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Biomedical subjects

D J Hearse

Publications and source records attributed to D J Hearse.

At least 109 records · Page 6Linked to original sources
PubMed1992

Effect of sodium aspartate on the recovery of the rat heart from long-term hypothermic storage.

We have investigated the reported ability of aspartate to enhance greatly the cardioprotective properties of the St. Thomas' Hospital cardioplegic solution after prolonged hypothermic storage. Rat hearts (n = 8 per group) were excised and subjected to immediate arrest with St. Thomas' Hospital cardioplegic solution (2 minutes at 4 degrees C) with or without addition of monosodium aspartate (20 mmol/L). The hearts were then immersed in the same solution for 8 hours (4 degrees C) before heterotopic transplantation into the abdomen of homozygous rats and reperfusion in vivo for 24 hours. The hearts were then excised and perfused in the Langendorff mode (20 minutes). Addition of aspartate to St. Thomas' Hospital cardioplegic solution gave a small but significant improvement in left ventricular developed pressure, which recovered to 82 +/- 3 mm Hg compared with 70 +/- 2 mm Hg in control hearts (p less than 0.05). However, coronary flow and high-energy phosphate content were similar in both groups. In subsequent experiments hearts (n = 8 per group) were excised, arrested (2 minutes at 4 degrees C) with St. Thomas' Hospital cardioplegic solution containing a 0, 5, 10, 20, 30, 40, or 50 mmol/L concentration of aspartate, stored for 8 hours at 4 degrees C, and then reperfused for 35 minutes. A bell-shaped dose-response curve was obtained, with maximum recovery in the 20 mmol/L aspartate group (cardiac output, 48 +/- 5 ml/min versus 32 +/- 5 ml/min in the aspartate-free control group; p less than 0.05). However, additional experiments showed that a comparable improvement could be achieved simply by increasing the sodium concentration of St. Thomas' Hospital cardioplegic solution by 20 mmol/L. Similarly, if sodium aspartate (20 mmol/L) was added and the sodium content of the St. Thomas' Hospital cardioplegic solution reduced by 20 mmol/L, no significant protection was observed when recovery was compared with that of unmodified St. Thomas' Hospital cardioplegic solution alone. In still further studies, hearts (n = 8 per group) were perfused in the working mode at either high (greater than 80 ml/min) or low (less than 50 ml/min) left atrial filling rates. Under these conditions, if functional recovery was expressed as a percentage of preischemic function, artifactually high recoveries could be obtained in the low-filling-rate group. In conclusion, assessment of the protective properties of organic additives to cardioplegic solutions requires careful consideration of (1) the consequences of coincident changes in ionic composition and (2) the characteristics of the model used for assessment.

Animals↗
PubMed1992

Comparison of ischemic vulnerability and responsiveness to cardioplegic protection in crystalloid-perfused versus blood-perfused hearts.

The possibility of differences between crystalloid-perfused and blood-perfused hearts in their vulnerability to ischemia and responsiveness to protective interventions has been investigated in isolated rabbit hearts perfused with bicarbonate buffer or arterial blood. In preliminary studies with 165 minutes of aerobic perfusion at constant perfusion pressure (55 +/- 3 mm Hg), the stability of left ventricular developed pressure was significantly better in blood-perfused hearts. In subsequent studies, hearts were subjected to 20 minutes of aerobic perfusion (coronary flow, 2.0 +/- 0.3 ml/min/gm wet weight in blood-perfused hearts versus 11.3 +/- 3.0 ml/min/gm wet weight in crystalloid-perfused hearts; left ventricular developed pressure, 90 +/- 4 and 91 +/- 2 mm Hg, respectively) followed by 30, 45, 60, 75, 90, or 105 minutes of normothermic global ischemia and 40 minutes of reperfusion (n = 4 per group). In the buffer-perfused groups the postischemic recoveries of left ventricular developed pressure were 74% +/- 6%, 45% +/- 7%, 39% +/- 6% 32%, +/- 5%, 27% +/- 4%, and 12% +/- 3% of preischemic control, respectively. In blood-perfused groups they were consistently greater (91% +/- 3%, 55% +/- 5%, 46% +/- 5%, 45% +/- 1%, 33% +/- 2%, and 19% +/- 3%, respectively). In further studies, hearts (n = 5 per group) were perfused with buffer (groups 1 and 2) or blood (groups 3 and 4), and each was subjected to 60 minutes of normothermic global ischemia, with (groups 2 and 4) or without (groups 1 and 3) a 3-minute preischemic infusion of St. Thomas' Hospital cardioplegic solution. After 60 minutes of reperfusion, the postischemic recoveries of left ventricular developed pressure in groups 1, 2, 3, and 4 were 32% +/- 3%, 44% +/- 4%, 43% +/- 7%, and 72% +/- 6%, respectively, with coronary flow recovering to 64% +/- 7%, 82% +/- 4%, 82% +/- 4%, and 110% +/- 5%, respectively. Left ventricular end-diastolic pressures were 20 +/- 5, 24 +/- 7, 15 +/- 4, and 4 +/- 3 mm Hg, and tissue water contents were 4.76 +/- 0.11, 4.87 +/- 0.55, 3.93 +/- 0.05, and 3.68 +/- 0.02 ml/gm dry weight, respectively. In conclusion, compared with crystalloid perfusion, the blood-perfused rabbit heart has a greater resistance to ischemia, a superior response to cardioplegic protection, and a lower tissue water content.

Animals↗
PubMed1992

Exogenous adenosine accelerates recovery of cardiac function and improves coronary flow after long-term hypothermic storage and transplantation.

Impaired coronary flow during postischemic reperfusion may limit functional recovery. In the present studies we used the heterotopically transplanted rat heart and the isolated working rat heart to assess whether adenosine, given during reperfusion, could improve either the rate or the extent of postischemic recovery. Hearts were arrested (2 minutes at 4 degrees C) with the St. Thomas' Hospital cardioplegic solution and stored by immersion in the same solution for 8 hours at 4 degrees C. Hearts were then transplanted into the abdomen of homozygous recipients. Immediately before reperfusion, adenosine (0.5 ml of a 1 mumol/L solution, equivalent to 0.13 micrograms) was injected into the left ventricle (control rats received an equivalent amount of saline). Hearts were reperfused in vivo for 30 minutes or 24 hours, after which they were excised and perfused (Langendorff) for 20 minutes for the assessment of function. They were then freeze clamped and taken for metabolic analysis. After 50 minutes of reperfusion, left ventricular developed pressure was 75 +/- 5 mm Hg (4 mm Hg end-diastolic pressure) in the adenosine group versus 61 +/- 4 mm Hg in the control group (p less than 0.05); however, after 24 hours function was identical in the two groups (52 +/- 4 versus 52 +/- 3 mm Hg). After 50 minutes of reperfusion coronary flow was greater in the adenosine group (11.0 +/- 0.4 versus 9.7 +/- 0.4 ml/min in control rats; p less than 0.05), a difference that was sustained for 24 hours (12.8 +/- 0.3 versus 11.4 +/- 0.4 ml/min in control rats; p less than 0.05). Adenosine triphosphate and creatine phosphate contents recovered to similar extents in control and adenosine groups after both 50 minutes and 24 hours of reperfusion. In further studies with an identical storage protocol (8 hours at 4 degrees C), hearts were not transplanted but were reperfused with crystalloid medium in the Langendorff mode for 15 minutes (creatine kinase leakage measured) and in the working mode for 180 minutes. In an attempt to mimic the heterotopic transplant protocol, adenosine (1 mumol/L) was included in the perfusion fluid for the first 2 minutes of reperfusion. Similar results to those of the transplant studies were obtained, with coronary flow being consistently improved in the adenosine group; however, this benefit was lost after only 2 hours of reperfusion.(ABSTRACT TRUNCATED AT 400 WORDS)

Abdomen↗
PubMed1991

Stunning: a radical re-view.

The recovery from trauma, whether ischemia or some other form of tissue injury, is never instantaneous; time is always required for repair and the return of normal metabolism and function. To what extent the delay in recovery of contractile activity (stunning) after a brief period of ischemia represents convalescence from ischemia-induced injury, as opposed to the expression of reperfusion-induced injury, is perhaps not as clear as the proponents of stunning would hope. Definitive evidence for a distinct reperfusion-induced pathology, which compromises the recovery of contractile function from the depressed state induced by ischemia, is elusive. If reperfusion-induced injury accounts for a significant proportion of stunning, then the molecular mechanisms responsible for initiating the event and those responsible for orchestrating the event at the level of the contractile protein are far from clear. Perturbations of calcium homeostasis are frequently cited as responsible for the depressed contractile state, however, some metabolic derangement must precede any pathologically induced ionic disturbance. In this connection, evidence indicates that free-radical-induced oxidant stress, during the early moments of reperfusion, may modify the activity of a number of thiol-regulated proteins that are directly, or indirectly, responsible for controlling the movement of calcium. Sarcolemmal sodium-calcium exchange and the calcium release channel of the sarcoplasmic reticulum may be activated, whereas the sarcolemmal calcium pump and sodium-potassium ATPase, together with the calcium pump of the sarcoplasmic reticulum, may be inhibited. Under the conditions prevailing during ischemia and reperfusion, this would be expected to promote an early intracellular calcium overload. It is difficult to reconcile such a change with the decreased inotropic state that characterizes stunning; however, it seems likely that the calcium overload is transient and that the stunned myocardium rapidly reestablishes normal levels of intracellular calcium. It is still difficult to explain adequately the reduced inotropic state; clearly, the mechanism of stunning is not quite as simple as its definition.

Animals↗
PubMed1991

Reperfusion-induced injury: a possible role for oxidant stress and its manipulation.

While some investigators recognize "reperfusion-induced injury" as an important component of the overall injury that occurs during ischemia and reperfusion, others question its existence. Resolution of this controversy is of considerable importance, particularly in an era of thrombolysis, since reperfusion-induced injury might be amenable to treatment. Although reperfusion is an absolute prerequisite for the recovery of ischemic tissue, it undoubtedly has some unfavorable effects. The identification of four (possibly sequential) components of reperfusion-induced injury helps to clarify the situation: a) Reperfusion after brief periods of ischemia can trigger arrhythmias in tissue that is potentially salvable; there is abundant experimental and clinical evidence for this form of reperfusion injury. b) Reperfusion may also be associated with "myocardial stunning"; however, given sufficient time, this prolonged postischemic contractile and metabolic dysfunction will recover. There is good experimental evidence and some clinical evidence for the existence of this type of reperfusion-induced injury. c) Reperfusion is commonly thought to cause lethal injury in cells that, until the time of reperfusion, were potentially salvable. However, conclusive evidence that reperfusion can kill cells does not yet exist. d) Reperfusion may alter the nature of necrotic processes in tissue that has already sustained lethal injury, while not altering the number of cells that die this may change the manner in which they die; this form of reperfusion injury could lead to differences in scar formation and vulnerability to aneurysm. There is considerable evidence for the existence of this form of reperfusion-induced injury. Many candidate mechanisms have been proposed for each form of reperfusion injury. Ionic disturbances (particularly for calcium) are often cited and, most recently, free radical-induced induced injury (oxidant stress) has been suggested as important. Considerable evidence exists that oxidant stress is involved in stunning and in reperfusion-induced arrhythmias, and characterization of underlying mechanisms might lead to novel therapeutic principles, such as antioxidant therapy. However, much remains to be learned.

Free Radicals↗
PubMed1991

Isolated, perfused neonatal rat heart preparation for studies of calcium and functional stability.

We describe an isolated, perfused preparation for neonatal rat hearts to assess the relationship between extracellular calcium and (1) cardiac function and (2) contractile stability over 2 hours of perfusion. Neonatal (3 to 5 days old) rat hearts (n = 6 per group) were perfused for 30 minutes (Langendorff) with oxygenated buffer (37 degrees C) containing 1.4 mmol/L calcium (control period) and 90 minutes with buffer containing 0.5, 0.8, 1.0, 1.2, 1.4, 1.8, or 2.5 mmol/L calcium. Upon changing from 1.4 mumol/L to either a higher or low calcium concentration there were no significant changes in left ventricular developed pressure, heart rate, or coronary flow. However, left ventricular developed pressure progressively deteriorated in a time-dependent and calcium-dependent manner. Thus, after 90 minutes, developed pressure fell to 18% +/- 2%, 27% +/- 3%, 41% +/- 5%, 47% +/- 8%, 55% +/- 10%, 64% +/- 5% and 76% +/- 4% of its initial value with 0.5, 0.8, 1.0, 1.2, 1.4, 1.8, and 2.5 mmol/L calcium. In conclusion, in studies with the neonatal rat heart, extracellular calcium concentrations in the range of 1.8 to 2.5 mmol/L are recommended.

Animals↗
PubMed1991

Pharmacological studies of arrhythmias induced by rose bengal photoactivation.

Singlet oxygen and superoxide production by rose bengal photoactivation leads to rapid electrophysiological changes and arrhythmias. To investigate which intermediate is causative and to probe possible mechanisms, hearts (n = at least 6/group) were perfused aerobically for 10 min without rose bengal followed by 5 min with rose bengal before illumination for 20 min. In controls, all or most hearts exhibited ventricular premature beats, ventricular tachycardia, and complete atrioventricular block. Most antioxidants tested had no protective effect; histidine, however, significantly delayed the onset of electrocardiographic (ECG) changes. In further studies, two antiarrhythmic agents (quinidine and verapamil) had no little protective effect, whereas R56865 significantly delayed the onset of ECG changes and reduced the incidence of arrhythmias. However, spectrophotometric and laser pulse radiolysis studies showed that this apparent protective effect might have resulted from an interaction between R56865 and the rose bengal molecule, leading to a reduction in singlet oxygen production. In conclusion, the electrophysiological changes induced by rose bengal photoactivation are likely to be due to singlet oxygen; antiarrhythmic drugs appear to be unable to protect against the injury unless there is some interaction with the photoactivation process.

Animals↗
PubMed1991

Detrimental effects of multidose hypothermic cardioplegia in the neonatal heart: the role of the frequency of cardioplegic infusions.

In the neonatal rabbit heart, multidose crystalloid cardioplegia is protective against normothermic ischemia, but its beneficial effects are lost under hypothermia. In order to determine the relationship between myocardial protection and the number of cardioplegic infusions administered during the ischemic period, we examined the effects of an increasing number of infusions on postischemic recovery at three temperatures (37 degrees, 20 degrees, or 10 degrees C). Isolated working hearts from rabbits aged 7-10 days were perfused aerobically (37 degrees C) for 20 min before infusion of St. Thomas' Hospital cardioplegic solution at the selected temperature. At each temperature, the cardioplegic solution was given either as a single 2-min infusion (single-dose) or as repeated 2-min infusions (multidose) at various intervals. Following the ischemic period, hearts were reperfused (15 min Langendorff, 20 min working) before assessment of the recovery of function. Ischemic durations (selected to result in approximately 55%-70% recovery in the single-dose group at each temperature) were 1, 10, or 18 h at 37 degrees, 20 degrees, and 10 degrees C. At 37 degrees C, there was a positive correlation between postischemic recovery and the number of infusions during the ischemic period. However, at 20 degrees or 10 degrees C the relationship was reversed and recovery was depressed with increasing number of infusions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Oxygen supply and oxygen demand in the isolated working rabbit heart perfused with asanguineous crystalloid solution.

STUDY OBJECTIVE: It has been suggested that oxygenation of the isolated, crystalloid perfused, Langendorff rabbit heart is inadequate and that consequent hypoxia limits mechanical performance. The isolated working rabbit heart, which has a higher oxygen requirement than the Langendorff preparation, was used to investigate the relationships between the ability of the heart to perform external work, myocardial oxygen consumption, and tissue high energy phosphate content. DESIGN: Hearts from adult rabbits (1.5-2.2 kg), paced at 200 beats.min-1, were perfused in the working mode with bicarbonate buffer (1.8 mmol.litre-1 Ca2+; PO2 greater than 85 kPa, 630 mm Hg). MEASUREMENTS AND MAIN RESULTS: The effects of (a) increasing preload (10, 14, 18, 22, 26 cm H2O) at fixed afterload (80 cm H2O) and (b) increasing afterload (60, 80, 100, 120 cm H2O) at fixed preload (18 cm H2O) on left ventricular power and myocardial oxygen consumption were determined. Increasing preload (from 10 to 26 cm H2O) resulted in linear increases in left ventricular power [from 1.36(SEM 0.06) to 2.81(0.19) J.min-1] and myocardial oxygen consumption [from 554(37) to 801(59) microliters.g dry wt-1.min-1]; this was made possible by increased oxygen supply secondary to increased coronary flow. Increasing afterload (from 60 to 120 cm H2O) also increased left ventricular power [from 1.76(0.05) to 2.16(0.09) J.min-1] and myocardial oxygen consumption [from 617(48) to 903(30) microliters.g dry wt-1.min-1]. For a given increase in left ventricular power, the increase in myocardial oxygen consumption was greater if the increased workload was due to an increased afterload than if it was due to an increased preload, suggesting that increasing afterload resulted in a reduced external mechanical efficiency. Prolonged perfusion under conditions of low and high workload (80 and 120 cm H2O afterload for 60 min) was associated with comparable myocardial contents of adenosine triphosphate [22.5(1.4) and 21.7(0.4) mumols.g dry wt-1] and creatine phosphate [21.8(4.5) and 23.7(1.9) mumols.g dry wt-1] and comparable rates of lactate efflux [34.7(13.0) and 36.7(12.5) mumols.g dry wt-1.60 min-1]. CONCLUSION: Our observation of increased myocardial oxygen consumption and comparable contents of high energy phosphates with increased workload would suggest that the crystalloid perfused working rabbit heart is adequately oxygenated.

Adenosine Triphosphate↗
PubMed1991

Effects of diltiazem as an additive to St Thomas's Hospital cardioplegic solution in isolated neonatal and adult rabbit hearts.

STUDY OBJECTIVE: The aim was to compare the protective efficacy of diltiazem as an additive to St Thomas's Hospital cardioplegic solution in isolated hearts from neonatal and adult rabbits. DESIGN: The relative responsiveness of the two age groups to diltiazem was first determined in Langendorff perfused hearts (n = 6 per group) by constructing concentration-response curves for the drug's negative inotropic effect. The IC20 and IC50 of diltiazem (the concentrations of diltiazem resulting in 20% or 50% reduction in developed pressure, respectively) were the doses subsequently included in the cardioplegic solution. Isolated working hearts (n = 8 per group) were perfused aerobically (37 degrees C) for 20 min followed by a 2 min infusion of St Thomas's Hospital cardioplegic solution with or without added diltiazem. All hearts were then subjected to global ischaemia (37 degrees C). The durations of ischaemia were 60 min in the neonatal and 45 min in the adult heart. Hearts were then reperfused (15 min Langendorff, 20 min working) before reassessment of function. EXPERIMENTAL ANIMALS: 30 neonatal (7-10 d) and 30 adult (2-3 months) New Zealand white rabbits were used. MEASUREMENTS AND MAIN RESULTS: The IC20 and IC50 of diltiazem were found to be 0.1 and 0.5 mumol.litre-1, respectively, in the neonatal heart, and 0.5 and 2.5 mumol.litre-1, respectively, in the adult heart. Postischaemic recovery of cardiac output was 57.9(SEM 6.7)% in the control group and 64.1(5.0)% (NS) and 47.7(3.8)% (NS) in the 0.5 mumol.litre-1 and 2.5 mumol.litre-1 diltiazem groups, respectively, in the adult hearts. In the neonatal hearts, cardiac output recovered to 55.6(4.8)% in the control group and 59.9(4.2)% (NS) and 62.0(5.6)% (NS) in the 0.1 mumol.litre-1 and 0.5 mumol.litre-1 diltiazem groups, respectively. CONCLUSIONS: The addition of diltiazem, at IC20 or IC50 negative inotropic concentrations, to St Thomas's Hospital cardioplegic solution does not improve postischaemic recovery in either neonatal or adult rabbit hearts. This suggests that the slow calcium channel may not be an important mediator of ischaemia and reperfusion induced injury in the cardioplegically arrested rabbit heart.

Aging↗
PubMed1991

Functional and electrophysiological effects of oxidant stress on isolated ventricular muscle: a role for oscillatory calcium release from sarcoplasmic reticulum in arrhythmogenesis?

STUDY OBJECTIVE: The aim was to investigate the cellular basis of oxidant stress induced arrhythmias by studying the influence of oxidant stress on the contractile and electrophysiological function of isolated cardiac muscle. DESIGN: Oxidant stress was induced by the photoactivation of rose bengal added to the solution superfusing isolated ventricular muscles from a number of species. Measurements of contractile and electrophysiological function were made under control conditions, during exposure to oxidant stress, and under a number of experimental conditions. EXPERIMENTAL MATERIAL: Isolated superfused papillary muscles or trabeculae from rat, rabbit, or frog hearts were used in all studies. MEASUREMENTS AND MAIN RESULTS: The contractile response to oxidant stress was assessed by measuring isometric developed tension and resting tension throughout the experiment, and the electrophysiological response was assessed by recording action potentials using conventional 3 M KCl filled intracellular electrodes. Oxidant stress induced a transient positive inotropy, after-contractions, and eventually contracture. Associated with these contractile changes were prolongation of the action potential, early afterdepolarisations, oscillations in resting membrane potential, and automaticity. These effects were concentration and species dependent and the oscillations in both tension and membrane potential were abolished by inhibition of calcium release from the sarcoplasmic reticulum with caffeine. CONCLUSIONS: The contractile and electrophysiological effects of rose bengal induced oxidant stress are consistent with a cellular calcium overload. The observation that the oscillations in tension and membrane potential were abolished by caffeine and that these effects were species dependent (rat greater than rabbit greater than frog) suggests a role for oscillatory sarcoplasmic reticulum calcium release in these effects. The oscillations in membrane potential and the automaticity induced by rose bengal are likely to underlie the arrhythmias observed in isolated hearts exposed to oxidant stress that have previously been described.

Animals↗
PubMed1991

Calcium and cardioplegia in neonates: dose-response and time-response studies in rats.

Isolated Langendorff-perfused rat hearts (n = 6/group) were subjected to 60, 90, 120, or 180 min of ischemia with or without a 2-min preischemic infusion with St. Thomas' Hospital cardioplegic solution that had been modified to contain concentrations of calcium of 0, 0.5, 0.8, 1.0, 1.2, 1.8, or 2.4 mM. In general, irrespective of the calcium concentration, hearts in the cardioplegia group recovered better than those in the noncardioplegia group. There was no consistent relationship between calcium content and postischemic recovery of function or enzyme leakage after any of the durations of ischemia studied. However, as expected, there was a strong inverse relationship between recovery and duration of ischemia. The recovery of function correlated with enzyme leakage but not with the time to onset or magnitude of ischemic contracture. In conclusion, although the neonatal rat heart benefits from cardioplegia the protection is less impressive than that reported for adult hearts. Nonetheless, the neonatal heart appears to be very resistant to ischemia. We propose that many of these differences can be explained on the basis of differences in myocardial calcium handling between neonate and adult.

Animals↗
PubMed1991

Reactive oxygen species modify the structure and function of the cardiac sarcoplasmic reticulum calcium-release channel.

Restoration of blood flow to the ischemic myocardium prevents continuing cell necrosis, but reperfusion may cause irreversible damage to potentially salvable tissue, possibly through the generation of toxic reactive oxygen species. Intracellular calcium overload, secondary to membrane lipid peroxidation, has been proposed as a general pathogenic mechanism. However, using the photosensitisation of rose bengal to generate singlet oxygen and superoxide radicals, we demonstrate a direct effect of reactive oxygen species on the cardiac sarcoplasmic reticulum calcium-release channel. Exposure of heavy sarcoplasmic reticulum vesicles to reactive oxygen species in vitro resulted in the progressive loss of specific [3H]ryanodine binding and the degradation of high molecular weight proteins identified by polyacrylamide gel electrophoresis. The gating of single channels incorporated into artificial planar phospholipid bilayers was modified during the exposure to reactive oxygen species: an initial increase in open probability being followed by irreversible loss of channel function. Degradation by reactive oxygen species of specific proteins, such as the calcium-release channel, may contribute to in vivo reperfusion injury.

Animals↗
PubMed1991

Perfusate calcium: effect on cardiac stability and response to ischemia and reperfusion.

OBJECTIVE: The aim of this study was to characterize the relationship of perfusate calcium concentration, contractile state and stability of the isolated crystalloid perfused working rat heart preparation, to ischemic duration and functional recovery, at a physiological perfusate calcium concentration. METHODS AND RESULTS: In the first protocol, hearts (n = 6 per group) were aerobically perfused for up to 300 mins with Krebs Henseleit solution containing calcium concentrations (total) of 1.0, 1.2, 1.4, 1.6, 1.8 and 2.5 mmol/L (equivalent to ionized concentrations of 0.76, 0.94, 1.15, 1.21, 1.58 and 2.25 mmol/L, respectively). After 120 mins, aortic flow decreased by less than 20% in all preparations except those perfused with 1.0 mmol/L, which fell by over 60%. For subsequent studies, a calcium concentration of 1.4 mmol/L (ionized calcium 1.15 mmol/L, a value equivalent to plasma ionized calcium) was identified as ideal and shown to be associated with stable function and adequate inotropic reserve. The second protocol was as follows: In additional studies (n = 6 per group), the relationship between normothermic global ischemic duration (with or without cardioplegic arrest) and post ischemic functional recovery was characterized. Increasing the ischemic duration (10, 15, 20, 25, 30, 35 or 40 mins) progressively impaired recovery of aortic flow to 86.7 +/- 3.2%, 71.7 +/- 4.9%, 27.7 +/- 5.0%, 14.5 +/- 12.3%, 0%, 0% and 0%, respectively, in the noncardioplegia group, and to 84.7 +/- 1.7%, 85.0 +/- 2.9%, 78.0 +/- 2.4%, 56.0 +/- 7.8%, 32.2 +/- 6.0%, 6.5 +/- 3.7% and 0%, respectively, in the cardioplegia group. These results were similar to those of previous studies in which 2.5 mmol/L calcium was used in the perfusate. CONCLUSIONS: Perfusion of isolated hearts with perfusate calcium concentrations up to 2.5 mmol/L (total) had no apparent detrimental effect on the stability of the preparation; however, a calcium concentration of 1.0 mmol/L resulted in a rapidly deteriorating preparation. In addition, under the conditions prevailing in the present study, a perfusate calcium content within the physiological range (1.4 mmol/L) appeared not to alter the vulnerability of the rat heart to injury during ischemia and reperfusion.

Animals↗
PubMed1991

Long-term preservation of the mammalian myocardium. Effect of storage medium and temperature on the vulnerability to tissue injury.

Human heart preservation for transplantation commonly involves infusion of cold cardioplegic solutions and subsequent immersion in the same solution. The objectives of the present study were (1) to establish the temporal relationship between storage time (at 10 degrees C) and the postischemic recovery of function in the isolated rat heart, (2) to assess, by metabolic and functional measurements, whether storing the heart in fluid as opposed to moist air had any effect on the viability of the preparation, and (3) to ascertain the optimal storage temperature. Isolated rat hearts (at least 6 in each group) were infused for 3 minutes with St. Thomas' Hospital cardioplegic solution No. 2 at 10 degrees C, stored at 10 degrees C for 6, 12, 18, or 24 hours, and then reperfused at 37 degrees C. Mechanical function, assessed by construction of pressure-volume curves (balloon volumes: 20, 40, 60, 80, 100, and 120 microliters), was measured before ischemia and storage and after 60 minutes of reperfusion. Function deteriorated in a time-dependent manner; thus at a balloon volume of 60 microliters the recovery of left ventricular developed pressure was 84.2% +/- 5.3% after 6 hours (p = not significant when compared with preischemic control); 69.1 +/- 3.3% after 12 hours (p less than 0.05); 55.6% +/- 4.4% after 18 hours (p less than 0.05), and 53.0% +/- 6.8% (p less than 0.05) after 24 hours of storage. Other indices of cardiac function, together with creatine kinase leakage and high-energy phosphate content, supported these observations. Since the recovery of the left ventricular developed pressure balloon volume curves were essentially flat after 18 and 24 hours of storage, either 6 or 12 hours of storage were therefore used in subsequent studies. Comparison of storage environment (hearts either immersed in St. Thomas Hospital cardioplegic solution No. 2 or suspended in moist air at 10 degrees C for 6 or 12 hours) revealed no significant differences in functional recovery between the groups. Thus hearts recovered 94.9% +/- 3.5% and 113.7% +/- 12.4%, respectively, after 6 hours of storage and 71.6% +/- 2.4% and 54.2% +/- 7.9%, respectively, after 12 hours of storage. Enzyme leakage and tissue water gain were also similar in both groups of hearts. Finally, hearts (n = 6 per group) were subjected to 12 hours' storage at 1.0 degree, 5.0 degrees, 7.5 degrees, 10.0 degrees, 12.5 degrees, 15.0 degrees, and 20.0 degrees C.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1991

Temperature-response studies of the detrimental effects of multidose versus single-dose cardioplegic solution in the rabbit heart.

Both single-dose and multidose cardioplegia are protective in the ischemic adult heart under normothermic and hypothermic conditions, but in the hypothermic neonatal rabbit heart single-dose cardioplegia only is protective, whereas multidose cardioplegia is damaging. The present studies in the isolated perfused working heart from neonatal rabbits (aged 7 to 10 days) were designed to characterize the interrelationships between temperature, frequency of cardioplegic infusion, and tissue protection. Hearts (n = 8/group) were subjected to 1, 1.5, 1.5, 3, 10, 12, or 18 hours of ischemia at 37.0 degrees, 34.5 degrees, 32.0 degrees, 28.0 degrees, 20.0 degrees, 15.0 degrees, or 10.0 degrees C, respectively. These times were selected to achieve approximately 55% to 75% recovery of cardiac output in hearts during normothermic reperfusion when single-dose (2 minutes) St. Thomas' Hospital cardioplegic solution was given at the onset of each ischemic period. Under these conditions actual recoveries of cardiac output were 55.7% +/- 5.6%, 68.5% +/- 6.8%, 73.8% +/- 4.1%, 54.6% +/- 5.3%, 56.3% +/- 7.5%, 59.5% +/- 7.7%, and 81.3% +/- 2.3% of the preischemic control values, respectively. By contrast, with multidose cardioplegia (given every 60 minutes in the 3- to 18-hour experiments and every 30 minutes in the 1- and 1.5-hour experiments) there was a temperature-dependent loss of protection when compared with single-dose cardioplegia; the recoveries of cardiac output were 75.7% +/- 1.5%, 78.4% +/- 4.8%, 65.0% +/- 5.8%, 36.7% +/- 5.8%, 34.6% +/- 7.5%, 25.9% +/- 6.0%, and 9.6% +/- 6.4%, respectively. These results were reflected in other indices of cardiac function and in changes in vascular resistance during cardioplegic infusion and reperfusion. To ascertain whether the progressive loss of protection was related to the degree of hypothermia or the duration of ischemia (which had to be increased as the temperature was lowered to permit a 55% to 75% recovery in the single-dose cardioplegia group), we conducted studies at a fixed temperature (20 degrees C) with variable durations of ischemia (6, 8, 10, and 12 hours). Finally, multidose and single-dose cardioplegia at 10.0 degrees, 20.0 degrees, and 37.0 degrees C were compared with hypothermia alone. We concluded that in the neonatal (in contrast to the adult) rabbit heart the protective properties of multidose cardioplegia relative to single-dose cardioplegia are progressively lost.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Ischemia, reperfusion, and the determinants of tissue injury.

Much of the damage arising during ischemia and reperfusion can be attributed to the consequences of flow deprivation. However, while reperfusion is a prerequisite for the survival of tissue, it may have an injurious component, which, if counteracted, might enhance postischemic recovery. The complex and dynamic changes that occur during ischemia in the diseased human heart are difficult to model in experimental preparations. As a consequence, much remains to be learned about the identity and manipulability of cellular changes leading to irreversible injury. Although the subject of most studies, injury to the myocyte may not be the primary determinant of tissue injury and changes in the endothelium or vascular smooth muscle may play an important role. Once critical ischemia-induced cellular changes have been identified, interventions can be developed to delay their progression such that at the time of reperfusion more cells are potentially salvable. Suboptimal reperfusion may limit the recovery of the tissue through the induction of "reperfusion injury." Much controversy surrounds the importance and even the existence of this phenomenon. It is proposed that reperfusion injury may express itself in four distinct forms: a) reperfusion-induced arrhythmias, which are potentially lethal (but preventable or reversible) events occurring in otherwise viable tissue; b) myocardial stunning, which is expressed as prolonged (but eventually fully reversible) contractile and metabolic dysfunction; c) the induction of lethal injury in tissue that was potentially viable in the moments before reperfusion; d) accelerated necrosis in tissue that is already irreversibly injured (the "oxygen paradox"). All but the third of these categories has been shown to exist experimentally and clinically, and can be advantageously manipulated. Although it is likely that lethal reperfusion injury also exists, there is as yet no definitive proof. Clarification of this issue is of considerable importance to those undergoing angioplasty or thrombolytic procedures.

Animals↗