Rat Vena Cava Research Articles

Hemostatic Capability of a Novel Tetra-Polyethylene Glycol Hydrogel

TetraStat is a tetra-armed polyethylene glycol (PEG) hydrogel. It is a synthetic sealant that solidifies instantly in response to pH changes. This study aimed to evaluate the hemostatic effect of TetraStat through experiments evaluating future clinical applications. We used TetraStat, oxidized regenerated cellulose (SURGICEL®), and fibrinogen and thrombin sealant patch (TachoSil®) using invitro and invivo experiments. For the invitro experiment, a closed circulatory system filled with phosphate-buffered saline under high pressure was used. Needle punctures were created and closed using the various sealants. For the invivo experiment, rat venae cavae were punctured with 18- and 20-gauge (G) needles, and hemorrhage was allowed to occur for several seconds. A porous PEG sponge soaked with TetraStat was applied as a hemostatic system. Hemostasis outcomes were compared among the various concentrations (40-100g/L) of TetraStat, SURGICEL, and TachoSil. The punctured holes in the prosthetic graft were successfully sealed with TetraStat in 1min. The success rate of hemostasis with TetraStat for the punctured holes in the rat vena cava was dose-dependent. TetraStat was effective in sealing the holes created with a 20G needle at all concentrations; however, the holes created with an 18G needle could be sealed only when the concentration ≥60g/L. Hemostasis using SURGICEL or TachoSil was less successful and sometimes required up to 5min. TetraStat has a high hemostatic ability. A porous PEG sponge soaked with TetraStat is a useful choice for effective hemostasis during massive hemorrhage.

Herbal Formulations Ameliorates Chronic Venous Insufficiency, Venotonicity and Elastase Inhibition in the Management of Varicose Veins: A Preclinical Study

Varicose vein is one of the common vascular diseases, in which veins become widened, bulged and twisted. Development of drug to combat varicose vein is a challenging task due to complex nature of the disease and non-availability of specific animal model system. In this context, relevant experimental models were developed and polyherbal formulations HVVL-041702 a liniment intended for topical use (200 µl/ animal) and HVVT-041701 a granule intended for oral use (250 mg/kg body weight, orally) were evaluated. In vitro elastase inhibition assay was carried out using the human leukocyte elastase enzyme. Ex vivo venotonic activity was performed in isolated rat vena cava. In vivo anti-inflammatory, analgesic and anti-edemagenic activity were carried out in Wistar rats. Along with the aforementioned activities, HVVT-041701 was also evaluated for chronic venous insufficiency. Both the formulations showed elastase inhibition, venotonic, anti-inflammatory, analgesic and anti-edemagenic activities. HVVT-041701 was also effective in ameliorating chronic venous insufficiency by decreasing the venous pressure. Both the formulations showed beneficial effects in the management of varicose veins by improving the tonicity, venous insufficiency and vascular hyper permeability which are the pathologic hallmark of varicose veins.

The Effectiveness of Long-term Use of Low-Molecular-Weight Heparin on Venous Thromboembolism After Sleeve Gastrectomy in Rats

Objectives: The aim of the study was to investigate the effects of bemiparin administration for 15 and 30 days on deep vein thrombosis (DVT) in high-fat diet-induced rats, followed by sleeve gastrectomy (SG) for DVT prophylaxis. Setting: The study was conducted at the Kobay Experimental Animals Laboratory. Materials and Methods: Forty rats were fed a high-fat diet to induce obesity. They were then equally divided into four groups (n = 10); group 1 (control group); group 2 (nonbemiparin group); and group 3 (15-day bemiparin group) and group 4 (30-day bemiparin group) in which bemiparin therapeutic doses were administered for 15 and 30 days, respectively. Sixteen weeks after feeding, SG was performed on rats from groups 2, 3, and 4. Doppler ultrasonography was performed to investigate thrombosis of the inferior vena cava and iliac veins in all rats before and 1 month after SG. Rat vena cava, iliac veins, and lung tissues were removed to determine venous thrombosis status and investigate microthrombi through histological examination. Results: No statistically significant difference was found between groups in terms of the thickness of intima–media (μm), thrombus area (μm2), and erythrocyte, leukocyte, and platelet/fibrin values of the iliac veins (p > 0.05). A statistically significant difference was found between groups in terms of the presence of thrombus and radiological status of the vena cava (p < 0.05). In addition, the measurement percentage was found to be 100% in group 2, 37.5% in group 3, and 12.5% in group 4. Conclusion: We believe that administration of bemiparin once a day for 30 days can be a safe and effective treatment method in the prevention of microthrombi, following SG.

Venous endothelium reactivity to Angiotensin II: A study in primary endothelial cultures of rat vena cava and portal vein

The role of the vascular endothelium in modulating the arterial system has been widely investigated, but poorly explored at the venous site. In the present work, primary cultures of venous endothelium from rat Vena Cava (VC) and Portal Vein (PV) were established, characterized and analyzed according to their growth pattern and ability to produce nitric oxide (NO) and prostanoids (PGF2 α and PGI2), at basal state and after stimulation with Angiotensin II (Ang II, 1μmol/L). Basal NO was detected in all examined cells in culture. Pre-incubation with Ang II increased NO production in cells from VC (but not in PV cultures), through activation of both AT1 and AT2 receptors. Both cultures exhibited detectable levels of PGF2 α at resting conditions, which were similarly enhanced by Ang II. Basal PGI2 levels were higher in PV, but increased after Ang II treatment in VC, with no further effect on PV cells. We conclude that endothelial cells from VC and PV exhibit important properties and react to Ang II, probably influencing the whole circulatory system. This experimental cell model gives support to further studies concerning intracellular pathways of the venous endothelium, analyzed in separate from the vascular smooth muscle wall.

Ryanodine receptors are uncoupled from contraction in rat vena cava

Ryanodine receptors (RyR) are Ca2+-sensitive ion channels in the sarcoplasmic reticulum (SR) membrane, and are important effectors of SR Ca2+ release and smooth muscle excitation–contraction coupling. While the relationship between RyR activation and contraction is well characterized in arteries, little is known about the role of RyR in excitation–contraction coupling in veins. We hypothesized that RyR are present and directly coupled to contraction in rat aorta (RA) and vena cava (RVC). RA and RVC expressed mRNA for all 3 RyR subtypes, and immunofluorescence showed RyR protein was present in RA and RVC smooth muscle cells. RA and RVC rings contracted when Ca2+ was re-introduced after stores depletion with thapsigargin (1μM), indicating both tissues contained intracellular Ca2+ stores. To assess RyR function, contraction was then measured in RA and RVC exposed to the RyR activator caffeine (20mM). In RA, caffeine caused contraction that was attenuated by the RyR antagonists ryanodine (10μM) and tetracaine (100μM). However, caffeine (20mM) did not contract RVC. We next measured contraction and intracellular Ca2+ (Ca2+i) simultaneously in RA and RVC exposed to caffeine. While caffeine increased Ca2+i and contracted RA, it had no significant effect on Ca2+i or contraction in RVC. These data suggest that ryanodine receptors, while present in both RA and RVC, are inactive and uncoupled from Ca2+ release and contraction in RVC.

Contraction of rat vena cava by endothelin‐1 is dependent on phospholipase‐Cβ, but independent of IP3 receptor activation

In vascular smooth muscle, inositol 1,4,5‐trisphosphate (IP3) regulates excitation‐contraction coupling by activating the release of sarcoplasmic Ca2+ stores. IP3 is produced through the activity of phospholipase Cβ (PLCβ), which cleaves phosphatidylinositol into diacylglycerol (DAG) and IP3. While the vasoconstrictor ET‐1 activates PLCβ and increases IP3 formation in arteries, it is unclear if this is so in veins. We hypothesized that contraction to ET‐1 in rat aorta (RA) and vena cava (RVC) depends upon IP3‐mediated Ca2+ release. To test if PLCβ was activated by ET‐1, isometric contraction was measured in RA and RVC rings exposed to vehicle, the PLCβ inhibitor U‐73122 or its inactive analog U‐ 73343 (1 μM), or the IP3 receptor antagonist 2‐APB (100 μM). While U‐73343 did not significantly inhibit contraction to ET‐1, U‐73122 significantly reduced maximum contraction to ET‐1 in RA (86±6% of control) and RVC (49±11% of control). Contrary to our hypothesis, 2‐APB significantly reduced maximum contraction to ET‐1 only in RA (55±4%) and not RVC (82±8%). These data were supported by Western blot analysis, showing 63.1 times more IP3R‐1 and 12.6 times more IP3R‐2 protein in RA than RVC, as measured by densitometry. These findings suggest that ET‐1 does activate PLCβ in RA and RVC, but only contraction to ET‐1 in RA is regulated by IP3. Rather, DAG and not IP3 may regulate contraction to ET‐1 in RVC. Supported by NIH P01HL70687.

S35972, a direct‐acting thrombin inhibitor with high oral bioavailability and antithrombotic efficacy

Dabigatran etexilate is the first oral thrombin inhibitor to demonstrate superior efficacy to warfarin for stroke prevention in patients with atrial fibrillation. This study describes the in vitro, ex vivo anticoagulant and in vivo antithrombotic effects of an oral thrombin inhibitor, S35972, in comparison with dabigatran etexilate. Enzyme assays with thrombin and related serine proteases were performed. Clotting times, including activated partial thromboplastin time (APTT) and thrombin time (TT), were measured in vitro in different species and ex vivo in dogs and rats to determine pharmacologic bioavailabilities. The formation of occlusive venous and arterial thrombi in the rat vena cava and aorta was induced with stasis plus thromboplastin or ferrous chloride, respectively. S35972 inhibited human thrombin with an IC(50) of 3.7 nm, and did not inhibit other serine proteases. The anticoagulant activities of S35972 in vitro were comparable in dog and human plasmas, and the sensitivity of the clotting times to S35972 was TT > APTT > prothrombin time. In the fasted dog, oral administration of 3 mg kg(-1) S35972 increased TT rapidly and for at least 8 h, and its pharmacologic bioavailability was 75.4% ± 0.1%. In the rat venous thrombosis model, 3 mg kg(-1) oral S35972 or dabigatran etexilate significantly decreased the thrombus weight. In the rat aortic thrombosis model, oral S35972 at 10mg kg(-1) significantly decreased thrombus weight, by approximately 50%, whereas, at this dose, no effect was obtained with dabigatran etexilate. S35972 is a non-prodrug thrombin inhibitor with high selectivity, oral bioavailability, and antithrombotic efficacy.

Ca 2+−dependent contraction by the saponoside escin in rat vena cava: Implications in venotonic treatment of varicose veins

Saponosides (horse chestnut seed extract, escin) and flavonoids (diosmin, Daflon 500, Servier, France) exhibit venotonic properties that have been utilized in treatment of varicose veins. However, the cellular mechanisms underlying the venotonic properties of escin and diosmin are unclear. Because Ca(2+) is a major regulator of venous smooth muscle (VSM) function, we tested the hypothesis that escin and diosmin promote Ca(2+)-dependent venous contraction. Rings of inferior vena cava (IVC) from male rats were suspended in a tissue bath for measurement of isometric contraction. Following control contraction to 96 mM KCl, the effects of escin and diosmin (10(-10) to 10(-4) M) on vein contraction were measured. To test the role of intracellular Ca(2+) release, the vein response to escin and diosmin was measured in Ca(2+)-free (2mM EGTA) Krebs. To test for Ca(2+)-dependent effects, IVC segments were pretreated with escin or diosmin (10(-4) M) in 0 Ca(2+) Krebs, then extracellular CaCl(2) (0.1, 0.3, 0.6, 1, 2.5 mM) was added and the [Ca(2+)](e)-contraction relationship was constructed. To test for synergistic effects of diosmin, IVC segments were pretreated with diosmin (10(-4) M), then stimulated with KCl (16-96 mM) or escin (10(-10) to 10(-4) M) and vein contraction was measured. Contraction data were presented as mg/mg tissue (means ± SEM). In IVC segments incubated in normal Krebs (2.5 mM Ca(2+)), escin caused concentration-dependent contraction (max 104.3 ± 19.6 at 10(-4) M). Escin-induced contraction was not a rigor state, because after washing with Krebs, the veins returned to a relaxed state. In Ca(2+)-free Krebs, there was essentially no contraction to escin. In escin-treated veins incubated in 0 Ca(2+) Krebs, stepwise addition of extracellular CaCl(2) caused corresponding increases in contraction (max 80.0 ± 11.1 at 2.5 mM). In the absence of escin, the α-adrenergic agonist phenylephrine (PHE, 10(-5) M), angiotensin II (AngII, 10(-6) M), and membrane depolarization by KCl (96 mM) caused significant contraction (122.5 ± 45.1, 114.2 ± 12.2 and 221.7 ± 35.4, respectively). In IVC segments pretreated with escin (10(-4) M), the contractile response to PHE (9.7 ± 2.6), AngII (36.0 ± 9.1), and KCl (82.3 ± 10.2) was significantly reduced. Diosmin (10(-4) M) caused small contractions in normal Krebs (11.7 ± 1.9) and Ca(2+)-free Krebs (4.2 ± 2.2). In diosmin-treated veins incubated in 0 Ca(2+) Krebs, addition of extracellular CaCl(2) caused minimal contraction. Diosmin did not enhance the IVC contraction to PHE, AngII, or escin, but enhanced the contractile response to KCl (24-51 mM). In rat IVC, escin induces extracellular Ca(2+)-dependent contraction, but disrupts α-adrenergic and AT(1)R receptor-mediated pathways and depolarization-induced contraction. The initial venotonic benefits of escin may be offset by disruption of vein response to endogenous venoconstrictors, limiting its long-term therapeutic benefits in varicose veins. Diosmin does not cause venous contraction or potentiate the venotonic effects of endogenous venoconstrictors or escin ex vivo, and its use as venotonic may need to be further evaluated.

Nitrates do not affect prostacyclin formation by rat arteries: this is unrelated to increased vascular prostacyclin formation with age.

The question of whether vasodilator nitrates act by releasing prostacyclin is controversial. Since the ability of blood vessels to form prostacyclin changes with age, we have investigated whether this may explain the discrepancies in the literature. It does not, since isosorbide dinitrate or glyceryl trinitrate incubated with rat aorta or vena cava from male Wistar rats had little or no effect on the release of prostacyclin, measured as 6-keto-PGF1 alpha. We confirm that the aorta produces substantially more prostacyclin than the vena cava. The arterial production of prostacyclin was greater in rats weighing 350-400 g than in those weighing 116-152 g, but the production by the veins was similar in both groups.

In situ quantification of endothelial cell damage caused by iodinated contrast media using a rat vena cava model

Quantification of vascular endothelial cell damage induced by iodinated contrast media using an in situ perfused rat vena cava model. The institutional review board approved this study protocol prior to the commencement of all studies. A laparotomy was performed in 90 rats divided into 18 groups of five, and an 18 G-catheter was inserted into the abdominal vena cava (mean length: ca 8mm). After sacrificing, a thoracotomy was done and the outflow perfusate was emitted via a polyethylene tube inserted into the thoracic vena cava through the right atrium for an open system. Iopamidol (300 or 370 mgI/mL, 50 or 100mL) was injected via the abdominal vena cava at a rate of 1, 4, or 8 mL/s. The abdominal vena cava was removed for histological analysis (n=5). Physiological saline was injected as a negative control. The detachment percentage of endothelial cells was calculated by measuring the circumference and detachment section of the endothelium. The difference of the detachment percentage and circumference between each group was compared with Tukey's range test. In contrast media groups, the severity of damage to the vascular endothelial cell was direct proportional to the increase of injection rate. The detachment percentage at 4 or 8 mL/s was significantly higher than that at 1 mL/s. As a result, the correlation between the injection rate and severity of cell damage was significant; however, the detachment percentage among contrast media groups was not significant at any injection rate. The in situ vena cava model was able to quantify contrast media injection related endothelial damage based on histopathological endpoints. Moreover, our results indicate that mechanical shear stress besides physico-chemical properties such as osmolality or viscosity cause endothelial damage.

Involvement of the AT 1 receptor in the venoconstriction induced by angiotensin II in both the inferior vena cava and femoral vein

Although angiotensin II-induced venoconstriction has been demonstrated in the rat vena cava and femoral vein, the angiotensin II receptor subtypes (AT 1 or AT 2) that mediate this phenomenon have not been precisely characterized. Therefore, the present study aimed to characterize the pharmacological receptors involved in the angiotensin II-induced constriction of rat venae cavae and femoral veins, as well as the opposing effects exerted by locally produced prostanoids and NO upon induction of these vasomotor responses. The obtained results suggest that both AT 1 and AT 2 angiotensin II receptors are expressed in both veins. Angiotensin II concentration–response curves were shifted toward the right by losartan but not by PD 123319 in both the vena cava and femoral vein. Moreover, it was observed that both 10 −5 M indomethacin and 10 −4 M L-NAME improve the angiotensin II responses in the vena cava and femoral vein. In conclusion, in the rat vena cava and femoral vein, angiotensin II stimulates AT 1 but not AT 2 to induce venoconstriction, which is blunted by vasodilator prostanoids and NO.

Hyaluronan‐based scaffold for in vivo regeneration of the rat vena cava: Preliminary results in an animal model

The aim of this study was to develop a prosthetic graft that could perform as a small-diameter vascular conduit for vein regeneration. The difficulty of obtaining significant long-term patency and good wall mechanical strength in vivo has been a significant obstacle in achieving small-diameter vein prostheses. Fifteen Male Wistar rats weighing 250-350 g were used. Tubular structures of hyaluronan (HYAFF-11 tubules, 2 mm diameter, and 1.5 cm length) were implanted in the vena cava of rats as temporary absorbable guides to promote regeneration of veins. Performance was assessed at 30, 60, and 90 days after surgery by histology (hematoxylin-eosin and Weighert solution) and immunohistochemistry (antibodies to von Willebrand factor and to Myosin Light-Chain Kinase). These experiments resulted in two novel findings: (1) sequential regeneration of vascular components led to complete vein wall regeneration 30 days after surgery; (2) the biomaterial used created the ideal environment for the delicate regeneration process during the critical initial phases, yet its biodegradability allowed for complete degradation of the construct 4 months after implantation, at which time, a new vein remained to connect the vein stumps. This work demonstrates the complete vena cava regeneration inside the hyaluronic acid-based prosthesis, opening new perspective of microsurgical applications, like replantation of the upper limb, elongation of vascular pedicle of free flaps, cardiovascular surgery, and pediatric microvascular surgery.

Abstract: P1137 ANGIOTENSIN II-STIMULATED HUMAN MONOCYTES ARE INVOLVED IN HYPERCHOLESTEROLEMIA

Although angiotensin II-induced venoconstriction has been demonstrated in the rat vena cava and femoral vein, the angiotensin II receptor subtypes (AT1 or AT2) that mediate this phenomenon have not been precisely characterized. Therefore, the present study aimed to characterize the pharmacological receptors involved in the angiotensin II-induced constriction of rat venae cavae and femoral veins, as well as the opposing effects exerted by locally produced prostanoids and NO upon induction of these vasomotor responses. The obtained results suggest that both AT1 and AT2 angiotensin II receptors are expressed in both veins. Angiotensin II concentration–response curves were shifted toward the right by losartan but not by PD 123319 in both the vena cava and femoral vein. Moreover, it was observed that both 10−5 M indomethacin and 10−4 M L-NAME improve the angiotensin II responses in the vena cava and femoral vein. In conclusion, in the rat vena cava and femoral vein, angiotensin II stimulates AT1 but not AT2 to induce venoconstriction, which is blunted by vasodilator prostanoids and NO.

Enzymatic sources of basal hydrogen peroxide (H2O2) levels in rat arterial and venous tissues

Reactive oxygen species (ROS) production in vascular tissues is linked with the initiation and progression of diseases such as hypertension and atherosclerosis. An important but less studied sector of the vasculature is the venous system. We have shown that ROS production is greater in rat vena cava (VC) compared to aorta (Ao). Here we investigated the relative contribution of ROS enzymes to basal vascular H2O2 levels, hypothesizing that xanthine oxidase (XO) would be the most important H2O2 source in veins. Using two rat artery‐vein pairs: Ao‐VC and carotid artery (CA)‐jugular vein (JV), we examined H2O2 production in the presence of inhibitors for NADPH oxidase (100μM apocynin), XO (100μM allopurinol/oxypurinol), eNOS (100μM LNNA), mitochondrial complex I (10μM rotenone), and cyclooxygenase (COX, 10μM indomethacin/10mM ketorolac). Aortic H2O2 production was abolished by apocynin, allopurinol and indomethacin. Allopurinol also abolished H2O2 production in the CA and decreased it by 88% in the JV, but did not significantly lower VC H2O2 production. Surprisingly, COX inhibition with indomethacin decreased H2O2 levels of the JV by 82% and of the CA by 41%, while ketorolac decreased H2O2 production in the VC by 38%. LNNA and rotenone had no effect in any tissue. These findings highlight the importance of investigating non‐classical sources of ROS in vascular tissues.Funding: PO1 HL70687 (SWW), AHA 0715679Z (TS).

Endothelin ETBReceptors in Arteries and Veins: Multiple Actions in the Vein

Endothelin receptors (ET(A) and ET(B)) mediate responses to ET-1. ET(B) receptor function seems to differ between a similarly sized arterial and venous pair, the rat vena cava (RVC) and rat thoracic aorta (RA). ET(B) receptors mediate RVC contraction directly, but it is unclear whether ET(B) receptors mediate contraction in RA. Because of these apparent differences in ET(B) receptor-mediated vascular contraction, we hypothesize that relaxant ET(B)-receptor mechanisms in RVC would be different from those in RA. RA and RVC rings were isolated from rats for measurement of isometric contraction. When contracted with prostaglandin F-2alpha (PGF-2alpha) (20 microM), the ET(B) receptor agonist sarafotoxin-6c (S6c) (100 nM) significantly relaxed RA and RVC. N(omega)-Nitro-L-arginine (LNNA) (100 microM) or endothelial denudation abolished relaxation to S6c in RA. By contrast, S6c-induced relaxation of RVC was attenuated but not abolished by LNNA and endothelial denudation. RVC (PGF-2alpha-contracted) relaxed to low concentrations of ET-1, whereas under the same conditions RA responded with contraction. ET-1-induced relaxation in RA was observed only with ET(A) receptor blockade. Vessels from dopamine-beta-hydroxylase-ET(B) transgenic rats, which lack functional ET(B) receptors in the vasculature, were also used. RVC (PGF-2alpha-contracted) from these rats did not relax to ET-1. Thus, although both RA and RVC possess endothelial relaxant ET(B) receptors, RA and RVC differ in that relaxant ET(B) receptors may also be present in smooth muscle of RVC. Moreover, the mechanisms of endothelial cell ET(B) receptor-mediated relaxation in RA and RVC are not the same.

Prolonged increases in vein wall tension increase matrix metalloproteinases and decrease constriction in rat vena cava: Potential implications in varicose veins

Increased venous hydrostatic pressure plays a role in the pathogenesis of varicose veins. Increased expression of matrix metalloproteinases (MMPs) has been identified in varicose veins. Also, we have shown that MMP-2 inhibits venous contraction. However, the relation between venous pressure, MMP expression, and venous dysfunction is unclear. The purpose of this study was to test the hypothesis that prolonged increases in venous wall tension cause overexpression of MMPs and decreased contractility, which in turn promote venous dilation. Circular segments of inferior vena cava (IVC) were isolated from male Sprague-Dawley rats and suspended between two wires in Krebs solution. Preliminary vein wall tension-contraction relation showed maximal potassium chloride (KCl) (96 mmol/L) contraction at 0.5 g basal tension, which remained steady with increases in tension up to 2 g. Vein segments were subjected to either control (0.5 g) or high (2 g) basal tension for short (1 hour) or long duration (24 hours). Isometric contraction in response to phenylephrine (Phe, 10(-5) mol/L), angiotensin II (AngII, 10(-6) mol/L), and KCl was measured. The veins were frozen to determine the expression and localization of MMPs using immunoblots and immunohistochemistry. In IVC segments subjected to 0.5 g tension for 1 hour, Phe and AngII produced significant contraction. At higher 2 g basal tension for 24 hours, both Phe and AngII contractions were significantly reduced. Reduction in KCl contraction was also observed at high 2 g basal tension for 24 hours, suggesting that the reduction in vein contraction is not specific to a particular receptor, and likely involves inhibition of a post-receptor contraction mechanism. In vein segments under 2 g tension for 24 hours and treated with TIMP-1, Phe, AngII, and KCl contractions were partially restored, suggesting the involvement of MMPs. IVC immunoblot analysis demonstrated prominent bands corresponding to MMP-2 and MMP-9 protein. High 2 g wall tension for 24 hours was associated with marked increase in the amount of MMP-2 and -9 relative to the housekeeping protein actin. There was a correlation between MMP expression and decreased vein contraction. Also, significant increases in MMP-2 and -9 immunostaining were observed in IVC segments subjected to high 2 g tension for 24 hours. Both MMP-2 and MMP-9 caused significant inhibition of Phe contraction in IVC segments. In rat IVC, increases in magnitude and duration of wall tension is associated with reduced contraction and overexpression of MMP-2 and -9. In light of our findings that MMP-2 and -9 promote IVC relaxation, the data suggest that protracted increases in venous pressure and wall tension increase MMPs expression, which in turn reduce venous contraction and lead to progressive venous dilation.

Do different Ca entry mechanisms mediate Endothelin‐1‐induced contraction of rat aorta and vena cava?

Endothelin‐1 (ET‐1) is a potent vasoconstrictor for venous and arterial vasculature. ET‐1 mediated contraction in rat thoracic aorta (RA) is Ca‐dependent, involving non‐selective cation channels (NSCC) and store‐operated Ca channels (SOCC) as sources of Ca influx. However, the Ca‐dependent contractile mechanisms of rat vena cava (RVC) to ET‐1 are unknown. We hypothesize that contraction to ET‐1 is dependent on Ca‐channel function, and that RA and RVC utilize different Ca channels due to differing function, physiology, and ET receptor expression. Of five antagonists tested, only the SOCC antagonist LOE‐908 (10 mM) significantly inhibited ET‐1‐induced contraction of RVC (logEC50[M]: −8.39±0.08 vs. −8.21±0.04). Zero Ca PSS/1mM EGTA abolished ET‐1 responses in RA, but only attenuated the response in RVC (125% ± 35% of NE response vs. 639% ± 50%). Thus, a component of RVC contraction to ET‐1 involves SOCC channels. RVC responded to ET‐1 even without [Ca]o, suggesting either large intracellular stores of Ca, or a Ca‐independent contractile pathway. This implies ET‐1–induced contraction of RA and RVC involve different Cainflux pathways, and different signaling mechanisms. We speculate that these differences may be attributed to differing interactions of ETA and ETB receptors in RVC compared to RA. Supported by NIH HL070687 to SWW and HL32469 to WFJ.

Preferential Myosin Heavy Chain Isoform B Expression May Contribute to the Faster Velocity of Contraction in Veins versus Arteries

Smooth muscle myosin heavy chains occur in 2 isoforms, SMA (slow) and SMB (fast). We hypothesized that the SMB isoform is predominant in the faster-contracting rat vena cava compared to thoracic aorta. We compared the time to half maximal contraction in response to a maximal concentration of endothelin-1 (ET-1; 100 nM), potassium chloride (KCl; 100 mM) and norepinephrine (NE; 10 µM). The time to half maximal contraction was shorter in the vena cava compared to aorta (aorta: ET-1 = 235.8 ± 13.8 s, KCl = 140.0 ± 33.3 s, NE = 19.8 ± 2.7 s; vena cava: ET-1 = 121.8 ± 15.6 s, KCl = 49.5 ± 6.7 s, NE = 9.0 ± 3.3 s). Reverse-transcription polymerase chain reaction supported the greater expression of SMB in the vena cava compared to aorta. SMB was expressed to a greater extent than SMA in the vessel wall of the vena cava. Western analysis determined that expression of SMB, relative to total smooth muscle myosin heavy chains, was 12.5 ± 4.9-fold higher in the vena cava compared to aorta, while SMA was 4.9 ± 1.2-fold higher in the aorta than vena cava. Thus, the SMB isoform is the predominant form expressed in rat veins, providing one possible mechanism for the faster response of veins to vasoconstrictors.

Increased serotonin uptake and decreased serotonin metabolism in veins: is there a role in the control of vascular tone and blood pressure?

A role for serotonin (5-hydroxytryptamine; 5-HT) in cardiovascular regulation has recently been supported after discovery of a functional local 5-HT system in peripheral arterial smooth muscle. The venous system redistributes blood volume and can significantly alter blood pressure (BP), and the presence of the 5-HT system in veins has not been investigated. We hypothesized that the 5-HT system is present and functional in veins as it is in arteries. The presence of 5-HT [pg/μg protein] (3.8 ± 1.1 vs. 0.2 ± 0.04; P < 0.05) and the 5-HT metabolite 5- hydroxyindole acetic acid (5-HIAA) [pg/μg protein] (0.6 ± 0.1 vs. 0.36 ± 0.08) was revealed by high performance liquid chromatography (HPLC) in rat vena cava (VC) and in rat aorta (RA), respectively. In rats treated with the monoamine oxidase-A (MAO-A) inhibitor pargyline, the enzyme responsible for 5-HT degradation, no 5-HIAA was detected in VC and RA. MAO-A expression was observed in VC and RA by Western Blot. In pargyline-treated rats, HPLC revealed higher basal 5-HT levels in VC (5.2 ± 1.5 pg/μg protein) than in RA (0.97 ± 0.2 pg/μg protein). 5-HT uptake was measured after the tissues were challenged with exogenous 5-HT (1 μM); uptake was higher in VC (15.9 +/− 1.5 pg/μg protein) than in RA (6.6 ± 1.4 pg/μg protein). The presence of the 5-HT transporter in VC was observed by immunohistochemistry. The presence of a functional 5-HT system in VC raises one more question as to the intriguing role of peripheral 5-HT in the control of vascular tone and consequently BP.

A model for passive elastic properties of rat vena cava

A two-dimensional model for the elastic properties of vena cava abdominalis under orthotropic deformation is introduced and tested against the experimental data obtained from six specimen of rat venae cavae by pressurization experiments. The model is based on membrane approximation and suited for vessels where most of the elastic elements are oriented axially, while circumferential contraction is exerted by redirecting axial stress by some network of oblique fibers. For the experimental data considered in this paper, the ratio between axial and circumferential stress depends almost exclusively on the circumferential extension ratio. As a consequence, the mechanical system can be formally decomposed in a kinematic system reacting by axial contraction on circumferential extension without any loss or storage of energy, serially connected to a hyperelastic system acting only in axial direction. Both systems are modeled separately by equations obtained by a purely phenomenological approach with two parameters for each system. This leads to reasonable reproduction of the experimental data. Introducing a correction parameter, which takes into account that the model assumption on the decomposition does not hold exactly, we get better reproduction of data. However, this is paid for by loss of physical rigor and in particular by departing from the assumption of hyperelasticity.