1
|
Saavedra JM, Ito T, Nishimura Y. Review: The role of angiotensin II AT1-receptors in the regulation of the cerebral blood flow and brain ischaemia. J Renin Angiotensin Aldosterone Syst 2016; 2:S102-S109. [DOI: 10.1177/14703203010020011801] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
Affiliation(s)
| | - Takeshi Ito
- Section on Pharmacology, NIMH, NIH, Bethesda MD 20892,
USA
| | | |
Collapse
|
2
|
Bradykinin antagonist counteracts the acute effect of both angiotensin-converting enzyme inhibition and of angiotensin receptor blockade on the lower limit of autoregulation of cerebral blood flow. J Cereb Blood Flow Metab 2014; 34:467-71. [PMID: 24326391 PMCID: PMC3948123 DOI: 10.1038/jcbfm.2013.219] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Revised: 10/19/2013] [Accepted: 11/13/2013] [Indexed: 01/13/2023]
Abstract
The lower limit of autoregulation of cerebral blood flow (CBF) can be modulated with both angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARB). The influence of bradykinin antagonism on ARB-induced changes was the subject of this study. CBF was measured in Sprague-Dawley rats with laser Doppler technique. The blood pressure was lowered by controlled bleeding. Six groups of rats were studied: a control group and five groups given drugs intravenously: an ACE inhibitor (enalaprilat), an ARB (candesartan), a bradykinin-2 receptor antagonist (Hoe 140), a combination of enalaprilat and Hoe 140, and a combination of candesartan and Hoe 140. In the control group, the lower limit of CBF autoregulation was 54±9 mm Hg (mean±s.d.), with enalaprilat it was 46±6, with candesartan 39±8, with Hoe 140 53±6, with enalaprilat/Hoe 140 52±6, and with candesartan/Hoe 140 50±7. Both enalaprilat and candesartan lowered the lower limit of autoregulation of CBF significantly. The bradykinin antagonist abolished not only the effect of the ACE inhibitor but surprisingly also the effect of the ARB on the lower limit of CBF autoregulation, the latter suggesting an effect on intravascular bradykinin.
Collapse
|
3
|
|
4
|
Edvinsson L. Cerebrovascular Angiotensin AT1 Receptor Regulation in Cerebral Ischemia. Trends Cardiovasc Med 2008; 18:98-103. [DOI: 10.1016/j.tcm.2008.01.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/06/2007] [Revised: 01/20/2008] [Accepted: 01/25/2008] [Indexed: 10/22/2022]
|
5
|
Hodges JC. Overview Cardiovascular & Renal: Angiotensin antagonists: agents that interact with the AT2 receptor and their potential therapeutic utilities. Expert Opin Ther Pat 2008. [DOI: 10.1517/13543776.4.11.1325] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
|
6
|
Takada J, Ibayashi S, Ooboshi H, Ago T, Ishikawa E, Kamouchi M, Kitazono T, Iida M. Valsartan improves the lower limit of cerebral autoregulation in rats. Hypertens Res 2007; 29:621-6. [PMID: 17137218 DOI: 10.1291/hypres.29.621] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The effects of angiotensin II type 1 receptor blockers (ARBs) on cerebral blood flow (CBF) autoregulation have not been fully clarified. Thus, we examined the acute effect of valsartan, the most selective ARB, on CBF autoregulation in spontaneously hypertensive rats. Intravenous administration of valsartan (0.3 mg/kg) reduced the mean arterial pressure (MAP) from 184+/-5 (mean+/-SEM) to 174+/-5 mmHg (p<0.001) without affecting CBF as measured by laser-Doppler flowmetry. The lower limit of CBF autoregulation (the MAP at which the CBF was 80% of the baseline value) in the valsartan-treated group (122+/-3 mmHg) was significantly lower than that in the control group (135+/-4 mmHg, p<0.05). Reverse transcribed-polymerase chain reaction and immunohistochemical staining demonstrated that both angiotensin II type 2 receptors and angiotensin II type 1 receptors (AT1Rs) were expressed in endothelial and smooth muscle cells of the rat cerebral arteries. These results suggest that specific inhibition of AT1Rs in the cerebral circulation causes the leftward shift of the lower limit of autoregulation.
Collapse
Affiliation(s)
- Junichi Takada
- Department of Medicine and Clinical Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | | | | | | | | | | | | | | |
Collapse
|
7
|
Pedersen TF, Paulson OB, Nielsen AH, Strandgaard S. Effect of nephrectomy and captopril on autoregulation of cerebral blood flow in rats. Am J Physiol Heart Circ Physiol 2003; 285:H1097-104. [PMID: 12750060 DOI: 10.1152/ajpheart.00098.2003] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present study investigated the effect of circulating versus locally present renin on cerebral blood flow (CBF) and its autoregulation in rats. CBF was measured repetitively with the intracarotid 133Xe injection method, whereas blood pressure was lowered to determine the lower limit of autoregulation. To remove renin from the blood, rats were bilaterally nephrectomized and kept alive with peritoneal dialysis for 48 h. Five groups of animals were studied: 1) nephrectomized dialyzed rats, 2) nephrectomized dialyzed rats given a single intravenous dose of the angiotensin-converting enzyme inhibitor captopril (10 mg/kg), 3) sham nephrectomized and dialyzed rats, 4) rats receiving drugs as dialyzed rats but no surgery, and 5) rats given the same diet as the other groups but no drugs and no surgery. Baseline blood pressure was significantly lower in nephrectomized rats compared with controls. Nephrectomy, captopril, sham operation, or dialysis did not influence baseline CBF. The lower limit of CBF autoregulation was significantly lower in nephrectomized (53 +/- 4 mmHg) and sham-operated (58 +/- 4 mmHg) rats compared with diet control rats (78 +/- 3 mmHg). Captopril significantly decreased the lower limit in nephrectomized rats (35 +/- 2 mmHg). Thus removal of circulating renin caused no change in the lower limit of autoregulation. By contrast, captopril lowered the lower limit even in the absence of circulating renin and hence appeared to exert its effect on components of the renin-angiotensin system in the cerebral resistance vessel walls.
Collapse
Affiliation(s)
- Trine Fischer Pedersen
- Neurobiology Research Unit 9201, Rigshospitalet, Copenhagen University Hospital, 9 Blegdamsvej, DK-2100 Copenhagen, Denmark
| | | | | | | |
Collapse
|
8
|
Estrup TM, Paulson OB, Strandgaard S. No effect of angiotensin II AT(2)-receptor antagonist PD 123319 on cerebral blood flow autoregulation. J Renin Angiotensin Aldosterone Syst 2001; 2:188-92. [PMID: 11881121 DOI: 10.3317/jraas.2001.026] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Blockade of the renin-angiotensin system with angiotensin-converting enzyme inhibitors (ACE-I) or angiotensin AT1-receptor antagonists shift the limits of autoregulation of cerebral blood flow (CBF) towards lower blood pressure (BP). The role of AT2-receptors in the regulation of the cerebral circulation is uncertain. Hence, the present study investigated the effect on CBF autoregulation of blocking of angiotensin AT2-receptors with PD 123319 in spontaneously hypertensive rats (SHR). Anaesthetised and ventilated SHR were given PD 123319, 0.36 mg/kg/min, intravenously, and compared with a control group. CBF was measured by the intracarotid 133xenon injection method and BP was raised by noradrenaline infusion and lowered by controlled haemorrhage in separate groups of rats. The limits of autoregulation were determined by computed least-sum-of-squares analysis. PD 123319 did not influence baseline CBF, but resulted in a minor BP decrease (10 control and 10 treated rats). The lower limit of CBF autoregulation (eight treated and eight control) as well as the upper limit of CBF autoregulation (eight treated and eight control) were not significantly different in PD 123319 and control animals (lower limit treated 102+/-4 mmHg and control 94+/-4; NS, and upper limit treated 171 +/- 10 mmHg and control 162+/-7; NS). These findings indicate that acute AT2-receptor blockade does not influence CBF autoregularion.
Collapse
Affiliation(s)
- T M Estrup
- Neurobiology Research Unit, Rigshospitalet, Copenhagen, Denmark
| | | | | |
Collapse
|
9
|
Affiliation(s)
- M J Robertson
- Astra Charnwood, Loughborough, Leicestershire, England
| |
Collapse
|
10
|
Abstract
In mammalian brain, angiotensin II AT1 and AT2 receptor subtypes are apparently expressed only in neurons and not in glia. AT1 and AT2 receptor subtypes are sometimes closely associated, but apparently expressed in different neurons. Brain AT1/AT2 interactions may occur in selective cases as inter-neuron cross talk. There are two AT1 isoforms in rodents. AT1A, which predominates, and AT1B. There are also important inter-species differences in receptor expression. Relative lack of amino acid conservation in the gerbil gAT1A receptor substantially decreases affinity for the AT1 antagonists. AT1 receptors are expressed in brain areas regulating autonomic and hormonal responses. AT1A receptors are heterogeneously regulated in a number of experimental conditions. In specific areas, AT1A receptors are not normally expressed, but are induced under influence of reproductive hormones in dopaminergic neurons. There are AT1 and AT2 receptors also in areas related to limbic, sensory and motor functions and their expression is developmentally regulated. A picture is emerging of widespread, neuronally localized, heterogeneously regulated, closely associated brain angiotensin receptor subtypes, modulating multiple functions including neuroendocrine and autonomic responses, stress, cerebrovascular flow, and perhaps brain maturation, neuronal plasticity, memory and behavior.
Collapse
Affiliation(s)
- J M Saavedra
- Section on Pharmacology, National Institute of Mental Health, Bethesda, MD 20892, USA.
| |
Collapse
|
11
|
Abstract
Cardiac muscle must maintain a continuous balance between its energy supply and work performed. An important mechanism involved in achievement of this balance is cross talk via chemical signals between cardiac myocytes and the cardiac muscle vascular system. This has been demonstrated by incubating isolated cardiac myocytes in different concentrations of oxygen and then assaying the conditioned media for vasoactive substances on isolated aortic rings and small-resistance arteries. With increasing oxygen concentrations above 6%, cardiac myocytes produce increasing amounts of angiotensin I, which is converted to angiotensin II by the blood vessel. The angiotensin II stimulates vascular endothelial cells to secrete endothelin and increase vascular tone. Below 6% oxygen, cardiac myocytes secrete adenosine, which acts directly on vascular smooth muscle to block the effect of alpha-adrenergic agonists and reduce vascular tone. In an intact heart, the net effect of these 2 regulatory systems would be the maintenance of oxygen concentration within a narrow range at the cardiac myocytes. By acting as oxygen sensors, cardiac myocytes modulate vascular tone according to the needs of the myocytes and reduce potential problems of hypoxia and extensive formation of reactive oxygen species.
Collapse
Affiliation(s)
- S Winegrad
- Department of Physiology, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6085, USA.
| | | | | | | |
Collapse
|
12
|
Affiliation(s)
- J M Saavedra
- Section on Pharmacology, National Institute of Mental Health, Bethesda, Maryland 20892-1264, USA.
| | | |
Collapse
|
13
|
Nuyt AM, Lenkei Z, Palkovits M, Corvol P, Llorens-Cort�s C. Ontogeny of angiotensin II type 2 receptor mRNA expression in fetal and neonatal rat brain. J Comp Neurol 1999. [DOI: 10.1002/(sici)1096-9861(19990503)407:2<193::aid-cne4>3.0.co;2-j] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
|
14
|
Gelband CH, Sumners C, Lu D, Raizada MK. Angiotensin receptors and norepinephrine neuromodulation: implications of functional coupling. REGULATORY PEPTIDES 1998; 73:141-7. [PMID: 9556076 DOI: 10.1016/s0167-0115(97)11050-3] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The objective of this review is to examine the role of neuronal angiotensin II (Ang II) receptors in vitro. Two types of G protein-coupled Ang II receptors have been identified in cardiovascularly relevant areas of the brain: the AT1 and the AT2. We have utilized neurons in culture to study the signaling mechanisms of AT1 and AT2 receptors. Neuronal AT1 receptors are involved in norepinephrine (NE) neuromodulation. NE neuromodulation can be either evoked or enhanced. Evoked NE neuromodulation involves AT1 receptor-mediated, losartan-dependent, rapid NE release, inhibition of K+ channels and stimulation of Ca2+ channels. AT1 receptor-mediated enhanced NE neuromodulation involves the Ras-Raf-MAP kinase cascade and ultimately leads to an increase in NE transporter, tyrosine hydroxylase and dopamine beta-hydroxylase mRNA transcription. Neuronal AT2 receptors signal via a Gi protein and are coupled to activation of PP2A and PLA2 and stimulation of K+ channels. Finally, putative cross-talk pathways between AT1 and AT2 receptors will be discussed.
Collapse
Affiliation(s)
- C H Gelband
- Department of Physiology, College of Medicine, University of Florida, Gainesville 32610, USA
| | | | | | | |
Collapse
|
15
|
Gelband CH, Sumners C, Lu D, Raizada MK. Angiotensin receptors and norepinephrine neuromodulation: implications of functional coupling. REGULATORY PEPTIDES 1997; 72:139-45. [PMID: 9652973 DOI: 10.1016/s0167-0115(97)01050-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The objective of this review is to examine the role of neuronal angiotensin II (Ang II) receptors in vitro. Two types of G protein-coupled Ang II receptors have been identified in cardiovascularly relevant areas of the brain: the AT1 and the AT2. We have utilized neurons in culture to study the signaling mechanisms of AT1 and AT2 receptors. Neuronal AT1 receptors are involved in norepinephrine (NE) neuromodulation. NE neuromodulation can be either evoked or enhanced. Evoked NE neuromodulation involves AT1 receptor-mediated, losartan-dependent, rapid NE release, inhibition of K+ channels and stimulation of Ca2+ channels. AT1 receptor-mediated enhanced NE neuromodulation involves the Ras-Raf-MAP kinase cascade and ultimately leads to an increase in NE transporter, tyrosine hydroxylase and dopamine beta-hydroxylase mRNA transcription. Neuronal AT2 receptors signal via a Gi protein and are coupled to activation of PP2A and PLA2 and stimulation of K+ channels. Finally, putative cross-talk pathways between AT1 and AT2 receptors will be discussed.
Collapse
MESH Headings
- Animals
- Brain/cytology
- Brain/drug effects
- Brain/enzymology
- Coculture Techniques
- Gene Expression Regulation, Enzymologic/drug effects
- Gene Expression Regulation, Enzymologic/genetics
- Humans
- Mixed Function Oxygenases/genetics
- Mixed Function Oxygenases/metabolism
- Neurons/drug effects
- Neurons/metabolism
- Norepinephrine/metabolism
- Norepinephrine/pharmacology
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Receptor, Angiotensin, Type 1
- Receptor, Angiotensin, Type 2
- Receptors, Angiotensin/drug effects
- Receptors, Angiotensin/genetics
- Receptors, Angiotensin/metabolism
- Signal Transduction/drug effects
- Signal Transduction/genetics
- Sympathomimetics/metabolism
- Sympathomimetics/pharmacology
- Synaptic Transmission/drug effects
- Synaptic Transmission/physiology
Collapse
Affiliation(s)
- C H Gelband
- Department of Physiology, College of Medicine, University of Florida, Gainesville 32610, USA
| | | | | | | |
Collapse
|
16
|
Merabet L, de Gasparo M, Casanova C. Dose-dependent inhibitory effects of angiotensin II on visual responses of the rat superior colliculus: AT1 and AT2 receptor contributions. Neuropeptides 1997; 31:469-81. [PMID: 9413025 DOI: 10.1016/s0143-4179(97)90042-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Angiotensin II (Ang II) has traditionally been regarded as a peripherally circulating and acting hormone involved in fluid homeostasis and blood pressure regulation. With the rather recent localization of Ang II receptors within the mammalian brain, renewed interest has emerged in the hope of elucidating the central impact and function of this hormone. One region that has been clearly demonstrated to express Ang II receptors is the superior colliculus (SC). This mesencephalic structure plays an important role in sensory visuomotor integration. Receptors for Ang II (of both the AT1 and AT2 subtypes) have been localized within the superficial layers of this structure, i.e. the areas that are visually responsive. In the hopes of characterizing the role of Ang II in the SC, we have attempted to physiologically activate these receptors in vivo and observe the effects of Ang II on visually evoked responses. In the attempt to identify the receptor subtype(s) responsible in mediating these effects, Ang II was injected concomitantly with selective receptor ligands. Experiments were performed on adult rats prepared in classical fashion for electrophysiological studies. Through microinjection of Ang II, and the simultaneous recording of visually evoked potentials to flash stimulation, we have observed that this peptide yields a strong suppressive effect on visual neuronal activity. By injecting Ang II at various concentrations (10(-3)-10(-10) M), we have further observed that the effects of this peptide express a dose-related dependency. Injection of Ang II in progressively more ventral layers yielded less pronounced effects, demonstrating physiologically the discrete localization of these receptors in the stratum griseum superficiale. Coinjection of Ang II with Losartan yielded a near complete blockade of Ang II suppressive effects, suggesting that AT1 receptors play a prominent role in mediating these responses. However, coinjection of Ang II with PD 123,319 yielded a slight, yet significant partial blockade. Coinjection of Ang II with both the AT1 and AT2 receptor antagonists yielded a complete blockade of the Ang II effect. Finally, some of the results suggest that the AT2 receptor ligand CGP 42,112 may possess agonist properties. Taken together, these findings suggest that the AT1 receptor is predominantly involved in mediating Ang II responses in the SC and there also appears to be some indication of AT2 receptor involvement. However, the underlying mechanisms (such as receptor interactions), the exact specificity of the ligands used, and the possibility of other receptor subtype implication have yet to be explored fully.
Collapse
Affiliation(s)
- L Merabet
- Département d'ophtalmologie, Faculté de médecine, Université de Sherbrooke, Québec, Canada
| | | | | |
Collapse
|
17
|
Broughton CM, Sherrington P, Pender NT, Clark RE. Molecular status of individual CFU-GM colonies derived from chemotherapy-mobilised peripheral blood stem cells in chronic myeloid leukaemia. Genes Chromosomes Cancer 1997. [DOI: 10.1002/(sici)1098-2264(199704)18:4<292::aid-gcc7>3.0.co;2-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
|
18
|
Kramár EA, Harding JW, Wright JW. Angiotensin II- and IV-induced changes in cerebral blood flow. Roles of AT1, AT2, and AT4 receptor subtypes. REGULATORY PEPTIDES 1997; 68:131-8. [PMID: 9110385 DOI: 10.1016/s0167-0115(96)02116-7] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Our laboratory has previously reported the discovery of a unique angiotensin binding site (termed AT4) specific for angiotensin IV (AngIV) in cultured vascular endothelial and smooth muscle cells. The present investigation employed laser-Doppler flowmetry to examine the effect of angiotensin II (AngII) and AngIV stimulation of these receptors on cerebral microcirculation in anesthetized Sprague-Dawley rats. Internal carotid artery infusion of AngII at a low dose (0.1 pmol min-1) revealed a 23% reduction in cerebral blood flow (CBF), while the infusion of AngIV increased CBF in a dose-dependent fashion with the highest dose (100 pmol min-1) resulting in an elevation of 30%. In a second experiment separate groups of rats were pre-treated with the AT1 receptor subtype antagonist DuP 753 (Losartan), the AT2 receptor subtype antagonist PD123177, or a newly synthesized AT4 receptor subtype antagonist Divalinal-AngIV (Divalinal), followed by AngII or AngIV for the purpose of determining which angiotensin receptor subtype is responsible for mediating these AngII- and AngIV-induced responses. Pre-treatment with Losartan completely blocked subsequent AngII-induced reductions in CBF, while both PD123177 and Divalinal failed to inhibit this response. In contrast, significant increases in CBF were measured due to AngIV stimulation following pre-treatment with Losartan and PD 123177, while Divalinal abolished this AngIV-induced response. These results suggest that AngII and IV play opposite roles in cerebral microcirculation, i.e., the AT1 receptor subtype mediates AngII-induced reductions in CBF, while the AT4 receptor subtype regulates increases in CBF.
Collapse
Affiliation(s)
- E A Kramár
- Department of Psychology, Washington State University, Pullman 99164-4820, USA
| | | | | |
Collapse
|
19
|
Liénard F, Thornton SN, Martial FP, Mousseau MC, Nicolaïdis S. Angiotensin II receptor subtype antagonists can both stimulate and inhibit salt appetite in rats. REGULATORY PEPTIDES 1996; 66:87-94. [PMID: 8899899 DOI: 10.1016/0167-0115(96)00061-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
In urethane-anaesthetised male Wistar rats iontophoretic application of the angiotensin II (Ang II) type 1 (AT-1) receptor specific nonpeptide antagonist losartan in the septo-preoptic continuum can produce neuronal excitation of short- and long-term duration which has been interpreted as removal of tonic Ang II-induced inhibition. Mineralocorticoid pretreatment, which increases neuronal sensitivity to Ang II to enhance salt appetite, also removes this losartan-induced long-term excitation. These results suggested steroid modulation of the AT-1 receptor and a complex involvement of Ang II in salt appetite. To investigate the role of the inhibitory action of central Ang II on salt appetite, we gave intracerebroventicular injections of a single, low dose (10 ng) of losartan in normal euhydrated rats and this produced, paradoxically, a progressive increase in salt intake (1.6 +/- 0.3 ml/day to 3.5 +/- 0.9 ml/day, n = 15, P < 0.05). Treatment of these salt enhanced rats with DOCA (0.5 mg/day, s.c., for 3 days) further increased the salt appetite, but then a second i.c.v. injection of the same dose of losartan significantly inhibited the enhanced salt appetite (4.7 +/- 0.7 to 1.3 +/- 0.4, n = 9, P < 0.05). These results provide evidence for a complex action of Ang II on the At-1 receptor mediating the generation of salt appetite that appears to involve either at least two functional subtypes of this AT-1 receptor, as already suggested by previous electrophysiological experiments, or one AT-1 receptor with several activation states.
Collapse
Affiliation(s)
- F Liénard
- Centre National de la Recherche Scientifique, Collège de France, Paris, France
| | | | | | | | | |
Collapse
|
20
|
Viswanathan M, Jöhren O, de Oliveira M, Saavedra JM. Increased non-angiotensin II [125I]CGP 42112 binding in rat carotid artery after balloon injury. Peptides 1996; 17:695-9. [PMID: 8804082 DOI: 10.1016/0196-9781(96)00064-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
In this study, [125I]CGP 42112, a ligand of high affinity and selectivity for the angiotensin II AT2 receptor, was used to detect and quantify a non-angiotensin II binding site in the balloon-injured carotid artery of the rat. The amount of [125I]CGP 42112 binding was significantly enhanced in the adventitia of the injured arteries. Localization of the binding site using emulsion autoradiography and immunocytochemistry suggests that the binding sites may be expressed by macrophages in the inflamed tissue surrounding the injured artery.
Collapse
Affiliation(s)
- M Viswanathan
- Section on Pharmacology, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892-1514, USA
| | | | | | | |
Collapse
|
21
|
Fluharty SJ, Reagan LP, Yee DK. The angiotensin type 1 and type 2 receptor families. Siblings or cousins? ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1995; 377:193-215. [PMID: 7484423 DOI: 10.1007/978-1-4899-0952-7_11] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The diverse actions of angiotensin II (AngII) are mediated by cell surface receptors. Molecular cloning techniques have identified two distinct subtypes of AngII receptors referred to as AT1 and AT2. It is now well accepted that multiple forms of the AT1 receptor exist, but similar diversity of the AT2 subtype has not been conclusively demonstrated. Nonetheless, several converging lines of evidence do suggest that multiple AT2 receptors may be present in brain and cultured neuron-like cells lines. For instance, some AT2 receptors are regulated by guanine nucleotides and sulfhydryl-reducing agents, whereas others are insensitive. AT2 receptor populations also exhibit differing pharmacological profiles particularly with respect to their affinity for peptidic and non-peptidic ligands. Moreover, a recently developed anti-AT2 polyclonal antisera reveals a unique pattern of immunohistochemical staining in brain and it does not immunoreact with the recently cloned AT2 receptor. Collectively, these results support the hypothesis of multiple AT2 receptors at least within the CNS. Future studies should reveal whether these putative AT2 receptor subtypes result from unique genes or cell-specific post-translational modifications of a single gene product.
Collapse
Affiliation(s)
- S J Fluharty
- Department of Animal Biology, University of Pennsylvania, Philadelphia, USA
| | | | | |
Collapse
|
22
|
Näveri L, Strömberg C, Saavedra JM. Angiotensin IV reverses the acute cerebral blood flow reduction after experimental subarachnoid hemorrhage in the rat. J Cereb Blood Flow Metab 1994; 14:1096-9. [PMID: 7523429 DOI: 10.1038/jcbfm.1994.143] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The effect of angiotensin (ANG) IV on CBF after experimental subarachnoid hemorrhage (SAH) was studied in rats using laser-Doppler flowmetry. ANG IV (1 microgram/kg/min i.v.) or saline treatments were started 20 min after SAH. ANG IV increased CBF (from 45 to 84% of baseline) by 60 min. In the saline group, CBF remained low (51%). Pretreatment with the specific ANG II antagonist Sar1, Ile8-ANG II did not antagonize ANG IV. Determination of nitric oxide synthase (NOS) activity in vitro or inhibition of NOS in vivo did not support a role for NO in the action of ANG IV.
Collapse
Affiliation(s)
- L Näveri
- Section on Pharmacology, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892
| | | | | |
Collapse
|
23
|
Näveri L, Strömberg C, Saavedra JM. Angiotensin II AT2 receptor stimulation increases cerebrovascular resistance during hemorrhagic hypotension in rats. REGULATORY PEPTIDES 1994; 52:21-9. [PMID: 7972928 DOI: 10.1016/0167-0115(94)90017-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The effects of the angiotensin II (ANG II) AT2 ligand PD 123319 and the AT1 antagonist losartan on cerebral blood flow (CBF) were studied during hemorrhagic hypotension in anesthetized rats using laser-Doppler flowmetry. In the control group CBF remained stable when mean arterial blood pressure (MABP) was lowered from 84 mmHg (baseline) to 45 mmHg, whereafter there was a pressure dependent decrease in CBF indicating inadequacy of autoregulation. Cerebrovascular resistance (CVR) was reduced until MABP 40 mmHg, where a maximum dilation was reached. PD 123319 dose-dependently (3-30 mg/kg i.v.) increased CVR through all blood pressures. Losartan 3 mg/kg i.v. had an effect similar to PD 123319. Selective stimulation of AT2 receptors with intravenous ANG II infusion, in the presence of AT1 receptor blockade by losartan, also increased CVR. As a result, reduced CBF was seen in the treatment groups. The effects of ANG II and PD 123319 30 mg/kg were antagonized by the nonselective ANG II antagonist Sar1,Ile8-ANG II (4 micrograms/kg/min i.v.). None of the treatments affected baseline CBF. The results confirm that ANG II contributes to cerebrovascular resistance and participates in the regulation of CBF apparently through AT2 receptors.
Collapse
Affiliation(s)
- L Näveri
- Section on Pharmacology, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892
| | | | | |
Collapse
|