外源性磷酸肌酸对未成熟心肌的保护作用
作者：金峰 李彤 杨景学 侯晓彬 朱海龙 谭红梅
单位：金峰(第四军医大学西京医院心血 管外科中心, 陕西 西安 710033)；李彤(第四军医大学西京医院心血 管外科中心, 陕西 西安 710033)；杨景学(第四军医大学西京医院心血 管外科中心, 陕西 西安 710033)；侯晓彬(第四军医大学西京医院心血 管外科中心, 陕西 西安 710033)；朱海龙(第四军医大学西京医院心血 管外科中心, 陕西 西安 710033)；谭红梅(第四军医大学西京医院心血 管外科中心, 陕西 西安 710033)
关键词：磷酸肌酸；未成熟心肌；心肌停搏液
第四军医大学学报000502 摘 要: 目的 探讨St.Thomas'Ⅱ心脏停搏液添加外源性磷酸肌酸(CP)对未成熟心 肌的保护效果, 并观察其抗心律失常作用. 方法 采用幼鼠(18～21 d)离体 工作心模型, 14℃低温缺血120 min,缺血前主动脉根部灌注4℃ St. Thomas' Ⅱ停搏液(对 照组)或St. Thomas' Ⅱ停搏液加 CP (10 mmol.L-1), 观察缺血再灌注后心功能.心肌ATP含量的恢复百分比,心肌CPK 漏出量及再 灌开始至窦性心律恢复的时间. 结果 ①CP组主动脉流量恢复比明显 增加[(86.8±4.2)% vs (70.2±3.3)%, P<0.01]. ②ATP恢复百分比显著升高[( 90.3±6.8)% vs (72.6±5.3)%, P<0.01]. ③心肌CPK漏出量明显减少(P<0.0 5). ④从再灌注开始至窦性心律恢复的时间显著缩短[ (3.3±1.5) min vs (8.2±2.0) min, P<0.05]. 结论 St. Tho mas' Ⅱ心脏停搏液中加外源 性磷酸肌酸不仅可显著改善幼鼠低温缺血后心功能的恢复,促进高能磷酸盐的重建及减少心 肌CPK的漏出,而且具有较好的抗心律失常作用,是目前一种比较理想的心肌保护药物.
, 百拇医药
中图号:R654.1 文献标识码: A
Exogenous creatine phosphate in protection of immature myocardium
JIN Feng, LI Tong, YANG Jing-Xue, HOU Xiao-Bin, ZHU Hai-Long, TAN Hong-Mei
(Center of Cardiovascular Surgery, Xijing Hospital, Fourth Military Medical Unive rsity, Xi'an 710033, China)
Abstract: AIM To determine whether creatine phosphate (CP) improves th e prote ctive effects of the St. Thomas' Hospital cardioplegia on immature myocardium an d to evaluate the antiarrhythmic effects of CP. METHODS In an i solated working h eart model, hearts from immature rats (18～21 days old) were subjected to 2 hours of 14℃ hypothermic ischemia with a 3 min preischemic infusion of either standa rd ST. Thomas'Ⅱ cardioplegic solution (control group) or the cardioplegia plus CP (10 mmol.L-1) (CP group). RESULTS The postischemic re covery of aortic flow was s ignificantly better in the CP group than that in the CP-free control group (P <0. 01). The percent recovery of myocardial ATP content was also higher in the CP gr oup than that in the control group (P<0.01). The myocardial creatine phospha te k inase (CPK) leakage was significantly lower in the CP group than that in the con trol group (P<0.05). CP reduced reperfusion arrhythmias, significantly decre asin g the time between cross clamp removal and return of regular rhythm. CON CLUSION Addition of CP to ST. Thomas'Ⅱ cardioplegia can significantly improve the funct ional recovery of immature myocardium following long period ischemia and attenua te postischemic myocardial arrhythmias.
, http://www.100md.com
Keywords: creatine phosphate; immature myocardium;cardioplegia
CLC number: R654.1 Document code: A
Article ID：1000-2790(2000) 05-0523-04
INTRODUCTION
The application of hypothermia and cold chemical cardioplegia has enhanced myoca rdial protection and improved survival rate following cardiac operations. Studie s have demonstrated a positive correlation between the postischmic recovery of myocardial performance and the cellular content of high-energy phosphates, such as adenosine triphosph a te (ATP) and CP. This indicates that maintaining ATP and CP during ischemia may help provide optimal myocardial protection. Despite the alleged impermeability o f plasma membrane to high-energy phosphates, exogenous administration of either CP or ATP has been reported to have improved myocardial protection during ischem ia in various models and species. In addition, recent studies suggest that extra cellular CP possesses antiarrhythmic effects associated with regional ischemia a nd reperfusion, effects which may be related in part to CP's protective effects on myocardial protection.
, http://www.100md.com
However, these studies were carried out in only adult patients or animals. The present study was designed to determine whether CP was as effective in prot ecting immature myocardium as in mature myocardium and to evaluate its antiarrhy thmic properties.
MATERIALS AND METHODS
Experimental model Hearts were obtained from infant male Sprague-Dawley rats (18 ～21 days old and 25～35 grams body mass). Each rat was anesthetized with ether, a nd 100 IU heparin was administered intrahepatically. After the induction of hypo thermia (by partial immersion of the animal in cold 4℃ KHBB solution for 1 min) , the chest wall was removed and the thoracic cavity was filled with cold (4℃) KHBB. The pulmonary trunk was incised near its origin and the aorta cannulated i n situ. The heart was then excised and mounted on the perfusion apparatus via th e aortic cannula. Then the Langendorff perfusion was initiated for a 10-minute w ashout and equilibration period with 8.0 kPa perfusion pressure. Control values f or aortic and coronary flow rates, aortic pressure and heart rate were recorded. The atrial and aortic cannulas were then clamped and heart was subjected to a 3 -minute coronary infusion of cardioplegia (4℃) with or without CP. Following t he infusion, the heart was maintained at 14℃ for 120 minutes of ischemic arrest. The heart was then reperfused in the Langendorff mode for 15 minutes, during whi ch coronary effluent was collected for CPK determination and the time from the i nitial postischemic reperfusion to the resumption of regular rhythm was recorded . Following the 15-minute reperfusion period, hearts were converted to the work i ng mode for a further 30 minutes and the recovery of function was recorded. Hear ts were then sampled and stored in -70℃ for the determination of ATP.
, 百拇医药
Cardioplegic solution The St. Thomas' Ⅱ cardioplegia contained ( in mmol.L-1): N aCl 110.0, NaHCO3 10.0, KCl 16.0, MgCl2 16.0, and CaCl2 1.2 (pH adjusted t o 7.8) . Since CP is available as the sodium salt, the sodium concentration of the cont rol solution was adjusted to the same level as that of the CP group. All solutio ns were filtered (pore size 5 μm) just before use.
Analysis methods All data were expressed as the mean±standard e rror. Statisti cal analysis of the results was made by t test and statistical significance was assumed when P values were 0.05 or less.
, 百拇医药
RESULTS
Hemodynamic values Table 1 showed that postischemic recovery of aortic fl ow was significantly better in the CP group compared with that in the control grou p [(86.8±4.2)% vs (70.2±3.3)%, P<0.01]. Similar substantial increase s were ob served for coronary flow and cardiac output. However, no significant effects on heart rate and aortic pressure were observed.HR: heart rate; CF: coronary flow; AF: aortic flow; CO: cardiac output;AP: aortic pressure; PIPR: postichemic percent recovery; STH II: St.Thomas' II cardioplegia.
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Tab 1 Preischemic cardiac function and postischemic percent recovery (
±s) Index
Condition
STH II
STH II+CP
HR/
Preischemia
310 ±19
325 ±14
(beat.min-1)
, 百拇医药
PIPR/%
84.7± 3.5
89.2± 7.0
CF/
Preischemia
6.5± 0.3
6.1± 0.8
(mL.min-1)
PIPR/%
74.2± 4.9
89.1± 5.2a
, 百拇医药
AF/
Preischemia
15.9± 1.8
15.6± 1.4
(mL.min-1)
PIPR/%
70.2± 3.3
86.8± 4.2b
CO/
Preischemia
21.6± 4.0
, 百拇医药
21.5± 2.0
(mL.min-1)
PIPR/%
71.2± 2.1
87.4± 3.8b
AP/
Preischemia
13.3± 0.8
14.1± 0.7
kPa
PIPR/%
, 百拇医药
78.1± 2.8
87.6± 4.9
aP<0.05, bP<0.01 vs STH II group. Myocardial CPK leakage Compared with that in the control group, CPK lea kage was significantly reduced in the CP group [(671±15)vs (439±9) nkat.g-1 , P<0.05].
Myocardial ATP content Postischemic recovery of myocardial ATP content was sign ificantly higher in the CP group than in the control group [(90.3±6.8)% vs (72.6±5.3)%, P<0.01].
, 百拇医药
Antiarrhythmic effects In this study, CP showed obvious antiarr hythmic ef fect. The time from the reperfusion to the return of regular sinus rhythm was si gnificantly shorter in the CP group than in the control group [(3.3±1.5) min vs (8.2±2.0) min, P<0.05].
DISCUSSION
Myocardial ischemia initiates a series of cellular changes that, unless checked, culminate in irreversible injury and cell death. Initially, mitochondrial oxida tive phosphorylation is severely reduced, and soon ATP and CP levels decline. De spite the cessation of contractive activity from oxygen and energy lack, cellula r metabolism continues, contributing to further ATP and CP depletion. This energ y depletion appears to play a vital role in determining cell viability, in parti cular whether contractile function resumes on reperfusion. Cardioplegic solution s conserve high-energy phosphates by hypothermia and by inducing rapid diastoli c arrest. However, neither potassium arrest nor hypothermia completely halts cell ular energy utilization, and cytoplasmic energy stores continue to dwindle. Cons ervation of high-energy phospates is therefore a primary objective in any proce dure designed to reduce ischemic injury.
, 百拇医药
In addition to reducing the rate of energy utilization during ischemia, va rious procedures have been designed to enhance energy availability by stimulatio n of adenine nucleotide synthetic pathways[1,2], for example, the use of substra tes for purine synthesis or inhibitors of the degradative enzymes. In addition, exogenous administration of either of the two major intracellular high-energy p h osphates, ATP and CP, has been suggested as being a benefit to the ischemic hear t despite the alleged inability of these compounds to cross the cell membrane.
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The present study has demonstrated improvement in functional recovery and a decrease in CPK release following hypothermic ischemia in immature rat heart r eceiving preischemic infusion with CP added cardioplegia. The results have also showed that CP has antiarrhythmic effects on immature myocardium. These effects of CP have been previously reported only on adult animals and patients.
The central role of CP, as Bessman and Beiger[3] summarized in the ir theor y of the CP shuttle, is regulating the energy supply and transport for contracti on. In addition to this, other studies have suggested that CP also controls the entry of activator calcium into the myoplasm by a direct effect upon the energy - dependent slow inward calcium current. As the sarcolemmal slow inward calcium cu rrent contributes to the plateau phase of the action potential, CP may play a re latively important role in regulating the duration of the action potential.
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A potential mechanism of action, by which CP has been suggested to exert i ts effect, is through the inhibition of free radical generation during reperfusi on[4，5]. Although not specifically designed to investigate the effects of CP on postischemic arrhythmias, previous studies showed that 10 mmol.L-1 CP pre vented co ntractile dysfunction induced by exogenous hydrogen peroxide, suggesting an anti oxidant effect of CP. Antioxidants may have a membrane-stabilizing effect, and t his may explain the antiarrhythmic effect of CP reported in this and other studi es. It is known that antioxidants are effective in reducing reperfusion-induced arrhythmias after relatively short periods of regional ischemia[6]. Howe ver, the susceptibility to developing reperfuion-induced arrhythmias after global ische m ia has been shown to require more prolonged ischemic duration such as those empl oyed for hypothermic cardioplegic arrest and ischemia during cardiac operation.
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Another mechanism CP exerting its beneficial effect is by binding a proporti on of the calcium content of the cardioplegic solution, thereby reducing the act ive ionized calcium content and reducing calcium overload during reperfusion. Ro binson and Harwood[7] reported that a similar improvement in recovery of functio n to that achieved with CP was obtained if the calcium content of the cardiopleg ia was reduced from 1.2 to 0.6 mmol.L-1 during hyphthermic ischemia. Howe ver, this theory has been challenged by Conorev and his colleagues[5], who sugges ted that CP may be acting as an antioxidant. They found that if the calcium binding by C P was compensated for by increasing the calcium concentration in the cardiplegia , the protective effect was maintained. In addition, CP prevented hydrogen perox ide-induced contraction and attenuated hydrogen peroxideinduced decrease in dev e loped pressure. Similar studies by Zucchi and his co-workers[4] confirm ed these findings, showing that CP attenuated the detrimental effect of hydrogen peroxide on myocardial function.
, 百拇医药
Exogenous CP may act via an extracellular or an intracellular locus. Rosen shtraukh and associates[8] demonstrated that myocardial cells of isolate d frog h eartpreparations were permeable to CP, intracellular CP concentration increasing linearly with the increase of perfusate concentrations in the range from 10 to 70 mmol.L-1. Associated with this was an increase in contractile force, w hich was sustained as long as the CP was elevated. CP is also known to overcome cyanide- i nduced contractile failure and action potential changes. These findings challeng e the established biochemical view that CP and other high-energy phosphates can n ot cross the cell membrane. If extracellular to intracellular transport is possi ble, particularly under conditions of ischemia where changes in membrane permeab ility occur, CP may act to replenish the dwindling cytoplasmic pool and so provi de more energy for the maintenance of myocardial integrity. If this was the mech anism, milllimolar concentrations of CP would be required for the significant pr otection.
, 百拇医药
Although the exact mechanism of CP requires further study, its cardioprote ctive and antiarrhythmic effects have been confirmed by our and many other studi es. CP can be used as an effective cardioprotective agent during open heart surg ery.
Editor Yuan Tian-Feng
Foundation item: Partly supported by the grant of National Natural Science Foundation (39500144)
Biography: JIN Feng (male, born in 1962 in To ngwei county, Gansu pro vince) got his MD degree from the Fourth Military Medical University in 1998.
, 百拇医药
T el.(029)3373198 Email.Zhjcai@fmmu.edu.cn
REFERENCES:
[1] Pasque MK, Spray TL, Pellom GK et al. Ribose-enhanced myo cardial recovery fo llowing ischemia in the isolated working rat heart [J]. J Thorac Cardiovasc Surg, 1984;83(3):390-398.
[2] Hickey PA. Prevention of intraoperative myocardial injury by pretrea tment with pharmacological agents [J]. Ann Thorac Surg, 1975;20(1):101-105 .
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[3] Bessman SP, Geiger PJ. Transport of energy in muscle. The phosphoryl creatine shuttle [J]. Science,1981;211(4481): 448-452.
[4] Zucchi R, Poddighe R, Limbruno U et al. Protection of isolated r at heart fro m oxidative stress by exogenous creatine phosphate [J]. J Mol Cell Cardiol , 1989;21(1):67-73.
[5] Conorev EA, Sharov VG, Saks VA. Improvement in contractile recovery of isola ted rat heart after cardioplegic ischaemic arrest with endogenous phosphocreatin e: Involvement of antiperoxidative effect [J]? Cardiovasc Res, 1991; 25(2) : 164-171.
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[6] Bernier M. Hearse DJ, Manning AS. Reperfusion-induced arrhythmias a nd oxygen -derived free radicals. Studies with "anti-free radical" interventions and a f re e radical-generating system in the isolated perfused rat hearts [J]. Circ R es, 1986;58(3):331-340.
[7] Robinson LA, Harwood DL, Exogenous creatine phosphate: Favorable cal cium-alt ering effects in St. Thomas' Hospital cardioplegic solution [J]. J Am Coll C ardiol, 1988;11(Suppl A):170A.
[8] Rosenshtraukh LV, Saks VA, Undrovinas AI et al. Studi es of energy transport in heart cells. The effect of creatine: Phosphate on the frog ventric ular contractile force and action potential duration [J]. Biochem Med,1978 ;19(1): 148-164.
Received date: 2000-01-18; Revised date: 2000-02-08, http://www.100md.com
单位：金峰(第四军医大学西京医院心血 管外科中心, 陕西 西安 710033)；李彤(第四军医大学西京医院心血 管外科中心, 陕西 西安 710033)；杨景学(第四军医大学西京医院心血 管外科中心, 陕西 西安 710033)；侯晓彬(第四军医大学西京医院心血 管外科中心, 陕西 西安 710033)；朱海龙(第四军医大学西京医院心血 管外科中心, 陕西 西安 710033)；谭红梅(第四军医大学西京医院心血 管外科中心, 陕西 西安 710033)
关键词：磷酸肌酸；未成熟心肌；心肌停搏液
第四军医大学学报000502 摘 要: 目的 探讨St.Thomas'Ⅱ心脏停搏液添加外源性磷酸肌酸(CP)对未成熟心 肌的保护效果, 并观察其抗心律失常作用. 方法 采用幼鼠(18～21 d)离体 工作心模型, 14℃低温缺血120 min,缺血前主动脉根部灌注4℃ St. Thomas' Ⅱ停搏液(对 照组)或St. Thomas' Ⅱ停搏液加 CP (10 mmol.L-1), 观察缺血再灌注后心功能.心肌ATP含量的恢复百分比,心肌CPK 漏出量及再 灌开始至窦性心律恢复的时间. 结果 ①CP组主动脉流量恢复比明显 增加[(86.8±4.2)% vs (70.2±3.3)%, P<0.01]. ②ATP恢复百分比显著升高[( 90.3±6.8)% vs (72.6±5.3)%, P<0.01]. ③心肌CPK漏出量明显减少(P<0.0 5). ④从再灌注开始至窦性心律恢复的时间显著缩短[ (3.3±1.5) min vs (8.2±2.0) min, P<0.05]. 结论 St. Tho mas' Ⅱ心脏停搏液中加外源 性磷酸肌酸不仅可显著改善幼鼠低温缺血后心功能的恢复,促进高能磷酸盐的重建及减少心 肌CPK的漏出,而且具有较好的抗心律失常作用,是目前一种比较理想的心肌保护药物.
, 百拇医药
中图号:R654.1 文献标识码: A
Exogenous creatine phosphate in protection of immature myocardium
JIN Feng, LI Tong, YANG Jing-Xue, HOU Xiao-Bin, ZHU Hai-Long, TAN Hong-Mei
(Center of Cardiovascular Surgery, Xijing Hospital, Fourth Military Medical Unive rsity, Xi'an 710033, China)
Abstract: AIM To determine whether creatine phosphate (CP) improves th e prote ctive effects of the St. Thomas' Hospital cardioplegia on immature myocardium an d to evaluate the antiarrhythmic effects of CP. METHODS In an i solated working h eart model, hearts from immature rats (18～21 days old) were subjected to 2 hours of 14℃ hypothermic ischemia with a 3 min preischemic infusion of either standa rd ST. Thomas'Ⅱ cardioplegic solution (control group) or the cardioplegia plus CP (10 mmol.L-1) (CP group). RESULTS The postischemic re covery of aortic flow was s ignificantly better in the CP group than that in the CP-free control group (P <0. 01). The percent recovery of myocardial ATP content was also higher in the CP gr oup than that in the control group (P<0.01). The myocardial creatine phospha te k inase (CPK) leakage was significantly lower in the CP group than that in the con trol group (P<0.05). CP reduced reperfusion arrhythmias, significantly decre asin g the time between cross clamp removal and return of regular rhythm. CON CLUSION Addition of CP to ST. Thomas'Ⅱ cardioplegia can significantly improve the funct ional recovery of immature myocardium following long period ischemia and attenua te postischemic myocardial arrhythmias.
, http://www.100md.com
Keywords: creatine phosphate; immature myocardium;cardioplegia
CLC number: R654.1 Document code: A
Article ID：1000-2790(2000) 05-0523-04
INTRODUCTION
The application of hypothermia and cold chemical cardioplegia has enhanced myoca rdial protection and improved survival rate following cardiac operations. Studie s have demonstrated a positive correlation between the postischmic recovery of myocardial performance and the cellular content of high-energy phosphates, such as adenosine triphosph a te (ATP) and CP. This indicates that maintaining ATP and CP during ischemia may help provide optimal myocardial protection. Despite the alleged impermeability o f plasma membrane to high-energy phosphates, exogenous administration of either CP or ATP has been reported to have improved myocardial protection during ischem ia in various models and species. In addition, recent studies suggest that extra cellular CP possesses antiarrhythmic effects associated with regional ischemia a nd reperfusion, effects which may be related in part to CP's protective effects on myocardial protection.
, http://www.100md.com
However, these studies were carried out in only adult patients or animals. The present study was designed to determine whether CP was as effective in prot ecting immature myocardium as in mature myocardium and to evaluate its antiarrhy thmic properties.
MATERIALS AND METHODS
Experimental model Hearts were obtained from infant male Sprague-Dawley rats (18 ～21 days old and 25～35 grams body mass). Each rat was anesthetized with ether, a nd 100 IU heparin was administered intrahepatically. After the induction of hypo thermia (by partial immersion of the animal in cold 4℃ KHBB solution for 1 min) , the chest wall was removed and the thoracic cavity was filled with cold (4℃) KHBB. The pulmonary trunk was incised near its origin and the aorta cannulated i n situ. The heart was then excised and mounted on the perfusion apparatus via th e aortic cannula. Then the Langendorff perfusion was initiated for a 10-minute w ashout and equilibration period with 8.0 kPa perfusion pressure. Control values f or aortic and coronary flow rates, aortic pressure and heart rate were recorded. The atrial and aortic cannulas were then clamped and heart was subjected to a 3 -minute coronary infusion of cardioplegia (4℃) with or without CP. Following t he infusion, the heart was maintained at 14℃ for 120 minutes of ischemic arrest. The heart was then reperfused in the Langendorff mode for 15 minutes, during whi ch coronary effluent was collected for CPK determination and the time from the i nitial postischemic reperfusion to the resumption of regular rhythm was recorded . Following the 15-minute reperfusion period, hearts were converted to the work i ng mode for a further 30 minutes and the recovery of function was recorded. Hear ts were then sampled and stored in -70℃ for the determination of ATP.
, 百拇医药
Cardioplegic solution The St. Thomas' Ⅱ cardioplegia contained ( in mmol.L-1): N aCl 110.0, NaHCO3 10.0, KCl 16.0, MgCl2 16.0, and CaCl2 1.2 (pH adjusted t o 7.8) . Since CP is available as the sodium salt, the sodium concentration of the cont rol solution was adjusted to the same level as that of the CP group. All solutio ns were filtered (pore size 5 μm) just before use.
Analysis methods All data were expressed as the mean±standard e rror. Statisti cal analysis of the results was made by t test and statistical significance was assumed when P values were 0.05 or less.
, 百拇医药
RESULTS
Hemodynamic values Table 1 showed that postischemic recovery of aortic fl ow was significantly better in the CP group compared with that in the control grou p [(86.8±4.2)% vs (70.2±3.3)%, P<0.01]. Similar substantial increase s were ob served for coronary flow and cardiac output. However, no significant effects on heart rate and aortic pressure were observed.HR: heart rate; CF: coronary flow; AF: aortic flow; CO: cardiac output;AP: aortic pressure; PIPR: postichemic percent recovery; STH II: St.Thomas' II cardioplegia.
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Tab 1 Preischemic cardiac function and postischemic percent recovery (
±s) IndexCondition
STH II
STH II+CP
HR/
Preischemia
310 ±19
325 ±14
(beat.min-1)
, 百拇医药
PIPR/%
84.7± 3.5
89.2± 7.0
CF/
Preischemia
6.5± 0.3
6.1± 0.8
(mL.min-1)
PIPR/%
74.2± 4.9
89.1± 5.2a
, 百拇医药
AF/
Preischemia
15.9± 1.8
15.6± 1.4
(mL.min-1)
PIPR/%
70.2± 3.3
86.8± 4.2b
CO/
Preischemia
21.6± 4.0
, 百拇医药
21.5± 2.0
(mL.min-1)
PIPR/%
71.2± 2.1
87.4± 3.8b
AP/
Preischemia
13.3± 0.8
14.1± 0.7
kPa
PIPR/%
, 百拇医药
78.1± 2.8
87.6± 4.9
aP<0.05, bP<0.01 vs STH II group. Myocardial CPK leakage Compared with that in the control group, CPK lea kage was significantly reduced in the CP group [(671±15)vs (439±9) nkat.g-1 , P<0.05].
Myocardial ATP content Postischemic recovery of myocardial ATP content was sign ificantly higher in the CP group than in the control group [(90.3±6.8)% vs (72.6±5.3)%, P<0.01].
, 百拇医药
Antiarrhythmic effects In this study, CP showed obvious antiarr hythmic ef fect. The time from the reperfusion to the return of regular sinus rhythm was si gnificantly shorter in the CP group than in the control group [(3.3±1.5) min vs (8.2±2.0) min, P<0.05].
DISCUSSION
Myocardial ischemia initiates a series of cellular changes that, unless checked, culminate in irreversible injury and cell death. Initially, mitochondrial oxida tive phosphorylation is severely reduced, and soon ATP and CP levels decline. De spite the cessation of contractive activity from oxygen and energy lack, cellula r metabolism continues, contributing to further ATP and CP depletion. This energ y depletion appears to play a vital role in determining cell viability, in parti cular whether contractile function resumes on reperfusion. Cardioplegic solution s conserve high-energy phosphates by hypothermia and by inducing rapid diastoli c arrest. However, neither potassium arrest nor hypothermia completely halts cell ular energy utilization, and cytoplasmic energy stores continue to dwindle. Cons ervation of high-energy phospates is therefore a primary objective in any proce dure designed to reduce ischemic injury.
, 百拇医药
In addition to reducing the rate of energy utilization during ischemia, va rious procedures have been designed to enhance energy availability by stimulatio n of adenine nucleotide synthetic pathways[1,2], for example, the use of substra tes for purine synthesis or inhibitors of the degradative enzymes. In addition, exogenous administration of either of the two major intracellular high-energy p h osphates, ATP and CP, has been suggested as being a benefit to the ischemic hear t despite the alleged inability of these compounds to cross the cell membrane.
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The present study has demonstrated improvement in functional recovery and a decrease in CPK release following hypothermic ischemia in immature rat heart r eceiving preischemic infusion with CP added cardioplegia. The results have also showed that CP has antiarrhythmic effects on immature myocardium. These effects of CP have been previously reported only on adult animals and patients.
The central role of CP, as Bessman and Beiger[3] summarized in the ir theor y of the CP shuttle, is regulating the energy supply and transport for contracti on. In addition to this, other studies have suggested that CP also controls the entry of activator calcium into the myoplasm by a direct effect upon the energy - dependent slow inward calcium current. As the sarcolemmal slow inward calcium cu rrent contributes to the plateau phase of the action potential, CP may play a re latively important role in regulating the duration of the action potential.
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A potential mechanism of action, by which CP has been suggested to exert i ts effect, is through the inhibition of free radical generation during reperfusi on[4，5]. Although not specifically designed to investigate the effects of CP on postischemic arrhythmias, previous studies showed that 10 mmol.L-1 CP pre vented co ntractile dysfunction induced by exogenous hydrogen peroxide, suggesting an anti oxidant effect of CP. Antioxidants may have a membrane-stabilizing effect, and t his may explain the antiarrhythmic effect of CP reported in this and other studi es. It is known that antioxidants are effective in reducing reperfusion-induced arrhythmias after relatively short periods of regional ischemia[6]. Howe ver, the susceptibility to developing reperfuion-induced arrhythmias after global ische m ia has been shown to require more prolonged ischemic duration such as those empl oyed for hypothermic cardioplegic arrest and ischemia during cardiac operation.
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Another mechanism CP exerting its beneficial effect is by binding a proporti on of the calcium content of the cardioplegic solution, thereby reducing the act ive ionized calcium content and reducing calcium overload during reperfusion. Ro binson and Harwood[7] reported that a similar improvement in recovery of functio n to that achieved with CP was obtained if the calcium content of the cardiopleg ia was reduced from 1.2 to 0.6 mmol.L-1 during hyphthermic ischemia. Howe ver, this theory has been challenged by Conorev and his colleagues[5], who sugges ted that CP may be acting as an antioxidant. They found that if the calcium binding by C P was compensated for by increasing the calcium concentration in the cardiplegia , the protective effect was maintained. In addition, CP prevented hydrogen perox ide-induced contraction and attenuated hydrogen peroxideinduced decrease in dev e loped pressure. Similar studies by Zucchi and his co-workers[4] confirm ed these findings, showing that CP attenuated the detrimental effect of hydrogen peroxide on myocardial function.
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Exogenous CP may act via an extracellular or an intracellular locus. Rosen shtraukh and associates[8] demonstrated that myocardial cells of isolate d frog h eartpreparations were permeable to CP, intracellular CP concentration increasing linearly with the increase of perfusate concentrations in the range from 10 to 70 mmol.L-1. Associated with this was an increase in contractile force, w hich was sustained as long as the CP was elevated. CP is also known to overcome cyanide- i nduced contractile failure and action potential changes. These findings challeng e the established biochemical view that CP and other high-energy phosphates can n ot cross the cell membrane. If extracellular to intracellular transport is possi ble, particularly under conditions of ischemia where changes in membrane permeab ility occur, CP may act to replenish the dwindling cytoplasmic pool and so provi de more energy for the maintenance of myocardial integrity. If this was the mech anism, milllimolar concentrations of CP would be required for the significant pr otection.
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Although the exact mechanism of CP requires further study, its cardioprote ctive and antiarrhythmic effects have been confirmed by our and many other studi es. CP can be used as an effective cardioprotective agent during open heart surg ery.
Editor Yuan Tian-Feng
Foundation item: Partly supported by the grant of National Natural Science Foundation (39500144)
Biography: JIN Feng (male, born in 1962 in To ngwei county, Gansu pro vince) got his MD degree from the Fourth Military Medical University in 1998.
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T el.(029)3373198 Email.Zhjcai@fmmu.edu.cn
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[2] Hickey PA. Prevention of intraoperative myocardial injury by pretrea tment with pharmacological agents [J]. Ann Thorac Surg, 1975;20(1):101-105 .
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[3] Bessman SP, Geiger PJ. Transport of energy in muscle. The phosphoryl creatine shuttle [J]. Science,1981;211(4481): 448-452.
[4] Zucchi R, Poddighe R, Limbruno U et al. Protection of isolated r at heart fro m oxidative stress by exogenous creatine phosphate [J]. J Mol Cell Cardiol , 1989;21(1):67-73.
[5] Conorev EA, Sharov VG, Saks VA. Improvement in contractile recovery of isola ted rat heart after cardioplegic ischaemic arrest with endogenous phosphocreatin e: Involvement of antiperoxidative effect [J]? Cardiovasc Res, 1991; 25(2) : 164-171.
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[6] Bernier M. Hearse DJ, Manning AS. Reperfusion-induced arrhythmias a nd oxygen -derived free radicals. Studies with "anti-free radical" interventions and a f re e radical-generating system in the isolated perfused rat hearts [J]. Circ R es, 1986;58(3):331-340.
[7] Robinson LA, Harwood DL, Exogenous creatine phosphate: Favorable cal cium-alt ering effects in St. Thomas' Hospital cardioplegic solution [J]. J Am Coll C ardiol, 1988;11(Suppl A):170A.
[8] Rosenshtraukh LV, Saks VA, Undrovinas AI et al. Studi es of energy transport in heart cells. The effect of creatine: Phosphate on the frog ventric ular contractile force and action potential duration [J]. Biochem Med,1978 ;19(1): 148-164.
Received date: 2000-01-18; Revised date: 2000-02-08, http://www.100md.com