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Angiotensin (ANG) II exerts a negative modulation on insulin signal transduction that might be involved in the pathogenesis of hypertension and insulin resistance. ANG-(1-7), an endogenous heptapeptide hormone formed by cleavage of ANG I and ANG II, counteracts many actions of ANG II. In the current study, we have explored the role of ANG-(1-7) in the signaling crosstalk that exists between ANG II and insulin. We demonstrated that ANG-(1-7) stimulates the phosphorylation of Janus kinase 2 (JAK2) and insulin receptor substrate (IRS)-1 in rat heart in vivo. This stimulating effect was blocked by administration of the selective ANG type 1 (AT(1)) receptor blocker losartan. In contrast to ANG II, ANG-(1-7) stimulated cardiac Akt phosphorylation, and this stimulation was blunted in presence of the receptor Mas antagonist A-779 or the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin. The specific JAK2 inhibitor AG-490 blocked ANG-(1-7)-induced JAK2 and IRS-1 phosphorylation but had no effect on ANG-(1-7)-induced phosphorylation of Akt, indicating that activation of cardiac Akt by ANG-(1-7) appears not to involve the recruitment of JAK2 but proceeds through the receptor Mas and involves PI3K. Acute in vivo insulin-induced cardiac Akt phosphorylation was inhibited by ANG II. Interestingly, coadministration of insulin with an equimolar mixture of ANG II and ANG-(1-7) reverted this inhibitory effect. On the basis of our present results, we postulate that ANG-(1-7) could be a positive physiological contributor to the actions of insulin in heart and that the balance between ANG II and ANG-(1-7) could be relevant for the association among insulin resistance, hypertension, and cardiovascular disease.

Angiotensin (Ang)-(1-7), a bioactive compound of the renin-angiotensin system, exerts effects leading to blood pressure reduction which counterbalance Ang II pressor actions. The present study was conducted to examine Ang-(1-7) and Ang II effects on superoxide anion production in rat aorta using the lucigenin chemiluminescence method. Ang II dose-dependently increased superoxide anion formation when compared to control levels; a maximal increase (2.5-fold) was observed with 1 x 10(-10)M peptide concentration. The Ang II-stimulated superoxide formation was blocked by 1 x 10(-10)M losartan, the specific AT(1) receptor antagonist, but not by 1 x 10(-10)M PD 123319, the AT(2) receptor antagonist, suggesting that the increased superoxide levels caused by Ang II are mediated through AT(1) receptors activation. The Ang II-stimulated superoxide production was not modified by 2 x 10(-8)M allopurinol or 1 x 10(-7)M indomethacin, but was completely abolished by NAD(P)H oxidase inhibitors: 1 x 10(-8)M diphenylene iodonium, or 2 x 10(-8)M apocynin, demonstrating that NAD(P)H oxidase participates in such response. In contrast to Ang II, Ang-(1-7) concentrations ranging 1 x 10(-12) to 1 x 10(-6)M did not modify superoxide anion levels, but prevented the Ang II-enhanced superoxide production. In conclusion, we demonstrated that Ang-(1-7) blocks the pro-oxidant effects of Ang II, thus reducing the superoxide anion production and delaying the hypertension development.

1. The aim of the present study was to investigate the activity of anterior hypothalamic beta-adrenoceptors and angiotensin (Ang) II receptors on blood pressure in normotensive rats and aortic-coarctated (ACo) animals at a chronic stage of hypertension. A possible interaction between beta-adrenoceptors and AngII pressor activity was also investigated. 2. Injection of isoproterenol (0.1-10 nmol) in the anterior hypothalamic area induced a dose-dependent decrease in mean arterial pressure (MAP) in sham-operated (SO), but not in ACo, animals. Isoproterenol (1 nmol) reduced blood pressure in SO rats (DeltaMAP -10.1+/-1.4 mmHg; n=10) but not in ACo animals (DeltaMAP -0.9+/-1.6 mmHg; n=10; P<0.05 vs SO rats). Whereas previous administration of atenolol (40 nmol) enhanced the cardiovascular effect of isoproterenol (1 nmol) in ACo rats but not in SO animals, propranolol (40 nmol) prevented the hypotensive action of isoproterenol in both experimental groups. Intrahypothalamic administration of clenbuterol decreased MAP in a dose-dependent manner; however, the depressor response to clenbuterol (10 nmol) was greater in ACo rats than in SO rats (DeltaMAP -26.8+/-3.2 vs -14.4+/-2.4 mmHg, respectively; n=5 for both; P<0.05). When AngII (50 ng) was injected into the anterior hypothalamic area, a greater pressor response was observed in ACo rats than in SO rats (DeltaMAP 19.6+/-1.1 vs 11.3+/-0.6 mmHg, respectively; n=5 for both; P<0.05). Atenolol (40 nmol) pretreatment partially and significantly prevented the pressor response to AngII in ACo rats, but not in SO rats. 3. In conclusion, these results provide pharmacological evidence for the existence of a beta1-adrenoceptor-mediated pressor mechanism in the anterior hypothalamic area of ACo rats that is absent in SO rats. The enhanced depressor beta2-adrenoceptor activity observed in chronic ACo rats could be a compensatory adjustment to pressor beta1-adrenoceptor activity. Conversely, pressor overactivity of AngII was observed in the anterior hypothalamic area of ACo rats at a chronic hypertensive stage; this enhancement could be explained, at least in part, by the pressor beta1-adrenoceptor activity.

Since it has been suggested that angiotensin (Ang) (1-7) functions as an antihypertensive peptide, we studied its effect on the Ang II-enhanced norepinephrine (NE) release evoked by K+ in hypothalami isolated from aortic coarcted hypertensive (CH) rats. The endogenous NE stores were labeled by incubation of the tissues with 3H-NE during 30 min, and after 90 min of washing, they were incubated in Krebs solution containing 25 mM KCl in the absence or presence of the peptides. Ang-(1-7) not only diminished the K+-evoked NE release from hypothalami of CH rats, but also blocked the Ang II-enhanced NE release induced by K+. Ang-(1-7) blocking action on the Ang II response was prevented by [D-Ala7]Ang-(1-7), an Ang-(1-7) specific antagonist, by PD 123319, an AT2-receptor antagonist, and by Hoe 140, a B2 receptor antagonist. Ang-(1-7) inhibitory effect on the Ang II facilitatory effect on K+-stimulated NE release disappeared in the presence of Nomega-nitro-L-arginine methylester and was restored by L-arginine. Our present results suggest that Ang-(1-7) may contribute to blood pressure regulation by blocking Ang II actions on NE release at the central level. This inhibitory effect is a nitric oxide-mediated mechanism involving AT2 receptors and/or Ang-(1-7) specific receptors and local bradykinin generation.

The objective of our work was to study the intrahypothalamic actions of irbesartan, an angiotensin receptor antagonist, on blood pressure and dopaminergic and serotoninergic neurotransmission in sham operated (SO) and aortic coarctated (ACo) rats by using the microdialysis perfusion technique. We also studied a possible enhanced pressor response to angiotensin II in aortic coarctated rats in the anterior and posterior hypothalamic area. Wistar urethane-chloralose anaesthetised rats were used. A cannula was inserted in the carotid artery. A concentric microdialysis probe was implanted into the anterior hypothalamus or posterior hypothalamus and irbesartan (6 microg ml(-1)) was perfused through the probe. Changes of mean arterial pressure (MAP) were measured. 3,4-Dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) levels were measured in dialysate samples by HPLC-EC. A greater response to irbesartan perfusion in the anterior hypothalamic area of aortic coarctated rats was observed (SO rats, DMAP: -4.3+/-2.3 mm Hg; ACo rats, DMAP: -11.4+/-1.5 mm Hg, P<0.05). The pressor response to angiotensin II in the anterior hypothalamic area (SO rats, DMAP: 4.2+/-1.2 mm Hg; ACo rats, DMAP: 21.7+/-3.7 mm Hg, P<0.05) but not in the posterior hypothalamic area was enhanced in aortic coarctated rats. The perfusion of irbesartan in the anterior hypothalamic area did not modify the extracellular levels of 5-HIAA in both experimental groups, but induced a slightly reduction of DOPAC levels in sham operated rats. The results suggest that the angiotensin system in the anterior hypothalamic area is involved in the maintenance of hypertension in ACo rats and it appears that the increased pressor reactivity to angiotensin II is related to this enhanced function. On the other hand, the effect of irbesartan on DOPAC dialysate levels suggests that the drug produces an alteration of the dopaminergic neurotransmission in the SO rats.

Angiotensin (ANG) II exerts a negative modulation on insulin signal transduction that might be involved in the pathogenesis of hypertension and insulin resistance. ANG-(1-7), an endogenous heptapeptide hormone formed by cleavage of ANG I and ANG II, counteracts many actions of ANG II. In the current study, we have explored the role of ANG-(1-7) in the signaling crosstalk that exists between ANG II and insulin. We demonstrated that ANG-(1-7) stimulates the phosphorylation of Janus kinase 2 (JAK2) and insulin receptor substrate (IRS)-1 in rat heart in vivo. This stimulating effect was blocked by administration of the selective ANG type I (AT1) receptor blocker losartan. In contrast to ANG II, ANG-(1-7) stimulated cardiac Akt phosphorylation, and this stimulation was blunted in presence of the receptor Mas antagonist A-779 or the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin. The specific JAK2 inhibitor AG-490 blocked ANG-(1-7)-induced JAK2 and IRS-1 phosphorylation but had no effect on ANG-(1-7)-induced phosphorylation of Akt, indicating that activation of cardiac Akt by ANG-(1-7) appears not to involve the recruitment of JAK2 but proceeds through the receptor Mas and involves PI3K. Acute in vivo insulin-induced cardiac Akt phosphorylation was inhibited by ANG II. Interestingly, coadministration of insulin with an equimolar mixture of ANG II and ANG-(1-7) reverted this inhibitory effect. On the basis of our present results, we postulate that ANG-(1-7) could be a positive physiological contributor to the actions of insulin in heart and that the balance between ANG II and ANG-(1-7) could be relevant for the association among insulin resistance, hypertension, and cardiovascular disease. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this work was to investigate the production of oxidative damage in homogenized kidney, liver and brain of spontaneously hypertensive rats (SHR), as well as the involvement of angiotensin (Ang) II in this process. Groups of 12-week-old SHR and Wistar Kyoto rats (WKY) were given 10 mg/kg/day losartan in the drinking water during 14 days. Other groups of WKY and SHR without treatment were used as controls. The production of thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH) and the activity of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (Gpx) were determined. No significant difference in TBARS was observed between untreated SHR or WKY rats; GSH content was lower in the liver but higher in the brain of SHR compared to WKY rats. In tissues from the SHR group, SOD and Gpx activities were reduced, whereas CAT activity was slightly increased in kidney. TBARS levels did not change in WKY rats after losartan administration, but were reduced in SHR liver and brain. Losartan treatment decreased GSH content in WKY kidney, but increased GSH in SHR liver. The activity of the antioxidant enzymes was not modified by losartan in WKY rats; however, their activities increased in tissues from treated SHR. The lower activity of antioxidant enzymes in tissues from hypertensive rats compared to those detected in normotensive controls, indicates oxidative stress production. Ang II seems to play no role in this process in normotensive animals, although AT1 receptor blockade in SHR enhances the enzymatic activity indicating that Ang II is implicated in oxidative stress generation in the hypertensive animals. [Copyright &y& Elsevier]

Abstract: This study was performed to provide insight into the regulatory role of angiotensin II and arterial pressure on the activity of antioxidant enzymes and oxidative stress generation in the hypertensive kidney from an experimental animal model of renovascular hypertension. Aortic coarcted and sham-operated rats received vehicle, losartan or minoxidil in their drinking water. After 7 d of treatment rats were sacrificed; hypertensive kidneys were excised, and the NAD(P)H oxidase subunits expression, TBARS production, glutathione level and the activity of heme oxygenase-1 and classical antioxidant enzymes, were evaluated. Losartan administration significantly reduced oxidative stress generation decreasing NAD(P)H oxidase expression, independently of the drop in arterial pressure. On the other hand, antioxidant enzymes were regulated by arterial pressure and they were not implicated in kidney protection against oxidative damage. Findings here reported strongly suggest that clinical therapeutics with the Ang II type 1 receptor blocker prevents oxidative stress generation and may attenuate the kidney oxidative damage in the renovascular hypertension. We hypothesize that the pathway followed by the Ang II blocker to achieve this renoprotection, though independent of the primary antioxidant enzymatic system, depends on NAD(P)H oxidase downregulation. [Copyright &y& Elsevier]

Abstract: Since angiotensin (Ang) (1–7) injected into the brain blocked Ang II pressor actions in rats made hypertensive by aortic coarctation (CH), we examined systemic and tissue angiotensin peptide levels, specifically concentrating on the hypothalamic Ang-(1–7) levels. Plasma, heart and kidney isolated from CH rats showed increased levels of Ang I, Ang II and Ang-(1–7) compared with the normotensive group, with Ang II being the predominant peptide in heart and kidney. In the hypothalamus, equimolar amounts of Ang II and Ang-(1–7) were found in the sham group, whereas only Ang-(1–7) levels increased in CH rats. We conclude that aortic coarctation activates systemic and tissue renin–angiotensin system. The increased central levels of Ang-(1–7) in the CH rats suggest a potential mitigating role of this peptide in central control of the hypertensive process. [Copyright &y& Elsevier]

Abstract: 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 AT1–7 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. [Copyright &y& Elsevier]

The effect of two different doses of angiotensin-(1–7) and angiotensin II on the oxidative stress generation was analyzed in rat kidney. Animals were injected intraperitoneally with a single dose of angiotensin-(1–7) or angiotensin II (20 or 50 nmol/kg body weight) and killed 3 h after injection. Production of thiobarbituric acid reactive substances (TBARS), measured as indicator of oxidative stress induction, was significantly increased in rat kidney after Ang-(1–7) administration up to 30% and 50% over controls, at 20 and 50 nmol/kg, respectively. Reduced glutathione (GSH), the most important soluble antioxidant defense in mammalian cells, showed a significant decrease of 13% and 20% at 20 and 50 nmol/kg of angiotensin-(1–7), respectively. When the antioxidant enzyme activities were determined, it was found that catalase activity was not altered by the assayed angiotensin-(1–7) doses while superoxide dismutase and glutathione peroxidase activities were significantly reduced by injection of 20 nmol/kg (34% and 13%, with respect to controls) and 50 nmol/kg of angiotensin-(1–7) (54% and 22%, respectively). In contrast, angiotensin II injections did not produce significant changes neither in TBARS levels nor in soluble and enzymatic defense parameters at the two doses used in this work. These results suggest that angiotensin-(1–7) is undoubtedly related to oxidative stress induction. [Copyright &y& Elsevier]