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CARDIOVASCULAR
Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (A.E.L., W.N., T.S., R.B., J.D., S.W.W.); and John D. Dingell VA Medical Center, Research and Development Service, Detroit, Michigan (T.J.G., D.M.K.)
Received December 20, 2007; accepted February 29, 2008.
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Abstract |
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; Erspamer and Asero, 1952). The function of 5-HT as a neurotransmitter is well established, as drugs that affect 5-HT concentration [e.g., Prozac (fluoxetine hydrochloride)] are widely used to treat conditions such as depression, anxiety, and obesity. However, its role in the cardiovascular system is far from being elucidated. For the last decade, accumulating evidence supports the involvement of 5-HT in the control of pulmonary circulation under normal and hypertensive conditions. However, a role for 5-HT in systemic vasculature is a matter of debate (for review, see Watts, 2005).
In the periphery, platelets represent a large 5-HT storage site, and they may function as a buffer, keeping the free circulating 5-HT in low levels (Nilsson et al., 1985; Vanhoutte, 1991; Brenner et al., 2007). Indeed, platelet 5-HT uptake is decreased with age and in hypertension accompanied by an increase in free 5-HT circulating levels (Amstein et al., 1991; Brenner et al., 2007).
5-HT is abundantly synthesized in the enterochromaffin cells of the intestine, representing more than 95% of total body 5-HT. 5-HT is also synthesized in the raphe nuclei of the brain, pineal gland, and in endothelial cells lining the lung. Potential sites of 5-HT synthesis in the systemic vasculature have not yet been identified. 5-HT is synthesized from the essential amino acid tryptophan in a two-step pathway. The hydroxylation of tryptophan forming 5-hydroxytryptophan (5-HTP) by the rate-limiting enzyme tryptophan hydroxylase (TPH) is the first step, followed by the conversion of 5-HTP into 5-HT by the enzyme amino acid decarboxylase.
Some of the effects exerted by 5-HT, such as pulmonary arterial smooth muscle proliferation, are mediated through receptor-independent, 5-HT transporter (SERT)-dependent signaling mechanisms (Marcos et al., 2003). 5-HT, as a protonated molecule, under physiological conditions, is not capable of diffusing across the membrane lipid bilayer. SERT, a bidirectional transporter, is for this reason the major protein responsible for uptake and release of 5-HT (for review, see Ni et al., 2006). SERT is a target of antidepressant drugs such as fluoxetine, fluvoxamine, citalopram, and paraxetine, and the anorexigen (+)-fenfluramine.
In addition to SERT, 5-HT concentration is regulated by the mitochondrial enzyme monoamine oxidase (MAO) and by 5-HT storage. 5-HT is deaminated via MAO to form 5-hydroxyindole acetaldehyde, which in turn is oxidized by aldehyde dehydrogenase to produce 5-hydroxyindole acetic acid (5-HIAA). Tissues or cells that contribute significantly to 5-HT metabolism include the lung, intestine, and endothelial cells of the vascular system, but any cell that can take up 5-HT and possesses MAO has the potential to metabolize 5-HT. MAO activity exists in peripheral arteries (Ni et al., 2004), suggesting that the peripheral vasculature has the ability to metabolize 5-HT and that it may be an important site for the serotonergic system. Our laboratory first demonstrated that peripheral arteries have a functional SERT, and therefore, they are also able to control intracellular and extracellular concentrations of 5-HT (Ni et al., 2004).
In comparison with arteries, less attention is given to the role of veins in the regulation of vascular tone. However, two thirds of the circulating blood volume is in the veins at any given time, indicating that veins have the potential to associate with platelets and 5-HT to a greater extent.
Preliminary data from our laboratory revealed that veins were able to take up 5-HT in a significantly larger amount than arteries (Linder et al., 2007). These novel findings suggest that veins, in addition to platelets, may function as a sink for 5-HT in the cardiovascular system. We presently hypothesize that the serotonergic system is present and functional in veins as it is in arteries. To test our hypothesis, 5-HT synthesis, metabolism, and uptake were investigated in veins and compared with arteries.
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Materials and Methods |
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), and their counterparts Wistar wild type (WT) (8–10 weeks old) were used in these studies. In some experiments, animals received injections with the MAO-A inhibitor pargyline (100 mg/kg i.p.) 30 min before euthanasia with pentobarbital (60 mg/kg i.p.). All animal use procedures were performed in accordance with the Institutional Animal Use and Care Committee at Michigan State University.
Reverse Transcription-Polymerase Chain Reaction. Total RNA from 
10-mg sections of vena cava and intestinal mucosa was isolated using the MELT Total RNA Isolation System (Ambion, Austin, TX), and it was quantified on a spectrophotometer (Nano-Drop, Wilmington, DE). One microgram of DNase-treated total RNA from each sample was reverse-transcribed using SuperScript II reverse transcriptase (Invitrogen, Carlsbad, CA) as described previously (Ni et al., 2004). Primers for rat TPH-1 sequence (GeneID 24848, mRNA sequence XM_341862): forward 5'-GCCTGCTTTCTTCCATCAGT-3'; reverse 5'-AGACATCCTGGAAGCTTGTGA-3'), designed using Primer3 software (Rozen and Skaletsky, 2000), were synthesized by the Macromolecular Structures and Synthesis Facility at Michigan State University (East Lansing, MI). Primers for rat β-2-microglobulin (B2m) were purchased from SuperArray (Frederick, MD). Results from pilot experiments screening the expression of several housekeeping genes indicated B2m as having the most stable expression in our tissue types. This gene has previously been used for real-time comparative gene expression studies (Wacker and Godard, 2005). Quantification of TPH-1 and B2m amplification was performed using the respective primers (0.1 µM) and the SYBR Green PCR Master Mix (Applied Biosystems, Foster City, CA) according to the manufacturer's protocol on the 7500 Real-Time PCR System (Applied Biosystems). For each reaction, the cycle threshold value was determined as the cycle number at which the fluorescence value reached the threshold level. The threshold level was set above the background fluorescence in the exponential phase of the real-time amplification curves.
TPH Activity Assay. TPH-1 activity was assayed for 15 min at 37°C as reported previously by measuring the formation of 5-HTP in the enzyme reaction (Johansen et al., 1995). The standard assay mixture contained 50 mM Tris-HCl, pH 7.4, 1 mM dithiothreitol, 0.05 mg/ml catalase, 200 µM tryptophan, 100 µM ferrous ammonium sulfate, 100 µMBH4, and 60 µg of tissue extract. Reactions were arrested after 60 min at 37°C with perchloric acid, and the 5-HTP formed in the reaction was determined by isocratic high-pressure liquid chromatography (HPLC), with fluorescent detection using a model LS5 spectrometer (PerkinElmer Life and Analytical Sciences, Boston, MA).
5-HT Uptake Assay. At room temperature, dissected and washed vessels were placed in physiological salt solution (130 mM NaCl, 4.70 mM KCl, 1.18 mM KH2PO4, 1.17 mM MgSO4·7H2O, 1.60 mM CaCl2·2H2O, 14.90 mM NaHCO3, 5.50 mM dextrose, and 0.03 CaNa2EDTA, pH 7.2) in 1.5-ml plastic centrifuge tubes containing either vehicle or inhibitor for 30 min. 5-HT (1 µM) or vehicle (deionized water) was then added for 15 min. Tissues were dipped several times in drug-free physiological salt solution to avoid extracellular 5-HT contamination, and then they were placed in 75 µl of 0.05 mM sodium phosphate and 0.03 mM citric acid buffer, pH 2.5, containing 15% methanol. Samples were frozen (-80°C) until assay. Samples were thawed, sonicated for 3 s. Supernatant was collected and transferred to new tubes. Tissue pellets were dissolved in 1.0 M NaOH and assayed for protein. Concentrations of 5-HIAA and 5-HT in tissue supernatants were determined by HPLC coupled with electrochemical detection. The supernatant (20 µl) was injected onto a C18 reverse phase analytical column (ESA Inc., Chelmsford, MA) protected by a precolumn cartridge filter. This column was coupled to a single coulometric electrode-conditioning cell positioned before autosampler (injection) in series with dual electrode analytical cells (ESA Inc.) positioned after the analytical column. The conditioning electrode potential was set at 0.45 V, whereas the coulometric analytical electrodes were set at 0.0 and 0.4 V. Amounts of 5-HIAA and 5-HT were determined by comparing peak areas in samples with those obtained from standards that were performed to obtain a standard curve, and they are reported as a concentration relative to protein content. Protein content was determined by the Lowry method (Lowry et al., 1951). The lower limit of sensitivity for detection of 5-HIAA and 5-HT was 0.5 pg/µl sample.
Immunohistochemistry. Vena cava and aorta were cleaned of fat, and then they were fixed in 10% formalin for 24 h. Tissues were paraffin-embedded, and 5-µm sections were collected onto glass slides. Sections were dried overnight at 37°C. Slides were dewaxed in Histochoice Clearing Agent (AMRESCO Inc., Solon, OH; two washes for 3 min each), and then they were washed in isopropanol (six washes, 3 min each). Slides were rinsed in deionized water. Slides were immersed in Antigen Unmasking Reagent (Vector Laboratories, Burlingame, CA), and then they were microwaved for 5 min total and subsequently air-dried before use. Endogenous peroxidases were blocked with 0.3% H2O2 in phosphate-buffered saline (PBS) for 30 min followed by blocking for nonspecific binding in PBS containing 1.5% blocking serum for 60 min. In a humidified chamber, samples were incubated overnight with antibody [2 µg/ml: SERT antibody against carboxyl terminus, C-20 (Santa Cruz Biotechnology, Inc., Santa Cruz, CA); or 5 µg/ml: MAO-A antibody H-70 (epitope corresponding to amino acids 458–527 of MAO-A of human origin; Santa Cruz Biotechnology, Inc.), with 1.5% blocking serum in PBS] or antibody neutralized with 5-fold excess of competing peptide (mass/mass). Development of slides proceeded according to the manufacturer's kit using 3,3'-diaminobenzidine as the developing substrate (Vector Laboratories), and slides were counterstained with hematoxylin (Vector Laboratories).
Protein Isolation. Vena cava and aorta were cleaned, pulverized in liquid nitrogen, and solubilized in lysis buffer (125 mM Tris HCl, pH 6.8, 4% SDS, and 20% glycerol) with protease inhibitors (0.5 mM phenylmethylsulfonyl fluoride, 10 µg/ml aprotinin, and 10 µg/ml leupeptin), and the tyrosine phosphatase inhibitor sodium orthovanadate (1 mM). Homogenates were centrifuged (11,000g for 10 min at 4°C), and supernatant total protein was measured (bicinchoninic acid kit; Sigma-Aldrich, St. Louis, MO).
Western Blotting. Equal amounts of total vascular protein (50 µg) from tissue samples were separated on 10% SDS-polyacrylamide gels and transferred to polyvinylidene difluoride membrane for Western analyses using an antibody against MAO-A (H-70, 1:1000; Santa Cruz Biotechnology, Inc.) or the SERT antibody against the amino terminus, N-14 (Santa Cruz Biotechnology, Inc.). Membranes were incubated overnight with primary antibody (4°C), and then they were washed three times with Tris-buffered saline + 0.1% Tween 20 and once with Tris-buffered saline. Blots were incubated with IRDye 680 goat anti-rabbit IgG (1:2000) for testing MAO-A and goat horseradish peroxidase-linked anti-rabbit secondary antibody (1:2000; Cell Signaling Technology Inc., Danvers, MA) for testing SERT for 1 h at 4°C with rocking. Blots were visualized using an Odyssey Infrared Imaging System (LI-COR Biosciences, Lincoln, NE) for MAO-A and by enhanced chemiluminescence reagents (GE Healthcare, Little Chalfont, Buckinghamshire, UK) for SERT. Smooth muscle 
-actin (1:400; Calbiochem, San Diego, CA) was used as a marker to ensure equal loading of protein.
Data Analysis. When comparing two groups, a Student's t test was used. When comparing three or more groups, a one-way analysis of variance followed by Newman-Keuls post hoc was used. In all cases, a P value of 0.05 was considered significant. All results are presented as mean ± S.E.M.
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Results |
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5-HT and Its Metabolite 5-HIAA Are Present in Veins and Arteries. 5-HT and 5-HIAA were detected by HPLC analysis in vena cava (Fig. 2A), jugular vein (Fig. 2B), aorta (Fig. 2C), and carotid artery (Fig. 2D). 5-HT content was greater in veins (Fig. 2, A and B) than in arteries (Fig. 2, C and D). The ratio of 5-HT to 5-HIAA was greater in veins than in arteries.
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5-HT Is Taken Up in Veins. Vessels were next exposed to exogenous 5-HT (1 µM) for 15 min. There was no significant change in 5-HT concentration in vena cava and jugular vein incubated with 5-HT (Fig. 3, A and C). However, there was an increase in 5-HIAA concentration (Fig. 3, B and D) in these tissues compared with vehicle-exposed vessels. In aorta and carotid arteries, an increase in 5-HT (Fig. 3, A and C) and 5-HIAA (Fig. 3, B and D) was observed after treatment with 1 µM 5-HT for 15 min compared with arteries treated with vehicle. Despite a lack of increase in 5-HT content in veins after exposure to exogenous 5-HT, 5-HT content was maintained higher in veins than in arteries.
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The Enzyme MAO-A Is Present in Veins. The presence of MAO-A in vena cava was confirmed by immunohistochemistry (Fig. 5A) and by Western analysis (Fig. 5B). Figure 5A (left) shows immunostaining for the antibody against MAO-A in vena cava (arrows) that was absent when the antibody was omitted (Fig. 5A, right). Figure 5B shows a band that migrated at 60 kDa in mass in vena cava and aorta that corresponds to the molecular mass of MAO-A.
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74 kDa correspondent to the molecular mass of the SERT. The SERT band was weaker and more diffuse in vena cava than in aorta, although an equivalent amount of total protein (50 µg) was loaded in each lane. We next investigated whether this transporter was responsible for 5-HT uptake in veins.
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5-HT Uptake in Vena Cava Is Independent of the SERT. The contribution of SERT to 5-HT uptake in veins was first evaluated in vessels from pargyline-treated rats to allow measurements of 5-HT alone without the interference of its metabolism to 5-HIAA. A 30-min incubation with the SERT inhibitor fluvoxamine (1 µM) before the challenge with exogenous 5-HT (1 µM) for 15 min had no effect in 5-HT uptake in vena cava (Fig. 7A) and jugular vein (Fig. 7B). By contrast, 5-HT uptake was significantly inhibited by fluvoxamine in aorta (Fig. 7C) and carotid (Fig. 7D) arteries from pargyline-treated rats. The SERT inhibitor fluoxetine (1 µM) was also tested in vena cava and aorta, and similar results were obtained (data not shown).
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5-HT in Veins. The effective driving force for venous return to the heart, mean circulatory filling pressure, can be determined in vivo by venous capacitance and blood volume (Yamamoto et al., 1980). It is interesting to note that in some models of hypertension, an increase in mean circulatory filling pressure is not associated with an increase in total blood volume, suggesting that mean circulatory filling pressure may only be driven by changes in venous tone under these circumstances (Fink et al., 2000).
5-HT modifies venous tone through direct interaction with venous 5-HT receptors (Cushing et al., 1994; Watts and Cohen, 1999; Watts, 2005; Linder et al., 2007) and indirectly by modifying sympathetic control of venous motor tone (Cohen et al., 1999). Thus, it is important to understand how 5-HT is handled by venous tissue, as modification in handling could ultimately affect the actions of 5-HT in veins and therefore blood pressure.
Several structural and functional differences exist between veins and arteries (Szasz et al., 2007; Thakali et al., 2007), making the comparison between the two vessels not a simple issue. In the present study, we compare vena cava with aorta and jugular vein with carotid artery. We chose similarly sized vessels for the comparison. Furthermore, we normalized the data by protein content. Using this comparison system, we observed that the content of 5-HT in these veins was higher than in same-sized arteries. Veins accommodate two thirds of the circulating blood volume at any time; thus, they are longer exposed to free circulating 5-HT. These data suggest that veins, compared with arteries, could be a reservoir of 5-HT in the periphery.
5-HT Synthesis in Veins. Cohen et al. (1999) observed that a TPH inhibitor decreased 5-HT content in saphenous vein, indicating 5-HT synthesis by nonperipheral veins (Cohen et al., 1999). Because of the likely possibility that the 5-HT was synthesized in low levels by vessels, addition of substrates would be necessary, and they were added. Under these conditions, 5-HTP, the intermediary in 5-HT synthesis, was detected in vena cava. This suggests the ability of peripheral veins to synthesize 5-HT.
The view on the peripheral vasculature has been that it is a target for 5-HT to induce its physiological responses by interacting with classic 5-HT receptors. The findings of the present study of an increase in 5-HTP content and TPH mRNA expression in vena cava introduce the new concept of 5-HT synthesis in peripheral vasculature.
5-HT Uptake in Veins. 5-HT synthesis alone is probably not the only source of 5-HT contributing to the high 5-HT content measured in veins. Another source of 5-HT is the external environment. Veins from pargyline-treated rats exposed to exogenous 5-HT took up 5-HT, and 5-HT uptake by peripheral arteries was confirmed.
Once inside the cell, 5-HT function is not terminated. 5-HT uptake by SERT mediates pulmonary arterial smooth muscle proliferation to 5-HT (Lee et al., 2001; Marcos et al., 2003). In addition, a finding in the platelet supports the idea that intracellular 5-HT exerts physiological effects. Walther et al. (2003) demonstrated that 5-HT in platelets, taken up by SERT, acts as a substrate for an enzyme class of transglutaminases to covalently modify proteins such as RhoA (transamidation or "serotonylation"). Intracellular 5-HT can also control nitric oxide production (Chanrion et al., 2007). Thus, intracellular 5-HT has functional effects, which could be regulated by SERT by changing intracellular 5-HT concentrations. It is currently unknown whether intracellular 5-HT can alter function in cell types of the peripheral vascular system.
In platelets, all the 5-HT content comes from the extracellular media via an uptake mechanism dependent on SERT, because platelets do not synthesize 5-HT. Consistent with this idea is that 5-HT was not detectable in platelets of the SERT-knockout rat, confirming previous observation by Dr. Cuppen's group (Homberg et al., 2006). We now know that the presence of SERT is not confined to brain sites and circulating platelets; it is also present in the intestine (Bian et al., 2007), vasculature (Ni et al., 2004), heart (Mekontso-Dessap et al., 2006), and immune system (Gordon and Barnes, 2003). SERT protein was weakly expressed in vena cava. However, 5-HT uptake in veins was not inhibited by the classic SERT inhibitor fluvoxamine, as opposed to arteries. Based on this surprising finding, we made use of an important tool to study the SERT in rats, the SERT-knockout rat. These rats were generated by N-ethyl-N-nitrosurea-driven, targeted selected mutagenesis, and they lack a functional SERT in the brain and in platelets without major changes in nonserotonergic systems (Homberg et al., 2006, 2007). We confirmed that 5-HT uptake in veins is independent of a functional SERT by showing that vena cava from rats lacking SERT could take up 5-HT in the same manner as vena cava from control rats. These data give further support to the conclusion that despite the presence of SERT in veins, SERT is not functional, at least under the conditions studied.
What SERT is doing in the vena cava if it is not functional remains the question. In aorta, at least, 5-HT uptake is partially dependent on SERT, confirming previous observations (Ni et al., 2004; Linder et al., 2008). In vena cava, it was surprising to observe a lack of functional SERT. According to the present findings, it is unlikely that 5-HT uptake via SERT would occur under acute exposure to 5-HT. However, the possibility of SERT gaining function in veins exposed to chronic increases in 5-HT, such as in hypertension, cannot be excluded. It is possible that in situations in which uptake via the other mechanisms is impaired, 5-HT uptake via SERT would take place. Additional monoamine transporters include the norepinephrine transporter (NET) and dopamine transporter that share many similarities with SERT in terms of function, mechanism, and regulation. Dopamine can be taken up by NET (Gu et al., 1994). It is possible that monoamine transporters have the ability to act promiscuously; thus, dopamine transporter and NET might take up 5-HT in veins. If this is true, norepinephrine and dopamine could also be transported by SERT. Other candidates responsible for non-SERT uptake include the organic cation transporters. Substrates for organic cation transporters can be as diverse as 5-HT, dopamine, norepinephrine, epinephrine, histamine, clonidine, and cimetidine. From a pharmacological perspective, organic cation transporters are difficult to distinguish from one another, but they can be distinguished from SERT by inhibition by corticosterone, O-methylisoprenaline, and levamisole (Horvath et al., 2003; Martel and Azevedo, 2003). Extending our studies to use of monoamine transporter knockout animals will help clarify the mechanisms by which veins take up 5-HT.
5-HT Metabolism. Pargyline treatment significantly inhibited 5-HIAA content in all vessels exposed to exogenous 5-HT, indicative of MAO inhibition and therefore MAO function in these vessels. Pargyline treatment increases the amount of 5-HT in saphenous vein (Cohen et al., 1999), indicating the presence of MAO in this vessel. The findings of the present study introduce the novel data supporting the presence and function of MAO-A in peripheral veins, and they confirm 5-HT metabolism by peripheral arteries.
This observation indicates that peripheral vessels (arteries and veins) might play an important role in the clearance of plasma 5-HT through uptake and metabolism. This is important, as increased circulating 5-HT is associated with hypertension (Amstein et al., 1991; Brenner et al., 2007), which could also theoretically be the result of dysfunction of serotonergic system in peripheral blood vessels.
Altogether, the results of the present study suggest the presence of the serotonergic system in veins, and they highlight the differences in 5-HT handling between peripheral arteries and veins. Several cardiovascular diseases, including hypertension, involve alterations in the synthesis of vasoactive hormones. Understanding the pharmacological and physiological function and regulation of these systems is of extreme value to understanding the pathophysiology and treatment of these diseases. Selective serotonin reuptake inhibitors are widely used for treatment of central disorders due to the ability of SERT inhibition. Because more blood is found in the venous system, veins may be exposed for longer periods to free circulating 5-HT than arteries. The unique findings in this study, showing increased basal intracellular 5-HT concentration in veins compared with arteries, led us to hypothesize that veins may function as a sink for 5-HT in the cardiovascular system and that they may represent a novel target for treatment of vascular diseases involving 5-HT.
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Acknowledgements |
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Footnotes |
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
ABBREVIATIONS: 5-HT, 5-hydroxytryptamine (serotonin); 5-HTP, 5-hydroxytryptophan; TPH, tryptophan hydroxylase; SERT, serotonin transporter; MAO, monoamine oxidase; 5-HIAA, 5-hydroxyindole acetic acid; KO, knockout; WT, wild type; B2m, β-2-microglobulin; PCR, polymerase chain reaction; HPLC, high-performance liquid chromatography; PBS, phosphate-buffered saline; NET, norepinephrine transporter; VC, vena cava; JV, jugular vein; RA, rat aorta; CA, carotid artery; BH4, tetrahydrobiopterin.
Address correspondence to: Dr. A. Elizabeth Linder, Department of Pharmacology and Toxicology, Michigan State University, B445 Life Sciences Bldg., East Lansing, MI 48824. E-mail: linderau{at}msu.edu
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References |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Amstein R, Fetkovska N, and Buhler FR (1991) Platelet serotonin-LDL interaction in essential hypertension. J Cardiovasc Pharmacol Ther 17(Suppl 5): S35-S40.[CrossRef]
Bian X, Patel B, Dai X, Galligan JJ, and Swain G (2007) High mucosal serotonin availability in neonatal guinea pig ileum is associated with low serotonin transporter expression. Gastroenterology 132: 2438-2447.[Medline]
Brenner B, Harney JT, Ahmed BA, Jeffus BC, Unal R, Mehta JL, and Kilic F (2007) Plasma serotonin levels and the platelet serotonin transporter. J Neurochem 102: 206-215.[CrossRef][Medline]
Chanrion B, Mannoury la Cour C, Bertaso F, Lerner-Natoli M, Freissmuth M, Millan MJ, Bockaert J, and Marin P (2007) Physical interaction between the serotonin transporter and neuronal nitric oxide synthase underlies reciprocal modulation of their activity. Proc Natl Acad Sci U S A 104: 8119-8124.
Cohen ML, Schenck KW, and Hemrick-Luecke SH (1999) 5-Hydroxytryptamine(1A) receptor activation enhances norepinephrine release from nerves in the rabbit saphenous vein. J Pharmacol Exp Ther 290: 1195-1201.
Cushing DJ, Baez M, Kursar JD, Schenck K, and Cohen ML (1994) Serotonin-induced contraction in canine coronary artery and saphenous vein: role of a 5-HT1D-like receptor. Life Sci 54: 1671-1680.[CrossRef][Medline]
Erspamer V and Asero B (1952) Identification of enteramine, the specific hormone of the enterochromaffin cell system, as 5-hydroxytryptamine. Nature 169: 800-801.[Medline]
Fink GD, Johnson RJ, and Galligan JJ (2000) Mechanisms of increased venous smooth muscle tone in desoxycorticosterone acetate-salt hypertension. Hypertension 35: 464-469.
Gordon J and Barnes NM (2003) Lymphocytes transport serotonin and dopamine: agony or ecstasy? Trends Immunol 24: 438-443.[CrossRef][Medline]
Gu H, Wall SC, and Rudnick G (1994) Stable expression of biogenic amine transporters reveals differences in inhibitor sensitivity, kinetics, and ion dependence. J Biol Chem 269: 7124-7130.
Homberg J, Mudde J, Braam B, Ellenbroek B, Cuppen E, and Joles JA (2006) Blood pressure in mutant rats lacking the 5-hydroxytryptamine transporter. Hypertension 48: e115-e116.
Homberg JR, Olivier JD, Smits BM, Mul JD, Mudde J, Verheul M, Nieuwenhuizen OF, Cools AR, Ronken E, Cremers T, et al. (2007) Characterization of the serotonin transporter knockout rat: a selective change in the functioning of the serotonergic system. Neuroscience 146: 1662-1676.[CrossRef][Medline]
Horvath G, Sutto Z, Torbati A, Conner GE, Salathe M, and Wanner A (2003) Norepinephrine transport by the extraneuronal monoamine transporter in human bronchial arterial smooth muscle cells. Am J Physiol Lung Cell Mol Physiol 285: L829-L837.
Johansen PA, Jennings I, Cotton RG, and Kuhn DM (1995) Tryptophan hydroxylase is phosphorylated by protein kinase A. J Neurochem 65: 882-888.[Medline]
Lee SL, Wang WW, and Fanburg BL (2001) Dexfenfluramine as a mitogen signal via the formation of superoxide anion. FASEB J 15: 1324-1325.
Linder AE, Diaz J, Ni W, Szasz T, Burnett R, and Watts SW (2008) Vascular reactivity, 5-HT uptake and blood pressure in the serotonin transporter knockout rat. Am J Physiol Heart Circ Physiol, in press.
Linder AE, Ni W, Diaz JL, Szasz T, Burnett R, and Watts SW (2007) Serotonin (5-HT) in veins: not all in vain. J Pharmacol Exp Ther 323: 415-421.
Lowry OH, Rosebrough NJ, Farr AL, and Randall RJ (1951) Protein measurement with Folin phenol reagent. J Biol Chem 193: 265-267.
Marcos E, Adnot S, Pham MH, Nosjean A, Raffestin B, Hamon M, and Eddahibi S (2003) Serotonin transporter inhibitors protect against hypoxic pulmonary hypertension. Am J Respir Crit Care Med 168: 487-493.
Martel F and Azevedo I (2003) An update on the extraneuronal monoamine transporter (EMT): characteristics, distribution and regulation. Curr Drug Metab 4: 313-318.[CrossRef][Medline]
Mekontso-Dessap A, Brouri F, Pascal O, Lechat P, Hanoun N, Lanfumey L, Seif I, Benhaiem-Sigaux N, Kirsch M, Hamon M, et al. (2006) Deficiency of the 5-hydroxytryptamine transporter gene leads to cardiac fibrosis and valvulopathy in mice. Circulation 113: 81-89.
Ni W, Lookingland K, and Watts SW (2006) Arterial 5-hydroxytryptamine transporter function is impaired in deoxycorticosterone acetate and N
-nitro-L-arginine but not spontaneously hypertensive rats. Hypertension 48: 134-140.
Ni W, Thompson JM, Northcott CA, Lookingland K, and Watts SW (2004) The serotonin transporter is present and functional in peripheral arterial smooth muscle. J Cardiovasc Pharmacol 43: 770-781.[CrossRef][Medline]
Nilsson O, Ericson LE, Dahlstrom A, Ekholm R, Steinbusch HW, and Ahlman H (1985) Subcellular localization of serotonin immunoreactivity in rat enterochromaffin cells. Histochemistry 82: 351-355.[CrossRef][Medline]
Rapport MM, Green AA, and Page IH (1948) Crystalline serotonin. Science 108: 329-330.
Rozen S and Skaletsky HJ (2000) Primer3 on the WWW for general users and for biologist programmers, in Bioinformatics Methods and Protocols: Methods in Molecular Biology (Kravetz S and Misener S eds) Humana Press, Totowa, NJ.
Szasz T, Thakali K, Fink GD, and Watts SW (2007) A comparison of arteries and veins in oxidative stress: producers, destroyers, function, and disease. Exp Biol Med (Maywood) 232: 27-37.
Thakali K, Galligan JJ, Fink GD, and Watts SW (2007) Arterial and venous function in hypertension., in Comprehensive Hypertension (Gregory YH and Lip JEH eds), Mosby Elsevier, Philadelphia, PA.
Vanhoutte PM (1991) Platelet-derived serotonin, the endothelium, and cardiovascular disease. J Cardiovasc Pharmacol 17 (Suppl 5): S6-S12.[CrossRef][Medline]
Wacker MJ and Godard MP (2005) Analysis of one-step and two-step real-time RT-PCR using SuperScript III. J Biomol Tech 16: 266-271.[Medline]
Walther DJ, Peter JU, Winter S, Holtje M, Paulmann N, Grohmann M, Vowinckel J, Alamo-Bethencourt V, Wilhelm CS, Ahnert-Hilger G, et al. (2003) Serotonylation of small GTPases is a signal transduction pathway that triggers platelet alphagranule release. Cell 115: 851-862.[CrossRef][Medline]
Watts SW (2005) 5-HT in systemic hypertension: foe, friend or fantasy? Clin Sci (Lond) 108: 399-412.[Medline]
Watts SW and Cohen ML (1999) Vascular 5-HT receptors: pharmacology and pathophysiology of 5-HT1B, 5-HT1D, 5-HT1F, 5-HT2B and 5-HT7 receptors. Neurotransmissions 15: 3-15.
Yamamoto J, Trippodo NC, Ishise S, and Frohlich ED (1980) Total vascular pressure-volume relationship in the conscious rat. Am J Physiol 238: H823-H828.[Medline]
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  S. W. Watts The beginning of a fantastic, unanswered question: is 5-HT involved in systemic hypertension? Am J Physiol Heart Circ Physiol, September 1, 2008; 295(3): H915 - H916. [Abstract] [Full Text] [PDF]
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4.
