ischaemic preconditioning of the human heart. - Leicester Research ...

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'rhe present studies have also shown a dose-response etfect in preconditioning the human myocardium so that the phenomenon should be identified as a graded rather than an all-or-nothing event. It is worth noting that the time window of protection was confined to a limited period, between 3 and 6 min of ischaernia, and therefore studies involving few ischaernic times may give the false impression that preconditioning is an all-or-nothing phenomenon. This thesis is supported by studies on anaesthetizcd pigs[2741 and rabbits[2641 where graded ischaernia determined the extent of infarct size reduction. It Is also worth noting that my findings are in agreement with those of Downey et al [3211 that preconditioning ischaernia less than 2 min did not confer protection, indicating that preconditioning has a threshold somewhere between 2 and 5 minutes. Their explanation was that the threshold of protection reflects the duration of ischaernia required to build up adenosine levels to the point where adenosine receptors are adequately populated. It should be mentioned however that preconditioning by repeated short periods of ischaernia and reperfusion may have resulted in wash-out of tissue adenosine and that in fact adenosine may not have been raised sufficiently to reach the threshold of protection. If this is the case then the mechanism of protection induced by repeated short ischaernic cycles should involve the stimulation of receptors other than or in addition to adenosine receptors. Indeed Downey [ 104] has previously suggested that the threshold of protection by preconditioning can be obtained by the additive effect of the stimulation of several membrane receptors (i e. adenosine receptors, ct, adrenoreceptors, bradykinin and oploid receptors). Another finding of my study that may have clinical implications is the loss of protection when the preconditioning ischaemic stimulus was extended to 10 min, a time that has been reported to elicit protection in several animal species. Thus, if my results are extrapolated to clinical situations it is possible that repeated occlusions of a coronary anery dunng PTCA or of the ascending aorta 79
during cardiac surgery totalling 10 or more min of ischerma may result inadvertently in loss of protection. The number of preconditioning cycles The results in Figures 3.6 and 3.7 clearly demonstrate that the number of preconditioning cycles perse do not influence the outcome and that in fact protection is determined by the intensity of the ischaernic stimulus. Clinical studies on preconditioning in the course of PTCA where changes in S-T segment shift and the severity of angina are reduced dufing the second and third coronary occlusion [781 may be the reflection of fulfilling the optimal ischaemic stimulus (i. e. 4-6 min) rather than an effect directly promoted by the increasing number of ischaernic cycles Animal studies in which preconditioning was elicited by increasing the number of cycles but using cycles of one ischaernic duration time only [57,224,341] cannot separate the effects of the number of preconditioning cycles from those corresponding to the total duration of ischaemia and hence, do not support or refute the above suggestion. Therefore, my results argue the conventional wisdom that preconditioning can be made more effective by increasing the number of ischaemic cycles. It should be emphasised however that this argument may apply to this model of i schaemia/reoxygenat ion used in this thesis and that it may not necessarily be valid for shorter or longer periods of ischaemia or different degrees of severity of tissue injury. Fir3t Window of Protection To the best of my knowledge, our studies are also the first to demonstrate that classical preconditioning of the human myocardium, also known as the early or first window of preconditioning, is restricted to the initial 2 hr following its application, and this has obvious clinical implications. A similar response has been reported in a variety of animal species [218,225,3211 supporting the view that the underlying mechanisms of the first window of FA)
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ISCHAEMIC PRECONDITIONING OF THE HU
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ABSTRACT Ischaemic preconditioning
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andomised clinical study with the f
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CHAPTERI Introduction 35 Matefials
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Discussion 151 CHAPTER Vill Conclus
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44 CK leakage and MTT reduction on
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The Wellcome Trust and The British
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Presentations International "The Ef
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Abbreviations An attempt has been m
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1.1 Introduction Ischaernic heart d
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1.2 Myocardial Ischaemia Myocardial
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hours up to several days to complet
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phosphates and its influence on hyd
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1.4 Myocardial Protection This refe
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performed. This process is repeated
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1.6 Possible Mechanisms of Ischaemi
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kilodalton stress proteins. These p
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and these proteins have been sugges
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K vi-1, channels were initially fou
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tissues the K.. %,.,, channels are
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Subsequently, Jaburek et al 1145] i
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venous capacitance vessels. At ther
Page 45 and 46: preconditioning to be investigated
Page 47 and 48: In the angioplasty model, Tomai et
Page 49 and 50: patients were randomized into two g
Page 51 and 52: CHAPTER 11 THE HUMAN RIGHT ATRIAL T
Page 53 and 54: inexpensive. Briefly in this model,
Page 55 and 56: of each ischemic period, slices wer
Page 57 and 58: 30 nini FO linlin L 60 min 120 inin
Page 59 and 60: In Study 3 (see Figure 2.4), slices
Page 61 and 62: D. Metabolite analysis Samples were
Page 63 and 64: leakage is calculated as the net LD
Page 65 and 66: B. Effect of the severity of ischae
Page 67 and 68: 2.11 DISCUSSION: The present studie
Page 69 and 70: clearly insufficient to induce myoc
Page 71 and 72: The present model may facilitate th
Page 73 and 74: 2.12 Conclusiow I have characterise
Page 75 and 76: 3.5 3 V 2.5 3: m Je m Z0 z 2 1.5 0.
Page 77 and 78: (3 3 2.5 a 1.5 - -r T 0 2 0.5 0 I P
Page 79 and 80: Q oro . 21 . 0 'a IP 10 '. R -C3 A
Page 81 and 82: =3 0 h X CD 0 x CD :3 0 , 7, CD 0 0
Page 83 and 84: CHAPTER III PRECONDITIONING THE HUM
Page 85 and 86: 3.2 MATERIALS AND METHODS-. 3.2.1 E
Page 87 and 88: A117'reduction- At the end of the e
Page 89 and 90: -4 ýi r. () .1 a 0 1 tli n F5* - C
Page 91 and 92: v M. %; n C) .0 ý U ý ý - - - -2
Page 93 and 94: leakage resulting from precondition
Page 95: 3.5 DISCUSSION: The present studies
Page 99 and 100: different. The cellular mechanisms
Page 101 and 102: cn Je 8 7 6 5 4 1 0 0.8 0.7 0.6 0.5
Page 103 and 104: 8 6 C) 2 0.7 0.6 Q) 0.5 0) E 25 0.4
Page 105 and 106: 6 5 CY) ,u3 CF) m -ýe m 2 1 0 -0.8
Page 107 and 108: CHAPTERIV THE ROLE OF THE KATPCHANN
Page 109 and 110: It has been reported that K.. %-I-p
Page 111 and 112: 0 a- I a 3 I cr =r Cl. 2 qQ 0'-ý 0
Page 113 and 114: Figure 4.7 shows that ischaemia alo
Page 115 and 116: Figure 4.2 Dosc-responsc experiment
Page 117 and 118: Figure 4.4 Dose-response experiment
Page 119 and 120: Figure 4.6 Dosc-response experiment
Page 121 and 122: 1 0.9 -ý 0.8 0.7 E 0.6 0.5 0.4 0.2
Page 123 and 124: activity, and showed that diazoxide
Page 125 and 126: Furthermore, Van den Hoek et al [3
Page 127 and 128: mechanism by which the opening of m
Page 129 and 130: 5.1 INTRODUCTION: Within the enormo
Page 131 and 132: 5.2 MATERIALS AND METHODS: 5.2.1 Ex
Page 133 and 134: M77'rechiction: At the end of the e
Page 135 and 136: oc 0 0 cr F; * 10 eb I ý; o I 5 0
Page 137 and 138: Pages missing original in the
Page 139 and 140: esulted in a decrease of CK leakage
Page 141 and 142: are on long-term hypoglycaernics or
Page 143 and 144: absence of uniformity of expeniment
Page 145 and 146: 5.7 Conclusion Preconditioning is a
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0.9 0.8 07 m 0.6 E -0 0t 4 0.3 02 0
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-0 1.2 1 &8 0.6 04 0.2 o Aerobic Is
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6.1 INTRODUCIFION' Life expectancv
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(MI-T) to blue t'()rmazan product C
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The demonstration that ischaemic in
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Table 61 Patients' demographic and
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Nure 6,1: Creatine Kinase (CK) leak
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CHAPTER VII IN VIVO STUDIES ON T"E
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The apparent discrepancy bet,.,,, e
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In the off-pump group, coronary byp
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eduction as described in section 3.
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7.4.2 In vitro studies Figures 7.3A
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preconditioning stimulus in man is
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myocardium. Several investigators [
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Table 7.2 - Patients haemod-v-namic
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(0 -I 3 CD CD CD 1 3 0 :3 0 0 =r w
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0 co t X 3 co 0 0 Cumulative Releas
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-& a) c) UT 0 =r w CD 3 CD 0 1ý (a
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When ischaernic preconditioning was
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evidence tbr the involvement ot'PKC
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institution o fcardiopu Imo nary by
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Biblioqraphv 1. Abete P, Ferrara N,
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14. Auchampach J, Cavero, I and Gro
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27. Becker LB, Van den Hoek TLV, Sh
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41. Bums PG, Krunkenkamp IB, Calder
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55. Cohen G, Shirai T, Weisel RD, e
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69. Currie RW and White FP (1983).
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83. Downey JM, Liu GS and Thornton
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97. Ganote C, Armstrong S and Downe
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110. Grover GJ, D'Alonzo A, Hess T,
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122. Hamilton T and Weston A (1989)
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137. Hu H, Sato T, Seharaseyon J, L
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151. Jennings R, Steenbergen C, Kin
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164. Kelpzig H, Kobert G, Mafter C,
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178. Lamping K, Christensen C, Pelc
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192. Liu GS, Thornton J, Van Winkle
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206. Maulik N, Yoshida T, Das DK. (
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219. Miyawaki H, Zhou X, Ashraf, M.
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233. Okazaki Y, Kodama K, Sato H, K
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248. Pryzlenk K, Li G, Whittaker P
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260. Saito S, Tamura Y, Moriuchi M,
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274. Schulz R, Post H, Valhaus C, e
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288. Stewart JR, Blackwell WH, Crut
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300. Tani M, Suganuma Y, Hasegawa H
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312. Tosaki A, Engelman DT, Engelma
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324. Walker D, Marber M, Walker J a
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337. Yamashita N, Nishida M, Hoshid
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351. Zhang JG, Lindup WE. (1993). R
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444 J. -G. Zhang and others are dif
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446 J. -G. Zhang and others Assessm
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448 J. -G. Zhang and others 0.9 0.8
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450 J. -G. Zhang and others C E 07
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4S2 J. -G. Zhang and othen effects
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ELSEVIER Abstract Cardiovascular Re
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936 S. Ghosh et al. / Cardiovascula
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938 S. Ghosh et al. / Cardiovascula
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940 S. Ghosh et al. [41 Goto M, Liu
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712 0" et &L h wcomMe geg in Obwa»
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714 Gbosb ot aL hmoo dmoWmbDbsnedH
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716 chmä et aL Pi unamOso äu In O
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718 ehe* et &L ditioning in the hum
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