Effects of endothelin-1 and L-arginine after cold ischemia in lamb hearts

Dynamic and differential changes in myocardial and plasma endothelin in patients undergoing cardiopulmonary bypass

OBJECTIVE

The bioactive peptide endothelin modulates left ventricular function by changing afterload, coronary vascular tone, and myocardial contractility. However, whether increased plasma endothelin levels observed in patients during and after coronary revascularization and cardiopulmonary bypass reflect actual myocardial interstitial levels are unknown.

METHODS

A microdialysis probe (outer diameter: 0.77 mm; length: 4 mm) was placed in the left ventricular apical midmyocardium in 20 patients and myocardial interstitial fluid was collected (2.5 microL/min) at baseline and up to 30 minutes after cardiopulmonary bypass. Myocardial interstitial and systemic arterial endothelin were measured by radioimmunoassay.

RESULTS

Baseline myocardial interstitial endothelin was over 6-fold higher than plasma (20.11 +/- 2.07 vs 3.19 +/- 0.25 fmol/mL, P < .05). Plasma endothelin increased by 23% +/- 12% at 60 minutes of cardiopulmonary bypass whereas myocardial interstitial endothelin increased by 105% +/- 24%, P < .05), and this change was higher than in the plasma ( P < .05). Although no further change in plasma endothelin occurred during cardiopulmonary bypass, myocardial interstitial levels increased further after crossclamp removal (400% +/- 75%) and remained significantly higher than plasma at separation from cardiopulmonary bypass.

CONCLUSION

The unique findings of this study were 2-fold: First, significant compartmentalization of endothelin exists within the human myocardium. Second, a significantly higher and temporally disparate change in myocardial interstitial endothelin occurs during and after cardiopulmonary bypass when compared with systemic levels. These dynamic changes in myocardial endothelin likely influence coronary vascular tone and contractility.

Endothelial Function Related to Vascular Tone in Cardiac Surgery

Vascular endothelium has multiple functions including regulating of vascular tone, preventing platelet aggregation, anti-proliferation, etc. An intact endothelial function is essential to the maintenance of an adequate vascular tone, to prevent platelet aggregation in the intimal surface of blood vessels, to prevent smooth muscle proliferation, and to prevent atherosclerosis. This review focuses on endothelial function related to the vascular tone in cardiac surgery. The review is composed by three sections. In the first section, normal endothelial function related to vascular tone is described. In the second section, coronary endothelial function related to cardiac arrest and cardioplegic exposure is reviewed. In the third section, the endothelial function in the coronary bypass grafts is summarised. It is particularly important to understand that coronary endothelial dysfunction may be one of the major causes of low perfusion of the myocardium after cardiac arrest or donor heart preservation. Further, endothelium plays a major role in the maintenance of vascular tone and in the long-term patency of CABG grafts. The characteristics of endothelium in arterial and venous grafts and the correlation to the long-term patency are now more understood. A number of methods have been suggested to protect endothelial function in either coronary circulation or in coronary artery bypass grafts during cardiac surgery but further investigations in this field are warranted.

Oxidative stress and adaptation of the infant heart to hypoxia and ischemia

The potential contribution of oxidative stress to cardioprotection in infants induced by adaptation to chronic hypoxia and by ischemic preconditioning is poorly understood. Under conditions of oxidative stress, reactive oxygen species and reactive nitrogen species may contribute to phenotypic changes in hearts adapted to chronic hypoxia and to the pathogenesis of myocardial injury during both ischemia/reperfusion and hypoxia/reoxygenation. Hearts from infant rabbits normoxic from birth can be preconditioned by brief periods of ischemia. In contrast, hearts from infant rabbits adapted to hypoxia from birth appear resistant to ischemic preconditioning. Chronically hypoxic infant rabbit hearts are already resistant to ischemia compared with age-matched normoxic controls, and thus additional cardioprotection by ischemic preconditioning may not be possible. Endothelial nitric oxide synthase (NOS3) protein and its product nitric oxide are increased, but not NOS3 message, in chronically hypoxic infant hearts to protect against ischemia. Chronic hypoxia from birth also increases cardioprotection of infant hearts by increasing association of heat shock protein 90 with NOS3. Normoxic infant hearts also generate more superoxide by an N(omega)-nitro-L-arginine methyl ester-inhibitable mechanism than chronically hypoxic hearts. Thus, NOS3 appears to be critically important in adaptation of infant hearts to chronic hypoxia and in resistance to subsequent ischemia by regulating the production of reactive oxygen and nitrogen species.

Phosphorylation in coronary artery cold-induced contraction in the newborn lamb

Myocardial dysfunction after hypothermic protection has been linked to various mechanisms. Coronary vasospasm in particular may be responsible for ischemic injury during reperfusion. Herein we hypothesized that coronary arteries (CA) sustain a cold-induced contraction during hypothermia mediated by a protein tyrosine kinase (PTK)-/protein tyrosine phosphatase (PTP)-dependent pathway. Isolated newborn lamb CA rings were studied in a tissue bath for isometric contraction during 2-h profound (17 degrees C) or ultra-profound (7 degrees C) hypothermia. In parallel, protein tyrosine phosphorylation was evaluated by use of the Western blot technique. Na-orthovanadate (SOV) and genestein (GEN) were used separately and in combination to evaluate the effect of PTK/PTP activation on CA contraction and tyrosine phosphorylation during cooling (17 or 7 degrees C) vs 37 degrees C. Cooling from 37 to 7 degrees C induced transient contraction at approximately 17 degrees C (29% KCl response), which was more prominent during rewarming to 37 degrees C (36% KCl). Cooling to 17 degrees C resulted in sustained contraction (7-10% KCl), which was reversible upon rewarming. Cold-induced contraction was significantly enhanced by SOV (7- to 10-fold at 17 degrees C; 2-fold at 7 degrees C) and abolished by GEN. Concurrently, tyrosine phosphorylation of 33-, 45-, and 104-kDa proteins increased during cooling (35-100% at 17 degrees C; 46-66% at 7 degrees C). Tyrosine phosphorylation was similarly enhanced by SOV (1.7- to 2.3-fold at 17 degrees C; 2.9- to 3.9-fold at 7 degrees C) and abolished by GEN in the presence or absence of SOV. These results support a prominent role for the PTK/PTP signal transduction pathway in the coronary artery cold-induced contraction. This information provides one possible biomolecular mechanism linked to ischemia/reperfusion pathophysiology of CA in neonatal hearts exposed to hypothermic myocardial protection.

L-arginine during long-term ischemia: effects on cardiac function, energetic metabolism and endothelial damage

BACKGROUND

We have evaluated the addition of L-arginine, a precursor of nitric oxide, to a cardioplegic solution (named CRMBM) designed for long-term heart preservation.

METHODS

Isolated isovolumic-perfused rat hearts (n = 22) were arrested with the CRMBM solution either with (Arg) or without L-arginine (2 mmol/L) (Arg group, n = 12, vs control group n = 10), submitted to 8 hours of cold storage (4 degrees C) in the solution, and then reperfused for 60 minutes at 37 degrees C. In 11 hearts, we evaluated the quality of cardiac preservation with P-31 magnetic resonance spectroscopy and the measure of function and cellular integrity. Endothelium-dependent and independent vasodilatations were measured in 11 other hearts, using 5-hydroxytryptamine and papaverine to assess endothelial and smooth muscle function.

RESULTS

Adding L-arginine to the cardioplegic solution improved functional recovery during reflow, as shown by the rate pressure product (31% +/- 3% for control vs 47% +/- 3% for Arg, p = 0.003) together with higher coronary flow and diminished contracture. Purine release in coronary effluents during reperfusion was lower in the Arg group. During ischemia and reflow kinetics of intracellular pH and high-energy phosphates were similar in both groups. Coronary endothelium-dependent vasodilatation was similarly impaired in both groups, but smooth muscle was less altered with L-arginine.

CONCLUSIONS

As an additive to the CRMBM cardioplegic solution, L-arginine provides a protective effect for long-term heart preservation. Our data do not show coronary endothelial protection as the prominent mechanism.

Myocardial protection during cardiac surgery from the viewpoint of coronary endothelial function

1. During cardiac surgery, the heart is arrested and subject to ischaemia-reperfusion injury. 2. To protect the heart, cardioplegia is usually used to initially stop and then maintain the still condition of the heart, which not only facilitates the precise operation but, more importantly, minimizes the energy consumption of the heart during this period. 3. The ischaemia-reperfusion injury may involve both myocytes and coronary endothelium-smooth muscle and, therefore, the protection of the heart should also involve these two aspects. 4. Injury to the heart involves: (i) ischaemia-reperfusion injury to the myocytes and coronary circulation; and (ii) possible injury to the coronary circulation by cardioplegia due to its hyperkalaemic components. 5. Injury to the coronary circulation may involve both endothelium-derived nitric oxide (EDNO) and endothelium-derived hyperpolarizing factor (EDHF) mechanisms. The EDNO mechanism is susceptible to ischaemia-reperfusion, whereas the EDHF mechanism may be altered by hyperkalaemic cardioplegia. 6. To further protect the heart, supplemental therapy for EDNO and optimizing the components of cardioplegia to restore the EDHF mechanism may be important.

Interaction of bradykinin with angiotensin, prostacyclin, and nitric oxide in myocardial preservation

This review focuses on the importance of bradykinin in myocardial preservation during ischemic arrest. Bradykinin is released from the heart spontaneously in response to ischemic stress, which may be viewed as a survival signal of the heart against ischemia. Bradykinin appears to function as a signaling molecule by controlling the release of other intracellular modulators, such as prostacyclins and nitric oxide, which also exert beneficial effects on the ischemic myocardium.

Inflammatory response to cardiopulmonary bypass: mechanisms involved and possible therapeutic strategies

BACKGROUND

Recent study of the inflammatory reactions occurring during and after cardiopulmonary bypass (CPB) has improved our understanding of the involvement of the inflammatory cascade in perioperative injury. However, the exact mechanisms of this complex response remain to be fully determined.

METHODS

Literature on the inflammatory response to CPB was reviewed to define current knowledge on the possible pathways and mediators involved, and to discuss recent developments of therapeutic interventions aimed at attenuating the inflammatory response to CPB.

RESULTS

CPB has been shown to induce complement activation, endotoxin release, leukocyte activation, the expression of adhesion molecules, and the release of many inflammatory mediators including oxygen-free radicals, arachidonic acid metabolites, cytokines, platelet-activating factor, nitric oxide, and endothelins. Therapies aimed at interfering with the inflammatory response include the administration of pharmacologic agents such as corticosteroids, aprotinin, and antioxidants, as well as modification of techniques and equipment by the use of heparin-coated CPB circuits, intraoperative leukocyte depletion, and ultrafiltration.

CONCLUSIONS

Improved understanding of the inflammatory reactions to CPB can lead to improved patient outcome by enabling the development of novel therapies aimed at limiting this response.

Time course of endothelin-1 and nitrate anion levels after cardiopulmonary bypass in congenital heart defects

BACKGROUND

The endothelium-derived vasoconstrictor endothelin-1 (ET-1) may be involved in pulmonary hypertension (PH), but production of the endothelium-derived vasodilator nitric oxide (NO) after cardiopulmonary bypass (CPB) in congenital heart disease is unclear.

METHODS

Twenty patients (age, 4 months to 12 years) were divided into three groups: severe PH (mean pulmonary-to-systemic arterial pressure ratio > 0.5) and high pulmonary flow (n = 8), mild PH (mean pulmonary-to-systemic arterial pressure ratio < 0.35) and high pulmonary flow (n = 6), and no PH and low pulmonary flow (n = 6). The mean pulmonary-to-systemic arterial pressure ratio was calculated and blood samples were taken, and NO3-, an NO metabolite, was measured.

RESULTS

Levels of ET-1 in the group with severe PH and high pulmonary flow were higher than in the other groups until 6 hours after CPB, and NO3- was not changed significantly in the group with severe PH and high pulmonary flow and or the group with mild PH and high pulmonary flow during CPB. Endothelin-1 in the group with no PH and low pulmonary flow was higher than in the group with mild PH and high pulmonary flow after CPB, and NO3- in the group with no PH and low pulmonary flow significantly decreased after CPB. A positive correlation was obtained between mean pulmonary-to-systemic arterial pressure ratio and ET-1 (r = 0.742 before CPB; r = 0.689 after CPB).

CONCLUSIONS

Imbalance between increased ET-1 and constant NO after CPB in the group with severe PH and high pulmonary flow could contribute to dominant effects of ET-1, which may injure the lung. The increased ET-1 and the decreased NO after CPB in the group with no PH and low pulmonary flow may induce a mechanism of protective vasoconstriction against an acute increase in pulmonary flow.