The physiological role of AT1 receptors in the ventrolateral medulla

Neurons in the rostral and caudal parts of the ventrolateral medulla (VLM) play a pivotal role in the regulation of sympathetic vasomotor activity and blood pressure. Studies in several species, including humans, have shown that these regions contain a high density of AT1 receptors specifically associated with neurons that regulate the sympathetic vasomotor outflow, or the secretion of vasopressin from the hypothalamus. It is well established that specific activation of AT1 receptors by application of exogenous angiotensin II in the rostral and caudal VLM excites sympathoexcitatory and sympathoinhibitory neurons, respectively, but the physiological role of these receptors in the normal synaptic regulation of VLM neurons is not known. In this paper we review studies which have defined the effects of specific activation or blockade of these receptors on cardiovascular function, and discuss what these findings tell us with regard to the physiological role of AT1 receptors in the VLM in the tonic and phasic regulation of sympathetic vasomotor activity and blood pressure.

Recent advances in angiotensin II signaling

Angiotensin II (Ang II)* is a multifunctional hormone that influences the function of cardiovascular cells through a complex series of intracellular signaling events initiated by the interaction of Ang II with AT1 and AT2 receptors. AT1 receptor activation leads to cell growth, vascular contraction, inflammatory responses and salt and water retention, whereas AT2 receptors induce apoptosis, vasodilation and natriuresis. These effects are mediated via complex, interacting signaling pathways involving stimulation of PLC and Ca2+ mobilization; activation of PLD, PLA2, PKC, MAP kinases and NAD(P)H oxidase, and stimulation of gene transcription. In addition, Ang II activates many intracellular tyrosine kinases that play a role in growth signaling and inflammation, such as Src, Pyk2, p130Cas, FAK and JAK/STAT. These events may be direct or indirect via transactivation of tyrosine kinase receptors, including PDGFR, EGFR and IGFR. Ang II induces a multitude of actions in various tissues, and the signaling events following occupancy and activation of Ang receptors are tightly controlled and extremely complex. Alterations of these highly regulated signaling pathways may be pivotal in structural and functional abnormalities that underlie pathological processes in cardiovascular diseases such as cardiac hypertrophy, hypertension and atherosclerosis.

Interaction between paraventricular nucleus and septal area in the control of physiological responses induced by angiotensin II

We determined the effects of losartan (40 nmol) and PD 123319 (40 nmol) (both non-peptides and selective antagonists of the AT1 and AT2 angiotensin receptors, respectively), and [Sar¹, Ala8] angiotensin II (ANG II) (40 nmol) (a non-selective peptide antagonist of angiotensin receptors) injected into the paraventricular nucleus (PVN) on the water and salt appetite, diuresis and natriuresis and mean arterial pressure (MAP) induced by administration of 10 nmol of ANG II into the medial septal area (MSA) of male Holtzman rats weighing 250-300 g. The volume of drug solution injected was 0.5 µl over a period of 10-15 s. The responses were measured over a period of 120 min. ANG II alone injected into the MSA induced an increase in all the above parameters (8.1 ± 1.2, 1.8 ± 0.3, and 17.1 ± 1.0 ml, 217 ± 25 µEq/120 min, and 24 ± 4 mmHg, respectively, N = 10-12) compared with vehicle-treated rats (1.4 ± 0.2, 0.6 ± 0.1, and 9.3 ± 0.5 ml, 47 ± 5 µEq/120 min, and 4.1 ± 0.8 mmHg, respectively, N = 10-14). Pretreatment with losartan and [Sar¹, Ala8] ANG II completely abolished the water and sodium intake, and the pressor increase (0.5 ± 0.2, 1.1 ± 0.2, 0.5 ± 0.2, and 0.8 ± 0.2 ml, and 1.2 ± 3.9, 31 ± 4.6 mmHg, respectively, N = 9-12), whereas losartan blunted the urinary and sodium excretion induced by ANG II (13.9 ± 1.0 ml and 187 ± 10 µEq/120 min, respectively, N = 9). Pretreatment with PD 123319 and [Sar¹, Ala8] ANG II blocked the urinary and sodium excretion (10.7 ± 0.8, 9.8 ± 0.7 ml, and 67 ± 13 and 57 ± 17 µEq/120 min, respectively, N = 9), whereas pretreatment with PD 123319 partially blocked the water and sodium intake, and the MAP induced by ANG II administration (2.3 ± 0.3, 1.1 ± 0.1 ml, and 12 ± 3 mmHg, respectively, N = 9-10). These results suggest the angiotensinergic effect of the MSA on the AT1 and AT2 receptors of the PVN in terms of water and sodium homeostasis and MAP modulation.

Angiotensin II type 1 receptor blockade partially attenuates hypoxia-induced pulmonary hypertension in newborn piglets: relationship with the nitrergic system

The objective of this study was to observe possible interactions between the renin-angiotensin and nitrergic systems in chronic hypoxia-induced pulmonary hypertension in newborn piglets. Thirteen chronically instrumented newborn piglets (6.3 ± 0.9 days; 2369 ± 491 g) were randomly assigned to receive saline (placebo, P) or the AT1 receptor (AT1-R) blocker L-158,809 (L) during 6 days of hypoxia (FiO2 = 0.12). During hypoxia, pulmonary arterial pressure (Ppa; P < 0.0001), pulmonary vascular resistance (PVR; P < 0.02) and the pulmonary to systemic vascular resistance ratio (PVR/SVR; P < 0.05) were significantly attenuated in the L (N = 7) group compared to the P group (N = 6). Western blot analysis of lung proteins showed a significant decrease of endothelial NOS (eNOS) in both P and L animals, and of AT1-R in P animals during hypoxia compared to normoxic animals (C group, N = 5; P < 0.01 for all groups). AT1-R tended to decrease in L animals. Inducible NOS (iNOS) did not differ among P, L, and C animals and iNOS immunohistochemical staining in macrophages was significantly more intense in L than in P animals (P < 0.01). The vascular endothelium showed moderate or strong eNOS and AT1-R staining. Macrophages and pneumocytes showed moderate or strong iNOS and AT1-R staining, but C animals showed weak iNOS and AT1-R staining. Macrophages of L and P animals showed moderate and weak AT2-R staining, respectively, but the endothelium of all groups only showed weak staining. In conclusion, pulmonary hypertension induced by chronic hypoxia in newborn piglets is partially attenuated by AT1-R blockade. We suggest that AT1-R blockade might act through AT2-R and/or Mas receptors and the nitrergic system in the lungs of hypoxemic newborn piglets.

Effects of V-1 and angiotensin receptor subtypes of the paraventricular nucleus on the water intake induced by vasopressin injected into the lateral septal area

In this study, we investigated the influence of d(CH2)(5)-Tyr (Me)-AVP (AAVP) an antagonist of V-1 receptors of arginine(8)-vasopressin (AVP) and the effects of losartan and CGP42112A (selective ligands of the AT, and AT, angiotensin receptors, respectively) injections into the paraventricular nucleus (PVN) on the thirst effects of AVP stimulation of the lateral septal area (LSA). AVP injection into the LSA increased the water intake in a dose-dependent manner. AAVP injected into the PVN produced a dose-dependent reduction of the drinking responses elicited by LSA administration of AVP. Both the AT(1) and AT(2) ligands administered into the PVN elicited a concentration-dependent inhibition in the water intake induced by AVP injected into the LSA, but losartan was more effective than CGP42112A the increase in the AVP response. These results indicate that LSA dipsogenic effects induced by AVP are mediated primarily by PVN AT(1) receptors. However, doses of losartan were more effective when combined with CGP42112A than when given alone, suggesting that the thirst induced by AVP injections into LSA may involve activation of multiple angiotensin II (ANG II) receptor subtypes. These results also suggests that facilitatory effects of AVP on water intake into the LSA are mediated through the activation of V-receptors and that the inhibitory effect requires V-receptors. Based on the present findings, we suggest that the administration of AVP into the LSA may play a role in the PVN control of water control. (C) 2003 Elsevier B.V. All rights reserved.

Expression of renin-angiotensin system signalling compounds in maternal protein-restricted rats: effect on renal sodium excretion and blood pressure

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Interaction between paraventricular nucleus and septal area in the control of physiological responses induced by angiotensin II

We determined the effects of losartan (40 nmol) and PD 123319 (40 nmol) (both non-peptides and selective antagonists of the AT1 and AT2 angiotensin receptors, respectively), and [Sar¹, Ala8] angiotensin II (ANG II) (40 nmol) (a non-selective peptide antagonist of angiotensin receptors) injected into the paraventricular nucleus (PVN) on the water and salt appetite, diuresis and natriuresis and mean arterial pressure (MAP) induced by administration of 10 nmol of ANG II into the medial septal area (MSA) of male Holtzman rats weighing 250-300 g. The volume of drug solution injected was 0.5 µl over a period of 10-15 s. The responses were measured over a period of 120 min. ANG II alone injected into the MSA induced an increase in all the above parameters (8.1 ± 1.2, 1.8 ± 0.3, and 17.1 ± 1.0 ml, 217 ± 25 µEq/120 min, and 24 ± 4 mmHg, respectively, N = 10-12) compared with vehicle-treated rats (1.4 ± 0.2, 0.6 ± 0.1, and 9.3 ± 0.5 ml, 47 ± 5 µEq/120 min, and 4.1 ± 0.8 mmHg, respectively, N = 10-14). Pretreatment with losartan and [Sar¹, Ala8] ANG II completely abolished the water and sodium intake, and the pressor increase (0.5 ± 0.2, 1.1 ± 0.2, 0.5 ± 0.2, and 0.8 ± 0.2 ml, and 1.2 ± 3.9, 31 ± 4.6 mmHg, respectively, N = 9-12), whereas losartan blunted the urinary and sodium excretion induced by ANG II (13.9 ± 1.0 ml and 187 ± 10 µEq/120 min, respectively, N = 9). Pretreatment with PD 123319 and [Sar¹, Ala8] ANG II blocked the urinary and sodium excretion (10.7 ± 0.8, 9.8 ± 0.7 ml, and 67 ± 13 and 57 ± 17 µEq/120 min, respectively, N = 9), whereas pretreatment with PD 123319 partially blocked the water and sodium intake, and the MAP induced by ANG II administration (2.3 ± 0.3, 1.1 ± 0.1 ml, and 12 ± 3 mmHg, respectively, N = 9-10). These results suggest the angiotensinergic effect of the MSA on the AT1 and AT2 receptors of the PVN in terms of water and sodium homeostasis and MAP modulation.

Paraventricular nucleus administration of DuP753 or PD123319 inhibits the effects of angiotensin on water and sodium intake

We determined the effects of DuP753 and PD123319 (both nonpeptides and selective antagonists of the AT(1) and AT(2) angiotensin receptors, respectively), and [Sar(1), Ala(8)]ANG II (a non-selective peptide antagonist of angiotensin receptors) on water and 3%NaCl intake induced by administration of angiotensin II (ANG II) into the paraventricular nucleus (PVN) of sodium-depleted Holtzman rats weighing 250-300 g. Twenty hours before the experiments, the rats were depleted of sodium using furosemide (10 ng/rat, sc). The volume of drug solution injected was 0.5 mu l over a period of 10-15 sec. Water and sodium intake were measured at 0.25, 0.5, 1.0 and 2.0 h. Pre-treatment with DuP753 (14 rats) at a dose of 60 ng completely abolished the water intake induced by injection of 12 ng of ANG II (15 rats) (6.4 +/- 0.6 vs 1.4 +/- 0.3 ml/2 h), where [Sar(1), Ala(8)]ANG II (12 rats) and PD123319 (10 rats) at the doses of 60 ng partially blocked water intake (6.4 +/- 0.6 vs 2.9 +/- 0.5 and 2.7 +/- 0.2 ml/2 h, respectively). In the same animals, [Sar(1), Ala(8)]ANG II, DuP753, and PD123319 blocked the sodium intake induced by ANG II (9.2 +/- 1.6 vs 3.3 +/- 0.6, 1.8 +/- 0.3, and 1.4 +/- 0.2 ml/2 h, respectively). These results indicate that both DuP753 and PD123319, administered into the PVN, blocked the water and sodium intake induced by administration of ANG II into the same site.

Renal effects of angiotensin II receptor subtype 1 and 2-selective ligands injected into the paraventricular nucleus of conscious rats

We determined the effects of losartan and CGP42112A (selective ligands of the AT1 and AT2 angiotensin receptors, respectively) and salarasin (a relatively nonselective angiotensin receptor antagonist) on urinary volume and urinary sodium and potassium excretion induced by administration of angiotensin II (ANG II) into the paraventricular nucleus (PVN) of conscious rats. Both the AT1 and AT2 ligands and salarasin administered in the presence of ANG II elicited a concentration-dependent inhibition of urine excretion, but losartan inhibited only 75% of this response. The IC50 for salarasin, CGP42112A, and losartan was 0.01, 0.05, and 6 nM, respectively. Previous treatment with saralasin, CGP42112A and losartan competitively antagonized the natriuretic responses to PVN administration of ANG II, and the IC50 values were 0.09, 0.48, and 10 nM, respectively. The maximum response to losartan was 65% of that obtained with saralasin. Pretreatment with saralasin, losartan, and CGP42112A injected into the PVN caused shifts to the right of the concentration-response curves, but the losartan concentrations were disproportionately greater compared with salarasin or CGP42112A. The IC50 values were 0.06, 0.5, and 7.0 for salarasin, CGP42112A, and losartan, respectively. These results suggest that both AT1 and AT2 receptor subtypes in the PVN are involved in ANG II-related urine, sodium, and potassium excretion, and that the inhibitory responses to AT2 blockade are predominant. Copyright (C) 1999 Elsevier Science B.V.

Influence of angiotensin II receptor subtypes of the paraventricular nucleus on the physiological responses induced by angiotensin II injection into the medial septal area

Objective - We determined the effects of losartan and PD 123319 (antagonists of the AT1 and AT2 angiotensin receptors, respectively), and [Sar1, Ala8] ANG II (a relatively peptide antagonist of angiotensin receptors) injected into the paraventricular nucleus (PVN) on water and 3% NaCl intake, and the diuretic, natriuretic, and pressor effects induced by administration of angiotensin II (ANG II) into the medial septal area (MSA) of conscious rats. Methods - Holtzman rats were used. Animals were anesthetized with tribromoethanol (20 mg) per 100 grams of body weight, ip. A stainless steel guide cannula was implanted into the MSA and PVN. All drugs were injected in 0.5-μl volumes for 10-15 seconds. Seven days after brain surgery, water and 3% NaCl intake, urine and sodium excretion, and arterial blood pressure were measured. Results - Losartan (40 nmol) and [Sar1, Ala8] ANG II (40 nmol) completely eliminated whereas PD 123319 (40 nmol) partially blocked the increase in water and sodium intake and the increase in arterial blood pressure induced by ANG II (10 nmol) injected into the MSA. The PVN administration of PD 123319 and [Sar1, Ala8] ANG II blocked whereas losartan attenuated the diuresis and natriuresis induced by MSA administration of ANG II. Conclusion - MSA involvement with PVN on water and sodium homeostasis and arterial pressure modulation utilizing ANGII receptors is suggested.

Endothelial and neuronal nitric oxide synthase inhibitors influences angiotensin II pressor effect in central nervous system

The present study investigated the central role of angiotensin II and nitric oxide on arterial blood pressure (MAP) in rats. Losartan and PD123349 AT 1 and AT 2 (selective no peptides antagonists angiotensin receptors), as well as FK 409 (a nitric oxide donor), N W-nitro-L-arginine methyl ester (L-NAME) a constituve nitric oxide synthase inhibitor endothelial (eNOSI) and 7-nitroindazol (7NI) a specific neuronal nitric oxide synthase inhibitor (nNOSI) were used. Holtzman strain, (Rattus norvergicus) weighting 200-250 g were anesthetized with zoletil 50 mg kg -1 (tiletamine chloridrate 125 mg and zolazepan chloridrate 125 mg) into quadriceps muscle anda stainless steel cannula was stereotaxically implanted into their Lateral Ventricle (LV). Controls were injected with a 0.5 μl volume of 0.15 M NaCl. Angiotensin II injected into LV increased MAP (19±3 vs. control 3±1 mm Hg), which is potentiated by prior injection of L-NAME in the same site 26±2 mm Hg. 7NI injected prior to ANG II into LV also potentiated the pressor effect of ANG II but with a higher intensity than L-NAME 32±3 mm Hg. FK 409 inhibited the pressor effect of ANG II (6±1 mm Hg). Losartan injected into LV before ANG II influences the pressor effect of ANG II (8±1 mm Hg). The PD 123319 decreased the pressor effects of ANG II (16±1 mm Hg). Losartan injected simultaneously with FK 409 blocked the pressor effect of ANG II (3±1 mm Hg). L-NAME produced an increase in the pressor effect of ANG II, may be due to local vasoconstriction and all at once by neuronal NOS inhibition but the main effect is of the 7-NIT an specific nNOS inhibitor. The AT 1 antagonist receptors improve basal nitric oxide (NO) production and release. These data suggest the involvement of constitutive and neuronal NOS in the control of arterial blood pressure induced by ANG II centrally, evolving AT 1 receptor-mediated vasoconstriction and AT 2 receptor-mediated vasodilatation. These results were confirmed by the experiment using FK 409. © 2006 Asian Network for Scientific Information.

Effects of nitric oxide and arginine vasopressin on sodium intake induced by central angiotensin II. Part 2

We study the effects of angiotensin receptors antagonists, arginine vasopressin receptor antagonist, L-arginine and L-NAME, injected into supraoptic nucleus of the hypothalamus (SON) on sodium intake induced by the injection of angiotensin II (ANGII). Holtzman rats weighing 200-250 g with canulae implanted into the SON were used. The drugs were injected in 0.5 μL over 30-60 sec. Sodium intake after injection of saline SAL+SAL 0.15 M NaCl was 0.10±00.1 mL 2 h -1; SAL+ANGII injected into SON increased sodium intake. Losartan injected prior to ANGII into SON decreased sodium intake induced by ANGII. PD123319 injected prior to ANGII produced no changes in sodium intake induced by ANGII. AVPA receptor V 1 antagonist injected prior to ANGII reduced sodium intake with a less intensity than losartan. L-arginine injected prior to ANGII decreases sodium intake at a same intensity than losartan. L-NAME injected prior to ANGII potentiated sodium intake induced by ANGII. Losartan injected simultaneously with L-arginine prior to ANGII blocked the natriorexigenic effect of ANGII. These results confirm the importance of SON in the control of sodium intake. Also suggest that both AT 1 and arginine vasopressin V 1 receptors interact with nitrergic pathways within the SON influencing the sodium metabolism by changing sodium appetite induced by ANGII. © 2007 Asian Network for Scientific Information.

Effects of nitric oxide and arginine vasopressin on water intake induced by central angiotensin II. Part 1

We determined the effects of AT 1 and AT 2 (selective no peptides antagonists angiotensin receptors), arginine vasopressin V 1 receptor antagonist as well as L-arginine, a nitric oxide donor and N W-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, injected into supraoptic nucleus (SON) on water and sodium intake induced by the injection of angiotensin II (ANGII). Male Holtzman rats weighing 200-250 g with canulae implanted into the SON were used. The drugs were injected in 0.5 μL over 30-60 sec. The water intake after injection of saline SAL+SAL 0.15 M NaCl was 0.40±0.1 mL 2 h -1; SAL+ANGII increase water intake. Losartan decreased the water intake induced by ANGII. PD123319 injected prior to produce no change in water intake induced by ANGII. AVPA prior to ANGII reduced the water intake with a less intensity than losartan. L-arginine prior to ANGII decreases the water intake at a same intensity than losartan. L-NAME prior to ANGII potentiated the dipsogenic effect of ANGII. Losartan injected simultaneously with L-arginine prior to ANGII blocked the dipsogenic effect of ANGII. These results confirm the importance of SON in the control of water intake and strongly suggest that AT 1, V 1 receptors interact with nitrergic pathways within the SON influencing the dipsogenic effect of ANGII.

The renin-angiotensin system plays a major role in voiding dysfunction of ovariectomized rats

Aims: The renin-angiotensin system (RAS) plays a major role in cardiovascular diseases in postmenopausal women, but little is known about its importance to lower urinary tract symptoms. In this study we have used the model of ovariectomized (OVX) estrogen-deficient rats to investigate the role of RAS in functional and molecular alterations in the urethra and bladder. Main methods: Responses to contractile and relaxant agents in isolated urethra and bladder, as well as cystometry were evaluated in 4-month OVX Sprague-Dawley rats. Angiotensin-converting enzyme activity and Western blotting for AT1/AT2 receptors were examined. Key findings: Cystometric evaluations in OVX rats showed increases in basal pressure, capacity and micturition frequency, as well as decreased voiding pressure. Angiotensin II and phenylephrine produced greater urethral contractions in OVX compared with Sham group. Carbachol-induced bladder contractions were significantly reduced in OVX group. Relaxations of urethra and bladder to sodium nitroprusside and BAY 41-2272 were unaffected by OVX. Angiotensin-converting enzyme activity was 2.6-fold greater (p < 0.05) in urethral tissue of OVX group, whereas enzyme activity in plasma and bladder remained unchanged. Expressions of AT1 and AT2 receptors in the urethra were markedly higher in OVX group. In bladder, AT1 receptors were not detected, whereas AT2 receptor expression was unchanged between groups. 17β-Estradiol replacement (0.1 mg/kg, weekly) or losartan (30 mg/kg/day) largely attenuated most of the alterations seen in OVX group. Significance: Prolonged estrogen deprivation leads to voiding dysfunction and urethral hypercontractility that are associated with increased ACE activity and up-regulation of angiotensin AT1/AT2 receptor in the urethral tissue. © 2013 Elsevier Inc. All rights reserved.

Synergist interaction between angiotensin II and DOCA on sodium and water balance in rats

Blockade of central angiotensin receptors with the specific antagonist [Leu8]-ANG II abolished water ingestion and water and sodium excretion induced by infusion of angiotensin II (ANGII) into the lateral ventricle (LV) of rats. The antagonist reduced but did not suppress the salt appetite induced by ANGII infusion. Subcutaneous injection of deoxycorticosterone acetate (DOCA) caused increases in water and 3% NaCl ingestion and decreases in sodium excretion. When central ANGII infusion was combined with peripheral DOCA, the water intake was similar to that induced by ANGII alone and the ingestion of 3% NaCl was increased, whereas sodium excretion was inhibited. When ANGII was infused alone, a detailed temporal analysis of fluid and sodium balance showed a negative balance similar those saline controls that persisted throughout the experiment. Combined administration of ANGII and DOCA induce significant changes in water and sodium balance. Sodium and water maintained a positive balance through out the 8-h experiment. The data support an interaction of central ANGII and DOCA on sodium intake and water and sodium balance. © 1994.