Receptors In Vascular Smooth Muscle Research Articles

A Critical Role for Vascular Smooth Muscle in Acute Glucocorticoid-Induced Hypertension

Although glucocorticoid (GC)-induced hypertension has commonly been attributed to promiscuous activation of the mineralocorticoid receptor by cortisol, thereby promoting excess reabsorption of sodium and water, numerous lines of evidence indicate that this is not the only or perhaps even the primary mechanism. GC induce a number of effects on vascular smooth muscle (VSM) in vitro that may be pertinent to hypertension, but their contribution in vivo is unknown. To address this question, a mouse model with a tissue-specific knockout (KO) of the GC receptor in the VSM was created and characterized. Similar to control mice, KO mice exhibited normal baseline BP and, interestingly, showed normal circadian variation in BP. When dexamethasone was administered, however, the acute hypertensive response was markedly attenuated in KO mice, and there was a trend toward a decreased chronic hypertensive response. These data suggest that the GC receptor in VSM plays a critical role in the acute hypertensive response to GC in vivo.

Gene expression changes of prostanoid synthases in endothelial cells and prostanoid receptors in vascular smooth muscle cells caused by aging and hypertension

The present study was designed to assess whether or not changes in genomic expression of cyclooxygenases (COX-1, COX-2), endothelial nitric oxide synthase (eNOS), and prostanoid synthases in the endothelium and of prostanoid receptors in vascular smooth muscle contribute to the occurrence of endothelium-dependent contractions during aging and hypertension. Gene expression was quantified by real-time PCR using isolated endothelial cells and smooth muscle cells (SMC) from the aorta of Wistar-Kyoto and spontaneously hypertensive rats. Genes for all known prostanoid synthases and receptors were present in endothelial cells and SMC, respectively. Aging caused overexpression of eNOS, COX-1, COX-2, thromboxane synthase, hematopoietic-type prostaglandin D synthase, membrane prostaglandin E synthase-2, and prostaglandin F synthase in endothelial cells and COX-1 and prostaglandin E(2) (EP)(4) receptors in SMC. Hypertension augmented the expression of COX-1, prostacyclin synthase, thromboxane synthase, and hematopoietic-type prostaglandin D synthase in endothelial cells and prostaglandin D(2) (DP), EP(3), and EP(4) receptors in SMC. The increase in genomic expression of endothelial COX-1 explains why in aging and hypertension the endothelium has greater propensity to release cyclooxygenase-derived vasoconstrictive prostanoids. The expression of prostacyclin synthase was by far the most abundant, explaining why the majority of the COX-1-derived endoperoxides are transformed into prostacyclin, substantiating the role of prostacyclin as an endothelium-derived contracting factor. The expression of thromboxane synthase was increased in the cells of aging or hypertensive rats, explaining why the prostanoid can contribute to endothelium-dependent contractions. It is uncertain whether the gene modifications caused by aging and hypertension directly contribute to endothelium-dependent contractions or rather to vascular aging and the vascular complications of the hypertensive process.

Knockout Mice Reveal That the Angiotensin II type 1B Receptor Links to Smooth Muscle Contraction

Rodents express two isoforms of the angiotensin II type 1 (AT(1)) receptor: AT(1A) and AT(1B). It is unclear which receptor subtype mediates contraction in response to angiotensin II in various arteries. We tested the hypothesis that the AT(1B) receptor is the predominant receptor that mediates contraction in the abdominal aorta in response to angiotensin II. Isometric tension responses to angiotensin II were determined in abdominal aortic rings obtained from male wild-type and AT(1B) receptor knockout mice. The rings were suspended in an organ bath of a wire myograph and contractions to angiotensin II and other vasoconstrictors were determined. Angiotensin II contracted aortic segments from wild-type mice; however, this response was virtually absent in rings obtained from AT(1B) receptor knockout mice. Contractions in response to K(+) and U46619 (thromboxane A(2) mimetic) were not different between rings obtained from wild-type and AT(1B) receptor knockout mice. Reduced angiotensin II contraction is not related to a generalized decrease in smooth muscle function, rather it is specifically due to genetic ablation of the AT(1B) receptor. Our data support the concept that AT(1B) receptors couple to contraction in the mouse abdominal aorta, a function that parallels the single known AT(1) receptor in human vascular smooth muscle.

Functional activity of BKCa channels is not coupled to the activity of ryanodine receptors in hamster cheek pouch arterioles

The activity of large conductance, calcium-activated potassium (BKCa) channels appears to be tightly coupled to the activity of ryanodine receptors (RYR) in vascular smooth muscle (VSM) cells in myogenically active arteries. In these vessels, blockade of BKCa channels or RYR causes equivalent membrane depolarization and constriction supporting this hypothesis. However, the linkage between BKCa channels and RYR in arterioles has not been established. Hamster cheek pouch arterioles (maximum diameter = 87 μm) were isolated, cannulated with glass micropipettes, pressurized to 70 cm H2O, and internal diameter measured as an index of VSM cell contractile activity. At rest, these arterioles developed substantial myogenic tone: resting diameters at 70 cm H2O were 53 ± 4 μm largely due to Ca2+ influx through L-type calcium channels. Superfusion with 1 mM tetraethyl ammonium (TEA) to block BKCa channels, constricted the arterioles 14 ± 3 μm (n = 15, P < 0.05). In contrast, superfusion of arterioles (resting diameter = 44 ± 3 μm) with 10 μM ryanodine had no significant effect: the vessels constricted 1 ± 1 micrometer (n = 7, P > 0.05). In these same vessels, in the presence of ryanodine, 1 mM TEA constricted the arterioles 7 ± 2 μm (n = 7, P < 0.05). These data indicate that the activity of BKCa channels is not coupled to the activity of RYR receptors in hamster cheek pouch arteriolar smooth muscle cells. Based on our previous observations, we speculate that it is Ca2+ influx through L-type voltage-gated Ca2+ channels that is responsible for active BKCa channels in microvascular smooth muscle cells. Supported by PHS grant HL32469.

Sensing in tissue bioreactors

Specialized sensing and measurement instruments are under development to aid the controlled culture of cells in bioreactors for the fabrication of biological tissues. Precisely defined physical and chemical conditions are needed for the correct culture of the many cell-tissue types now being studied, including chondrocytes (cartilage), vascular endothelial cells and smooth muscle cells (blood vessels), fibroblasts, hepatocytes (liver) and receptor neurones. Cell and tissue culture processes are dynamic and therefore, optimal control requires monitoring of the key process variables. Chemical and physical sensing is approached in this paper with the aim of enabling automatic optimal control, based on classical cell growth models, to be achieved. Non-invasive sensing is performed via the bioreactor wall, invasive sensing with probes placed inside the cell culture chamber and indirect monitoring using analysis within a shunt or a sampling chamber. Electroanalytical and photonics-based systems are described. Chemical sensing for gases, ions, metabolites, certain hormones and proteins, is under development. Spectroscopic analysis of the culture medium is used for measurement of glucose and for proteins that are markers of cell biosynthetic behaviour. Optical interrogation of cells and tissues is also investigated for structural analysis based on scatter.

The vascular endothelin system in hypertension--recent patents and discoveries.

The discovery of endothelin two decades ago has now evolved into an intricate vascular endothelin (ET) system. Several ET isoforms, receptors, signaling pathways, agonists, antagonists, and clinical applications have been identified and documented in first-rate patents. The role of ET as one of the most potent endothelium-derived vasoconstricting factors is now complemented by a newly discovered role in vascular relaxation. ET synthesis is initiated by the transcription of ET genes in endothelial cells and the generation of the gene products preproET and big ET, which are further cleaved by specific ET converting enzymes into ET-1, -2, -3 and -4 isoforms. ET isoforms bind with different affinities to ET(A) and ET(B2) receptors in vascular smooth muscle, and stimulate [Ca(2+)](i), protein kinase C, mitogen-activated protein kinase and other signaling mechanisms of smooth muscle contraction, growth and proliferation. ET also binds to endothelial ET(B1) receptors, which mediate the release of vasodilator substances such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor. Endothelial ET(B1) receptors may also function in ET re-uptake and clearance. Although the effects of ET on vascular function and growth are well-recognized, the role of ET and its receptors in the regulation of blood pressure and in the pathogenesis of hypertension is not clearly established. Salt-dependent hypertension in experimental animals and some forms of moderate to severe hypertension in human may show elevated levels of plasma or vascular ET; however, other forms of hypertension show normal ET levels. The currently available ET receptor antagonists reduce blood pressure in some forms of experimental hypertension. Careful examination of recent patents may identify more effective and specific modulators of the vascular ET system for clinical use in human hypertension.

Suppression of Type II Bone Morphogenic Protein Receptor in Vascular Smooth Muscle Induces Pulmonary Arterial Hypertension in Transgenic Mice

Bone morphogenic proteins have a well-described role in development, and targeted disruption of the pathway in mice results in fetal lethality prior to gastrulation. Thus, it was surprising when the gene responsible for the majority of cases of hereditary pulmonary arterial hypertension (PAH) was identified as the type II bone morphogenic protein receptor (BMPRII). We therefore constructed a conditional, smooth-muscle-specific transgenic mouse expressing a dominant-negative BMPRII mutation identified in a family with PAH (SM22-tet-dnBMPRII mice). We then addressed the following questions: (1) is loss of functional BMPRII in smooth muscle sufficient to produce the disease phenotype, and (2) despite generalized smooth-muscle expression of the mutant gene, are abnormalities restricted to the pulmonary circulation? Just as is seen in humans, SM22-tetdnBMPRII mice acquired severe PAH at sea level, associated with increased muscularization of small pulmonary arteries with no abnormality in systemic BP. Analysis of gene expression patterns by GeneChip (Affymetrix; Santa Clara, CA) showed a pattern of gene regulation markedly different from that in hypoxic pulmonary hypertension, including differential regulation of genes involved in cytoskeletal rearrangement, inflammation, and vascular tone. The mice were hyperresponsive to hypoxia, becoming even more severely hypertensive when kept at Denver altitude. In conclusion, we report the first transgenic model of PAH, establishing that selective smooth-muscle expression of a mutant BMPRII gene found in a family with PAH recapitulates the disease phenotype in transgenic mice.

Vascular Endothelin and Hypertension - From Receptors to Medicine

The last two decades have witnessed great advances in our understanding of the role of the vascular endothelin (ET) system in the control of blood pressure. The role of ET as one of the most potent endothelium-derived vasoconstrictors is now complemented with a newly discovered role in vascular relaxation. The transcription of the ET genes in endothelial cells leads to the formation of preproET and big ET, which are further metabolized by ET converting enzymes into ET-1, -2, -3 and -4 isoforms. ET isoforms bind with different affinities to ETA and ETB2 receptors in vascular smooth muscle, and stimulate [Ca2+]i and other signaling mechanisms of smooth muscle contraction and growth. ET also binds to endothelial ETB1 receptors, which are coupled to increase production of vasodilator substances such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor, and may also function in ET clearance. Despite the prominent effects of ET on vascular function and growth, the role of ET and its receptors in the regulation of blood pressure and in the pathogenesis of hypertension has not been clearly established. Some forms of moderate to severe hypertension in human and salt-dependent hypertension in experimental animals may show elevated levels of plasma or vascular ET; however, other forms of hypertension may show normal levels. Also, while ET antagonists could reverse some forms of experimental hypertension, their potential use in medicine needs to be carefully examined particularly with regard to their effectiveness and specificity.

Interaction of D 1 dopamine and ETB endothelin receptors in renal proximal tubule and vascular smooth muscle

Interaction of D 1 dopamine and ETB endothelin receptors in renal proximal tubule and vascular smooth muscle

Chemokine receptors in vascular smooth muscle.

Atherosclerosis is considered to be an inflammatory disease. Chemokines are low-molecular-weight proteins that exert their effects, in part, through mediating leukocytic infiltration into the vessel wall. Recently, studies have determined that chemokines and their receptors are present, and function on other cellular components comprising the arterial wall, such as the endothelium and vascular smooth muscle. Smooth muscle cells (SMC) constitute the major cellular element of the arterial wall and are located predominantly in the arterial media. Recent studies have demonstrated that SMC possess a number of functional chemokine receptors, including CCR5, CXCR4, and a receptor for monocyte chemoattractant protein-1 (MCP-1). It is likely that SMC are increasingly recognized as potential targets for chemokines, and that these effects may influence a variety of normal and pathological processes involving SMC such as atherosclerosis and arterial injury.

117 C-reactive protein upregulates angiotensin type 1 receptors in vascular smooth muscle in-vitro and in-vivo

117 C-reactive protein upregulates angiotensin type 1 receptors in vascular smooth muscle in-vitro and in-vivo

Chemokine Receptors in Vascular Smooth Muscle

Chemokine Receptors in Vascular Smooth Muscle

Alpha2-adrenoceptor ligands inhibit alpha1-adrenoceptor-mediated contraction of isolated rat arteries.

The experiments in this study were designed to investigate the potential relaxing effects of different compounds known as alpha2-imidazoline ligands (either agonists or antagonists) in isolated rat arteries, and to test the role of nitric oxide (NO) and prostaglandins, in addition to the influence of the nature of the contracting agent in these responses. Segments of mesenteric arteries were isolated and mounted in a small vessel myograph (JP Trading, Aarhus, Denmark) for isometric tension recording, while segments of gracilis muscle arteries were cannulated and studied in the pressurized state using an arteriograph (Living Systems Instrumentation, Burlington, VT, USA). In phenylephrine precontracted mesenteric arteries, the agonists clonidine, BHT920, UK 14304, and rilmenidine, as well as the antagonists idazoxan, yohimbine and rauwolscine, all induced marked relaxations. Similarly, clonidine and idazoxan, both induced marked dilatations of phenylephrine preconstricted gracilis muscle arteries. In both mesenteric and gracilis muscle arteries, the responses to clonidine and idazoxan were not affected by the NO synthase inhibitor (omega)-nitro-L-arginine (L-NA, 10(-5) M) or the cyclooxygenase inhibitor diclofenac (10(-5) M). In mesenteric arteries, the responses to clonidine or idazoxan were similar when the arteries were precontracted by different alpha1-adrenoceptor agonists (phenylephrine, methoxamine or norepinephrine). In contrast, in arteries precontracted by PGF2alpha or endothelin, clonidine induced contractions while idazoxan induced very modest relaxations. Thus, alpha2-adrenoceptor/imidazoline ligands (whether agonists and antagonists) induce paradoxical relaxation of small mesenteric or gracilis muscle arteries of rats, which are not affected by NO-synthase or cyclooxygenase inhibition, and appear related to direct non specific interactions of the alpha2-imidazoline ligands with alpha1-adrenergic receptors in vascular smooth muscle.

Expression of functional delta opioid receptors in vascular smooth muscle.

We evaluated smooth muscle from human internal mammary artery and rat aorta for the presence of delta opioid receptors. Radioligand receptor competition studies using the delta-receptor selective agonist, [3H]-[D-Ala2, Met5] enkephalinamide (DAMA) suggested the expression of a high affinity binding site in rat and human blood vessels that was consistent with the delta-2 opioid receptor subtype. Using RT-PCR with primers to the cloned delta opioid receptor (DOR), a cDNA fragment identical to the known DOR sequence was obtained from the smooth muscle cell line, A-10. Stimulation of A-10 cells with DAMA resulted in a significant mobilization of intracellular calcium and membrane depolarization. Exposure of aortic rings denuded of endothelium to DAMA induced a naltrindole-senstive increase in contractile tone. These data demonstrate the presence of a functional DOR in vascular smooth muscle and a direct impact of opioids on vascular contractile tone.

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Vascular actions of brain natriuretic peptide: modulation by atherosclerosis and neutral endopeptidase inhibition

ObjectivesWe sought to define the vascular actions of the cardiac hormone brain natriuretic peptide (BNP) on cellular proliferation and cyclic guanosine monophosphate (cGMP) in human aortic vascular smooth muscle cells (HAVSMCs). Secondly, we investigated BNP and acetylcholine (ACh) vasorelaxations in aortic rings from normal and atherosclerotic rabbits in the presence and absence of long-term oral inhibition of neutral endopeptidase (NEP).BackgroundThe vascular actions of BNP are not well defined, despite the presence of its receptor in vascular smooth muscle and the upregulation of NEP, the ectoenzyme that degrades BNP, in the vascular wall in atherosclerosis.MethodsHAVSMCs stimulated with fetal calf serum (FCS) were pulsed with bromodeoxyuridine (BrdU) with and without BNP. The HAVSMCs were incubated in the presence and absence of BNP to assess cGMP. Vasorelaxations to BNP and ACh were assessed in rings in normal and atherosclerotic rabbits in the presence and absence of long-term oral inhibition of NEP, together with assessment of atheroma formation.ResultsFCS-stimulated BrdU uptake in HAVSMCs was suppressed with BNP. BNP potentiated cGMP in HAVSMCs. BNP resulted in potent vasorelaxation in normal isolated aortic rings, which were impaired in atherosclerotic versus normal rabbits and preserved with NEP inhibition, which also decreased atheroma formation. Relaxations to ACh, which were also impaired in atherosclerosis, were preserved with inhibition of NEP.ConclusionsWe conclude that BNP potently inhibits vascular smooth muscle cell proliferation and potentiates the generation of cGMP. BNP potently relaxes the normal rabbit aorta, and this response is impaired in atherosclerosis but preserved with inhibition of NEP, together with a reduction in atheroma formation and preservation of relaxations to ACh.

Inhibition by adrenomedullin of amine release from adrenergic nerves in dog mesenteric arteries

Adrenomedullin and calcitonin gene-related peptide (CGRP) inhibited the pressor response to transmural electrical stimulation in perfused isolated canine mesenteric arteries. The response was abolished by treatment with either prazosin or tetrodotoxin. Adrenomedullin-(22–52), an adrenomedullin receptor antagonist, reduced the inhibitory effect of adrenomedullin (10 −10 to 10 −8 mol/l), but did not alter the action of CGRP. CGRP-(8–37), a CGRP 1 receptor antagonist, did not affect the inhibition induced by adrenomedullin, but reversed the CGRP-induced inhibition. In helical strips of the arteries, adrenomedullin (up to 10 −8 mol/l) did not influence the contraction induced by noradrenaline, whereas CGRP attenuated the response. Adrenomedullin decreased the release of noradrenaline from adrenergic nerves elicited by transmural electrical stimulation, but CGRP had no effect. Adrenomedullin-(22–52) reversed the decrease in noradrenaline release induced by adrenomedullin. The adrenomedullin-induced relaxation of vascular strips precontracted with prostaglandin F 2α was suppressed by CGRP-(8–37) but was unaffected by adrenomedullin-(22–52). These findings suggest that adrenomedullin impairs noradrenaline release from adrenergic nerves by acting on adrenomedullin receptors located in the nerve terminals, whereas arterial relaxation caused by adrenomedullin and CGRP is due to activation of CGRP 1 receptors in vascular smooth muscle.

Gene substitution/knockout to delineate the role of alpha 2-adrenoceptor subtypes in mediating central effects of catecholamines and imidazolines.

Adrenergic receptors form the interface between the sympathetic nervous system and the cardiovascular system as well as many endocrine and parenchymal tissues. For the three alpha 2-adrenergic receptors (alpha 2A, alpha 2B, and alpha 2C), genetic mouse models have been developed that can be used to elucidate the physiologic function of each receptor subtype in vivo. Different strategies for homologous recombination in embryonic stem cells were applied to generate lines of mice with gene knockouts of the individual alpha 2-receptor subtypes (alpha 2A-KO, alpha 2B-KO, and alpha 2C-KO) or with a substitution of a mutant receptor at the wild-type locus (alpha 2-D79N). In these transgenic mice, the cardiovascular effects of alpha 2-agonists and imidazoline receptor agonists were tested. Stimulation of alpha 2B receptors in vascular smooth muscle produces hypertension and counteracts the clinically beneficial hypotensive effect of stimulating alpha 2A receptors in the central nervous system.

Variant estrogen and progesterone receptor messages in human vascular smooth muscle.

Estrogens stimulate growth of breast or uterine cells but have the opposite effect on vascular smooth muscle cells, in which they protect against coronary artery disease with or without concomitant administration of progesterone. A possible cause of differences in hormone action is variable tissue-specific expression of hormone receptor. Therefore, we analyzed the structure of estrogen receptors (ERs) and progesterone receptors (PRs) in human vascular smooth muscle. RNA was isolated from human vascular smooth muscle, and the functional domains of ER-alpha and PR were characterized by reverse transcriptase and polymerase chain reaction. Interestingly, in addition to wild-type ER-alpha and PR, 5 variant ER-alpha and 2 variant PR transcripts were found. These variants contained precise deletions of exons encoding regions of the hormone-binding domain. The PR transcripts lacked exon 4 (PRDelta4) and exon 6 (PRDelta6). The ER-alpha transcripts were missing exon 4 (ERDelta4), exon 5 (ERDelta5), exon 6 (ERDelta6), exon 7 (ERDelta7), and exons 6 and 7, (ERDelta6,7). ER-beta variants were also detected. The PR variants were functionally characterized, and PRDelta6 was found to be a dominant-negative transcription inhibitor of wild-type receptors. Variant PR was present in premenopausal women but absent in postmenopausal women. Variant PR and ER transcripts are extensively expressed in human vascular smooth muscle. The complex tissue-specific effects of sex hormones may be mediated by the expression of heterogeneous forms of their cognate receptors. The presence of variant ERs and PRs may be of importance in altering the physiological effects of estrogens or progestins in vascular smooth muscle.

Reduced Blood Pressure and Increased Sensitivity of the Vasculature to Parathyroid Hormone-Related Protein (PTHrP) in Transgenic Mice Overexpressing the PTH/PTHrP Receptor in Vascular Smooth Muscle

PTH-related protein (PTHrP) is produced in vascular smooth muscle, where it is postulated to exert vasorelaxant properties by activation of the PTH/PTHrP type 1 receptor. As a model for studying the actions of locally produced PTHrP in vascular smooth muscle in vivo, we developed transgenic mice that overexpress the PTH/PTHrP receptor (PTHrP-R) in smooth muscle. Oocyte injection with a SMP8-PTHrP-R fusion construct yielded six founder mice. F1 offspring were viable and demonstrated selective overexpression of the SMP8-PTHP-R messenger RNA in smooth muscle-rich tissues. Baseline blood pressure measured in conscious mice by tail sphygmomanometry was significantly lower in the receptor-overexpressing mice than that in controls (117 ± 4 vs. 133 ± 3 mm Hg; P < 0.05). In anesthetized animals, iv infusion of PTHrP-(1–34)NH2 caused a significantly greater reduction in blood pressure and total peripheral resistance in transgenic mice than in control animals. Vascular contractility was studied in paired, isometrically mounted aortas from 9-week-old transgenic and wild-type mice. The force of contraction in response to phenlyephrine was not significantly different between transgenic and wild-type mice. However, PTHrP-(1–34) NH2 relaxed aortic vessel preparations from transgenic mice to a greater extent than in controls (77.1 ± 3% vs. 38.4 ± 4%; P < 0.001). To determine the impact of overexpression of PTH/PTHrP type 1 receptor and its ligand on the development of the cardiovascular system, double transgenic mice were created by crossing SMP8-PTHrP-R transgenic mice with mice overexpressing PTHrP (SMP8-PTHrP). Double transgenic mice died around day E9 with abnormalities in the developing heart. In conclusion, overexpression of PTH/PTHrP type 1 receptor in vascular smooth muscle of transgenic mice reduces blood pressure, probably through sustained activation of the receptor by endogenous ligand. The cardiovascular defects observed in mice overexpressing both PTHrP and its receptor suggest that PTHrP may play a role in the normal development of the cardiovascular system.