缺血预处理合并低温及晶体停搏液对兔未成熟心肌的保护作用

本文拟探讨缺血预处理(ischemic preconditioning,IP)合并低温及晶体停搏液对幼兔的离体心脏是否具有心肌保护作用.采用Langendorff离体心脏灌注模型,灌注液为Krebs-Henseleit液(K-H液).取3～4周龄幼兔心脏,在第一部分实验中分为Con、IP1、IP2、IP3组(n=6),分别给予0、1、2、3次IP,其后各组心脏均在20℃低温下停灌2 h,37℃常温下再灌注30 min.在第二部分实验中分为SConI、SCon2、SCon3、SIPl、SIP2、SIP3组(n=8),其中SIPl、SIP2、SIP3组给予2次IP后灌注St.Tho-mas Ⅱ晶体停搏液(CCS)使心脏停搏,然后分别使心脏在32℃、25℃、20℃下停灌30、90和120min,其后各组均在37℃再灌注30 min.SConl,SCon2,SCon3三组则不给予IP,继续灌注20min后灌注CCS使心脏停搏,然后分别在32℃、25℃、20℃下停灌30、90和120 min,其后各组均在37℃再灌注30 min.以Maclab/4 s生理实验系统记录平衡末、缺血前、再灌注后1、3、5、10、20、30 min时心率(HR)、左心室发展压(LVDP)以及左心室内压上升及下降最大速率(±dp/dtmax),测定再灌注末心肌组织中ATP和丙二醛(MDA)的含量,以及超氧化物歧化酶(SOD)的活性.在20℃低温停灌且停灌期间不给予CCS时,再灌注末IP2组LVDP×HR、+dp/dtmax和-dp/dtmax的恢复率分别为96%±21%、101%±19%和84%±15%,显著高于Con组和IP3组(P＜0.01,P＜0.05);心肌组织的ATP含量亦高于Con组(P＜0.01).在不同低温停灌且停灌期间给予CCS时,再灌注末SIP1、SIP2组的LVDP×HR、+dp/dtmax分别恢复到87%±14%、99%±26%(P＜0.05,vs SConl group)和87%±16%、102%±20%(P＜0.05,vs SCon2 group);心肌组织的ATP含量均分别显著高于SCon1组和SCon2组(P＜0.05),心肌组织MDA含量亦分别低于SCon1组和SCon2组(P＜0.05).上述结果提示,IP对在20℃低温停灌的兔未成熟心脏具有一定的心肌保护作用,2次IP的保护效应优于1次或3次IP.在停灌期间应用CCS,IP的心肌保护作用随停灌期间低温程度的升高而减弱.

Myocardioprotective effects of the combination of ischemic preconditioning with hypothermia and crystalloid cardioplegia in immature rabbits

This study was undertaken to explore the myocardioprotective effects of the combination of ischemic preconditioning (IP) with hypothermia and St.II Thomas crystalloid cardioplegic solution (CCS) on immature hearts in the rabbit. Isolated immature rabbit hearts were perfused with Krebs-Henseleit bicarbonate buffer on Langendorff apparatus. In experiment 1, 24 hearts were divided into 4 groups (n=6 in each group): Con, IP1, IP2 and IP3 group. Hearts of the four groups underwent 0, 1, 2 or 3 cycles of IP respectively. Then all the hearts were subjected to a sustained ischemia period of 2 h at 20 degrees C and a postischemic reperfusion period of 30 min at 37 degrees C. In experiment 2, 48 hearts were divided into 6 groups (n=8 in each group): SCon1, SIP1, SCon2, SIP2, SCon3 and SIP3 group, according to hypothermia and the duration of sustained ischemia (30 min at 32 degrees C; 90 min at 25 degrees C, 2 h at 20 degrees C). The SIP1, SIP2 and SIP3 groups were preconditioned twice before the sustained hypothermic ischemia, while the SCon1, SCon2 and SCon3 groups were not preconditioned. CCS was applied during sustained ischemia, all the hearts were reperfused for 30 min at 37 degrees C. Heart rate (HR), left ventricular developed pressure (LVDP) and peak rate of increase or decrease of left ventricular pressure (+/-dp/dt(max)) were recorded. Tissue concentration of adenosine triphosphate (ATP), malondialdehyde (MDA) and the activity of superoxide dismutase (SOD) were measured. At the end of reperfusion, values of product of LVDP and HR, +/-dp/dt(max) in IP2 group were 96%+/-21%, 101%+/-19% and 84% +/-15% of the baseline values respectively, which were significantly higher than those of Con group and IP3 group (P<0.01, P<0.05); also, the ATP content of IP2 group was higher than that of the Con group (P<0.01). When CCS was applied during sustained period of hypothermic ischemia at 32 degrees C or 25 degrees C, recovery rates of RPP (rate product, =LVDPxHR) and +dp/dt(max) in SIP1 group were 87% +/-14% or 99% +/-26% of the baseline values respectively (P<0.05, vs SCon1 group), the values in SIP2 group changed to 87% +/-16% or 102% +/-20% respectively (P<0.05, vs SCon2 group). Contents of ATP in SIP1 and SIP2 groups were significantly higher than those of SCon1 or SCon2 groups respectively (P<0.05), but MDA content of the two groups were significantly lower than those of SCon1 or SCon2 groups (P<0.05) respectively. The study indicates that IP attenuates hypothermic ischemia/reperfusion injury to immature rabbit hearts under 20 degrees C ischemia, two cycles of IP showing better myocardioprotective effects than 1 or 3 cycles of IP. When IP was combined with CCS which were applied during hypothermic ischemia period, the beneficial effects of IP were weakened as the temperature during the hypothermic period was elevated.