Coronary endothelial dysfunction after ischemia and reperfusion in the dog: a functional and morphological investigation

5-hydroxytryptamine has an endothelium-derived hyperpolarizing factor-like effect on coronary flow in isolated rat hearts

Background

5-hydroxytryptamine (5-HT)-induced coronary artery responses have both vasoconstriction and vasorelaxation components. The vasoconstrictive effects of 5-HT have been well studied while the mechanism(s) of how 5-HT causes relaxation of coronary arteries has been less investigated. In isolated rat hearts, 5-HT-induced coronary flow increases are partially resistant to the nitric oxide synthase inhibitor Nω-Nitro-L-arginine methyl ester (L-NAME) and are blocked by 5-HT₇ receptor antagonists. In the present study, we investigated the role of 5-HT₇ receptor in 5-HT-induced coronary flow increases in isolated rat hearts in the absence of L-NAME, and we also evaluated the involvement of endothelium-derived hyperpolarizing factor (EDHF) in 5-HT-induced coronary flow increases in L-NAME-treated hearts with the inhibitors of arachidonic acid metabolism and the blockers of Ca²⁺-activated K⁺ channels.

Results

In isolated rat hearts, 5-HT and the 5-HT₇ receptor agonist 5-carboxamidotryptamine induced coronary flow increases, and both of these effects were blocked by the selective 5-HT₇ receptor antagonist SB269970; in SB269970-treated hearts, 5-HT induced coronary flow decreases, which effect was blocked by the 5-HT_2A receptor blocker R96544. In L-NAME-treated hearts, 5-HT-induced coronary flow increases were blocked by the phospholipase A₂ inhibitor quinacrine and the cytochrome P450 inhibitor SKF525A, but were not inhibited by the cyclooxygenase inhibitor indomethacin. As to the effects of the Ca²⁺-activated K⁺ channel blockers, 5-HT-induced coronary flow increases in L-NAME-treated hearts were inhibited by TRAM-34 (intermediate-conductance Ca²⁺-activated K⁺ channel blocker) and UCL1684 (small-conductance Ca²⁺-activated K⁺ channel blocker), but effects of the large-conductance Ca²⁺-activated K⁺ channel blockers on 5-HT-induced coronary flow increases were various: penitrem A and paxilline did not significantly affect 5-HT-induced coronary flow responses while tetraethylammonium suppressed the coronary flow increases elicited by 5-HT.

Conclusion

In the present study, we found that 5-HT-induced coronary flow increases are mediated by the activation of 5-HT₇ receptor in rat hearts in the absence of L-NAME. Metabolites of cytochrome P450s, small-conductance Ca²⁺-activated K⁺ channel, and intermediate-conductance Ca²⁺-activated K⁺ channel are involved in 5-HT-induced coronary flow increases in L-NAME-treated hearts, which resemble the mechanisms of EDHF-induced vasorelaxation. The role of large-conductance Ca²⁺-activated K⁺ channel in 5-HT-induced coronary flow increases in L-NAME-treated hearts needs further investigation.

Restoration of coronary collateral growth in the Zucker obese rat: impact of VEGF and ecSOD

The metabolic syndrome (MS), a condition characterized by several risk factors for coronary artery disease, including obesity, is associated with endothelial dysfunction and oxidative stress. Because proper endothelial function is essential for signaling of certain growth factors (vascular endothelial growth factor, VEGF) we hypothesized that coronary collateral growth (CCG) is impaired in a model of the MS. To test this hypothesis, we stimulated coronary collateral growth in pre-diabetic Zucker obese fatty rats (OZR) and lean littermates (LZR) by using episodic, repetitive ischemia (RI: 40 s left anterior descending arterial occlusion, 24/d for 14 d). Myocardial blood flow (MBF, radioactive microspheres) was measured in the normal (NZ) and collateral-dependent (ischemic) zones (CZ); CCG was assessed as a ratio of CZ/NZ flow (unity represents complete restoration of CZ flow). In LZR, CZ/NZ ratio increased from 0.18 +/- 0.03 to 0.81 +/- 0.07 after RI (P < 0.05). In contrast, in OZR rats CZ/NZ did not increase after RI (0.15 +/- 0.04 vs 0.18 +/- 0.04). To rectify abrogated collateral growth in OZR, we employed VEGF gene therapy (VEGF-transduced, strained-matched, cultured vascular smooth muscle cells [cVSMCs], delivered intracoronary). VEGF therapy modestly but not significantly increased the CZ/NZ ratio after RI (0.16 +/- 0.05 vs 0.33 +/- 0.06). To facilitate VEGF signaling,we reduced oxidative stress by transducing cVSMCs with both ecSOD and VEGF. This increased the CZ/NZ flow ratio after RI to 0.52 +/- 0.04 (p < 0.05 vs. OZR [(0.19 +/- 0.04]) indicating partial restoration of collateral growth. Our results demonstrate that coronary collateral growth is impaired in a model of the metabolic syndrome and that growth factor gene therapy with VEGF is made far more effective when it is coupled to an intervention that reduces oxidative stress.

Assessment of changes in hemostatic markers in Cavalier King Charles Spaniels with myxomatous mitral valve disease

OBJECTIVE

To evaluate markers of hemostasis and their relationship to the degree of mitral regurgitation (MR) and platelet function in Cavalier King Charles Spaniels (CKCSs) with myxomatous mitral valve disease.

ANIMALS

76 clinically healthy CKCSs and 24 control dogs.

PROCEDURE

All dogs underwent echocardiographic examination; various hemostatic, hematologic, and biochemical variables were evaluated in blood. The CKCSs were allocated to 1 of 3 groups on the basis of MR severity. In 8 control dogs and 8 CKCSs, plasma von Willebrand factor (vWF) multimer analysis was performed.

RESULTS

Compared with control dogs, plasma fibrinogen concentration was higher in all CKCSs and related to left ventricular end diastolic diameter and left atrial-to-aortic root ratio among all CKCSs. The activated partial thromboplastin times and plasma D-dimer concentration were similar among the 4 groups. Plasma vWF concentration was lower in CKCSs with moderate to severe MR, compared with that of CKCSs with no MR and control dogs. There was a relationship between plasma vWF concentration and platelet function in CKCSs but not in control dogs. In 4 CKCSs with moderate to severe MR and low plasma vWF concentration, amounts of vWF high-molecular-weight multimers (HMWMs) were low.

CONCLUSIONS AND CLINICAL RELEVANCE

In CKCSs, MR appeared to be associated with a low plasma vWF concentration and likely a loss of vWF HMWMs (possibly through their destruction via shear stress to the blood). The importance of the changes in plasma fibrinogen concentration and the thromboembolic risk in dogs with MR remain to be investigated.

High levels of circulating endothelial microparticles in patients with acute coronary syndromes

BACKGROUND

Endothelial injury plays a critical role in coronary artery disease (CAD), but the assessment of this injury has been problematical. Recently, it has been shown in vitro that endothelial cells (ECs) release endothelial microparticles (EMPs) on activation or apoptosis and that an assay of EMPs can provide useful information on EC status in patients with thrombotic disorders. This study is aimed at assessing possible correlations between EMPs, which are markers of endothelial injury, and clinical subgroups of patients with CAD.

METHODS

A prospective, case-controlled study was conducted on 84 patients with CAD and 42 control subjects to investigate EMP profiles. Included were 64 patients with acute coronary syndromes ([ACS], 38 with myocardial infarction [MI] and 26 with unstable angina [UA]) and 20 patients with stable angina (SA). EMPs in platelet-poor plasma were measured flow cytometrically with combinations of fluorescent antibodies (anti-CD31, -51, -42), allowing distinction of EMPs from platelet microparticles (PMPs). Clinical subgroups of patients were correlated with EMP and PMP levels in blood.

RESULTS

Two species of EMPs (CD31+ and CD51+) were evaluated. Both were significantly higher in patients with CAD than in control subjects. CD31+ EMP was higher in ACS than SA. Among patients with first MI, CD31+ EMP was higher in patients with MI than in patients with UA and was significantly higher than in patients with recurring MI. CD51+ EMP did not discriminate ACS from SA. A simultaneous assay of PMP showed correlation between EMPs and PMPs. However, PMPs did not discriminate patients with SA from control subjects.

CONCLUSIONS

EMP assay appears promising for assessing EC injury in CAD.

Involvement of adenosine A2 receptors in the changes of tissue factor-dependent coagulant activity induced by polymorphonuclear leukocytes in endothelial cells

We have already reported that polymorphonuclear leukocytes (PMNs) could increase tissue factor-dependent coagulant activity (TF activity) in endothelial cells mediated by adhesion of PMNs to endothelial cells. In the present study, the role of adenosine receptors in the changes of TF activity and of adhesion between PMNs and endothelial cells was examined. The increases of the TF activity and adhesion were significantly reduced in a concentration-dependent manner by pretreatment of adenosine (0.1 and 1.0 mM); an adenosine A1/A2-receptor agonist, CGS-21680 (5, 10 and 50 microM); and an adenosine A2-receptor agonist, 5'-(N-cyclopropyl)-carboxamidoadenosine (CPCA; 1.0, 10 and 100 nM). An adenosine A2-receptor antagonist, 3,7-dimethyl-1-(2-propynyl) xanthine (DMPX; 1.0 and 100 nM), antagonized significantly the reduction of the TF activity and the adhesion induced by adenosine (1.0 mM), while 8-cyclopentyl-1,3-dimethylxanthine (CPDMX; 1.0 and 100 nM), an adenosine A1-receptor antagonist, did not affect it. On the other hand, the TF activity and the adhesion were not changed by N6-cyclohexyladenosine (CHA; 10 and 100 nM) and 2-chloro-N-cyclopentyladenosine (CCPA; 10 and 100 nM), adenosine A1-receptor agonists in the same conditions. These results suggest that the reduction in the TF activity stimulated by PMNs is closely related to the adhesive inhibition between PMNs and endothelial cells through the adenosine A2-receptor-mediated system.