Angiotensin AT1 Receptor Antagonist Losartan Research Articles

Antihypertensive treatment with hydrochlorothiazide-hydralazine combination aggravates medial vascular calcification in CKD rats with mineral bone disorder.

Arterial stiffness and medial vascular calcification, leading to isolated systolic blood pressure (BP), are major cardiovascular risk factors in patients with chronic kidney disease (CKD) and mineral bone disorders (MBD). The impact of BP on MBD-induced medial vascular calcification in CKD remains uncertain. We investigated whether BP reduction improves arterial stiffness and medial vascular calcification in a rat model of CKD-MBD. CKD was induced in Wistar rats by subtotal nephrectomy. Then, MBD was generated by a Ca/P-rich diet with calcitriol supplementation to induce medial vascular calcification. Two antihypertensive treatments were evaluated: (1) the angiotensin AT1 receptor antagonist losartan, and (2) the combination of the thiazide diuretic hydrochlorothiazide and the direct vasodilator hydralazine (HCTZ/HY). After 5 weeks, mean BP (MBP), pulse pressure (PP), and pulse wave velocity (PWV) were determined. Vascular calcification was assessed in the thoracic aorta. While MBP was similar in CKD-MBD and control CKD rats, PP and PWV were increased in CKD-MBD rats. The heightened arterial stiffness in CKD-MBD rats was associated with diffused medial calcification along the thoracic aorta. Although both losartan and HCTZ/HY reduced MBP in CKD-MBD rats, losartan did not affect PP and PWV nor medial vascular calcification, whereas HCTZ/HY, unexpectedly, further increased arterial stiffness and medial vascular calcification. In the rat model of CKD-MBD, antihypertensive treatment with losartan did not affect arterial stiffness or medial vascular calcification. However, HCTZ/HY treatment aggravated arterial stiffness and vascular calcification despite a similar reduction of MBP, suggesting a blood pressure-independent mechanism for vascular calcification.

Protective effects of losartan on some type 2 diabetes mellitus-induced complications in Wistar and spontaneously hypertensive rats.

Diabetes mellitus type 2 (T2DM) is characterized by resistance of insulin receptors and/or inadequate insulin secretion resulting in metabolic and structural complications including vascular diseases, arterial hypertension and different behavioral alterations. We aimed to study the effects of the antihypertensive angiotensin AT1 receptor antagonist losartan on the T2DM-induced changes of exploratory behavior, anxiety, nociception and short term memory in normotensive Wistar and spontaneously hypertensive rats (SHRs). The experimental model of T2DM induced by a combination of high fat diet and streptozotocin, decreased exploratory activity and increased the level of carbonylated proteins in selected brain structures in both strains; as well it increased corticosterone level, pain threshold, anxiety-like behavior, and decline short term memory only in SHRs. Losartan treatment alleviated some of the T2DM- induced metabolic complications, abolished the T2DM-induced hypo activity, and normalized the corticosterone level, carbonylated proteins in brain, nociception and memory. Losartan did not exert effect on the anxiety behavior in both strains. We showed that T2DM exerted more pronounced negative effects on the rats with comorbid hypertension as compared to normotensive rats. Overall effects on the studied behavioral parameters are related to decreased exploration of the new environment, increased anxiety-like behavior, and decline in short-term memory. The systemic sub-chronic treatment with an angiotensin AT1 receptor antagonist losartan ameliorated most of these complications.

A15194 INVOLVEMENT OF ENDOTHELIN AND ANGIOTENSIN II IN CHRONIC KIDNEY DISEASE-RELATED ARTERIAL STIFFNESS

Objectives: Increased risk of cardiovascular disease in patients with chronic kidney disease (CKD) has been related to vascular stiffness and isolated systolic hypertension. Using a rat model of CKD with mineral imbalance, we reported that endothelin (ET)A receptor blockade reduced vascular stiffness and hypertension revealing a role for endothelin. This study was designed to investigate whether the protective effect of ETA receptor blockade on vascular stiffness is independent of blood pressure reduction. Methods: CKD was induced in Wistar rats by renal mass ablation and mineral imbalance by a calcium/phosphate-rich diet and vitamin D supplementation (Ca/P/VitD) which increased vascular stiffness. CKD rats given Ca/P/VitD were treated either with the ETA receptor antagonist atrasentan (10 mg/kg/d), the angiotensin AT1 receptor antagonist losartan (25 mg/kg/d) or the combination of hydrochlorothiazide/hydralazine (Hy/Hy; 100 mg/L and 25 mg/L, respectively) for 5 weeks. Hemodynamic parameters were determined by vessels catheterisation in anesthetised animals. Results: Systolic blood pressure and carotid-femoral pulse wave velocity were higher in CKD+Ca/P/VitD rats as compared to CKD control (p < 0.05). Treatment of CKD+Ca/P/VitD rats with atrasentan, losartan and Hy/Hy reduced mean, diastolic and systolic blood pressure (p < 0.05). However, treatment with atrasentan and losartan, but not Hy/Hy, reduced carotid-femoral pulse wave velocity (p < 0.05). Conclusion: The protective effect of ETA and AT1 receptor blockade on vascular stiffness is independent of the blood pressure lowering effect in CKD rats with mineral imbalance. This study reveals a role for both endothéline and angiotensin II in CKD-related vascular stiffness.

α2-Adrenoreceptor Constraint of Catecholamine Release and Blood Pressure Is Enhanced in Female Spontaneously Hypertensive Rats.

α2-adrenoceptors (α2AR) lower central sympathetic output and peripheral catecholamine release, and may therefore prevent sympathetic hyperactivity and hypertension. The α2AR are dysfunctional in male spontaneously hypertensive rats (SHR). Premenopausal females are less hypertensive than males. The purpose of this study was to test if this difference could be explained by functional α2AR in the female SHR. A 15-min tyramine-infusion was used to stimulate norepinephrine release through the re-uptake transporter, consequently preventing re-uptake. Presynaptic control of vesicular release will therefore be reflected as differences in overflow to plasma. The surgical trauma activates secretion of epinephrine, also subjected to α2AR auto-inhibition. Blood pressure was monitored through a femoral artery catheter and cardiac output by ascending aorta flow in 12-14 weeks-old (early hypertension) SHR and normotensive rats (WKY). Total peripheral vascular resistance (TPR) was calculated. Female SHR, unlike male, were close to normotensive. Pre-treatment with none-selective (clonidine) or non-A-selective (ST-91) α2AR agonist reduced, and none-selective α2AR antagonist (L-659,066) increased tyramine-induced norepinephrine overflow in female WKY and SHR. L-659,066 also increased secretion of epinephrine. The L-659,066-induced increase in catecholamine release was further enhanced by additional pre-treatment with ST-91 or angiotensin AT1 receptor antagonist (losartan) in SHR only. L-659,066 eliminated the tyramine-induced rise in TPR in both strains in female rats. Conclusion: α2AR-mediated control of catecholamine release and vascular tension was therefore functional in female SHR, unlike that previously observed in male SHR. Functional α2AR is likely to have a protective function and may explain the lack of hypertension in the young female SHR.

Angiotensinergic neurotransmission in the paraventricular nucleus of the hypothalamus modulates the pressor response to acute restraint stress in rats

We tested the hypothesis that the angiotensinergic neurotransmission, specifically in the paraventricular nucleus of the hypothalamus (PVN), is involved in the cardiovascular modulation during acute restraint stress (RS) in rats. The intravenous pretreatment with the angiotensin AT1 receptor antagonist losartan (5mg/kg) inhibited the pressor response to RS, but did not affect the concomitant RS-evoked tachycardiac response. Because similar effects were observed after the PVN pretreatment with CoCl2, and considering the high density of angiotensin receptors reported in the PVN, we studied the effect of the pretreatment of the PVN with either losartan or the angiotensin-converting enzyme (ACE) inhibitor lisinopril on the RS-evoked cardiovascular response. The bilateral microinjection of losartan (0.5nmol/100nL) or lisinopril (0.5nmol/100nL) into the PVN inhibited the RS-related pressor response without affecting the tachycardiac response, suggesting that the PVN angiotensinergic neurotransmission modulates the vascular component of the stress response. Finally, to exclude the possibility that centrally injected drugs could be leaking to the circulation and acting on peripheral vascular receptors, we tested the effect of the intravenous pretreatment with either losartan (0.5nmol/animal) or lisinopril (0.5nmol/animal), assuming the hypothesis of a total spread of drugs from the CNS to the peripheral circulation. When animals were pretreated with such doses of either losartan or lisinopril, the cardiovascular RS-evoked response was not affected, thus indicating that even if there were a complete leakage of the drug to the periphery, it would not affect the cardiovascular response to RS. This observation favors the idea that the effect of the intravenous injection of 5mg/kg of losartan on the RS-related cardiovascular response would be explained by an action across the blood–brain barrier, possibly in the PVN. In conclusion, the results suggest that an angiotensinergic neurotransmission in the PVN acting on AT1-receptors modulates the vascular component of the RS-evoked cardiovascular response.

Molecular mechanisms of angiotensin II stimulation on aquaporin-2 expression and trafficking

ANG II plays a major role in renal water and sodium regulation. In the immortalized mouse renal collecting duct principal cells (mpkCCD(cl4)) cell line, we treated cells with ANG II and examined aquaporin-2 (AQP2) protein expression, trafficking, and mRNA levels, by immunoblotting, immunofluorescence, and RT-PCR. After 24-h incubation, ANG II-induced AQP2 protein expression was observed at the concentration of 10(-10) M and increased in a dose-dependent manner. ANG II (10(-7) M) increased AQP2 protein expression and mRNA levels at 0.5, 1, 2, 6, and 24 h. Immunofluorescence studies showed that ANG II increased the apical membrane targeting of AQP2 from 30 min to 6 h. Next, the signaling pathways underlying the ANG II-induced AQP2 expression were investigated. The PKC inhibitor Ro 31-8220 (5 × 10(-6) M) and the PKA inhibitor H89 (10(-5) M) blocked ANG II-induced AQP2 expression, respectively. Calmodulin inhibitor W-7 markedly reduced ANG II- and/or dDAVP-stimulated AQP2 expression. ANG II (10(-9) M) and/or dDAVP (10(-10) M) stimulated AQP2 protein levels and cAMP accumulation, which was completely blocked by pretreatment with the vasopressin V2 receptor (V2R) antagonist SR121463B (10(-8) M). Pretreatment with the angiotensin AT(1) receptor (AT1R) antagonist losartan (3 × 10(-6) M) blocked ANG II (10(-9) M)-stimulated AQP2 protein expression and cAMP accumulation, and partially blocked dDAVP (10(-10) M)- and dDAVP+ANG II-induced AQP2 protein expression and cAMP accumulation. In conclusion, ANG II regulates AQP2 protein, trafficking, and gene expression in renal collecting duct principal cells. ANG II-induced AQP2 expression involves cAMP, PKC, PKA, and calmodulin signaling pathways via V2 and AT(1) receptors.

Intracerebroventricular injection of losartan inhibits angiotensin II-sensitive neurons via GABA inputs in the anterior hypothalamic area of rats

Previously, we have demonstrated that pressure-ejected application of angiotensin II and losartan, an angiotensin AT1 receptor antagonist, onto some neurons in the anterior hypothalamic area (AHA) of the rat increases and decreases, respectively, the basal firing rate of the neurons. To investigate possible participation of these AHA neurons in the brain angiotensin system, we examined whether intracerebroventricular injection of the angiotensin AT1 receptor antagonist losartan inhibits the neuronal activity of angiotensin II-sensitive neurons via GABA inputs in the AHA of rats. Intracerebroventricular injection of losartan decreased the firing rate of AHA angiotensin II-sensitive neurons. However, the intracerebroventricular injection of losartan did not affect the increase in firing rate of AHA angiotensin II-sensitive neurons induced by pressure application of angiotensin II onto the same neurons, although losartan similarly injected abolished the increase in firing rate of AHA angiotensin II-sensitive neurons induced by intracerebroventricular injection of angiotensin II. The losartan-induced decrease of unit firing in AHA neurons was abolished by pressure application of the GABAA receptor antagonist bicuculline onto the same neurons. Bicuculline itself did not affect the basal firing rate of AHA neurons. These findings suggest that intracerebroventricular injection of losartan inhibits AHA angiotensin II-sensitive neurons via GABA inputs to the neurons.

Centrally injected angiotensin II trans-synaptically activates angiotensin II-sensitive neurons in the anterior hypothalamic area of rats

Previously, we have demonstrated that pressure-ejected application of angiotensin II onto some neurons in the anterior hypothalamic area (AHA) of rats increases their firing rate. In contrast, pressure application of the angiotensin AT1 receptor antagonist losartan onto AHA neurons blocked the basal firing of the neurons. To investigate possible participation of these AHA neurons in the brain angiotensin system, we examined whether intracerebroventricular injection of angiotensin II results in an activation of angiotensin II-sensitive neurons in the AHA of rats. Intracerebroventricular injection of angiotensin II increased the firing rate of AHA angiotensin II-sensitive neurons. The angiotensin II-induced increase of unit firing in AHA neurons was abolished by pressure application of losartan onto the same neurons. In addition, the angiotensin II-induced increase of firing in AHA neurons was abolished by pressure application of N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W7), a calmodulin inhibitor, onto the same neurons. Pressure application of W7 onto AHA neurons affected neither the basal firing rate nor the increase in unit firing induced by pressure application of angiotensin II onto the same neurons. Intracerebroventricular injection of the cholinergic agonist carbachol did not affect the firing rate of angiotensin II-sensitive neurons in the AHA. These findings suggest that intracerebroventricular injection of angiotensin II activates AHA angiotensin II-sensitive neurons via angiotensinergic inputs to the neurons.

Centrally administered interleukin-1 beta sensitizes to the central pressor action of angiotensin II

The objective of the present study was to find out whether brain vasopressin (AVP) and angiotensin II (Ang II) are involved in pressor response to intracerebroventricular (ICV) infusion of interleukin-1 beta (IL-1β). The experiments were performed on conscious, 12- to 14-week-old Sprague–Dawley rats. Mean arterial blood pressure (MAP) and heart rate (HR) were recorded continuously under baseline conditions and during ICV infusion periods. In the first part of the study, the rats were ICV-infused with one of the following: 0.9% NaCl saline (5 μl/h—control), IL-1β (100 ng/h), angiotensin AT1 receptor antagonist (losartan 10 μg/h), IL-1β together with losartan, V1 receptors antagonist (V1ANT), d(CH2) 5[Tyr(Me) 2,Ala-NH 2 9]AVP, 400 ng/h) or IL-1β together with V1ANT. Saline infusion did not influence MAP, while administration of IL-1β elicited a significant but transient increase in MAP. The pressor response to IL-1β was abolished by losartan but not by V1ANT. On the other hand, combined administration of IL-1β and V1ANT resulted in increase in HR, which was absent during infusion of IL-1β alone. In the second part of the study after ICV pretreatment with IL-1β or 0.9% NaCl (control), the rats received ICV infusion of one of the following: 0.9% NaCl saline, subpressor dose of Ang II (5 ng/15 s) or subpressor dose of AVP (5 ng/15 s). Subpressor doses of Ang II and AVP did not influence MAP and HR in saline-pretreated rats. The same dose of Ang II but not AVP applied in IL-1β-pretreated rats resulted in a significant increase in MAP. The study provides evidence that IL-1β through its action in the brain increases sensitivity to central pressor action of Ang II. Additionally, we found that AVP and in particular V1 receptors do not play important role in the central pressor action of IL-1β, however, they may influence its effect on HR regulation.

Brain microvascular endothelial cell proliferation with angiotensin stimulation and receptor blockade

Aim Hypertension is a major risk factor for stroke. The angiotensin (ANGII) AT1 receptor antagonist losartan (LOS) is a commonly prescribed hypertension medication. AT1 receptor activation stimulates angiogenesis in most tissues, yet chronic in vivo blockade of the AT1 receptor results in angiogenesis in the brain. Since this paradoxical response could be due to alterations in cerebral blood flow rather than direct actions of receptor blockade in the microvessels, this study tested the growth response of human brain microvascular endothelial cells (HBMEC) to ANGII receptor stimulation or blockade in vitro. Methods Cultured HBMEC were exposed to serum-free media (SFM) alone and in the presence of LOS (10 μM), ANGII (1 μM), or both for 24 hours in 96-well plates. Cell density was quantified by CyQUANT (Molecular Probes) cell proliferation assay. Results Average fluorescence increased in cells receiving LOS alone (46,358±2771), and was even greater with ANGII stimulation (59,582 ± 7400) compared to SFM (6,940±168). Results from combined LOS + ANGII stimulation (49,583 ±3197) were not different from LOS treatment alone. Conclusions These data suggest that, unlike in other tissues, AT1 receptor blockade results in brain endothelial cell proliferation. This supports our previous findings that AT1 receptor blockade induces cerebral angiogenesis. It is possible that chronic hypertension therapy using ARBs such as losartan might improve brain blood flow through angiogenesis, potentially protecting high-risk patients from stroke. Supported in part by Frontiers in Physiology Professional Development Fellowship, APS.

Evidence suggesting that angiotensins released not via synaptic inputs are involved in the basal activity of anterior hypothalamic neurons in rats

Previously, we have demonstrated that angiotensin II-sensitive neurons exist in the anterior hypothalamic area (AHA) and that these neurons are tonically activated by endogenous angiotensins in rats. Chemical stimulation of the lateral septal area (LSV) and medial amygdaloid nucleus (MeA), and intracerebroventricular injection of hypertonic saline, activated AHA angiotensin II-sensitive neurons. To investigate mechanisms of the basal activity of AHA angiotensin II-sensitive neurons, we examined the effect of N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W7), a calmodulin inhibitor, applied onto AHA neurons on the basal activity and the stimulus-evoked activation of these neurons. Male Wistar rats were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Microinjections of carbachol into the LSV and corticotropin-releasing factor into the MeA, and intracerebroventricular injection of hypertonic saline, activated AHA angiotensin II-sensitive neurons. These three kinds of injection-induced activations of AHA neurons were abolished by pressure application of W7 onto the same neurons, while the calmodulin inhibitor did not affect the increase in firing of AHA neurons induced by pressure application of angiotensin II onto the same neurons. The pressure application of W7 did not affect the basal activity of AHA angiotensin II-sensitive neurons, whereas the angiotensin AT1 receptor antagonist losartan similarly applied inhibited it. These findings suggest that the basal activity of AHA angiotensin II-sensitive neurons is mediated by angiotensins released not via synaptic inputs.

Increased counteracting effect of NOS and NOS on an α-adrenergic rise in total peripheral vascular resistance in spontaneous hypertensive rats

The hypertension in spontaneous hypertensive rats (SHR) may result from a hyperactive sympathetic nervous system or from insufficient bioactive nitric oxide (NO) due to increased oxidative stress. The present investigation aimed to elucidate the balance between these two systems by studying the ability of NO to oppose an adrenergic rise in total peripheral vascular resistance (TPVR). In anesthetized, open-chest SHR and normotensive controls (WKY) on a respirator, blood pressure was recorded in the femoral artery and cardiac output measured by ascending aorta flow. Tyramine infusion (15 min, intravenously) was used to stimulate neuronal noradrenaline release. Tyramine induced an immediate but transient increase in TPVR, which was 4.5 times greater in SHR. After the non-selective NO synthase (NOS) inhibitor (L-NAME: N(omega)-nitro-L-arginine methyl ester), DeltaTPVRimm was 8.6 and 5.3 times increased in SHR and WKY, respectively, and TPVR remained elevated throughout the infusion period. Addition of alpha1-adrenoceptor antagonist (prazosin+L-NAME) abolished the TPVR response to tyramine. Neuronal NOS inhibitor (7-introindazole) increased DeltaTPVRimm only in SHR (2.1 times), and TPVR remained elevated. Inducible NOS inhibitor (1400W), free radical scavenger (tempol), NAD(P)H oxidase inhibitor (apocynin), angiotensin AT1 receptor antagonist (losartan), and ganglion blocker (hexamethonium) had no effect on the tyramine TPVR response in either strain. DeltaTPVR to hexamethonium, prazosin, and L-NAME were greater in SHR than WKY, and hexamethonium reduced DeltaTPVR to L-NAME in SHR only. The alpha1-adrenoceptor TPVR response to endogenous noradrenaline release was increased in SHR. This was not due to reduced bioavailable NO; on the contrary, NO counteraction was greatly increased, derived from endothelial NOS, with an additional role of neuronal NOS not seen in WKY. An influence of oxidative stress on these responses was not detected in either strain. In addition, a central eNOS sympathoinhibitory component appeared to influence baseline TPVR in SHR.

Angiotensin-converting enzyme inhibition and angiotensin AT1-receptor antagonism equally improve endothelial vasodilator function in l-NAME-induced hypertensive rats

Male Sprague–Dawley rats given Nω-nitro-l-arginine methyl ester (l-NAME) in drinking water for 8 weeks showed: (1) a clear-cut increase in systolic blood pressure; (2) a consistent decrease of endothelial-cell nitric oxide synthase (eNOS) gene expression in aortic tissue; (3) a marked reduction of plasma nitrite/nitrate concentrations; (4) a reduction of the relaxant activity of acetylcholine (ACh, from 10−10 to 10−4 M) on norepinephrine-precontracted aortic rings (reduction by 48±5%); (5) a marked decrease (−58%) of the basal release of 6-keto-prostaglandin F1α (6-keto-PGF1α) from aortic rings. In l-NAME-treated rats, administration in the last 4 weeks of either the angiotensin-converting enzyme (ACE) inhibitor enalapril (10 mg/kg/day in tap water) or the angiotensin AT1-receptor antagonist losartan (10 mg/kg/day in tap water) decreased systolic blood pressure levels, completely restored eNOS mRNA levels in aortic tissue and plasma nitrite/nitrate levels, and allowed a consistent recovery of both the relaxant activity of acetylcholine and the generation of 6-keto-PGF1α. Coadministration of icatibant, a bradykinin B2-receptor antagonist (200 μg/kg/day), with enalapril blunted the stimulatory effect of the ACE inhibitor on eNOS mRNA expression, circulating levels of nitrite/nitrate, the relaxant activity of ACh and the release of 6-keto-PGF1α in l-NAME-treated rats. The generation of 6-keto-PGF1α from aortic rings was also decreased in rats coadministered icatibant with losartan. These findings indicate that (1) the ACE inhibitor enalapril and the angiotensin AT1-receptor blocker losartan are equally effective to reverse NAME-induced endothelial dysfunction; (2) the beneficial effect of enalapril on the endothelial vasodilator function in l-NAME-treated rats is mediated by bradykinin B2-receptor activation; and (3) the enhanced endothelial generation of prostacyclin induced by losartan in l-NAME rats is also mediated by bradykinin B2-receptor activation.

Central injection of hypertonic saline activates angiotensin II-sensitive neurons in the anterior hypothalamic area of rats

We have previously reported that microinjection of angiotensin II into the anterior hypothalamic area (AHA) produces pressor responses and that angiotensin II-sensitive neurons in the AHA are tonically activated by endogenous angiotensins in rats. Central injection of hypertonic saline causes pressor responses via release of angiotensins in brain. In this study, we examined whether angiotensin II-sensitive neurons in the AHA are responsive to intracerebroventricular injection of hypertonic saline and whether endogenous angiotensins in the AHA are involved in the central hypertonic saline-induced pressor response. Male Wistar rats were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Intraventricular injection of hypertonic saline increased the neural activity of angiotensin II-sensitive neurons, whereas pressure application of hypertonic saline onto angiotensin II-sensitive neurons themselves did not affect their neural activities. The intraventricular hypertonic saline-induced increase of unit activity of AHA neurons was inhibited by pressure application of the angiotensin AT1 receptor antagonist losartan onto the same neurons. The hypertonic saline-induced increase of unit firing was also blocked by intraventricular injection of the amiloride-sensitive sodium channel blocker benzamil. In conscious rats, intraventricular injection of hypertonic saline produced pressor responses, and the hypertonic saline-induced pressor response was inhibited by bilateral microinjection of losartan into the AHA. Repeated intraventricular injection of hypertonic saline caused an increase in the release of angiotensins in the AHA of anesthetized rats. These findings indicate that intracerebroventricular injection of hypertonic saline increases neural activity of angiotensin II-sensitive neurons trans-synaptically via endogenous angiotensins in the AHA. In addition, these findings also indicate that the intracerebroventricular injection of hypertonic saline produces a pressor response at least partly via release of angiotensins in the AHA.

Angiotensin AT1 receptor antagonist losartan and the defence reaction in the anaesthetised rat. Effect on the carotid chemoreflex.

Modulation at the level of the nucleus tractus solitarii (NTS) appears to be an effective way of controlling cardiovascular reflexes. Angiotensin II acting on angiotensin AT1 receptors at the central nervous system appears to have an important role in these modulatory processes. The hypothalamic defence area (HDA) is a potential source of descending fibres containing angiotensin II that innervate the NTS. We investigated the effect of AT1 receptor blockade in the NTS on the response to stimulation of HDA in anaesthetised rats treated with the neuromuscular blocking agent pancuronium bromide. The characteristic increase in heart rate, blood pressure and phrenic nerve activity evoked by electrical stimulation of HDA is decreased by the microinjection of the AT1 receptor antagonist losartan into the NTS and the cardiovascular response to carotid body chemical stimulation is also reduced. These results support the hypothesis that AT1 receptors in the NTS play a role in the modulation of cardiovascular reflexes, and modify the influence exerted on the processing of these reflexes by other areas of the central nervous system.

Angiotensin receptor blockade in the anterior hypothalamic area inhibits stress-induced pressor responses in rats

Central angiotensin systems are involved in expression of pressor responses induced by immobilization stress. In this study, we examined whether angiotensin receptors in the anterior hypothalamic area are involved in the pressor response during stress exposure in rats. Intracerebroventricular injections of the angiotensin AT1-receptor antagonist losartan (6.5 and 22 nmol) attenuated pressor responses to immobilization stress dose-dependently. Injections of losartan (0.065 and 0.22 nmol) into the anterior hypothalamic area also suppressed the stress-induced pressor response dose-dependently, whereas intraventricular injection of losartan (2.2 nmol) did not affect it. Immobilization stress caused increases in plasma catecholamine levels. The stress-induced increase of plasma catecholamine levels was also inhibited by angiotensin receptor blockade in the anterior hypothalamic area. The present results suggest that angiotensin receptors in the anterior hypothalamic area are involved in expression of the pressor response and sympathetic activation induced by immobilization stress.

Acute effects of ACE inhibition on coronary endothelial dysfunction.

The prerequisite of atherosclerosis, endothelial dysfunction, is characterised by impaired endothelium-dependent vasodilation caused by the reduced bioavailibility of nitric oxide (NO). In order to assess the role of acute ACE inhibition in this setting, coronary arterial endothelial function was quantified following acute intracoronary administration of the angiotensin-converting enzyme (ACE) inhibitor quinapril. Twenty-one patients with non-limiting coronary artery disease were studied before and after acute intracoronary administration of 10 mg quinapril. Nine patients received pre-treatment with the angiotensin AT(1)-receptor antagonist losartan (2 x 50 mg, p.o.). Coronary cross-sectional diameter was measured via quantitative angiography and microvascular reaction was investigated by intracoronary Doppler flow measurement during intracoronary infusion of 0.1 to 10 micromol/l acetylcholine. Quinapril acutely improved endothelial dysfunction on the macro- as well as the microvascular level. Losartan did not alter macrovascular function but facilitated microvascular endothelial function. Acute quinapril application led to no further improvement of endothelial dysfunction in patients pre-treated with losartan. Acute quinapril infusion improved endothelial function in patients with coronary heart disease. Treatment with the AT(1)-receptor antagonist losartan led to a slight improvement in microvascular endothelial function, but pre-treatment with losartan blunted the vascular effect of quinapril, suggesting that the combination of ACE inhibition and AT(1)-receptor antagonism may not exert a synergistic benefical impact on the coronary vasculature.

Angiotensin II Activates the Proinflammatory Transcription Factor Nuclear Factor-κB in Human Monocytes

The renin-angiotensin system may contribute to the pathogenesis of atherosclerosis. A common feature of all stages of atherosclerosis is inflammation of the vessel wall. The transcription factor nuclear factor-κB (NF-κB) participates in most signaling pathways involved in inflammation. This study therefore examined the effect of angiotensin (ANG) II on NF-κB activation in monocytic cells, a major cellular component of human atheroma, by electrophoretic mobility shift assay. ANG II, like TNFα, caused rapid activation of NF-κB in human mononuclear cells isolated from peripheral blood by Ficoll density gradient. This ANG II effect was blocked by the angiotensin AT1 receptor antagonist losartan. Specificity of ANG II-induced NF-κB activation was ascertained by supershift and competition experiments. Moreover, ANG II stimulated NF-κB activation in human monocytes, but not in lymphocytes from the same preparation. Together, the data demonstrate the ability of the vasoactive peptide ANG II to activate inflammatory pathways in human monocytes.

Central losartan blocks natriuretic, vasopressin, and pressor responses to central hypertonic NaCl in sheep.

This study investigated the effect of intracerebroventricular administration of the angiotensin AT1 receptor antagonist losartan on the natriuresis, pressor effect, and arginine vasopressin (AVP) secretion caused by intracerebroventricular infusion of either ANG II, hypertonic saline, or carbachol. Losartan (1 mg/h) or artificial cerebrospinal fluid (CSF) was infused into the lateral ventricle before, during, and after infusions of either ANG II at 10 microg/h for 1 h, 0.75 mol/l NaCl at 50 microl/min for 20 min, or carbachol at 1.66 microg/min for 15 min. Intracerebroventricular infusions of ANG II, 0.75 mol/l NaCl, or carbachol caused increases in renal Na+ and K+ excretion, arterial pressure, and plasma AVP levels. Increases in arterial pressure, Na+ excretion, and plasma AVP concentration ([AVP]) in response to intracerebroventricular ANG II or intracerebroventricular 0.75 mol/l NaCl were either abolished or attenuated by intracerebroventricular infusion of losartan but not by intracerebroventricular infusion of artificial CSF or intravenous losartan. Intracerebroventricular losartan did not reduce the increase in plasma [AVP] or arterial pressure in response to intracerebroventricular carbachol, but it did attenuate the natriuretic response to intracerebroventricular carbachol. We conclude that an intracerebroventricular dose of losartan (1 mg/h) that inhibits responses to intracerebroventricular ANG II also inhibits vasopressin secretion, natriuresis, and the pressor response to intracerebroventricular hypertonic saline. These results suggest that common neural pathways are involved in the responses induced by intracerebroventricular administration of ANG II and intracerebroventricular hypertonic NaCl. We propose that intracerebroventricular infusion of hypertonic saline activates angiotensinergic pathways in the central nervous system subserving the regulation of fluid and electrolyte balance and arterial pressure in sheep.

Central angiotensin AT1 and muscarinic receptors in ITF expression on intracerebroventricular NaCl.

In the present study, we investigated the expression pattern of the inducible transcription factors (ITF) c-Fos, c-Jun, JunB, JunD, and Krox-24 following intracerebroventricular injections of hyperosmolar saline (0.2, 0.3, and 0.6 M NaCl) and its mediation via angiotensin and/or muscarinic receptors. c-Fos, c-Jun, and Krox-24 were differentially expressed in organum vasculosum laminae terminalis, median preoptic area, subfornical organ (SFO), and paraventricular and supraoptic nuclei. Expression of c-Fos and c-Jun was inhibited by pretreatment with the angiotensin AT1 receptor antagonist losartan (10 and 20 nmol icv) following 0.20 and 0.30 M saline. Pretreatment with atropine (15 nmol icv) inhibited the 0.30 and 0.60 M NaCl-induced expression of c-Fos, c-Jun, and Krox-24 in all areas except the SFO. Coexpression of the ITF with vasopressin and oxytocin, the major effector peptides in osmoregulation, was demonstrated, implying the corresponding genes as putative target genes of the ITF. The results show a highly differentiated ITF expression pattern in the brain mediated by angiotensinergic and muscarinergic pathways, suggesting a finely tuned regulation of target genes.