Plasma endothelin-1 levels in adult patients undergoing coronary revascularization

Endothelin-A receptor inhibition after cardiopulmonary bypass: cytokines and receptor activation

BACKGROUND

Basic studies have suggested that cross-talk exists between the endothelin-A receptor (ET-AR) and tumor necrosis factor signaling pathway. This study tested the hypothesis that administration of an ET-AR antagonist at the separation from cardiopulmonary bypass would alter the tumor necrosis factor activation in the early postoperative period.

METHODS

Patients (n = 44) were randomly allocated to receive bolus infusion of vehicle, 0.1, 0.5, 1, or 2 mg/kg of the ET-AR antagonist (sitaxsentan), at the separation from cardiopulmonary bypass (n = 9, 9, 9, 9, and 8, respectively). Plasma levels of tumor necrosis factor-alpha and soluble tumor necrosis factor receptor 1 and 2 were measured.

RESULTS

Compared with the vehicle group at 24 hours, plasma levels of tumor necrosis factor-alpha and tumor necrosis factor receptor 2 (indicative of receptor activation) were reduced in the 1 mg/kg ET-AR antagonist group (by approximately 13 pg/mL and approximately 0.5 ng/mL, respectively; p < 0.05). Plasma tumor necrosis factor receptor I levels also decreased (by approximately 1 ng/mL) after infusion of the higher doses of the ET-AR antagonist and remained lower (by approximately 3 ng/mL) at 24 hours after infusion (p < 0.05). In addition, a dose effect was observed between the ET-AR antagonist and these indices of tumor necrosis factor activation (p < 0.01).

CONCLUSIONS

This study demonstrated a mechanistic relationship between the ET-AR and tumor necrosis factor receptor activation in the post-cardiac surgery period. Thus, in addition to the potential cardiovascular effects, a selective ET-AR antagonist can modify other biological processes relevant to the post-cardiac surgery setting.

Potential role of endothelin receptor antagonists in the setting of cardiopulmonary bypass: relevance to myocardial performance

The ET system is activated in cardiac surgical setting as evidenced by elevated systemic and myocardial ET-1 levels after coronary bypass grafting surgery which requires hypothermic cardioplegic arrest and cardiopulmonary bypass. Increased ET-1 may influence a number of clinical parameters in this setting. First, ET-1 may directly modulate myocardial contractile performance in the early postoperative period resulting in LV dysfunction and a complex postoperative course. Second, elevated ET-1 levels may exacerbate increased pulmonary vascular resistance and contribute to the development of transient pulmonary hypertension following bypass. Finally, augmented postoperative ET-1 levels could contribute to changes in the caliber and flow of vascular conduits used for coronary bypass. In this review, a current perspective on the ET system in the setting of cardiopulmonary bypass grafting surgery is provided and the potential use of ET receptor antagonists in this setting is discussed.

The endothelin system in human saphenous vein graft disease

Saphenous vein graft stenosis is a significant clinical complication for coronary artery bypass patients. Endothelin-1, a peptide synthesised by vascular endothelial cells, is the most potent known vasoconstrictor and has mitogenic properties. Recent advances in our knowledge of endothelin-1 synthesis and endothelin receptor expression and function in normal and atherosclerotic human saphenous vein imply a role for the peptide in the progression of vein graft failure. Manipulation of the endothelin system, by selective receptor antagonism or inhibition of the specific endothelin-converting enzymes may, therefore, represent a novel therapeutic target for treating vein graft disease.

Temporal endothelin dynamics of the myocardial interstitium and systemic circulation in cardiopulmonary bypass

OBJECTIVE

Increased systemic levels of the bioactive peptide endothelin 1 during and after cardioplegic arrest and cardiopulmonary bypass have been well documented. However, endothelin 1 is synthesized locally, and therefore myocardial endothelin 1 production during and after cardiopulmonary bypass remains unknown.

METHODS

Pigs (n = 11) were instrumented for cardiopulmonary bypass, and cardioplegic arrest was initiated. Myocardial interstitial and systemic arterial levels of endothelin 1 were measured before cardiopulmonary bypass, throughout bypass and cardioplegic arrest (90 minutes), and up to 90 minutes after separation from bypass. Myocardial interstitial endothelin 1 was determined by microdialysis and radioimmunoassay.

RESULTS

Baseline myocardial endothelin 1 levels were higher than systemic endothelin 1 levels (25.6 +/- 6.7 vs 8.3 +/- 1.1 fmol/mL, P <.05). With the onset of bypass, myocardial endothelin 1 increased by 327% +/- 92% from baseline (P <.05), which preceded the increase in systemic endothelin 1 levels.

CONCLUSION

Myocardial compartmentalization of endothelin 1 exists in vivo. Cardiopulmonary bypass and cardioplegic arrest induce temporal differences in endothelin 1 levels within the myocardial interstitium and systemic circulation, which, in turn, may influence left ventricular function in the postbypass period.

Endothelin receptor expression and pharmacology in human saphenous vein graft

1. We have investigated the expression and pharmacology of endothelin (ET) receptors in human aortocoronary saphenous vein grafts. 2. Subtype-selective ligands were used to autoradiographically identify ET(A) ([125I]-PD151242) and ET(B)([125I]-BQ3020) receptors. In graft saphenous vein ETA receptors predominated in the media, with few ET(B) receptors identified. Neither subtype was detected in the thickened neointima. 3. The ratio of medial ET(A):ET(B) receptors was 75%: 25% in both graft and control saphenous vein. 4. ET-1 contracted control (EC50 2.9 nM) and graft (EC50 4.5 nM) saphenous vein more potently than diseased coronary artery (EC50 25.5 nM). 5. In all three blood vessels ET-1 was 100 times more potent than ET-3 and three times more potent than sarafotoxin 6b (S6b). Little or no response was obtained in any vessel with the ET(B) agonist sarafotoxin 6c (S6c). 6. The ET(A) antagonist PD156707 (100 nM) blocked ET-1 responses in all three vessels with pKb values of approximately 8.0. 7. For individual graft veins the EC50 value for ET-1 and 'age' of graft in years showed a significant negative correlation. 8. In conclusion there is no alteration in ET receptor expression in the media of saphenous veins grafted into the coronary circulation compared to control veins. ETA receptors predominantly mediate the vasoconstrictor response to ET-1 in graft vein, with no apparent up-regulation of ET(B) receptors. The sensitivity of the graft vein to ET-1 increased with graft 'age', suggesting that these vessels may be particularly vulnerable to the increased plasma ET levels that are detected in patients with cardiovascular disease.