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![Saturation of [ 125 I]AngII binding sites in chicken liver membranes. Membranes (100 µg of protein) were incubated at 22°C for 30 min in the presence of increasing concentrations of [ 125 I]AngII. Nonspecific binding was determined in the presence of 1 µM AngII. Linearization of these data is shown as a Scatchard transformation (inset). Each point represents the mean ± SD of triplicate determinations. Similar data were obtained in four separate experiments.](profile/Emanuel-Escher/publication/13944707/figure/fig2/AS:341309383561217@1458385906347/Saturation-of-125-IAngII-binding-sites-in-chicken-liver-membranes-Membranes-100-g.png)
Saturation of [ 125 I]AngII binding sites in chicken liver membranes. Membranes (100 µg of protein) were incubated at 22°C for 30 min in the presence of increasing concentrations of [ 125 I]AngII. Nonspecific binding was determined in the presence of 1 µM AngII. Linearization of these data is shown as a Scatchard transformation (inset). Each point represents the mean ± SD of triplicate determinations. Similar data were obtained in four separate experiments.
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![Fig. 1. Concentration-dependent inhibition of [ 125 I]AngII binding to...](profile/Emanuel-Escher/publication/13944707/figure/fig1/AS:341309383561216@1458385906315/Concentration-dependent-inhibition-of-125-IAngII-binding-to-chicken-liver-membranes-by_Q320.jpg)
![Fig. 2. Saturation of [ 125 I]AngII binding sites in chicken liver...](profile/Emanuel-Escher/publication/13944707/figure/fig2/AS:341309383561217@1458385906347/Saturation-of-125-IAngII-binding-sites-in-chicken-liver-membranes-Membranes-100-g_Q320.jpg)
![Fig. 3. (Upper panel) Association rate of [ 125 I]AngII (0.12 nM) to...](profile/Emanuel-Escher/publication/13944707/figure/fig3/AS:341309383561218@1458385906366/Upper-panel-Association-rate-of-125-IAngII-012-nM-to-chicken-liver-membranes-The_Q320.jpg)
We have characterized a specific binding site for angiotensin II (AngII) in chicken liver membranes. Pseudo-equilibrium studies at 22 degrees C for 30 min have shown that this binding site recognizes AngII with a high affinity (pKD of 8.13 +/- 0.21). The binding sites are saturable and relatively abundant (maximal binding capacity varies from 0.318...
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The sections in this article are:
Components of the Renin–Angiotensin System
Prorenin/Renin
Renin Gene Structure, Evolutionary Function, and Regulation
Biosynthesis and Chemiosmotic Activation
Tissue Distribution in Health and Disease
Kidney
Heart and Blood Vessels
Adrenal
Brain
Eye, Liver, and Intestine
Ovary, Uterus, Testis, and Sex Accessory and Subcutaneous Tissue
Submandibular Gland
Spontaneously Hypertensive Rat
Renal Hypertensive Rat
Growth Retardation
Relative Renin Plasma Levels and Suggestive Meaning
Angiotensinogen
Biochemical Properties
Tissue Expression and In Situ Regulation
Factors Regulating Release
Mechanism of Action and Physiological Effects
Summary and Challenges
Angiotensin I–Converting Enzyme
Molecular Structure and Regulation
Active Sites and Catalytic Properties
Tissue Distribution
Summary and Challenges
Angiotensin Peptides
Aldosterone
Biosynthesis and Metabolism
Secretion and Its Regulation
Angiotensin II
Potassium
Corticotropin and Other Proopiomelanocortin Peptides
Various Stimulators of Aldosterone Secretion
Various Inhibitors of Aldosterone Secretion
Cellular Actions
Disorders of Aldosterone Secretion
Systemic Regulation of Sodium Volume Homeostasis
Regulation of Sodium Volume Homeostasis
Integrative Regulation of Sodium Volume and Blood Pressure Homeostasis
Integrative Regulation of Sodium and Potassium Homeostasis
Integrative Regulation by Potassium and Hydrogen in Volume Homeostasis
Polyendocrinopathy Type III: Systemic Dysregulation of Sodium Volume Homeostasis
Primary and Pseudoprimary Aldosteronism
Secondary Aldosteronism: Renin Tumors and Edematous States
High‐Renin States and Low‐Renin Syndromes
Summary and Challenges: Defining Functions and Processing Strategies of Renin–Angiotensin System Molecules
The predominant angiotensin II receptor expressed in the human myometrium is the angiotensin AT2 receptor. This preparation was used for a structure-activity relationship study on angiotensin II analogues modified in positions 1 and 8. The angiotensin AT2 receptor present on human myometrium membranes displayed a high affinity (pKd = 9.18) and was relatively abundant (53-253 fmol/mg of protein). The pharmacological profile was typical of an angiotensin AT2 receptor with the following order of affinities: (angiotensin III > or = angiotensin II > angiotensin I > PD123319 > angiotensin-(1-7) > angiotensin-(1-6) approximately angiotensin IV > Losartan). Modifications of the N-terminal side chain and of the primary amine of angiotensin II were evaluated. Neutralisation of the methylcarboxylate (Asp) to a methylcarboxamide (Asn) or to a hydroxymethyl (Ser) or substitution for a methylsulfonate group (cysteic acid) improved the affinity. Extension from methylcarboxylate (Asp) to ethylcarboxylate (Glu) did not affect the affinity. Introduction of larger side chains such as the bulky p-benzoylphenylalanine (p-Bpa) or the positively charged Lys did not substantially affect the affinity. Complete removal of the side chain (angiotensin III), however, resulted in a significant affinity increase. Removal or acetylation of the primary amine of angiotensin II did not noticeably influence the affinity. Progressive alkylation of the primary amine significantly increased the affinity, betain structures being the most potent. It appears that quite important differences exist between the angiotensin AT1 and AT2 receptors concerning their pharmacological profile towards analogues of angiotensin II modified in position 1. On position 8 of angiotensin II, a structure-activity relationship on the angiotensin AT2 receptor was quite similar to that observed with angiotensin AT1 receptor. Bulky, hydrophobic aromatic residues displayed affinities similar to or even better than [Sarcosine1]angiotensin II. Aliphatic residues, especially those of reduced size, caused a significant decrease in affinity especially [Sarcosine1, Gly8]angiotensin II who showed a 30-fold decrease. Introduction of a positive charge (Lys) at position 8 reduced the affinity even further. Stereoisomers in position 8 (L-->D configuration) also induced lower affinities. The angiotensin AT2 receptor display a structure-activity relationship similar to that observed on the AT1 receptor for the C-terminal position of the peptide hormone. Position 1 structure-activity relationships are however fundamentally different between the angiotensin AT1 and AT2 receptor.
Angiotensin II mediates its effects through angiotensin receptors. The use of specific angiotensin receptor ligands and the cloning of these receptors allows their classification. So far, the AT1, AT2 and atypical angiotensin II receptors are recognised. The AT1 receptor is responsible for the classical effects of the renin-angiotensin system such as vasoconstriction, renal salt and water retention, central osmo-control and stimulation of cell growth. The function of the AT2 receptor is far from clear but this receptor appears to be important in fetal development, cell growth inhibition and differentiation processes. This review describes the angiotensin receptors and focuses on the possible functions of the AT2 receptor.
The cloning of the avian Ang II receptor shows that it is molecularly close to the AT(1)-type mammalian receptor. However, pharmacological characterization in transfected cells shows that, even though the avian receptor is coupled to the phospholipase C, as is the AT(1), its profile of specificity towards antagonists appears different from that of the two angiotensin II mammalian receptor types. The fowl Ang II receptor mRNA is expressed in classical adult target organs for Ang II and, interestingly, also in endothelial cells, but not in vascular smooth muscle cells. In the endothelial cells, it may mediate the peculiar vasorelaxation effect of Ang II already reported in the chicken. The recent description of the expression pattern in the chick embryo shows that the avian Ang II receptor is expressed in many different mesenchymal tissues, a feature which is the signature of the AT(2) mammalian receptor. Altogether, these data imply that the avian Ang II receptor is an atypical receptor that cannot be readily classified as either of the two mammalian Ang II receptor types and, therefore, reinforce the evidence for another Ang II receptor in the avian class.
The structure of the angiotensin molecule has been well preserved throughout the vertebrate scale with some amino acid variations. Specific angiotensin receptors (AT receptors) that mediate important physiological functions have been noted in a variety of tissues and species. Physiological and pharmacological characterization of AT receptors and, more recently, molecular cloning studies have elucidated the presence of AT receptor subtypes. Comparative studies suggest that an AT receptor subtype homologous to the mammalian type 1 receptor subtype (AT(1)), though pharmacologically distinct, is present in amphibians and birds, whereas AT receptors cloned from teleosts show low homology to both AT(1) and AT(2) receptor subtypes. Furthermore, receptors differing from both the AT(1)-homologue receptor and AT(2) receptor exist in some non-mammalian species. This may suggest that the prototype AT receptor evolved in primitive vertebrates and diverged to more than one type of AT receptor subtype during phylogeny. Furthermore, phenotypic modulation of AT receptors appears to occur during individual development/maturation.
Intermolecular inverse electron demand cycloadditions of 2-substituted imidazoles with various 1,2,4-triazines produced both imidazo[4,5-c]pyridines (3-deazapurines) and pyrido[3,2-d]pyrimid-4-ones (8-deazapteridines). The product distribution was controlled by reactant substituents and influenced by reaction temperature. A regioselective method for the preparation of 6-unsubstituted 1,2,4-triazines was also developed. By using this route to 8-deazapteridines, a new 8-deazafolate analogue was prepared.
Earlier studies indicate that binding sites of type II angiotensin (AT2) receptors are detected all over the pancreas, as well as in the pancreatic exocrine cell line AR4-2J. However, lack of corresponding functional AT2 receptor responses can be detected in the exocrine pancreas. The aim of present study is to determine the protein expression of AT2 receptors in the pancreas by probing with an AT2 receptor-specific antibody, and to examine the role of AT2 receptors in the regulation of pancreatic endocrine hormone release. In Western protein analysis of adult rat tissues, expression of AT2 receptor-immunoreactive bands of 56, 68, and 78 kDa was detected in the adrenal, kidney, liver, salivary glands, and pancreas. In adult rat pancreas, strong immunoreactivity was detected on cells that were located at the outer region of Langerhans islets. Immunohistochemical studies indicated that AT2 receptors colocalized with somatostatin-producing cells in the endocrine pancreas. Consistent with the findings in adult pancreas, abundant expression of AT2 receptors was also detected in immortalized rat pancreatic endocrinal cells lines RIN-m and RIN-14B. To examine the role of AT2 receptors on somatostatin secretion in the pancreas, angiotensin-stimulated somatostatin release from pancreatic RIN-14B cells was studied by an enzyme immunoassay in the absence or presence of various subtype-selective angiotensin analogues. There was a basal release of somatostatin from RIN-14B cells at a rate of 8.72 +/- 4.21 ng/10(6) cells (n = 7). Angiotensin II (1 nM-10 microM) stimulated a biphasic somatostatin release in a dose-dependent manner with an apparent EC50 value of 49.3 +/- 25.9 nM (n = 5), and reached maximal release at 1 microM angiotensin II (982 +/- 147.34% over basal secretion; n = 5). Moreover, the AT2 receptor-selective angiotensin analogue, CGP42112, was 1000 times more potent than the AT1 receptor-selective angiotensin analogue, losartan, in inhibiting angiotensin II-stimulated somatostatin release. These results suggest that angiotensin may modulate pancreatic hormone release via regulation of somatostatin secretion.
