Renin-angiotensin system-mediated nitric oxide signaling in podocytes.

Nitric oxide (NO) is widely recognized for its role in regulating renal function and blood pressure. However, the precise mechanisms by which NO affects renal epithelial cells remain understudied. Our previous research has shown that NO signaling in glomerular podocytes can be initiated by Angiotensin II (ANG II) but not by ATP. This study aims to elucidate the crucial interplay between the renin-angiotensin system (RAS) and NO production in podocytes. To conduct our research, we used cultured human podocytes and freshly isolated rat glomeruli. A variety of RAS peptides were used, alongside confocal microscopy, to detect NO production and NO/Ca2+ cross talk. Dynamic changes in the podocyte cytoskeleton, mediated by RAS-NO intracellular signaling, were observed using fluorescent labeling for F-actin and scanning probe microscopy. The experiments demonstrated that ANG II and ANG III generated high levels of NO by activating the angiotensin II type 2 receptor (AT2R). We did not detect functional MAS receptor presence in podocytes, and the moderate NO response to ANG 1-7 was also mediated through AT2R. Furthermore, NO production impacted intracellular Ca2+ signaling and correlated with an increase in podocyte volume and growth. Scanning probe experiments revealed that AT2R activation and the corresponding NO generation are responsible for the protrusion of podocyte lamellipodia. Taken together, our data indicate that AT2R activation enhances NO production in podocytes and subsequently mediates changes in Ca2+ signaling and podocyte volume dynamics. These mechanisms may play a significant role in both physiological and pathophysiological interactions between the RAS and podocytes.NEW & NOTEWORTHY The renin-angiotensin system plays a crucial role in the production of intracellular nitric oxide within podocytes. This mechanism operates through the activation of the angiotensin II type 2 receptor, leading to dynamic modifications in intracellular calcium levels and the actin filament network. This intricate process is vital for linking the activity of angiotensin receptors to podocyte function.

Renal functional effects of the highly selective AT2R agonist, ß-Pro7 Ang III, in normotensive rats.

Recently, we designed a group of peptides by sequential substitution of the naturally occurring α-amino acid throughout the Ang III peptide sequence with the corresponding ß-amino acid. ß-Amino acid substitution at the proline residue of Ang III (ß-Pro7-Ang III) resulted in a highly selective AT2R ligand, demonstrating remarkable selectivity for the AT2R in both binding and functional studies. To provide additional functional evidence for the suitability of ß-Pro7 Ang III as a novel AT2R agonist, we tested effects of acute systemic administration of ß-Pro7-Ang III on renal hemodynamic and excretory function in anesthetized normotensive male and female rats. We also compared the natriuretic effects of acute intrarenal administration of native Ang III and ß-Pro7-Ang III in the presence of systemic AT1R blockade in anesthetized female rats to allow for the differentiation of systemic versus direct intrarenal natriuretic actions of ß-Pro7-Ang III. In both male and female rats, acute systemic administration of ß-Pro7-Ang III elicited renal vasodilatation and natriuresis. Notably, greater renal vasodilatory effects were observed in female versus male rats at the highest dose of ß-Pro7-Ang III administered. Moreover, intra-renal administration of ß-Pro7-Ang III produced significant natriuretic effects in female rats and, like Ang III, evoked AT2R translocation to the apical plasma membrane in renal proximal tubular cells. Taken together, our findings support the use of ß-Pro7-Ang III as a novel AT2R agonist and experimental tool for exploring AT2R function and its potential as a therapeutic target. Furthermore, our findings provide further evidence of a sex-specific influence of AT2R stimulation on renal function.

Angiotensin III Induces JAK2/STAT3 Leading to IL-6 Production in Rat Vascular Smooth Muscle Cells.

The Janus kinase-2/ signal transducer and activators of transcription-3 (JAK2/STAT3) pathway and interleukin-6 (IL-6) are pleiotropic signal transduction systems that are responsible for induction of many cytokines and growth factors. It is unknown whether the renin angiotensin aldosterone system (RAAS) peptide, angiotensin (Ang) III induces JAK2/STAT3 and IL-6 in vascular smooth muscle cells (VSMCs). Thus, the purpose of this study was to investigate whether Ang III induces the JAK2/STAT3 pathway leading to IL-6 production in cultured VSMCs isolated from Wistar rats and determine whether differences exist in spontaneously hypertensive rat (SHR) VSMCs. We gauged Ang III's effects on this pathway by measuring its action on STAT3 as well as IL-6 production. Ang III behaved similarly as Ang II in stimulation of STAT3 phosphorylation in Wistar and SHR VSMCs. Moreover, there were no differences in this Ang III effect in SHR versus Wistar VSMCs. In Wistar VSMCs, Ang II and Ang III significantly induced IL-6 protein secretion and mRNA expression. However, IL-6 protein secretions mediated by these peptides were significantly greater in SHR VSMCs. Ang III induced the JAK2/STAT3 pathway, leading to IL-6 protein secretion and IL-6 mRNA expression via actions on AT1Rs. Moreover, the actions of Ang III to induce IL-6 production was dysregulated in SHR VSMCs. These findings suggest that Ang III acts on AT1Rs to induce JAK2/STAT3, leading to an increase in IL-6 in cultured VSMCs. These findings are important in establishing Ang III as an important physiologically relevant peptide in VSMCs.

ß-Pro7Ang III is a novel highly selective angiotensin II type 2 receptor (AT2R) agonist, which acts as a vasodepressor agent via the AT2R in conscious spontaneously hypertensive rats.

We have previously shown that individual ß-amino acid substitution in angiotensin (Ang) II reduced Ang II type 1 receptor (AT1R) but not Ang II type 2 receptor (AT2R)-binding and that the heptapeptide Ang III exhibited greater AT2R:AT1R selectivity than Ang II. Therefore, we hypothesized that ß-amino-acid-substituted Ang III peptide analogues would yield highly selective AT2R ligands, which we have tested in binding and functional vascular assays. In competition binding experiments using either AT1R- or AT2R-transfected human embryonic kidney (HEK)-293 cells, novel ß-substituted Ang III analogues lacked appreciable AT1R affinity, whereas most compounds could fully displace (125)I-Sar(1)Ile(8) Ang II from AT2R. The rank order of affinity at AT2R was CGP42112 > Ang III > ß-Pro(7) Ang III=Ang II > ß-Tyr(4) Ang III ≥ PD123319 >> ß-Phe(8) Ang III >> ß Arg(2) Ang III=ß-Val(3) Ang III >> ß-Ile(5) Ang III. The novel analogue ß-Pro(7) Ang III was the most selective AT2R ligand tested, which was >20,000-fold more selective for AT2R than AT1R. IC50 values at AT2R from binding studies correlated with maximum vasorelaxation in mouse aortic rings. Given that ß-Pro(7) Ang III was an AT2R agonist, we compared ß-Pro(7) Ang III and native Ang III for their ability to reduce blood pressure in separate groups of conscious spontaneously hypertensive rats. Whereas Ang III alone increased mean arterial pressure (MAP), ß-Pro(7) Ang III had no effect. During low-level AT1R blockade, both Ang III and ß-Pro(7) Ang III, but not Ang II, lowered MAP (by ∼30 mmHg) at equimolar infusions (150 pmol/kg/min for 4 h) and these depressor effects were abolished by the co-administration of the AT2R antagonist PD123319. Thus, ß-Pro(7) Ang III has remarkable AT2R selectivity determined in binding and functional studies and will be a valuable research tool for insight into AT2R function and for future drug development.

Central ventilatory and cardiovascular actions of angiotensin peptides in trout.

In the brains of teleosts, angiotensin II (ANG II), one of the main effector peptides of the renin-angiotensin system, is implicated in various physiological functions notably body fluid and electrolyte homeostasis and cardiovascular regulation, but nothing is known regarding the potential action of ANG II and other angiotensin derivatives on ventilation. Consequently, the goal of the present study was to determine possible ventilatory and cardiovascular effects of intracerebroventricular injection of picomole doses (5-100 pmol) of trout [Asn(1)]-ANG II, [Asp(1)]-ANG II, ANG III, ANG IV, and ANG 1-7 into the third ventricle of unanesthetized trout. The central actions of these peptides were also compared with their ventilatory and cardiovascular actions when injected peripherally. Finally, we examined the presence of [Asn(1)]-ANG II, [Asp(1)]-ANG II, ANG III, and ANG IV in the brain and plasma using radioimmunoassay coupled with high-performance liquid chromatography. After intracerebroventricular injection, [Asn(1)]-ANG II and [Asp(1)]-ANG II two ANG IIs, elevated the total ventilation through a selective stimulatory action on the ventilation amplitude. However, the hyperventilatory effect of [Asn(1)]-ANG II was threefold higher than the effect of [Asp(1)]-ANG II at the 50-pmol dose. ANG III, ANG IV, and ANG 1-7 were without effect. In addition, ANG IIs and ANG III increased dorsal aortic blood pressure (P(DA)) and heart rate (HR). After intra-arterial injections, none of the ANG II peptides affected the ventilation but [Asn(1)]-ANG II, [Asp(1)]-ANG II, and ANG III elevated P(DA) (50 pmol: +80%, +58% and +48%, respectively) without significant decrease in HR. In brain tissue, comparable amounts of [Asn(1)]-ANG II and [Asp(1)]-ANG II were detected (ca. 40 fmol/mg brain tissue), but ANG III was not detected, and the amount of ANG IV was about eightfold lower than the content of the ANG IIs. In plasma, ANG IIs were also the major angiotensins (ca. 110 fmol/ml plasma), while significant but lower amounts of ANG III and ANG IV were present in plasma. In conclusion, our study suggests that the two ANG II isoforms produced within the brain may act as a neurotransmitter and/or neuromodulator to regulate the cardioventilatory functions in trout. In the periphery, two ANG IIs and their COOH-terminal peptides may act as a circulating hormone preferentially involved in cardiovascular regulations.

Angiotensin III induces c-Jun N-terminal kinase leading to proliferation of rat astrocytes.

Previously, we showed in cultured rat astrocytes that angiotensin (Ang) III induced astrocyte proliferation and phosphorylation of ERK1/2 mitogen activated protein (MAP) kinases through interaction with the AT(1) receptor. In the current study, we determined whether the c-Jun N terminal kinase (JNK) MAP kinase pathway was similarly affected by the peptide in cultured brainstem astrocytes. Ang III induced JNK phosphorylation in a concentration- and time-dependent manner. Similar to ERK1/2 phosphorylation, maximal phosphorylation occurred with 100 nM Ang III and was apparent within a minute of exposure to the peptide. Peak effects were observed over a 5-15 min time range. Pretreatment of brainstem astrocytes with the JNK inhibitor, SP600125, prevented Ang III phosphorylation of JNK, as well as Ang III-mediated astrocyte growth. The selective AT(1) receptor antagonist, Losartan, prevented Ang III-induced JNK phosphorylation. Pretreatment of astrocytes with the AT(2) receptor blocker PD123319 was ineffective in preventing JNK phosphorylation by Ang III. Interestingly, both Ang II and Ang III induced JNK phosphorylation to a similar extent suggesting that the two peptides were equipotent in this effect. Our findings suggest that Ang III interacts with Ang AT(1) receptors to directly stimulate the JNK MAP kinase pathway leading to astrocyte growth. This study is the first to show that Ang III actions may involve the JNK MAP kinase pathway in astrocytes and provide key information that may lead to a better understanding of the functions of Ang III in the central nervous system, in particular in astrocytes.

Effects of angiotensin III on c-Jun N terminal kinase in Wistar and hypertensive rat vascular smooth muscle cells.

Proliferation of vascular smooth muscle cells (VSMCs) and inflammation are well known actions associated with hypertension. Angiotensin (Ang) II mediates these physiological actions through the c-Jun N terminal Kinase (JNK), mitogen-activated proteins kinase (MAPK) pathway. Ang III effects on this pathway in VSMCs are unknown. The aim of this study was to determine whether Ang III activates JNK MAPK in Wistar VSMCs and determined whether the response was different in spontaneously hypertensive rat (SHR) VSMCs. We also ascertained whether this effect leads to VSMC proliferation. Western blots were used to determine the time and concentration effects of Ang II on JNK MAPK phosphorylation in Wistar VSMCs. Similar studies were conducted for Ang III in Wistar and SHR VSMCs. Both peptides induced JNK phosphorylation in a concentration- and time-dependent manner in Wistar VSMCs. Ang III also increased JNK phosphorylation in a concentration- and time-dependent fashion in SHR VSMCs as well. However, the ability of Ang III to induce JNK MAPK was different in SHR VSMCs as the phosphorylation levels of JNK were significantly higher in Wistar VSMCs as compared to SHR VSMCs at several time points and concentrations. Further, Ang III-mediated DNA synthesis, a measure of VSMC proliferation, occurred through activation of JNK MAPK. This study is the first to show Ang III effects on the JNK MAPK pathway in VSMCs and the role of JNK in Ang III-mediated cellular proliferation. These findings impart key information for the understanding of Ang III functions, especially in VSMCs and possible cardiovascular diseases.

Mammalian AT2 receptors expressed in Xenopus laevis oocytes couple to endogenous chloride channels and stimulate germinal vesicle break down.

BACKGROUND AND AIMS: A comparative analysis was performed of the properties of cloned AT1 and AT2 receptors and their ability to induce ion currents and oocyte maturation. METHODS: Frog oocytes were injected with cRNA that codes for rat AT1A and AT2 and bovine AT1 receptors and membrane currents were recorded by using the two-microelectrode voltage-clamp technique. Oocyte maturation was scored by observation of the germinal vesicle breakdown (GVBD). RESULTS: Xenopus oocytes expressing AT1 or AT2 generated oscillatory chloride currents by coupling to the diacylglycerol/inositol-3-phosphate (DAG/IP(3)) cascade. Ang II activation of collagenase-defolliculated oocytes expressing rat AT1A yielded larger chloride currents (9.2+/-3.4 A) than those generated by oocytes expressing bovine AT1 (3.78+/-2.6 A). Oocytes expressing rat AT1A were recovered from desensitization after 0.5 h and completely after 10.5 h; whereas oocytes expressing bovine AT1 receptors were unable to do so. Expression of rat AT2 generated smaller chloride currents (32-210 nA). Expression of AT2 receptors triggered GVBD whereas AT1 did not. The proportion of oocytes developing GVBD was greater for folliculated oocytes than for oocytes that were defolliculated. Furthermore, oocytes injected with AT2 secreted into the media, a heat-resistant factor(s) that stimulated GVBD of oocytes. This media elicited inward and outward membrane currents when applied to non-injected oocytes. CONCLUSION: Activation of AT1 and AT2 receptors couple to similar metabolic cascades in Xenopus laevis oocytes. However, the pathway activated by AT2 diverges to induce oocyte maturation.

Angiotensin regulates release and synthesis of serotonin in brain.

Angiotensin II released serotonin from neuron terminals and accelerated synthesis of the serotonin. This increase in synthesis depended on the activation of tryptophan hydroxylase. A biphasic effect was observed: at high doses the stimulatory effect depended on conversion of angiotensin II to angiotensin III. At low doses an inhibitory effect was found, possible dependent on an angiotensin II metabolite. These actions represent a subtle regulation of the open-loop serotonin system.

Evaluation of role of angiotensin III and aminopeptidases in prostate cancer cells.

BACKGROUND: The aim of this study was to perform a comprehensive evaluation of angiotensin III (Ang-III) and related converting enzymes, aminopeptidase A (APA) and N (APN), in prostate cancer. METHODS: We investigated the effects of Ang-III on the in vitro growth of human prostate cancer cells and the expression of APA and APN in cells treated with Ang-III or hormonal agents. Furthermore, we performed real-time quantitative PCR to investigate the expression pattern of APA and APN in 86 prostate tissue samples including normal prostate, untreated and hormone refractory prostate cancer (HRPC). RESULTS: Ang-III stimulated cell proliferation, and the proliferative effect was inhibited by olmesartan, an AT(1) receptor blocker (ARB). Western blot analysis showed that phosphorylation of mitogen-activated protein kinase (MAPK) was enhanced by Ang-III and inhibited by olmesartan. APN mRNA level in HRPC was significantly lower than that in normal prostate and untreated prostate cancer tissue. In LNCaP cells, APN expression was augmented by Ang-III, whereas APA expression was not modulated. Hormonal agents, such as estradiol (E2) and dexamethasone (Dex), enhanced APA expression, but did not modulate APN expression in LNCaP cells. CONCLUSIONS: Our results suggest that Ang-III and related converting enzymes contribute to cell proliferation of prostate cancer, and may be implicated in cancer progression.

Angiotensin II and III suppress food intake via angiotensin AT(2) receptor and prostaglandin EP(4) receptor in mice.

Intracerebroventricularly administered angiotensin (Ang) II and III dose-dependently suppressed food intake in mice and their anorexigenic activities were inhibited by AT(2) receptor-selective antagonist. Ang II did not suppress food intake in AT(2) receptor-knockout mice, while it did significantly in wild-type and AT(1) receptor-knockout mice. The suppression of food intake in AT(1) receptor-knockout mice was smaller than that in wild-type. The anorexigenic activities of Ang II and III were also blocked by a selective antagonist for prostaglandin EP(4) receptor. Taken together, centrally administered Ang II and III may decrease food intake through AT(2) receptor with partial involvement of AT(1) receptor, followed by EP(4) receptor activation, which is a novel pathway regulating food intake.

Effects of angiotensin II and its metabolites in the rat coronary vascular bed: is angiotensin III the preferred ligand of the angiotensin AT2 receptor?

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.

[Angiotensin III participation in mechanisms of development of an alcoholism and other kinds of behavioural activity].

To study the involvement of angiotensin III in the development of alcoholism and other types of behavioural activity the research on 24 male rats of Vistar species with 180-250 g weight was conducted. Alcoholic motivation was created by alcoholic beverage consisting of 20% ethyl alcohol water solution. The experiment lasted 30-day time period. It was concluded that the effect of angiotensin III depend on the individual resistance or predisposition to alcohol.

Angiotensin antagonists with increased specificity for the renal vasculature.

This study was designed to ascertain whether renal vascular angiotensin receptors differ from other systemic angiotensin receptors and whether, on that basis, antagonists with greater specificity for the renal vasculature can be defined. Femoral and renal blood flow and their responses to angiotensin II (AII) and its heptapeptide analogue, 1-des Asp AII (AIII), were measured with an electromagnetic flowmeter in 26 dogs. For the kidney, the threshold doses of AII and AIII were identical (2.5+/-0.27 vs. 2.3+/-0.35 pmol/100 ml renal blood flow, with similar dose-response curves. In contrast, AII had a greater pressor effect (P less than 0.001) and produced more femoral vasoconstriction (P less than 0.001) than AIII. All four antagonists studied (1-Sar, 8-Ala AII [P113]; 8-Ala AII; 1-des Asp, 8-Ala AII; 1-des Asp, 8-Ile AII) induced parallel shifts in the renal blood flow response to AII and AIII. P113 induced greater blockade than 8-Ala AII (P less than 0.001) which, in turn, was more effective than 1-des Asp, 8-Ala AII (P less than 0.001). 1-des Asp, 8-Ile AII was as effective as P113. Each analogue induced an identical inhibition of the renal vascular response to AII and AIII. In addition, AII and AIII induced cross-tachyphylaxis. All lines of evidence suggested that AII and AIII act on a single receptor in the kidney, which differs at least functionally from other systemic vascular receptors. The possibility that heptapeptide analogues represent angiotensin antagonists with greater specificity for the renal vasculature was pursued in a model in which the renin-angiotensin system is activated. Acute, partial thoracic inferior vena caval occlusion was induced in an additional 16 dogs. P113 induced progressive, dose-related hypotension and a limited increase in renal blood flow in this model. The 1-des Asp, 8-Ile AII analogue, conversely, induced a consistent, larger, dose-related renal blood flow increase, with significantly less hypotension over a wide dose range. We conclude that the renal vascular receptor differs sufficiently from systemic angiotensin receptors that heptapeptide analogues of AII will be useful in exploring angiotensin's role in states characterized by disordered renal perfusion and function.

Effector peptides of the renin-angiotensin system in the central mechanisms of acquired and innate behavior in thirst in rats.

We report here a comparative analysis of the involvement of a number of components of the renin-angiotensin system in the performance of simple and complex forms of drinking behavior and thirst-associated non-drinking types of behavior. On central (intracerebroventricular) microinjection, [des-Asp1]-angiotensin I at doses equieffective to those of angiotensins II and III was found to be involved only in the performance of simple (taking water from the bowl) and linked forms of activity (comfort behavior, stress grooming, orientational-investigative, and feeding behavior). Angiotensin II was involved in the central mechanisms of complex acquired drinking behavior, selectively modulating its key stages (initial, final), while angiotensin III was involved only in the mechanisms of reproduction of the complex skill. All three substances induced "innate patterns of behavior" specific for each compound, these occurring at fixed periods of time after intracerebral microinjection. The effects of these substances were selectively suppressed by the AT1 receptor blocker losartan potassium.

Tyrosine kinase and mitogen-activated protein kinase/extracellularly regulated kinase differentially regulate intracellular calcium concentration responses to angiotensin II/III and bradykinin in rat cortical thick ascending limb.

The cortical thick ascending limb (CTAL) coexpresses angiotensin (Ang) II/Ang III receptor type 1A (AT(1A)-R) and bradykinin (BK) receptor type 2 (B2-R). In several cell types, these two receptors share the same signaling pathways, although their physiological functions are often opposite. In CTAL, little is known about the intracellular transduction events leading to the final physiological response induced by these two peptides. We investigated and compared in this segment the action of Ang II/III and BK on intracellular calcium concentration ([Ca2+]i) response and metabolic CO2 production, an index of Na+ transport, by using inhibitors of protein kinase C (bisindolylmaleimide), Src tyrosine kinase (herbimycin A and PP2), and MAPK/ERK (PD98059 and UO126). Ang II/III and BK (10(-7) mol/liter) released Ca2+ from the same intracellular pools but activated different Ca2+ entry pathways. Ang II/III- or BK-induced [Ca2+]i increases were similarly potentiated by bisindolylmaleimide. Herbimycin A and PP2 decreased similarly the [Ca2+]i responses induced by Ang II/III and BK. In contrast, PD98059 and UO126 affected the effects of BK to a larger extent than those of Ang II/III. Especially, the Ca2+ influx induced by BK was more strongly inhibited than that induced by Ang II/III in the presence of both compounds. The Na+ transport was inhibited by BK and stimulated by Ang II/III. The inhibitory action of BK on Na+ transport was blocked by UO126, whereas the stimulatory response of Ang II/III was potentiated by UO126 but blocked by bisindolylmaleimide. These data suggest that the inhibitory effect of BK on Na+ transport seems to be directly mediated by an increase in Ca2+ influx dependent on MAPK/ERK pathway activation. In contrast, the stimulatory effect of Ang II/III on Na+ transport is more complex and involves PKC and MAPK/ERK pathways.

Ang II and Ang III modulate PTZ seizure threshold in non-stressed and stressed mice: possible involvement of noradrenergic mechanism.

The present study evaluated the effects of Angiotensin (Ang) Ang II and Ang III on pentylenetrazol (PTZ) seizure threshold in non-stressed and stressed mice as well as the possible participation of noradrenergic (NA) mechanism in their effects. While intracerebroventricular (i.c.v.) administered Ang II and Ang III increased the PTZ threshold for myoclonic twitch (MTW), generalized clonus (GNCL) and tonic hindlimb extension (THE) in non-stressed mice, they attenuated the anticonvulsant effects of acute restraint stress. The selective AT(1) receptor antagonist losartan rather than the selective AT(2) receptor antagonist PD 123319 antagonized the effects of Ang II in both non-stressed and stressed animals. Losartan also reversed the effects of Ang III on the thresholds for MTW and GNCL in stressed mice. Concurrent administration of desipramine (NA-uptake inhibitor) and either Ang II or Ang III produced a greater effect on MTW and GNCL in non-stressed mice. However, desipramine reversed the peptide-induced attenuation on PTZ seizure threshold in stressed mice. Prazosin (alpha(1)-adrenoreceptor (AR) antagonist) blocked the effects of Ang II on PTZ seizure threshold for the three convulsive phases in both non-stressed and stressed mice. Prazosin potentiated the anti-seizure effect of Ang III against MTW, GNCL, and THE in non-stressed mice while it reversed the seizure threshold-decreasing effect of this heptapeptide on MTW and GNCL in stressed mice. Yohimbine (alpha(2)-AR antagonist) blocked only the effects exerted by Ang II on the PTZ seizure threshold in non-stressed mice. Our findings suggest that the responses of Ang II and Ang III on PTZ seizure threshold can be mediated by AT(1) receptors in non-stressed and even more in stressed mice. We also hypothesize that the NA-dependent mechanism plays a major role in the effects of Ang peptides in both non-stressed and stressed mice.

The bradykinin B2 receptor antagonist icatibant (Hoe 140) blocks aminopeptidase N at micromolar concentrations: off-target alterations of signaling mediated by the bradykinin B1 and angiotensin receptors.

The N-terminal sequence of icatibant, a widely used peptide antagonist of the bradykinin B(2) receptors, is analogous to that of other known aminopeptidase N inhibitors. Icatibant competitively inhibited the hydrolysis of L-Ala-p-nitroanilide by recombinant aminopeptidase N (K(i) 9.1 microM). In the rabbit aorta, icatibant (10-30 microM) potentiated angiotensin III, but not angiotensin II (contraction mediated by angiotensin AT(1) receptors), and Lys-des-Arg(9)-bradykinin, but not des-Arg(9)-bradykinin (effects mediated by the bradykinin B(1) receptors), consistent with the known susceptibility of these agonists to aminopeptidase N. At concentrations possibly reached in vivo (e.g., in kidneys), icatibant alters physiological systems different from bradykinin B(2) receptors.

[Effector peptides of the brain renin-angiotensin system in central mechanisms of learned and natural forms of drinking behavior in rats].

Central mechanisms of angiotensin involvement in initiation and realization of operant forms of drinking behavior were investigated. It was suggested that intracerebroventricular microinjection of angiotensin-II and angiotensin-IIl specifically affected the learned forms of drinking behavior. The experiments demonstrated that [des-Asp1]-angiotensin-I produced only the natural forms of drinking behavior. Angiotensins modulated specific forms of thirst-associated behavior such as exploring, grooming, and ingestive behavior. Injections of AT1 receptor antagonist losartan were associated with acute water intake decrease and sharp operant behavior inactivation.

Angiotensin III increases monocyte chemoattractant protein-1 expression in cultured human proximal tubular epithelial cells.

BACKGROUND/AIMS: We investigated whether angiotensin III (Ang III) is involved in monocyte recruitment through regulation of the chemokine monocyte chemoattractant protein-1 (MCP-1) in cultured human proximal tubular epithelial cells (HK-2 cells). METHODS: We measured MCP-1 levels in HK-2 cells that had been treated with various concentrations of Ang III and Ang II type-1 (AT1) receptor antagonists at various time points. The phosphorylation states of p38, c-Jun N-terminal kinases (JNK), and extracellular-signal-regulated kinases were measured in Ang III-treated cells to explore the mitogen-activated protein kinase (MAPK) pathway. MCP-1 levels in HK-2 cell-conditioned media were measured after pre-treatment with the transcription factor inhibitors curcumin or pyrrolidine dithiocarbamate. RESULTS: Ang III increased MCP-1 protein production in dose- and time-dependent manners in HK-2 cells, which was inhibited by the AT1 receptor blocker losartan. p38 MAPK activity increased significantly in HK-2 cells exposed to Ang III for 30 minutes, and was sustained at higher levels after 60 minutes (p < 0.05). Total phosphorylated JNK protein levels tended to increase 20 minutes after stimulation with Ang III. Pre-treatment with a p38 inhibitor, a JNK inhibitor, or curcumin significantly inhibited Ang III-induced MCP-1 production. CONCLUSIONS: Ang III increases MCP-1 synthesis via stimulation of intracellular p38 and JNK MAPK signaling activity and subsequent activated protein-1 transcriptional activity in HK-2 cells.