(1-7) and bradykinin interaction in diabetes mellitus: in vivo study

The interaction between angiotensin-(1-7) (Ang-(1-7)) and bradykinin (BK) was determined in the mesentery of anesthetized Wistar alloxan-diabetic and non-diabetic rats using intravital microscopy. Impaired BK vasodilation observed in arterioles of diabetic rats was restored by acute and chronic insulin treatment as well as by enalapril. Though capable of potentiating BK in non-diabetic rats, Ang-(1-7) did not potentiate BK in diabetic rats. Chronic but not acute insulin treatment restored the potentiation, whereas enalapril did not. Potassium channel blockade (by tetraethylammonium (TEA)) but not nitric oxide (NO) synthase inhibition (by N-omega-nitro-L-arginine-methyl-esther (L-NAME)) abolished the restorative effect of insulin. Our data allow us to suggest that the alteration observed is restored by insulin by a mechanism involving membrane hyperpolarization but not NO release. The beneficial effect of enalapril in diabetes might not involve the potentiation of BK by Ang-(1-7).     

Synergistic effect of angiotensin-(1-7) on bradykinin arteriolar dilation in vivo

The interaction between angiotensin [Ang-(1-7)] and bradykinin (BK) was determined in the mesentery of anesthetized Wistar rats using intravital microscopy. Topical application of BK and Ang-(1-7) induced vasodilation that was abolished by the BK B2 receptor antagonist HOE-140 and the Ang-(1-7) antagonist A-779, respectively. BK (1 pmol)-induced vasodilation, but not SNP and ACh responses, was potentiated by Ang-(1-7) 10 pmol and 100 pmols. The effect of 100 pmol of Ang-(1-7) on BK-induced vasodilation was abolished by A-779, indomethacin, and L-nitroarginine methyl esther, whereas losartan was without effect. Enalaprilat treatment enhanced the BK- and Ang-(1-7)-induced vasodilation and the potentiating effect of Ang-(1-7) on BK vasodilation. The potentiation of BK-induced vasodilation by Ang-(1-7) is a receptor-mediated phenomenon dependent on cyclooxygenase-related products and NO release.     

Characterization of angiotensin-(1-7) receptor subtype in mesenteric arteries

Mesenteric arteries from male Sprague-Dawley rats were mounted in a pressurized myograph system. Ang-(1-7) concentration-dependent responses were determined in arteries preconstricted with endothelin-1 (10(-7)M). The receptor(s) mediating the Ang-(1-7) evoked dilation were investigated by pretreating the mesenteric arteries with specific antagonists of Ang-(1-7), AT(1) or AT(2) receptors. The effects of Ang-(3-8) and Ang-(3-7) were also determined. Ang-(1-7) caused a concentration-dependent dilation (EC(50): 0.95 nM) that was blocked by the selective Ang-(1-7) receptor antagonist D-[Ala(7)]-Ang-(1-7). Administration of a specific antagonist to the AT(2) receptor (PD123319) had no effect. On the other hand, losartan and CV-11974 attenuated the Ang-(1-7) effect. These results demonstrate that Ang-(1-7) elicits potent dilation of mesenteric resistance vessels mediated by a D-[Ala(7)]-Ang-(1-7) sensitive site that is also sensitive to losartan and CV-11974.     

Lack of potentiation of bradykinin by angiotensin-(1-7) in a type 2 diabetes model: role of insulin

Considering the growing importance of the interaction between components of kallikrein-kinin and renin-angiotensin systems in physiological and pathological processes, particularly in diabetes mellitus, the aim of the present study was to investigate the interaction between angiotensin-(1-7) (Ang-(1-7)) and bradykinin (BK), important components of these systems in an insulin resistance model of diabetes, and the effect of insulin on it. For this the response of mesenteric arterioles of anesthetized neonatal streptozotocin-induced (n-STZ) diabetic and control rats was evaluated using intravital microscopy. Though capable of potentiating BK in non-diabetic rats, Ang-(1-7) did not potentiate BK in n-STZ rats. Chronic but not acute insulin treatment restored the potentiation. This restorative effect of insulin was abolished by a K+ channel blocker (tetraethylammonium), by nitric oxide synthase inhibitor (N-nitro-L-arginine methyl ester) and by a cyclooxygenase inhibitor (indomethacin). On the other hand, Na(+)-,K(+)-ATPase inhibition (by ouabain) did not abolish the effect of insulin. There was no difference in mRNA and protein expression of B1 and B2 kinin receptor subtypes between n-STZ diabetic and control rats. Insulin treatment did not alter the kinin receptor expression. Our data allow us to conclude that diabetes impaired the interaction between BK and Ang-(1-7) and that insulin restores it. The restoring effect of insulin depends on membrane hyperpolarization, nitric oxide release and cyclooxygenease metabolites but not Na+K+-ATPase. Alteration of kinin receptor expression might not be involved in the restoring effect of insulin on the potentiation of BK by Ang-(1-7).     

Enalapril treatment corrects the reduced response to bradykinin in diabetes increasing the B2 protein expression

Considering the growing importance of the interaction between components of kallikrein-kinin and renin-angiotensin systems in physiological and pathological processes, particularly in diabetes mellitus, the aim of the present study was to investigate the effect of enalapril on the reduced response of bradykinin and on the interaction between angiotensin-(1-7) (Ang-(1-7)) and bradykinin (BK), important components of these systems, in an insulin-resistance model of diabetes. For the above purpose, the response of mesenteric arterioles of anesthetized neonatal streptozotocin-induced (n-STZ) diabetic and control rats was evaluated using intravital microscopy. In n-STZ diabetic rats, enalapril treatment restored the reduced response to BK but not the potentiation of BK by Ang-(1-7) present in non-diabetic rats. The restorative effect of enalapril was observed at a dose that did not correct the altered parameters induced by diabetes such as hyperglycemia, glicosuria, insulin resistance but did reduce the high blood pressure levels of n-SZT diabetic rats. There was no difference in mRNA and protein expressions of B1 and B2 kinin receptor subtypes between n-STZ diabetic and control rats. Enalapril treatment increased the B2 kinin receptor expression. From our data, we conclude that in diabetes enalapril corrects the impaired BK response probably by increasing the expression of B2 receptors. The lack of potentiation of BK by Ang-(1-7) is not corrected by this agent.     

Involvement of angiotensin-(1-7) in the hypothalamic hypotensive effect of captopril in sinoaortic denervated rats

The role of anterior hypothalamic angiotensin-(1-7) (Ang-(1-7)) on blood pressure regulation was studied in sinoaortic denervated (SAD) rats. Since angiotensin-converting enzyme inhibitors increase endogenous levels of Ang-(1-7), we addressed the involvement of Ang-(1-7) in the hypotensive effect induced by captopril in SAD rats. Wistar rats 7 days after SAD or sham operation (SO) were anaesthetized and the carotid artery was cannulated for monitoring mean arterial pressure (MAP). A needle was inserted into the anterior hypothalamus for drug administration. Intrahypothalamic administration of Ang-(1-7) (5 pmol) was without effect in SO rats but reduced MAP in SAD rats by 15.5+/-3.2 mm Hg and this effect was blocked by 250 pmol [D-Ala(7)]-Ang-(1-7), a Mas receptor antagonist. Angiotensin II (Ang II) induced an increase in MAP in both groups being the effect greater in SAD rats (DeltaMAP=15.8+/-1.4 mm Hg) than in SO rats (DeltaMAP=9.6+/-1.0 mm Hg). Ang-(1-7) partially abolished the pressor response caused by Ang II in SAD rats. Whilst the captopril intrahypothalamic injection did not affect MAP in SO animals, it significantly reduced MAP in SAD rats (DeltaMAP=-13.3+/-1.9 mm Hg). Either [D-Ala(7)]-Ang-(1-7) or an anti-Ang-(1-7) polyclonal antibody partially blocked the MAP reduction caused by captopril. In conclusion, whilst Ang-(1-7) does not contribute to hypothalamic blood pressure regulation in SO normotensive animals, in SAD rats the heptapeptide induces a reduction of blood pressure mediated by Mas receptor activation. Although Ang-(1-7) is not formed in enough amount in the AHA of SAD animals to exert cardiovascular effects in normal conditions, our results suggest that enhancement of hypothalamic Ang-(1-7) levels by administration of captopril is partially involved in the hypotensive effect of the ACE inhibitor.     

Elevated glucose blocks angiotensin-(1-7) and bradykinin interaction: the role of cyclooxygenase products

The interaction between angiotensin-(1-7) [Ang-(1-7)] and bradykinin (BK) was studied in the isolated mesenteric arteriolar bed of control and diabetic rats perfused with either 5.5 or 22 mM of glucose. Prostanoids release after the administration of BK, Ang-(1-7) and Ang-(1-7)+BK was also studied. In control and diabetic preparations perfused with Krebs Henseleit solution with 5.5mM of glucose, Ang-(1-7) potentiates BK-induced vasodilation. On the other hand, the potentiating effect disappeared in control and diabetic preparations perfused with 22 mM of glucose. Prostaglandin F(2alpha) (PGF(2alpha)) release induced by BK and Ang-(1-7)+BK was increased in perfusates of diabetic preparations containing 22 mM of glucose. The release of thromboxane A(2) (TXA(2)) (measured as TXB(2)) or prostaglandin I(2) (PGI(2)) (measured as 6-keto-PGF(1alpha)) did not differ in control and diabetic preparations perfused with 5.5 and 22 mM of glucose. Our data allow us to suggest that hyperglycemia may be involved in the lack of potentiation in control and diabetic preparations; increase in PGF(2alpha) release, but not other cyclooxygenase products, may explain the absence of potentiation in diabetic preparations.     

Evidence for a new angiotensin-(1-7) receptor subtype in the aorta of Sprague-Dawley rats

We have recently described, in the mouse aorta, the vasodilator effect of angiotensin-(1-7) (Ang-(1-7)) was mediated by activation of the Mas Ang-(1-7) receptor and that A-779 and D-Pro7-Ang-(1-7) act as Mas receptor antagonists. In this work we show pharmacological evidence for the existence of a different Ang-(1-7) receptor subtype mediating the vasodilator effect of Ang-(1-7) in the aorta from Sprague-Dawley (SD) rats. Ang-(1-7) induced an endothelium-dependent vasodilator effect in aortic rings from SD rats which was inhibited by removal of the endothelium and by L-NAME (100 microM) but not by indomethacin (10 microM). The Ang-(1-7) receptor antagonist D-Pro7-Ang-(1-7) (0.1 microM) abolished the vasodilator effect of the peptide. However, the other specific Ang-(1-7) receptor antagonist, A-779 in concentrations up to 10 microM, did not affect vasodilation induced by Ang-(1-7). The Ang II AT1 and AT2 receptors antagonists CV11974 (0.01 microM) and PD123319 (1 microM), respectively, the bradykinin B2 receptor antagonist HOE 140 (1 microM) and the inhibitor of ACE captopril (10 microM) did not change the effect of Ang-(1-7). Our results show that in the aorta of SD rats, the vasodilator effect of Ang-(1-7) is dependent on endothelium-derived nitric oxide. This effect is mediated by the activation of Ang-(1-7) receptors sensitive to D-Pro7-Ang-(1-7), but not to A-779, which suggests the existence of a different Ang-(1-7) receptor subtype.     

Role of PGI2 and effects of ACE inhibition on the bradykinin potentiation by angiotensin-(1-7) in resistance vessels of SHR

The present study determined the participation of PGI2 in the angiotensin-(1-7) [Ang-(1-7)]/bradykinin (BK) interaction, in the presence and absence of Angiotensin Converting Enzyme (ACE) inhibition, trying to correlate it with tissue levels of both peptides. The isolated mesenteric arteriolar bed of Spontaneously Hypertensive Rats (SHR) was perfused with Krebs or Krebs plus enalaprilat (10 nM), and drugs were injected alone or in association. BK (10 ng)-induced relaxation was potentiated by Ang-(1-7) (2.2 microg) in the presence or absence of enalaprilat. Ang-(1-7) receptor blockade [A-779 (4.8 microg)] did not interfere with the BK effect in preparations perfused with normal Krebs, but reversed the increased BK relaxation observed after ACE inhibition. PGI2 release by mesenteric vessels was not altered by BK or Ang-(1-7) alone, but was increased when both peptides were injected in association, in the absence or in the presence of enalaprilat. ACE inhibition caused a 2-fold increase in the BK tissue levels, and a significant decrease in the Ang-(1-7) values. We conclude that endogenous Ang-(1-7) has an important contribution to the effect of ACE inhibitors participating in the enhancement of BK response. The mechanism of Ang-(1-7) potentiating effect probably involves an increased production of PGI2. Our results suggest that a different enzymatic pathway (non-related to ACE) is involved in the local Ang-(1-7) metabolism.     

Angiotensin-(3-7) pressor effect at the rostral ventrolateral medulla

Ang-(3-7) is a fragment of the renin-angiotensin system that can be derived both from Ang II or Ang-(1-7). In the present study we determined the cardiovascular effects produced by angiotensin-(3-7) [Ang-(3-7)] microinjection into the rostral ventrolateral medulla (RVLM), a key region for the control of sympathetic drive to the periphery. RVLM microinjection of Ang-(3-7) (20, 40 or 80 ng) in male Wistar rats anesthetized with urethane produced significant increases in MAP (19+/-3.8 mm Hg, n=5; 16+/-1.6 mm Hg, n=15 and 11+/-1.2 mm Hg, n=4, respectively) as compared to saline (4+/-0.7 mm Hg, n=6). These alterations were similar to that induced by Ang-(1-7) (14+/-1.3 mm Hg, 40 ng; n=12) and Ang II (17+/-2.3 mm Hg, 40 ng; n=7). Microinjection of losartan (AT(1) receptor antagonist, 100 pmol) or A779 (selective Mas receptor antagonist, 100 pmol) did not alter the pressor effect caused by Ang-(3-7). Microinjection of an Ang-(3-7) analogue, d-Ala(7)-Ang-(3-7) (100 pmol), completely abolished the pressor effect caused by Ang-(3-7). These results suggest that Ang-(3-7) may be an additional peptide of the RAS to act as neuromodulator, at least at the RVLM. Further, the Ang-(3-7) pressor effect is not mediated by the interaction with AT(1) or the Ang-(1-7), Mas, receptors.     

The Angiotensin-(1-7)/Mas Receptor Axis Is Expressed in Sinoatrial Node Cells of Rats

The authors’ previous studies have indicated that angiotensin(Ang)-(1-7) protects the heart against reperfusion arrhythmias. The aim of this study was to determine whether a functional angiotensin-converting enzyme2 (ACE2)/Ang-(1-7)/Mas receptor axis is present in the sinoatrial node (SAN) of Wistar rats. SAN cells were identified by Masson’s trichrome staining, HCN4 expression, and lack of connexin43 expression. Immunohistochemistry technique was used to detect the expression of ACE2, Ang-(1-7), and Mas in the SAN. To evaluate the role of this axis in the SAN function, atrial tachyarrhythmias (ATs) were induced in isolated rat atria perfused with Krebs-Ringer solution (KRS) alone (control) or KRS containing Ang-(1-7). The specific Mas antagonist, A-779, was used to evaluate the role of Mas in the Ang-(1-7) effects. The findings showed that all components of the ACE2/Ang-(1-7)/Mas branch are present in the SAN of rats. Importantly, it was found that this axis is functional because perfusion of atria with Ang-(1-7) significantly reduced the duration of ATs. Additionally, this anti-arrhythmogenic effect was attenuated by A-779. No significant changes were observed in heart rate, contractile tension, or ±dT/dt. These observations demonstrate that the ACE2/Ang-(1-7)/Mas axis is expressed in SAN cells of rats. They provide the morphological support to the anti-arrhythmogenic effect of Ang-(1-7).     

Exercise training enhances flow-induced vasodilation in skeletal muscle resistance arteries of aged rats: role of PGI2 and nitric oxide

Flow-induced vasodilation is attenuated with old age in rat skeletal muscle arterioles. The purpose of this study was to determine whether diminished cyclooxygenase (COX) signaling contributes to the age-induced attenuation of flow-induced vasodilation in gastrocnemius muscle arterioles and to determine whether, and through which mechanism(s), exercise training restores this deficit in old rats. Fischer 344 rats (3 and 22 mo old) were assigned to a sedentary or exercise-trained group. First-order arterioles were isolated from the gastrocnemius muscles, cannulated, and pressurized to 70 cm H(2)O. Diameter changes were determined in response to graded increases in intraluminal flow in the presence and absence of nitric oxide synthase (NOS) inhibition [10(-5) M N(G)-nitro-L-arginine methyl ester (L-NAME)], COX inhibition (10(-5) M indomethacin), or combination NOS (10(-5) M L-NAME) plus COX (10(-5) M indomethacin) inhibition. Aging reduced flow-induced vasodilation in gastrocnemius muscle arterioles. Exercise training restored responsiveness to flow in arterioles of aged rats and enhanced flow-induced vasodilation in arterioles from young rats. L-NAME inhibition of flow-induced vasodilation was greater in arterioles from old rats compared with those from young rats and was increased after exercise training in arterioles from both young and old rats. Although the indomethacin-sensitive portion of flow-induced dilation was not altered by age or training, both COX-1 mRNA expression and PGI(2) production increased with training in arterioles from old rats. These data demonstrate that exercise training restores flow-induced vasodilation in gastrocnemius muscle arterioles from old rats and enhances flow-induced vasodilation in gastrocnemius muscle arterioles from young rats. In arterioles from both old and young rats, the exercise training-induced enhancement of flow-induced dilation occurs primarily through a NOS mechanism.     

Vasodilator effect of angiotensin-(1-7) in mature and sponge-induced neovasculature

Angiotensin-(1-7) (Ang-(1-7)), a peptide constituent of the renin-angiotensin system, has been shown to act as a vasodilator mediator in pre-existing (skin) and newly formed vasculatures (14-day-old sponge implants). Blood flow was determined by the outflow rate of sodium fluorescein applied intradermally or intraimplant and the results were expressed in t(1/2) values (time taken for the fluorescence to reach 50% of the peak in the systemic circulation). We showed that the t(1/2) value was significantly lower (4.1+/-0.46) in the implants compared with the cutaneous vasculature (5.7+/-0.5). Ang-(1-7) 20 ng was able to decrease t(1/2) values in both vasculatures. The specific receptor antagonist, D-Ala7-Ang-(1-7) (A-779), prevented Ang-(1-7)-induced vasodilation and altered the basal vascular tone of the implants. The vasodilator effect was also abolished by nitric oxide (NO) synthase inhibitors in both vasculatures and by indomethacin in the implant. Selective AT(1) and AT(2) receptor antagonists did not alter the vasodilation induced by the peptide. These results establish the vasodilator effect of Ang-(1-7) in the cutaneous and implant vasculature and that the peptide is produced endogenously by the fibrovascular tissue, and suggest that this peptide contributes for the vasodilation found in newly formed vascular beds (wound healing, chronic inflammatory processes and tumors).     

Hypothalamic cardiovascular effects of angiotensin-(1-7) in spontaneously hypertensive rats

The objective of the present work was to study the cardiovascular actions of the intrahypothalamic injection of Ang-(1-7) and its effects on the pressor response to Ang II in spontaneously hypertensive (SH) rats and Wistar Kyoto (WKY) animals. In anaesthetized SH and WKY rats, a carotid artery was cannulated for mean arterial pressure (MAP) measurement and a stainless-steel needle was inserted into the anterior hypothalamus for drug administration. The cardiovascular effects of the intrahypothalamic administration of Ang-(1-7) were determined in SH and WKY rats. In SH rats, the effect of irbesartan and D-Ala-Ang-(1-7) on Ang-(1-7) cardiovascular effect was also evaluated. Ang II was administered in the hypothalamus of SH and WKY rats and changes in blood pressure and heart rate were measured followed by the administration of Ang II, Ang II+Ang-(1-7) or Ang II+D-Ala-Ang-(1-7). Ang-(1-7) did not the change basal MAP in WKY rats, but induced a pressor response in SH animals. Whilst the co-administration of D-Ala-Ang-(1-7) did not affect the response to Ang-(1-7), the previous administration of irbesartan prevented the effect of the peptide. The intrahypothalamic injection of Ang II induced a significantly greater pressor response in SH animals compared to normotensive rats. The co-administration of Ang-(1-7) with Ang II did not affect the pressor response to Ang II in the WKY group. In SH rats, whilst the co-administration of Ang-(1-7) with Ang II reduced the pressor response to Ang II, the concomitant application of D-Ala-Ang-(1-7) with Ang II increased the pressor response to the octapeptide after 5 and 10 min of intrahypothalamic administration. In conclusion, our result demonstrated that the biologically active peptide Ang-(1-7) did not participate in the hypothalamic blood pressure regulation of WKY animals. In SH rats, Ang-(1-7) exerted pleiotropic effects on blood pressure regulation. High dose of the heptapeptide produced a pressor response because of an unspecific action by activation of AT1 receptors. The concomitant administration of lower doses of Ang-(1-7) with Ang II reduced the pressor response to the octapeptide. Finally, the effect of AT(1-7) antagonist on Ang II pressor response suggested that hypothalamic formed Ang-(1-7) are implicated in the regulation of the cardiovascular effects of Ang II.     

Chronic infusion of angiotensin-(1-7) reduces heart angiotensin II levels in rats

We tested the hypothesis that the actions of Angiotensin (Ang)-(1-7) in the heart could involve changes in tissue levels of Ang II. This possibility was addressed by determining the effect of chronic infusion of Ang-(1-7) on plasma and tissue angiotensins. Ang-(1-7) was infused subcutaneously (osmotic minipumps) in Wistar rats. Angiotensins were determined by radioimmunoassay (RIA) in plasma, heart, and kidney. Tissue and plasma angiotensin-converting enzyme (ACE) activity and plasma renin activity (PRA) were also measured. Cardiac and renal ACE2 mRNA levels and cardiac angiotensinogen mRNA levels were assessed by semi-quantitative polymerase chain reaction (PCR). AT1 receptor number was evaluated by autoradiograph. Chronic infusion of Ang-(1-7) (2 microg/h, 6 days) produced a marked decrease of Ang II levels in the heart. A less pronounced but significant decrease of Ang-(1-7) was also observed. No significant changes were observed for Ang I. Ang II was not altered in the kidney. In this tissue, a significant increase of Ang-(1-7) and Ang I concentration was observed. A significant increase of plasma Ang-(1-7) and Ang II was also observed. Ang-(1-7) infusion did not change ACE activity or PRA. A selective slight significant increase in ACE2 expression in the heart was observed. Heart angiotensinogen mRNA as well as the number of Ang II binding sites did not change. These results suggest that AT1 receptors-independent changes in heart Ang II concentration might contribute for the beneficial effects of Ang-(1-7) in the heart. Moreover, these results reinforce the hypothesis that this angiotensin plays an important site-specific role within the renin-angiotensin system.     

Age impairs Flk-1 signaling and NO-mediated vasodilation in coronary arterioles

Impairment of flow-induced vasodilation in coronary resistance arterioles may contribute to the decline in coronary vasodilatory reserve that occurs with advancing age. This study investigated the effects of age on flow-induced signaling and activation of nitric oxide (NO)-mediated vasodilation in coronary resistance arterioles. Coronary arterioles were isolated from young (approximately 6 mo) and old (approximately 24 mo) male Fischer-344 rats to assess vasodilation to flow, vascular endothelial growth factor (VEGF), and ACh. Flow- and VEGF-induced vasodilation of coronary arterioles was impaired with age (P相似文献   

Angiotensin-(1–7) attenuates collagen-induced arthritis via inhibiting oxidative stress in rats

The present study was designed to investigate the anti-rheumatic effects and the mechanism of angiotensin (Ang)-(1–7) in rat models with collagen-induced arthritis (CIA). The CIA model was established using male Wistar rats by intradermal injection of bovine collagen-II in complete Freund's adjuvant at the base of the tail. The levels of angiotensin converting enzyme 2 (ACE2)/Ang-(1–7)/Mas receptor (MasR) were reduced in CIA rats. The attenuation of paw swelling and arthritis scores and improvement of indexes of spleen and thymus were done by Ang-(1–7) injection in CIA rats. The increased levels of inflammatory cytokines, such as interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ in the serum and hind paw were blocked by Ang-(1–7) administration. In addition, enhanced NADPH oxidase (Nox) activity, increased levels of superoxide anions and malondialdehyde (MDA), and weakened superoxide dismutase (SOD) activity, were all reversed by treatment with Ang-(1–7). Nox1 overexpression reversed the suppressing effects of Ang-(1–7) on paw swelling and arthritis scores in CIA rats. The Ang-(1–7)-induced improvement in spleen and thymus indexes in CIA rats was abolished by Nox1 overexpression. Nox1 overexpression reversed the inhibitory effects of Ang-(1–7) by increasing IL-1β, IL-6, TNF-α, and IFN-γ levels in the serum and hind paw of CIA rats. These results demonstrated that Nox1 increased the oxidative stress in arthritis, and Ang-(1–7) improved rheumatism in arthritis via inhibiting oxidative stress.

     

Potentiation of the hypotensive effect of bradykinin by angiotensin-(1-7)-related peptides.

In this study, we evaluated the bradykinin potentiating activity and ACE inhibitory activity of several Ang-(1-7)-related peptides: Ang-(2-7), Ang-(3-7), Ang-(4-7), Ang-(1-6), Ang-(1-5) and the selective antagonist of Ang-(1-7): D-[Ala7]Ang-(1-7) (A-779). In vivo experiments were performed in freely moving Wistar rats. ACE activity was evaluated by a fluorometric assay in rat plasma using Hip-His-Leu as a substrate. Intravenous injections of Ang-(1-7) (2.2 nmol) transformed the effect of a single dose of bradykinin (1 nmol) into the effect produced by a double dose. A similar bradykinin potentiating activity was demonstrated for Ang-(2-7) and Ang-(3-7). On the other hand, Ang-(1-5), Ang-(1-6), Ang-(4-7) and A-779 did not change the hypotensive effect of bradykinin in doses ranging from 8 up to 25 nmols. The hypotensive effect of bradykinin was increased by intravenous infusion (0.3 ng/min) of Ang-(1-7) > Ang-(2-7) > Ang-(3-7). Conversely, Ang-(1-5), Ang-(1-6), Ang-(4-7) or A-779 did not change the hypotensive effect of bradykinin. ACE inhibition with Ang-(1-7) related peptides occurred in the order: Ang-(2-7) > or = Ang-(3-7) > Ang-(1-7) [>] Ang-(1-5) > Ang-(4-7) > or = Ang-(1-6) > or = A-779. A-779 in concentrations up to 10(-5) M did not change the ACE inhibitory activity of Ang-(1-7). These results suggest that Ang-(1-7), Ang-(2-7) and Ang-(3-7) can modulate bradykinin actions in vivo. More important, our data pointed out that alternative mechanisms besides interaction with ACE are required to explain the bradykinin potentiating activity of Ang-(1-7).     

Regulation of insulin sensitivity,insulin production,and pancreatic β cell survival by angiotensin-(1-7) in a rat model of streptozotocin-induced diabetes mellitus

The aim of this study is to determine the antidiabetic activity of Ang-(1-7), an important component of the renin–angiotensin system, in a rat model of streptozotocin (STZ)-induced type 2 diabetes mellitus (DM). A total of 36 male Wistar rats were randomly divided into 3 groups: control group fed standard laboratory diet, DM group fed high-fat diet and injected with STZ, and Ang-(1-7) group receiving injection of STZ followed by Ang-(1-7) treatment. Body weight, blood glucose levels, fasting serum Ang II and insulin levels, and homeostasis model assessment of insulin resistance (HOMA-IR) were measured. The pancreas was collected for histological examination and gene expression analysis. Notably, the Ang-(1-7) group showed a significant decrease in fasting blood glucose and serum Ang II levels and HOMA-IR values and increase in fasting serum insulin levels. Pancreatic β cells in the control and Ang-(1-7) groups were normally distributed in the center of pancreatic islets with large clear nuclei. In contrast, pancreatic β cells in the DM group had a marked shrinkage of the cytoplasm and condensation of nuclear chromatin. Ang-(1-7) treatment significantly facilitated insulin production by β cells in diabetic rats. The DM-associated elevation of inducible nitric oxide synthase (iNOS), caspase-3, caspase-9, caspase-8, and Bax and reduction of Bcl-2 was significantly reversed by Ang-(1-7) treatment. Taken together, Ang-(1-7) protects against STZ-induced DM through improvement of insulin resistance, insulin secretion, and pancreatic β cell survival, which is associated with reduction of iNOS expression and alteration of the Bcl-2 family.     

Hypotensive function of the brain angiotensin-(1-7) in Sprague Dawley and renin transgenic rats.

Angiotensin-(1-7) (Ang-[1-7]) is present in the brain of normotensive Sprague Dawley (SD) rats, and its hypothalamic content is elevated in TGRmRen2(27) rats (TGR) with renin dependent transgenic hypertension. The purpose of the present study was to determine the role of intrabrain Ang-(1-7) in the regulation of cardiovascular functions in SD and TGR rats under resting conditions and during haemodynamic challenge produced by rapid bleeding. Two groups of experiments were performed on conscious SD and TGR rats that were chronically instrumented with a lateral cerebral ventricle (LCV) cannula and an intraarterial catheter. Blood pressure (MAP) and heart rate period (Hp=distance between two systolic peaks) were continuously monitored: 1) under resting conditions during an LCV infusion of either artificial cerebrospinal fluid (aCSF, 5 microl/hr) or Ang-(1-7) in aCSF (100 pmol/5 microl/hr), and 2) before and after haemorrhage performed during LCV infusion of either aCSF or Ang-(1-7) antagonist (A-779, 4 nmol/5 microl/hr). Cerebroventricular infusion of Ang-(1-7) did not affect baseline MAP in the SD rats but it caused a significant decrease in blood pressure in the TGR rats. In the control experiments, haemorrhage significantly reduced MAP in the SD and TGR rats and heart rate in the TGR rats. Cerebroventricular infusion of Ang-(1-7) antagonist eliminated posthaemorrhagic hypotension in both strains and bradycardia in the TGR rats. The results indicate that intrabrain Ang-(1-7) may contribute to posthaemorrhagic hypotension and bradycardia. Moreover, the manner in which it centrally regulates the cardiovascular functions in the SD and TGR rats may be considerably different.