Contraction Of Venous Smooth Muscle Research Articles

Mechanisms of Lower Extremity Vein Dysfunction in Chronic Venous Disease and Implications in Management of Varicose Veins.

Chronic venous disease (CVD) is a common venous disorder of the lower extremities. CVD can be manifested as varicose veins (VVs), with dilated and tortuous veins, dysfunctional valves and venous reflux. If not adequately treated, VVs could progress to chronic venous insufficiency (CVI) and lead to venous leg ulcer (VLU). Predisposing familial and genetic factors have been implicated in CVD. Additional environmental, behavioral and dietary factors including sedentary lifestyle and obesity may also contribute to CVD. Alterations in the mRNA expression, protein levels and proteolytic activity of matrix metalloproteinases (MMPs) have been detected in VVs and VLU. MMP expression/activity can be modulated by venous hydrostatic pressure, hypoxia, tissue metabolites, and inflammation. MMPs in turn increase proteolysis of different protein substrates in the extracellular matrix particularly collagen and elastin, leading to weakening of the vein wall. MMPs could also promote venous dilation by increasing the release of endothelium-derived vasodilators and activating potassium channels, leading to smooth muscle hyperpolarization and relaxation. Depending on VVs severity, management usually includes compression stockings, sclerotherapy and surgical removal. Venotonics have also been promoted to decrease the progression of VVs. Sulodexide has also shown benefits in VLU and CVI, and recent data suggest that it could improve venous smooth muscle contraction. Other lines of treatment including induction of endogenous tissue inhibitors of metalloproteinases (TIMPs) and administration of exogenous synthetic inhibitors of MMPs are being explored, and could provide alternative strategies in the treatment of CVD.

MMP-2 Induced Vein Relaxation via Inhibition of [Ca 2+] e-Dependent Mechanisms of Venous Smooth Muscle Contraction. Role of RGD Peptides

Matrix metalloproteinases (MMPs) are implicated in the pathogenesis of varicose veins. We have shown that MMP-2 causes relaxation of venous segments and suggested a role of venous smooth muscle (VSM) hyperpolarization; however, the downstream mechanisms are unclear. We tested whether MMP-2 induced venous relaxation involves inhibition of the Ca(2+) mobilization mechanisms of VSM contraction due to generation of Arg-Gly-Asp (RGD)-containing peptides. Circular segments of inferior vena cava (IVC) were isolated from male Sprague-Dawley rats, suspended between two wires in a tissue bath, and isometric contraction was measured. Contraction data in mg/mg tissue were presented as means +/- SEM. In IVC incubated in normal Krebs (2.5 mM Ca(2+)), the alpha-adrenergic agonist phenylephrine (Phe, 10(-5) M) caused initial peak (133.2 +/- 17.5) followed by a maintained contraction (73.4 +/- 11.6), that was inhibited by MMP-2 (1 microg/mL) to 32.4 +/- 12.8 in 30 min. The inhibitory effects of MMP-2 were reversible by washing the tissue with Krebs or in the presence of the MMP inhibitors TIMP-1 (1 microg/mL), Ro 28-2653, and BB-94 (10(-6) M), and were not associated with changes in IVC structure, demonstrating specificity. Angiotensin II (AngII, 10(-6) M) caused a monophasic contraction (114.2 +/- 12.2), that was also inhibited by MMP-2 (66.0 +/- 7.4), suggesting a post-receptor effect on the downstream mechanisms of VSM contraction. To test the role of Ca(2+) release from the sarcoplasmic reticulum, IVC was incubated in Ca(2+)-free 2 mM ethylene glycol-bis(2-aminoethyl ether-N,N,N',N'-tetra-acetic acid (EGTA) Krebs with or without MMP-2. In Ca(2+)-free Krebs, caffeine did not cause contraction, suggesting a limited role of the Ca(2+)-induced Ca(2+)-release mechanism, and Phe and AngII caused a small contraction (7.2 +/- 1.7 and 14.9 +/- 2.8) that was slightly increased by MMP-2 (10.4 +/- 3.0 and 33.8 +/- 10.0), suggesting little effect on IP(3)-induced Ca(2+) release. To test the role of Ca(2+) entry through membrane channels, after eliciting a transient Phe contraction in nominally 0 Ca(2+) Krebs, increasing concentrations of CaCl(2) (0.1, 0.3, 0.6, 1, 2.5 mM) were added and the extracellular Ca(2+) concentration [Ca(2+)](e)-contraction relationship was constructed. The [Ca(2+)](e)-contraction relation was reduced in MMP-2 treated IVC, suggesting inhibition of Ca(2+) entry. In IVC treated with MMP-2, the Ca(2+) channel blocker diltiazem (10(-5)M) did not cause any further inhibition of Phe contraction, suggesting that Ca(2+) entry is already inhibited by MMP-2. To test whether MMP-2 actions involve generation of RGD and modulation of integrin receptors, experiments where repeated in IVC segments saturated with RGD (10(-5) M), or pretreated with the alpha(v)beta(3) integrin blocker cyclo(Ala-Arg-Gly-Asp-3-aminomethylbenzoyl) (cyclo-RGD). RGD-peptide caused only small relaxation of Phe contracted IVC (6.4 +/- 3.4%), and addition of MMP-2 to RGD-treated IVC caused further relaxation (69.7 +/- 3.0%). Pretreatment of IVC with cyclo-RGD did not significantly affect MMP-2 induced relaxation (55.0 +/- 5.0%). In rat IVC, MMP-2 attenuates [Ca(2+)](e)-dependent VSM contraction without affecting Ca(2+) release from intracellular Ca(2+) stores. MMP-2 induced VSM relaxation may not involve RGD generation or activation of alpha(v)beta(3) integrin receptor. MMP-2 induced inhibition of the Ca(2+) entry mechanism of VSM contraction may play a role in the venous dilation associated with varicose vein formation.

COUNTERPOINT: ACTIVE VENOCONSTRICTION IS NOT IMPORTANT IN MAINTAINING OR RAISING END-DIASTOLIC VOLUME AND STROKE VOLUME DURING EXERCISE AND ORTHOSTASIS

Veins were considered merely as passive conduits of blood until Mellander ([13][1]) reported that stimulation of sympathetic nerves supplying the cat's hindquarters resulted in a decrease in regional blood volume. This and other work led Folkow and Mellander ([4][2]) to assert that veins were “at

Inhibition by midazolam of the adrenergic function in the isolated canine mesenteric vein.

Midazolam has been reported to cause hypotension or to depress sympathetic activity following intravenous injection. However, little information is available concerning the mechanism of these effects. The aim of the present study was to determine the effects of midazolam on release of noradrenaline (NA) at nerve terminals and on receptors in the venous smooth muscle. The effect of midazolam at nerve terminals was examined by measuring the amount of NA release from superfused canine mesenteric vein helical strips during electrical stimulation (ES; 5 Hz, 2 ms, 9 V). The NA was quantified by high-performance liquid chromatography with electrochemical detection; tension development evoked by ES was also recorded simultaneously. In a separate series of experiments, ring preparations from the isolated vein were mounted in Krebs-Ringer solution for isometric tension recording to assess the effect of midazolam on alpha-adrenoceptors. Application of tetrodotoxin (10(-6) M) or replacement of superfusate with Ca(2+)-free solution decreased both the release of NA and the tension development evoked by ES. Yohimbine (5 x 10(-8) M) increased the ES-evoked release of NA, whereas it decreased tension development in the vein strips. Midazolam (10(-4) M) did not affect either the basal release of NA or the basal tension, but inhibited both the NA release (P < 0.01) and the tension development (P < 0.01) during ES; midazolam at 10(-5) M inhibited the tension development (P < 0.05) but had no effect on NA release. In the ring preparations, midazolam (10(-5) and 10(-4) M) attenuated responses to NA (a mixed alpha 1- and alpha 2-adrenoceptor agonist, 10(-8) to 10(-3) M), phenylephrine (the alpha 1-adrenoceptor agonist, 10(-8) to 10(-3) M) and 5-bromo-6-[2-imidazolin-2yl-amino]-quinoxaline (UK14304; the alpha 2-adrenoceptor agonist, 10(-7) to 10(-3) M) in a dose-dependent manner. The data obtained in the present study suggest that midazolam at 10(-4) M may reduce venous tone by inhibiting the release of NA from sympathetic nerve endings and both alpha 1- and alpha 2-adrenoceptor mediated smooth muscle contractions. It is also postulated that a stage of the post-receptor transduction mechanism linked to the venous smooth muscle contraction may be more sensitive to midazolam than the NA release mechanism at nerve terminals since midazolam at the low concentration tested inhibited ES-evoked tension development with no effect on the release of NA.

Bradykinin-induced contractions of canine saphenous veins: mediation by B2 receptors and involvement of eicosanoids.

1. Experiments were designed to determine the subtype of kinin-receptors mediating the contraction of venous smooth muscle to bradykinin and to investigate the involvement of metabolites of arachidonic acid in this response. 2. Bradykinin (10(-9) to 10(-6) M) caused concentration-dependent contractions of the canine isolated saphenous vein without endothelium, which were potentiated by indomethacin (10(-5) M, an inhibitor of cyclo-oxygenase). The concentration-response curve was biphasic, reaching an asymptote at 10(-8) M and a secondary maximal response at 10(-6) M. 3. Bradykinin (10(-8) M to 3 x 10(-6) M) caused a three fold stimulation in the release of the vasodilator prostaglandin E2 (PGE2) and a two fold stimulation of that of the vasodilator prostacyclin, measured by the production of 6-keto-PGF1 alpha (its stable breakdown product). 4. Under control conditions, nordihydroguaiaretic acid (NDGA, 10(-5) M), an inhibitor of lipoxygenase, did not affect the response to bradykinin. In the presence of indomethacin (10(-5) M), NDGA reduced contractions to bradykinin, suggesting the involvement of lipoxygenase metabolites in the potentiation evoked by the inhibitor of cyclo-oxygenase. 5. The selective B1 receptor agonist [des-Arg9]-bradykinin, in the concentration-range 10(-6) to 10(-5) M, induced contractions, which were abolished by the B2 receptor antagonist D-Arg-[Hyp3, Thi5, D-Tic7, Oic8]-bradykinin (Hoe 140; 10(-6) M). The selective B1 receptor antagonist [des-Arg9, Leu8]-bradykinin, (10(-7) to 10(-5) M) had no significant effect on bradykinin-induced contractions. 6. The B2 receptor antagonists Hoe 140 (10(-8) to 10(-6) M) and D-Arg [Hyp3, D-Phe7]-bradykinin (10(-7) to 10(-5) M) shifted the concentration-response curve to bradykinin to the right in a concentration-dependent manner. 7. These results indicate that, in the canine saphenous vein, bradykinin causes contraction by activating B2 receptors. This results in the production of metabolites of arachidonic acid, which play a key role in the contraction of canine saphenous venous smooth muscle.

Intracellular Ca 2+ Release in Flow-Induced Contraction of Venous Smooth Muscle

We designed the present study to determine whether Ca2+ release from intracellular stores contributes to flow-induced contraction. We carried out experiments on segments of rabbit facial vein under isometric conditions. Intraluminal flow by perfusion of physiological salt solution (10 to 80 microL/min) caused contraction in this vessel, which was significantly inhibited by (1) 30-minute pretreatment with 10 mumol/L ryanodine, the sarcoplasmic reticulum Ca2+ channel opener, and (2) 30-minute pretreatment with concomitant application of 20 mmol/L caffeine and 1 mumol/L cyclopiazonic acid in Ca(2+)-free medium to deplete the sarcoplasmic reticulum. In comparison, contraction initiated by 300 nmol/L histamine was significantly attenuated by the same interventions. K+ (25 mmol/L)-induced contraction was unaffected by ryanodine but was reduced after depletion of the sarcoplasmic reticulum. The phospholipase C inhibitor 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (10 mumol/L) inhibited contractions induced by flow and histamine but not by K+. These findings indicate that Ca2+ release from intracellular stores, presumably via the phosphatidylinositol pathway, contributes to flow- and histamine- but not raised K(+)-induced contractions in this vessel.

Chronic hypoxia impairs pulmonary venous smooth muscle contraction

Chronic hypoxia increases total pulmonary vascular resistance and causes pulmonary hypertension. Although the effect of chronic hypoxia on pulmonary arterial tissue has been extensively studied, very little is known about the effects on the pulmonary vein. The purpose of the present investigation was to determine the effect of chronic hypoxia on pulmonary venous reactivity to several vasoactive agonists and on the venous response to acute hypoxia. Isolated pulmonary venous rings were taken from rats exposed to 2, 7, and 14 days of hypoxia (FI o 2 = 0.1). A decrease in the response of the pulmonary vein to KCl was observed after 14 days of hypoxia. The reactivity (maximum active force produced) of the pulmonary vein in response to phenylephrine (PE) was reduced after 7 days of hypoxia. The response of the pulmonary vein to angiotensin II (AII) was more sensitive to the effects of chronic hypoxia since decreased reactivity to angiotensin II occurred after only 2 days of hypoxia. Prolonged hypoxia (14 days) had no further effect on the decreased reactivities to PE and AII. The sensitivities of pulmonary venous muscle to PE and AII were decreased (increased ED 50 values) by 2 days of chronic hypoxia, but tended to return to control levels after 7 and 14 days of hypoxia. However, the contractile response of the pulmonary vein to acute hypoxia was not changed even after 14 days of chronic hypoxia. These results suggest that chronic hypoxia: (1) impairs pulmonary venous smooth muscle contractility; (2) reduces pulmonary venous reactivity and sensitivity to phenylephrine and angiotensin II; and (3) does not alter the pulmonary venous contractile response to acute hypoxia.

Two Different Endothelin B Receptor Subtypes Mediate Contraction of the Rabbit Saphenous Vein

To study endothelin receptor subtypes that mediate venous smooth muscle contraction, effects of some endothelin receptor agonists and antagonists on the rabbit lateral saphenous vein were examined and compared with those on the saphenous artery. In the artery, endothelin (ET)-l elicited concentration-dependent contractions, while selective ETB-receptor agonists, IRLI620 (Suc-[Glu9,Ala11,15]ET-1(8-21)) and sarafotoxin 6c (S6c) had almost no effect. The ET-1-induced responses shifted in parallel to the right by BQ-123 (cyclo (-D-Trp-D-Asp-Pro-D-Val-Leu-)), an ETA-receptor antagonist, or PD 142893 (Ac-D-Dip-Leu-Asp-Ile-Ile-Trp), an ETA/ETB-receptor antagonist, indicating the involvement of the ETA receptor in this response. In the saphenous vein, not only ET-1 and ET-3, but also ETB-receptor agonists, IRL1620, S6c and [Glu9]sarafotoxin 6b ([Glu9]S6b), produced concentration-dependent, BQ-123-insensitive contractions. PD142893 did not affect the ΕΤ-1-induced contraction, but it shifted greatly the IRL1620-induced concentration-response curve in parallel to the right. The major components of ET-3-, S6c- and [Glu9]S6b-induced contractions were resistant to PD142893. These results indicate that two different vasoconstrictive ETB-receptor subtypes, ETB1 (sensitive to IRLI620 and PD 142893) and ETB2 (insensitive to IRL1620 and PD142893), are located on the smooth muscle of the saphenous vein.

Subtypes of Endothelin ETA and ETB Receptors Mediating Venous Smooth Muscle Contraction

In rabbit saphenous vein, endothelin (ET)-1 and ET-3 induced sustained contractions whereas the selective agonists of the ETB receptor, sarafotoxin S6c (STXc) and IRL 1620, induced transient contractions. In the presence of an ETA antagonist, BQ-123, contractions induced by ET-1, STXc and IRL 1620 did not change whereas ET-3 induced only transient contraction. The ETB antagonists, RES-701-1 and IRL 1038, only weakly antagonized the effects of these stimulants. In the muscle pretreated with STXc, neither STXc nor IRL 1620 was effective whereas ET-3 induced sustained contraction at higher concentrations than ET-1. In the muscle pretreated with STXc, BQ-123 weakly antagonized the effect of ET-1 and abolished the effect of ET-3. These results suggest that there are two types of ET receptors; less tachyphylactic and isopeptide-selective ETA receptor, and tachyphylactic and isopeptide-nonselective ETB receptor. The ETA receptors may be further classified as a BQ-123-sensitive ETA1 and a BQ-123-insensitive ETA2 subtypes. The ETB receptors may also be subclassified as the ETB1 and ETB2 subtypes based on the sensitivity to the ETB antagonists.

Myosin light chain phosphorylation and evidence for latchbridge formation in norepinephrine stimulated canine veins

The role of 20000 dalton myosin light chain phosphorylation in mediating venous smooth muscle contraction was studied in isolated preparations of canine jugular and femoral vein. One min 10 −5M norepinephrine-induced contraction was accompanied by significant increases in phosphorylation (jugular — 21 to 46%; femoral — 19 to 54%) which were reversed within 10 min after agonist washout. During 40 min stimulation, phosphorylation and isometric force redevelopment rates declined to near basal levels while force was maintained. These findings implicate light chain phosphorylation as a prerequisite for initial tension development by crossbridge cycling in venous smooth muscle. However, long term tension can be maintained through a process similar to the latchbridge state in tracheal and arterial smooth muscle.

Ethanol and Contraction of Venous Smooth Muscle

Low concentrations of ethanol (17 mM) inhibited development of spontaneous mechanical activity (vasomotion) in isolated rat portal veins. Low concentrations of ethanol potentiated, however, contractions induced by epinephrine, but not those induced by angiotensin or potassium. Higher concentrations of ethanol, such as those associated with surgical anesthesia (100-170 mM), resulted in almost complete suppression of spontaneous contratile responses. These higher concentrations of ethanol: a) attenuate contractions induced by epinephrine, angiotensin, and potassium (K+); b) cause noncompetitive displacement of the dose-response curves of these vasoactive compounds; c) attenuate calcium (Ca++)-induced contractions of K+-depolarized portal veins; d) relax drug-induced, as well as Ca++-induced, contractions of portal veins. The profound depressant actions of ethanol are not mimicked by alpha-adrenergic, histaminergic, cholinergic, or serotonergic blocking drugs, nor are they attributable to actions on beta-adrenergic receptors. The direct vasodepressant actions of ethanol on isolated venous smooth muscle may play a significant role in alcohol-induced peripheral vasodiatation seen in man and animals.