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      Participation of hepatic α/β-adrenoceptors and AT 1 receptors in glucose release and portal hypertensive response induced by adrenaline or angiotensin II

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          Abstract

          It has been previously demonstrated that the hemodynamic effect induced by angiotensin II (AII) in the liver was completely abolished by losartan while glucose release was partially affected by losartan. Angiotensin II type 1 (AT 1) and adrenergic (∝1- and β-) receptors (AR) belong to the G-proteins superfamily, which signaling promote glycogen breakdown and glucose release. Interactive relationship between AR and AT 1-R was shown after blockade of these receptors with specific antagonists. The isolated perfused rat liver was used to study hemodynamic and metabolic responses induced by AII and adrenaline (Adr) in the presence of AT 1 (losartan) and ∝1-AR and β-AR antagonists (prazosin and propranolol). All antagonists diminished the hemodynamic response induced by Adr. Losartan abolished hemodynamic response induced by AII, and AR antagonists had no effect when used alone. When combined, the antagonists caused a decrease in the hemodynamic response. The metabolic response induced by Adr was mainly mediated by ∝ 1-AR. A significant decrease in the hemodynamic response induced by Adr caused by losartan confirmed the participation of AT 1-R. The metabolic response induced by AII was impaired by propranolol, indicating the participation of β-AR. When both ARs were blocked, the hemodynamic and metabolic responses were impaired in a cumulative effect. These results suggested that both ARs might be responsible for AII effects. This possible cross-talk between β-AR and AT 1-R signaling in the hepatocytes has yet to be investigated and should be considered in the design of specific drugs.

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          Vascular adrenoceptors: an update.

          The total and regional peripheral resistance and capacitance of the vascular system is regulated by the sympathetic nervous system, which influences the vasculature mainly through changes in the release of catecholamines from both the sympathetic nerve terminals and the adrenal medulla. The knowledge of the targets for noradrenaline and adrenaline, the main endogenous catecholamines mediating that influence, has recently been greatly expanded. From two types of adrenoceptors (alpha and beta), we have now nine subtypes (alpha1A, alpha1B, alpha1D, alpha2A/D, alpha2B, alpha2A/D, beta1, beta2, and beta3) and two other candidates (alpha1L and beta4), which may be conformational states of alpha1A and beta1-adrenoceptors, respectively. The vascular endothelium is now known to be more than a pure anatomical entity, which smoothly contacts the blood and forms a passive barrier against plasma lipids. Instead, the endothelium is an important organ possessing at least five different adrenoceptor subtypes (alpha2A/D, alpha2C, beta1, beta2, and beta3), which either directly or through the release of nitric oxide actively participate in the regulation of the vascular tone. The availability of transgenic models has resulted in a stepwise progression toward the identification of the role of each adrenoceptor subtype in the regulation of blood pressure and fine-tuning of blood supply to the different organs: alpha2A/D-adrenoceptors are involved in the central control of blood pressure; alpha1-(primarily) and alpha2B-adrenoceptors (secondarily) contribute to the peripheral regulation of vascular tone; and alpha2A/D- and alpha2C-adrenoceptors modulate transmitter release. The increased knowledge on the involvement of vascular adrenoceptors in many diseases like Raynaud's, scleroderma, several neurological degenerative diseases (familial amyloidotic polyneuropathy, Parkinson disease, multiple-system atrophy), some kinds of hypertension, etc., will contribute to new and better therapeutic approaches.
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            Effects of Citrus aurantium (Bitter Orange) Fruit Extracts and p -Synephrine on Metabolic Fluxes in the Rat Liver

            The fruit extracts of Citrus aurantium (bitter orange) are traditionally used as weight-loss products and as appetite supressants. An important fruit component is p-synephrine, which is structurally similar to the adrenergic agents. Weight-loss and adrenergic actions are always related to metabolic changes and this work was designed to investigate a possible action of the C. aurantium extract on liver metabolism. The isolated perfused rat liver was used to measure catabolic and anabolic pathways, including oxygen uptake and perfusion pressure. The C. aurantium extract and p-synephrine increased glycogenolysis, glycolysis, oxygen uptake and perfusion pressure. These changes were partly sensitive to α- and β-adrenergic antagonists. p-Synephrine (200 μM) produced an increase in glucose output that was only 15% smaller than the increment caused by the extract containing 196 μM p-synephrine. At low concentrations the C. aurantium extract tended to increase gluconeogenesis, but at high concentrations it was inhibitory, opposite to what happened with p-synephrine. The action of the C. aurantium extract on liver metabolism is similar to the well known actions of adrenergic agents and can be partly attributed to its content in p-synephrine. Many of these actions are catabolic and compatible with the weight-loss effects usually attributed to C. aurantium.
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              Influence of sympathetic and AT-receptor blockade on angiotensin II and adrenergic agonist-induced renal vasoconstrictions in spontaneously hypertensive rats.

              This study investigated the influence of angiotensin II (Ang II) receptor and adrenergic blockade on the renal vasoconstrictions caused by Ang II and adrenergic agonists in spontaneously hypertensive rats (SHR). Forty-eight SHR were subjected to 7 days of losartan (10 mg kg(-1) day(-1) p.o.), carvedilol (5 mg kg(-1) day(-1) p.o.) or losartan + carvedilol (10 mg kg(-1) day(-1) + 5 mg kg(-1) day(-1) p.o.). On day 8, the rats were anaesthetized and renal vasoconstrictor experiments performed. One group of rats underwent acute unilateral renal denervation. There were significant (P < 0.05) reductions in the renal vasoconstrictor responses to noradrenaline, phenylephrine, methoxamine and Ang II after losartan and carvedilol treatments compared with that in untreated rats (all P < 0.05). However, in renally denervated SHR treated with carvedilol, the vasoconstrictor responses to all the vasoactive agents were enhanced compared with those in SHR with intact renal nerves treated with carvedilol. Intact SHR given both losartan and carvedilol showed greater renal vasoconstrictor responses to the vasoactive agents than when given either losartan or carvedilol alone (all P < 0.05). Carvedilol reduced the vasoconstrictor response to Ang II and all the adrenergic agonists in the presence of the renal nerves, but, following the removal of renal sympathetic activity, carvedilol enhanced the sensitivity of both renal alpha(1)-adrenoceptors and AT(1) receptors to the vasoactive agents. Co-treatment with losartan and carvedilol reduced the renal vasoconstrictor responses to exogenously administered vasoactive agents but to a lesser extent than losartan or carvedilol alone. The results obtained demonstrate an interaction between Ang II receptors and adrenergic neurotransmission in the SHR.
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                Author and article information

                Journal
                Braz J Med Biol Res
                Braz. J. Med. Biol. Res
                bjmbr
                Brazilian Journal of Medical and Biological Research
                Associação Brasileira de Divulgação Científica
                0100-879X
                1414-431X
                14 November 2018
                2018
                : 51
                : 12
                : e7526
                Affiliations
                [1 ]Departamento de Bioquímica, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP, Brasil
                [2 ]Departamento de Biociências, Universidade Federal de São Paulo, Baixada Santista, SP, Brasil
                [3 ]Departamento de Medicina, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP, Brasil
                Author notes
                Correspondence: L.J.T. de Araújo: < biomedleonardo@ 123456gmail.com >
                Article
                00604
                10.1590/1414-431X20187526
                6247243
                30462770
                a4413f63-a044-4015-9a67-d4a9aac27731

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 13 June 2018
                : 27 August 2018
                Page count
                Figures: 2, Tables: 0, Equations: 0, References: 16
                Categories
                Research Article

                liver perfusion,angiotensin ii,adrenaline,at1r,adrenoceptors

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