Beneficial effects of iloprost cardioplegia in ischemic arrest in isolated working rat heart

Prostaglandins, Leukotrienes and Essential FattyAcids (1996) 54(4), 279-283 © PearsonProfessionalLtd 1996

Beneficial e f f e c t s of iloprost c a r d i o p l e g i a in i s c h e m i c arrest in isolated working rat heart Jun Feng ~, Guozen Wu 2, Shuben Tang 3, Ramez Chahine ~, Danial Lamontagne 1 1Department of Physiology, Faculty of Medicine, Research Center of Sacre-Coeur Hospital, 5400 Gouin Boulevard West, Montreal H4J 1C5, Quebec, Canada. 2Department of Thoracic and Cardiovascular Surgery, First Teaching Hospital, 3Department of Physiology, Henan Medical Unfversity, Zhengzhou, People's Republic of China.

Summary To determine whether the prostacyclin analog iloprost plays a beneficial role in crystalloid cardioplegia in isolated working rat hearts, 20 isolated rat hearts were studied after sustaining 90 min of cardioplegic arrest under hypothermia (20°C). The findings indicated that thromboxane A2 (TXA2) levels in coronary effluent were increased during reperfusion. Iloprost (12 rim/I) inhibited the release of TXA2 and improved the recovery of cardiac hemodynamics after ischemia. These data demonstrated that cardiac-derived TXA2 appeared to mediate reperfusion injury after prolonged aortic clamp or cardiac transplantation and iloprost cardioplegic infusion resulted in the inhibition of release of cardiac-derived TXA2 and in a better preservation of cardiac function after ischemic arrest.

INTRODUCTION

Beneficial effects of prostacyclin (PGI2) have been convincingly demonstrated in a number of animal models of myocardial ischemia. 1-3 Vasodilation by PGI2 reduces myocardial ischemia. 4 Iloprost (ZK36374), a prostacyclin analog, exhibited a cardioprotective action comparable to that of PGI2 but possessed a less profound blood pressure lowering activity in animals 5 and humans. 6 However, the effects of iloprost have not been reported in the isolated working rat heart undergoing ischemic arrest. Moreover, significant perioperative injury is still reported after cardiac operations z8 and has stimulated further research into cardioplegic techniques 9 and recipe modifications. 1° The cardiac-derived mediators of reperfusion injury have been the subject of recent investigations, ~1,~ but no clear conclusions have been drawn. The present study was designed to evaluate the release of TXA2 after ischemic arrest and Received 24 May 1995 Accepted 21 August 1995 Correspondence to: Jun Feng, Tel. (514)338-2507; Fax. (514)338-2694

the influence of floprost on TXA2 and on the recovery of cardiac hemodynamics in a working rat heart model.

MATERIALS AND METHODS Experimental model

The preparation was a modification of the isolated working rat heart model described by Neely and colleagues. ~3 Briefly, the oxygenated perfusate entered the left atrium at a pressure of 12 cmH20 (preload). Langendorff perfusion was carried out at a constant perfusion pressure of 80 cmH20. The standard perfusate was Krebs-Henseleit-bicarbohate (KHB) buffer containing the following compounds (in mmol/1): NaC1, 118.0; KC1, 4.7; NaHCO3, 25.0; MgSO4, 1.2; CaC12, 2.55; KH2PO4, 1.2; and glucose, 11.1. All perfusates were maintained at pH 7.4 (37°C). The cardioplegic solution was the St Thomas Hospital cardioplegic solution NO.2 (in mmol/1): NaC1, 110.0; KC1, 16.0; CaC12, 1.2; NaHCO3, 10.0; pH 7.8 (4°C), osmolarity (mosm/kgH20) 285-300.14

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Experimental time-course

Statistical analysis

Male Sprague-Dawley rats, 250-300 g, were anesthetized with Nembutal (50 mg/kg, i.p), the femoral vein exposed and heparin (200 IU) was administered intravenously. The abdominal cavity was opened by making a transverse incision with scissors. The diaphragm was transected and lateral incisions were made along both sides of the rib cage. The anterior chest wall was folded back, the thymus dissected free and the pulmonary artery cut to permit the flow of coronary venous returns. The heart was connected to an aortic cannula within 1 rain of its removal and a left atrial cannula was inserted. Langendorff perfusion was initiated and continued for a 10 min washout equilibration period. The hearts were then converted to the working mode for a 15 rain control period by commencing left atrial perfusion. During this time, preischemic control values for the indices of cardiac function were obtained. During the ischemic arrest, the hypothermic (4°C) cardioplegic solution (5ml) was infused using the Langendorff model at a pressure of 80 cmH20 and the heart chamber was simultaneously switched to the hypothermic heart chamber (20°C). The cardioplegic solution was re-administered every 30 rain while the arrest hearts were maintained at 20°C for 90 min. All hearts were then reperfused in the Langendorff perfusion for 10 rnin followed by the working model perfusion for 30 min. During the working period, the recovery of function was recorded.

Data are presented as means + SEM. Analysis of variance (ANOVA) was used for hemodynamic and TXB2 data to determine significant differences between groups. Comparisons between control and iloprost groups were tested by Student's t-test for unpaired data with the Bonferroni correction. P < 0.05 was considered to be the limit of statistical significance.

Measurements

Aortic flow (AF) and stroke volume (SV) were measured with a Nihon-Kohden MFV-1200 electromagenetic flowmeter (Tokyo, Japan). Left ventricular systolic pressure (LVSP) and left ventricular end diastolic pressure (LVEDP) were measured with a Statham P23D pressure transducer and the indices were recorded on a Nihon-Kohden 8K recorder (Tokyo, Japan). Coronary flow (CF) was measured volumetrically by timed collection. Cardiac output (CO) was derived from the sum of aortic and coronary flows. Coronary effluent from control and iloprost-treated hearts was collected (2 ml) before and after ischemia during the Langendorff mode and stored frozen (-80°C) until assayed for thromboxane B~ (TXB2) using a radioimmunoassay.15

RESULTS TXB2 release

The data for TXB2 release are presented in Figure 1. There were no significant differences in preischemic coronary effluent TXB2between the two groups. Postischemic coronary effluent TXB2 in the control group (168 + 40 pg/ml) was significantly elevated compared with its preischemic values (96 + 35pg/ml) (P(0.05). Postischemic TXB2 levels in the iloprost group (81 + 42 pg/ml) were not significantly increased compared with its preischemic values (88 + 29 pg/ml). Postischemic TXB2 levels in the control group were significantly higher than the postischemic TXB2 values in the floprost group (P< 0.05). The recovery of left ventricular systolic and diastolic function

There were no statistical differences in preischemic values of LVSP (Fig. 2) and LVEDP (Fig. 3) between control and iloprost groups. At the end of the 30 rain reperfusion, 240 220

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Two groups of hearts were studied. In the control group, 10 hearts received only cold cardioplegia. In the iloprosttreated group, 10 hearts received floprost (12nmol/1, Schering AG, Berlin) in cardioplegia, as well as a continuous intraaortic infusion at the start of reperfusion over 30 rain.

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Fig. 1 Coronary effluent levels of TXB2 during preischemia and reperfusion. Data are expressed as mean + SEM. n = 8 for each group, e p < 0.05 vs preischemia, * P < 0.05 vs control group.

Prostaglandins, Leukotrienes and Essential Fatty Acids (1996) 54(4), 279-283

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Fig. 2 A increase in LVSP recovery at the end of 30 min reperfusion after ischemic arrest in iloprost group (101 + 5.2 mmHg vs 72 + 4.1 mmHg of control group, * P < 0.05). Data are expressed as mean _+SEM. n = 10 for each group.

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Fig. 4 Graph showing the coronary flow (CF), aortic flow (AF), and cardiac output (CO) at the end of 30 rain reperfusion after ischemic arrest, n = 10 for each group. Data are expressed as mean + SEM • P < 0.05 vs control group.

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Fig. 3 A decrease in LVEDP at the end of 30 rain reperfusion after ischemic arrest in iloprost group (9.5 _+0.4 mmHg VS 17.4 + 1.2 mmHg, * P < 0.05).

iloprost increased the recovery of LVSP and decreased LVEDP. The recovery of cardiac output

Figures 4 and 5 show that the recoveries of CF, AF, CO © Pearson Professional Ltd 1996

Fig. 5 Graph showing the stroke volume (SV) at the end of 30 rain reperfusion after ischemic arrest, n = 10 for each group. Data are expressed as mean + SEM. * P < 0.05 vs control group.

and SV at the end of 30 rain reperfusion after 90 rain ischemic arrest were significantly better in the iloprost group (13.5 + 0.gml/min, 37.9 + 4.8ml/min, 51.4 _+ 5.7 ml/min, and 0.18 + 0.01 ml/min) than in control group (6.8 + 1.1 ml/min, P<0.05; 24.9 + 2.4 ml/min, P<0.05, 31.8 + 2.8ml/min, P<0.05; and 0.13 + 0.01ml/min, P< 0.05).

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DISCUSSION

The cardiac-derived mediators of reperfusion injury have b e e n the subject of recent investigations. 11,12 Global norm o t h e r m i c myocardial ischemia m a y induce platelet deposition within the coronary microcirculation, indicating that intracoronary t h r o m b o s i s participated in the pathogenesis of reperfusion injury. 16 It has b e e n reported that cardioplegia does not prevent reperfusion injury induced b y intracoronary platelet depositionY Significant alterations in transcardiac gradients of TXA2 occurred during surgical cardioplegia with transcardiac platelet gradients increasing. TM These findings were obtained in vivo during c o r o n a r y p u l m o n a r y bypass. The present studies concentrated on investigating the role of cardiac-derived TXA2 in mediating reperfusion injury in the isolated rat heart perfused with a blood-free m e d i u m , thus indicating that platelets and neutrophils were not required for the effect of reperfusion injury. Studies on this m o d e l m a y attribute TXA2 production to endothelial cells, 19,2° m a s t cells, 2j or myocardial cells. 22,23 The present studies demonstrate that TXA 2 is a major arachidonic acid metabolite released from the isolated rat heart. They suggest that the elevated postischemic coronary effluent TXA2 appeared to have caused TXA 2m e d i a t e d coronary vasoconstriction and deterioration of coronary flow and left ventricular functional recovery. Recent studies have d o c u m e n t e d that e n d o g e n o u s PGI2 p r o d u c t i o n in severe or prolonged ischemia might be impaired b o t h because it was an oxygen-requiring process and b e c a u s e its site of generation, the vascular endothelium, was vulnerable to ischemic injury 2a and cardioplegic cytotoxicityY Atherosclerotic tissues are p r o b a b l y unable to produce PGI2Y Therefore, exogenous PGI2 m i g h t be beneficial to the ischemic heart) -3 Iloprost infusion in this study resulted in better preservation of myocardial function after 90 rain of global ischemia. The first report of synthetic prostacyclin analogs for protection of the ischemic m y o c a r d i u m was m a d e by Schror and colleagues; 5,6 and the same results have b e e n confirmed b y others. 28,2~ T h e y are associated with (i) the complete inhibition of induced changes in the STsegment, ~ (ii) preservation of the myocardial CK specific activity from the ischemic area, 5 (iii) preservation of myocardial cell integrity and inhibition of lysosomal e n z y m e release, 3° (iv) preservation of b o u n d cathepsin D in the ischemic myocardium, s (v) inhibition of local norepinephrine release in ischemic myocardium, 3~ (vi) vasodilation and inhibition of platelet aggregation, s,6 (vii) inhibition of the ischemia-induced loss of phospholipids, 28 and preservation of superoxide dismutase specific activity. 29 Moreover, our results have s h o w n that iloprost inhibited the release of cardiac-derived TXA2 and improved the recovery of cardiac function.

In conclusion, cardiac-derived TXA2 appears to mediate reperfusion injury after cardioplegic arrest and m a y play an important role in reperfusion injury after prolonged aortic cross clamp or cardiac transplantation. Iloprost cardoplegic infusions r e s u k in the inhibition of the release of cardiac-derived TXA 2 and lead to an improvem e n t of functional recovery after ischemic arrest.

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