Aortic Output Research Articles

The Effects of Dietary α-Tocopherol and Polyunsaturated Fat on Modulating Ischemia-Reperfusion Injury

We investigated the effects of dietary α-tocopherol and polyunsaturated fatty acids (PUFA) on ischemia-reperfusion injury and cardiac lipid composition. Rats were fed corn oil (CO) diets either deficient (CO-E) or supplemented (CO+E) with RRR-α-tocopherol (100 IU kg-1 diet), or butter oil (BO) diets either deficient (BO-E) or supplemented (BO+E) with RRR-α-tocopherol (100 IU kg-1 diet). Intact rat hearts were subjected to ischemia before reperfusion. Dietary RRR-α-tocopherol supplementation contributed to recovery of aortic output, cardiac output and diastolic pressure after ischemia-reperfusion. In contrast, the type of dietary fat did not influence most measures of cardiac recovery. RRR-α-tocopherol levels in cardiac tissues and plasma were significantly higher for rats fed the BO+E diet than for rats fed the CO+E diet. In contrast to plasma, PUFA in cardiac tissues were maintained at a high level even when rats were fed BO containing diets. Our results suggest that dietary RRR-α-tocopherol, but not dietary PUFA levels, modulate oxidative damage to intact rat hearts during ischemia-reperfusion.

PNEUMOPERITONEUM-INDUCED HEMODYNAMIC CHANGES IN PIGS

S190 Hemodynamic alterations after pneumoperitoneum (PMOP) during laparoscopic procedures have been widely investigated in the recent past. Increasing number of the authors are reporting the absence of major hemodynamic changes [1]. However there is to date no study to evaluate hemodynamic changes during the insufflation. The aim of our study was to assess the effect of posture and PMOP during insufflation at different flow rates. METHODS: 10 pigs (weight 20-25 kg) were anesthetized with propofol, sufentanil and pancuronium. Mechanical ventilation (FiO2 0.6) maintained arterial pH, PO (2) and PCO2 in normal range. Monitored variables included: heart rate (HR), mean arterial pressure (MAP), airways pressure (PIP), tidal volume (VT) and aortic output (AO) using a trans-esophageal echo-Doppler ultrasound allowing a continuous monitoring (Dynemo 3000-Sometec, Paris). The PMOP involved intraperitoneal insufflation of CO2 to an intra-abdominal pressure of 15 mmHg at different flow rates (8L/min, 4L/min, 2L/min) in supine position (5 pigs) or in Trendelenburg position (5 pigs). Data were collected at baseline (T1), at the end of insufflation (T2) and 5 min after insufflation (T3) and were analyzed using ANOVA for repeated measures. RESULTS: expressed as mean +/- SD. Hemodynamic variations at the end of insufflation with different outputs (8L/min, 4L/min, 2L/min) in supine position (Table 1) and Trendelenburg (Table 2). *: P < 0.005 vs T1Table 1Table 2DISCUSSION: The current study using a continuous hemodynamic monitoring demonstrates that AO always increases during insufflation of the PMOP. This increase was higher when insufflation output was high in supine position. This suggests that the increase in AO is a consequence of a transitory increase in venous return to right ventricle in response to the insufflation. Frank-Starling law may explain that a lower insufflation output (4 L/min or 2L/min) induces a lower increase in venous return allowing an adaptation of cardiac output. 5 min after insufflation AO returned to basal values. CONCLUSIONS: The transitory increase in AO during a pneumoperitoneum depends on the speed and output of insufflation and position. These results suggest that the increase in preload by increase in venous return is involved in the phenomenon. These findings suggest that hemodynamic tolerance could be improved when pneumoperitoneum is created with a low insufflation output in supine position.

Coronary flow response after myocardial ischemia may predict level of functional recovery.

Is there a quantity, potentially measurable in the operating theater, which predicts rapid recovery of heart power output after surgical intervention with ischemia? We have enhanced our blood-perfused, ejecting, isolated rat heart model for use inside the magnet of an NMR spectrometer, in order to conduct fundamental research into cardioprotective techniques. To provide a baseline, we investigated the effect of normothermic ischemic insults of varying duration. Hemodynamic and metabolic data were collected, and analyzed to seek measures predictive of rapid recovery of aortic power output, which was selected as the most important measure of function. The presence of erythrocytes in the perfusate ensures that oxygen supply is sufficient to support a physiological workload, and that there is reserve coronary flow. On reperfusion, reactive hyperemia occurs: coronary flow increases to a peak, then declines to a steady value. This response was mathematically modeled, and the data for each of fifteen experiments were fitted to the model. Correlating power output recovery against time to reach peak coronary flow yielded the following equation: R = -0.45 log10tp + 1.74 where R is the ratio of power output ten minutes after reperfusion to that before the ischemic insult, and tp is the time taken to reach peak coronary flow, in seconds. The correlation is very significant (p = 0.005). In the clinic, coronary flow response on reperfusion could be used to predict the patient's need for post-operative support.

Protective effect of the sodium/hydrogen exchange inhibitors during global low-flow ischemia.

We investigated the potential role of the Na+/H+ exchanger (NHE) during global low-flow ischemia. Isolated working rat hearts were subjected to a low-flow ischemic period of 30 or 60 min at 37 degrees C and then reperfused for 30 min. Under those conditions, the effects of two NHE inhibitors 3-methylsulphonyl-4-piperidinobenzoyl guanidine methanesulphonate (HOE-694, 1 microM) and 5-(N-ethyl-N-isopropyl) amiloride (EIPA, 1 microM), were compared. When added to the perfusion fluid 15 min before induction of ischemia, EIPA partially preserved aortic output (AO) during either a 30- or 60-min low-flow period. A lesser effect, which was not statistically significant, was observed with HOE-694. Therefore, after 30-min ischemia, AO was 18.7 +/- 2.7, 31.4 +/- 3.3% (p < 0.05 vs. control group) and 25.8 +/- 3.2% of the preischemic value in control and EIPA- and HOE-694-treated groups, respectively. Similarly, after 60-min low-flow ischemia, AO was 15.7 +/- 1.8, 32.7 +/- 4.2% (p < 0.05 vs. control group) and 23.3 +/- 5.6% in control and EIPA- and HOE-694-treated groups, respectively. When EIPA and HOE-694 were added to the perfusion solution during the 60-min ischemic period, i.e., at 15 min of low-flow ischemia, AO was maintained at 38.9 +/- 4.9 and 30.2 +/- 2.4% (vs. 15.7 +/- 1.8% in the controls) in HOE-694- and EIPA-treated groups, respectively. EIPA but not HOE-694 also significantly (p < 0.05) improved the AO recovery during reperfusion. When administered later during ischemia, EIPA but not HOE-694 caused some recovery of AO during the remainder of the ischemic period but did not aid recovery during reperfusion. Our data suggest that although inhibition of NHE may be of some benefit during low-flow ischemia, additional effects may be necessary to provide a more efficient cardioprotection. An additional action, e.g., inhibition of the Na+/HCO3- cotransporter, could explain the superior effect of EIPA with respect to HOE-694.

Effects of cyclosporin and cremophor on working rat heart and incidence of myocardial lipid peroxidation.

Cyclosporin A (CsA) is widely used as the immunosuppressant of choice for preventing graft rejection. However, its clinical use is hampered by certain side effects, especially its nephrotoxicity and other cardiovascular side effects. CsA for intravenous infusion contains cremophor (Cre) and this vehicle has significant adverse effects on endothelial function and vascular muscle. The present study was aimed at investigating the direct effects of CsA and Cre on isolated and perfused rat hearts in the dosage that closely approximates the peak level achieved for the prevention of graft rejection in the rat. Transplantation is a clinical setting in which the myocardium may be exposed to transient ischemia. In this study, we have shown that the vehicle of CsA, namely Cre, has significant adverse effects on cardiac function. We observed a reduction in coronary flow and aortic output. Addition of CsA appeared to induce a further reduction of aortic flow. We have also shown that a significant increase of thiobarbituric acid reactive substances, considered as an index of lipid peroxidation, occurred in the reperfused heart in the presence of Cre+CsA. Our experimental study shows that Cre turned out to be toxic to myocardium by itself. In the heart, potential Cre-CsA interactions possibly potentiating CsA toxicity could not be excluded. The increase of lipid peroxidation in the heart perfused with CsA suggests that reactive oxygen species may be involved in the detrimental effects of this substance on the heart.

Effects of aldosterone and spironolactone on the isolated perfused rat heart.

Aldosterone antagonists are used in the treatment of hypertension. However, the cardiac influences of aldosterone and its antagonists have not been thoroughly investigated. In the present study, we investigated the effects of aldosterone and spironolactone on an isolated rat working heart model. Aldosterone (10(-8) mol/l) decreased the coronary flow and increased aortic flow and cardiac output. Spironolactone (10(-5) mol/l) inhibited these effects. These results suggest that aldosterone directly influences the cardiac function. Spironolactone appears able to inhibit the adverse cardiac effects of aldosterone. The exact mechanisms remain to be elucidated, but the early effects of aldosterone under our experimental conditions on the functional parameters of the heart suggest a nongenomic response including activation of receptors different from those transmitting genomic steroid actions.

The role of the pericardium and the effects of adrenaline and changes in oxygen tension on the performance of an in situ perfused crocodile heart

An in situ perfused crocodile (Crocodylus porosus) heart preparation was used to examine the mechanical responses of the heart to increases in adrenaline concentration, to a decrease in oxygen tension and to opening of the pericardium. Starling and power curves were constructed before and after these experimental manipulations. Increasing adrenaline concentration in the perfusate from 5 nmol l-1 to 0.5 &micro;mol l-1 produced a significant increase in heart rate and a decrease in stroke volume, leaving cardiac output unchanged. With maximal adrenergic stimulation, the left ventricle was able to generate greater power outputs at high right aortic output pressures; however, the right ventricle showed a decrease in performance with increasing output pressure. Decreasing the PO2 of the perfusate to 10 kPa resulted in a significant bradycardia. Both the flow and pressure-generating capabilities of the perfused heart preparation were reduced, although the heart was able to maintain low work levels at this PO2. Opening the pericardium permitted greater movement/expansion of the cardiac chambers and resulted in an increase in heart rate. Higher flows were generated at low filling pressures during the input pressure challenge as a result of an increase in the sensitivity of the Starling response.

Effect of In Vivo Heart Irradiation on the Development of Antioxidant Defenses and Cardiac Functions in the Rat

During radiotherapy of thoracic tumors, the heart is often included in the primary treatment volume, and chronic impairment of myocardial function occurs. The cellular biomolecules are altered directly by radiation or damaged indirectly by free radical production. The purpose of this investigation was to evaluate the biochemical and functional responses of the rat heart to a single high dose of radiation. The effect of 20 Gy local X irradiation was determined in the heart of Wistar rats under general anesthesia. Mechanical performances were measured in vitro using an isolated perfused working heart model, and cardiac antioxidant defenses were also evaluated. Hearts were studied at 1 and 4 months after irradiation. This single dose of radiation induced a marked drop in the mechanical activity of the rat heart: aortic output was significantly reduced (18% less than control values) at 1 month postirradiation and remained depressed for the rest of the experimental period (21% less than control 4 months after treatment). This suggests the development of myocardial failure after irradiation. The decline of functional parameters was associated with changes in antioxidant defenses. The decrease in cardiac levels of vitamin E (-30%) was associated with an increase in the levels of Mn-SOD and glutathione peroxidase (+45.5% and +32%, respectively, at 4 months postirradiation). However, cardiac vitamin C and catalase levels remained constant. Since these antioxidant defenses were activated relatively long after irradiation, it is suggested that this was probably due to the production of free radical species associated with the development of inflammation.

Responses of the branchial circulation to hypoxia in the Atlantic cod, Gadus morhua.

Simultaneous measurements of ventral aortic pressure, dorsal aortic pressure, cardiac output, and branchial venous flow were made to assess the effects of external hypoxia on the branchial vasculature in vivo. In addition, the effects of exogenously added amines (epinephrine and serotonin) and their antagonists (prazosin, sotalol, and methysergide) were assessed. The net effect of hypoxia was to increase branchial venous flow. Mechanisms involved in the branchial vasomotor control include an alpha-adrenoceptor-mediated vasoconstriction, as well as a nonadrenergic, possibly serotonergic, vasodilation of the arteriovenous pathway. The arterioarterial vascular resistance remained largely constant during hypoxia: a beta-adrenoceptor vasodilator effect was offset by vasoconstrictor factors that could be unmasked by sotalol treatment. One of these arterioarterial vasoconstrictors may be serotonin (released from serotonergic nerves or neuroepithelial cells), acting on the efferent filamental artery sphincters. The vascular adjustments during hypoxia increased the portion of cardiac output that flowed to the arteriovenous pathway. This may be of importance in providing the heart and the ion-regulatory cells of the filamental epithelium with oxygenated blood.

Inhibitors of Ca2+ ATPase pump of sarcoplasmic reticulum attenuate reperfusion stunning in isolated rat heart.

We tested for the first time the hypothesis that lessened uptake of Ca2+ into sarcoplasmic reticulum by inhibitors of the Ca(2+)-ATPase pump can decrease the severity of reperfusion stunning (postischemic mechanical dysfunction). We used two novel inhibitors of the Ca(2+)-ATPase pump: (a) cyclopiazonic acid (CPA, 10(-6)-10(-8)M), and (b) thapsigargin (10(-6) or 2.5 x 10(-8)M). The isolated working rat heart was subjected to 20-min global ischemia before 20-min reperfusion. The inhibitor was added either before onset of ischemia or at time of reperfusion. Reperfusion mechanical function (aortic output, AO) was measured and compared with the preischemia values. Pretreatment with CPA improved recovery of AO after 20-min reperfusion from 78.2 +/- 3.0 (n = 12) to 93.3 +/- 1.6% (n = 7) (p < 0.002) while CPA added during reperfusion only, improved AO recovery from 78.2 +/- 3.0 (n = 12) to 90.2 +/- 2.7% (n = 6) (p < 0.05). Pretreatment with thapsigargin (2.5 x 10(-8) M) improved reperfusion AO recovery from 63.5 +/- 1.1 (n = 6) to 96.8 +/- 4.2% (n = 6) (p < 0.002), but when thapsigargin was added only during reperfusion AO recovery did not change. We conclude that inhibition of the Ca2+ uptake pump represents a new principle of control of cell calcium fluxes and that CPA is more effective than thapsigargin. The proposed mechanism of protection against stunning may include inhibition of oscillations of intracellular calcium, and/or depletion of calcium in sarcoplasmic reticulum (SR).

Effects of R 56865 on postischemic ventricular function in isolated rat working heart preparations obtained from healthy, diabetic and hypertensive animals

The present study was undertaken to evaluate the effects of R 56865 (N-[1-[4-(4-fluorophenoxy)-butyl]-4-piperidinyl)- N-methyl-2-benzothiazolamine) (Fig. 1) on postischemic ventricular function, an inhibitor of the Na+/Ca2+ overload, in the working heart preparation of the rat. The hearts were paced at 5 Hz and perfused with Tyrode solution of 37 degrees C at a physiological pH. After 15 min of pretreatment with R 56865, low-flow ischemia (30 min) was induced by reducing the perfusion pressure from 51.5 mmHg to 11.0 mmHg and R 56865 was infused simultaneously. The hemodynamic effects of R 56865 were evaluated in the concentration range [10(-8)-3.10(-6) M]. The five parameters measured were: LVP (Left Ventricular Pressure), +dP/dtmax (maximal rate of pressure increase), AO (Aortic Output), CF (Coronary Flow) and CO (Cardiac Output). They were determined in the working heart mode after 15 min of equilibration and at the end of the experiment. From these data the recovery percentages were calculated. The recovery percentages for the LVP, +dP/dtmax, AO, CF and CO for the control hearts (3.3%, 0.0%, 7.9%, 10.4% and 8.5%, respectively) differed significantly from those at 10(-7) M (39.6%, 40.8%, 25.0%, 41.8% and 29.9% respectively). The recovery percentage were the highest at 10(-6) M (79.6%, 82.1%, 54.7%, 92.7% and 67.2%, respectively). The concentration of 10(-7) M was associated with a smaller reduction in LVP (12.9%) than at 10(-6) M (25.7%).(ABSTRACT TRUNCATED AT 250 WORDS)

Antiischemic Effects of Nifedipine in Isolated Working Heart Preparations of Healthy, Diabetic, and Hypertensive Rats

We evaluated the antiischemic effects of nifedipine in isolated working rat hearts from age-matched normotensive Wistar-Kyoto rats (WKY), diabetic WKY, spontaneously hypertensive rats (SHR), and diabetic SHR. Diabetes was induced by streptozotocin. First, we constructed concentration-response curves for the negative inotropic effect of nifedipine in every group. After 15 min of pretreatment with nifedipine (EC60), low-flow ischemia (30 min) was induced by reducing the afterload from 51.5 to 11.0 mm Hg and nifedipine was infused simultaneously. The six measured parameters were left ventricular pressure (LVP), maximum rate of pressure increase (+dP/dtmax), maximum rate of pressure decrease (-dP/dtmax), aortic output (AO), coronary flow (CF), and cardiac output (CO), determined after 15-min equilibration in the working heart mode and at the end of the experiment. From these data, the recovery percentages were calculated. There were no significant differences in sensitivity to nifedipine (as measured by the EC50 concentration) between the four groups with respect to LVP, +dP/dtmax, -dP/dtmax, CF, and CO. However, hearts from SHR were less sensitive to nifedipine than those from diabetic SHR and nondiabetic WKY with regard to AO. In isolated hearts from nondiabetic WKY and SHR, there were no significant differences between vehicle-treated organs and nifedipine-treated preparations. In hearts from diabetic WKY and diabetic SHR, however, the nifedipine-treated group (LVP 87.1 +/- 3.3 and 60.5 +/- 12.1%, respectively) recovered significantly (p < 0.05) better from ischemia as compared with the control group (LVP 35.7 +/- 14.7 and 10.7 +/- 9.8%, respectively) (n = 6 for each group).(ABSTRACT TRUNCATED AT 250 WORDS)

Inhaled nitric oxide partially reverses hypoxic pulmonary vasoconstriction in the dog.

Nitric oxide (NO) inhaled during a hypoxia-induced increase in pulmonary vasomotor tone decreases pulmonary arterial pressure (Ppa). We conducted this study to better characterize the hemodynamic effects induced by NO inhalation during hypoxic pulmonary vasoconstriction in 11 anesthetized ventilated dogs. Arterial and venous systemic and pulmonary pressures and aortic flow probe-derived cardiac output were recorded, and nitrosylhemoglobin (NO-Hb) and methemoglobin (MetHb) were measured. The effects of 5 min of NO inhalation at 0, 17, 28, 47, and 0 ppm during hyperoxia (inspiratory fraction of O2 = 0.5) and hypoxia (inspiratory fraction of O2 = 0.16) were observed. NO inhalation has no measurable effects during hyperoxia. Hypoxia induced an increase in Ppa that reached plateau levels after 5 min. Exposure to 28 and 47 ppm NO induced an immediate (< 30 s) decrease in Ppa and calculated pulmonary vascular resistance (P < 0.05 each) but did not return either to baseline hyperoxic values. Increasing the concentration of NO to 74 and 145 ppm in two dogs during hypoxia did not induce any further decreases in Ppa. Reversing hypoxia while NO remained at 47 ppm further decreased Ppa and pulmonary vascular resistance to baseline values. NO inhalation did not induce decreases in systemic arterial pressure. MetHb remained low, and NO-Hb was unmeasurable. We concluded that NO inhalation only partially reversed hypoxia-induced increases in pulmonary vasomotor tone in this canine model. These effects are immediate and selective to the pulmonary circulation.

Ferrylmyoglobin formation induced by acute magnesium deficiency in perfused rat heart causes cardiac failure

The oxidation states in intracellular myoglobin and cytochrome oxidase aa 3 were monitored by reflectatnce spectrophotometry in isoltaed perfused rat hearts subjected to an acutely magnesium deficient environment. After exposure to low extracellular [Mg 2+] o (i.e., 0.3 mM) for 30 min, more than 80% of the oxymyoglobin converted to its deoxygenated form. The level of reduced cytochrome oxidase aa 3 also increased about 80% in low [Mg 2+] o. the deoxymyoglobin was converted further to a species identified as ferrymyoglobin by its reaction with Na 2S to form ferrous sulfmyoglobin which was optically visible. This process, set into motion by acute Mg deficiency, resulted from a direct accessibility of the exogenous peroxide to the cytosolic protein. The results suggest that a pathway leading to cardiac tissue damage, induced magnesium deficiency, is probably involved in the generation of a ferrylmyoglobin radical which could be prevented by addition of ascorbate, which is known to be a one-electron reductant of this hypervalent form of myglobin. In further studies, we also investigated whether addition of different concentrations of ascorbic acid (AA) to the perfusate could enhance myocardial function after exposure to log [Mg 2+] o perfusion. Four concentrations of AA (0.5, 1, 5, 10 mM) were tested, indicate that they exert their effects in a concentration-dependent manner; 1 mM AA was the most effective dose in improving aortic output in a Mg-deficient heart. Ferrylmyoglobin formation was found to be formed considerably before intracellylar release of either creatine phosphokinase or lactic dehydrogenase. These studies may have wide implications as a new mechanisms by which extracellular Mg 2+ can induce myocardial injury and subsequent cardiac failure.

Role for the Na+/H+ exchanger in reperfusion stunning in isolated perfused rat heart.

We tested the hypothesis that Na+/H+ exchange contributes to reperfusion stunning and arrhythmias. The effects of amiloride, an established inhibitor of Na+/H+ exchange, were compared with those of a new inhibitor (HOE 694). Working hearts, subjected to 20-min global ischemia and reperfused for 30 min, were pretreated (for 5 min before ischemia) or reperfused (initial 2 min) with HOE 694 or amiloride. Pretreatment with 10(-7) M HOE increased recovery of aortic output (AO) after 30-min reperfusion: As a percentage of the preischemic controls, values were 38.5 +/- 3.6% (n = 7) for controls versus 50.6 +/- 3.9% (n = 5) for the treated group (p < 0.05). Pretreatment with HOE (10(-6) M) increased AO recoveries from 38.2 +/- 2.0% (n = 5) to 52.9 +/- 2.7% (n = 5) (p < 0.05). Amiloride (10(-5) M) pretreatment improved AO recoveries from 41.6 +/- 2.7% (n = 6) to 55.8 +/- 4.0% (n = 6) (p < 0.05). Thus, pretreatment by both HOE 694 and amiloride decreased reperfusion stunning. Adding HOE (10(-7) M) only in the reperfusion period increased AO recoveries from 36.4 +/- 1.2% (n = 6) to 62.4 +/- 3.2% (n = 11) (p < 0.002). Amiloride (10(-5) or 10(-3) M) added only during reperfusion did not improve recovery of AO. HOE 694, active in much lower concentrations than amiloride, was the only compound active against stunning when added only during reperfusion. In addition, both compounds inhibited reperfusion arrhythmias when added at reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term heart preservation by intermittent perfusion with crystalloid medium

This study was undertaken to determine whether hearts preserved with intermittent coronary perfusion would recover physiologic function after a prolonged period of hypothermic preservation. Intermittent perfusion is commonly used for cardioplegia, but its efficacy in long-term heart preservation has not yet been demonstrated. Five groups of isolated rat hearts were studied (n = 7 per group): (1) fresh nonpreserved control hearts; (2) hearts preserved with continuous low-pressure perfusion via the aorta; (3) hearts preserved with cycles of 5 minutes of perfusion followed by 25 minutes of nonperfusion; (4) hearts preserved with cycles of 10 minutes of perfusion followed by 25 minutes of nonperfusion; (5) hearts preserved with submersion storage without perfusion. An oxygenated extracellular-type crystalloid medium (oxygen tension = 820 +/- 5 mm Hg) was used as a preservation medium; preservation was for 12 hours. During preservation, the coronary resistance of the intermittent perfusion-preserved hearts increased significantly, and these hearts produced significantly more excess lactate than did hearts in the other two preservation groups. The submersion-stored hearts exhibited no postpreservation ventricular function in an isolated perfused working rat heart system. The poststorage function of the other four groups, which was quantified during a 4-hour, 37 degrees C perfusion period at constant heart rate, indicated that there were no significant group differences with respect to output or energetics (coronary flow, aortic output, cardiac output, myocardial oxygen consumption, and external work efficiency). The intermittent perfusion-preserved hearts had significantly lower postpreservation contractile function (left ventricular systolic pressure, peak rates of left ventricular pressure development and relaxation, peak aortic flow rate, stroke work, and peak power) and higher left ventricular end-diastolic pressure compared with the control group. Although hearts preserved with intermittent perfusion had a loss of contractile function and decreased compliance compared with fresh hearts, after preservation they had better function than did hearts preserved with submersion storage and the same function as hearts preserved with continuous perfusion.

Cardioprotection by Nifedipine in Isolated Working Hearts

Cardiac ischemia can be provoked by different methods in animal models and in isolated organs. Accordingly, three different procedures were followed to find the most sensitive model for the analysis of the anti-ischemic activity of calcium antagonists. The experiments were performed in the isolated working heart preparation of the rat, paced at the frequency of 5 Hz and perfused with Tyrode solution at 37 degrees C. Global ischemia was achieved by closing off the supply of the perfusion medium and surrounding the heart with Tyrode solution of 37 degrees C gassed with N2; low-flow ischemia was achieved by reducing the cardiac afterload from 51.5 to 11.0 mm Hg; ligation of the left descending coronary artery was performed in order to provoke regional ischemia. Nifedipine was applied in a concentration (EC50) known to reduce the contractile force by one-half of its basal value. The following parameters were determined after 15 min of nifedipine pretreatment and at the end of the experiment: LVP (left ventricular pressure),+dP/dtmax (LVP's first derivative), AO (aortic output), CF (coronary flow), and CO (cardiac output). From the data obtained, the percentages of recovery were calculated. Nifedipine caused a significant improvement in the functional recovery of most of the parameters studied. This improvement, however, was much more pronounced in the model of the low-flow ischemia, which is obviously more sensitive to the anti-ischemic activity of calcium antagonists than the other experimental procedures studied. Low-flow ischemia appears to be preferable to other procedures for the screening of the potential anti-ischemic activity of calcium antagonists and other drugs.

Role of catalase in myocardial protection against ischemia in heat shocked rats.

It was recently reported that in rats exposure to heat shock leads to appearance of a myocardial heat shock protein (HSP 70) and to an increase in myocardial catalase activity. This correlated with an improvement in post-ischemic function either in Langendorff-perfused hearts after low-flow ischemia or in working hearts after short-term, no-flow ischemia. We investigated the effect of the same hyperthermic treatment on functional recovery from no-flow ischemia of various durations in isolated working rat hearts performing at high or low external workloads. Rats were heated to core temperature of 42 degrees C for 15 min. No significant protein oxidation (% oxidized methionine) was observed 2.5 hr after treatment. A protein with migration characteristics similar to HSP 70 was observed in hearts of heat shocked rats 24 hr after this treatment while their myocardial catalase activity was not increased. Hearts of similarly treated rats were excised 24 hr after hyperthermia and perfused in a working mode with Krebs-Henseleit buffer (1.25 mM Ca2+, 11 mM glucose). At 15 cm H2O preload and 100 cm H2O afterload after 30 min no-flow ischemia, control hearts recovered to 36.9%, 2%, 47.6%, and 21.5% of the preischemic values of heart rate-peak systolic pressure product (RPP), aortic output, coronary flow, and cardiac output, respectively. After only 25 min of ischemia the respective recovered values were 61.6%, 11.5%, 58.7%, and 33.5%. Throughout the recovery period these hemodynamic values were consistently higher in hearts of heat shocked animals than in those of control hearts but the differences were not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolated biventricular working rat heart preparation

The isolated perfused heart from small animals has been used extensively for hemodynamic and metabolic studies. The left working heart preparation proved superior to the Langendorff model for functional evaluations but has not allowed study of right heart function. A simple and inexpensive biventricular working heart preparation has been developed by modifying the left working rat heart model. Under general anesthesia the heart was removed surgically leaving sufficient vessels attacked to it. Cannulation of the aorta, left atrium, right atrium, and pulmonary artery was completed in 10 minutes. A pressurized compliance chamber allowed rapid and reliable regulation of aortic impedance. For the 7 hearts that were subjected to 3-hour biventricular perfusion (their end points expressed as percent of their initial values), the aortic output (95% ± 3%), pulmonary flow (88% ± 9%), mean aortic pressure (109% ± 5%), mean pulmonary pressure (100% ± 2%), heart rate (106% ± 8%), myocardial adenosine triphosphate level (85% ± 8%), and creatine phosphate level (89% ± 4%) were all maintained at physiologic levels. For the 11 hearts that were converted from left working heart preparation to biventricular working mode, significant improvement in stroke volume, aortic and cardiac output, and pressure development were observed. Experimental results indicate that the biventricular working model for isolated perfused rat hearts is superior to the left working preparation for studying the function of the total heart. Further study of the biventricular perfused working rat heart appears warranted.

Endothelin release during ischaemia and reperfusion of isolated perfused rat hearts

The hypothesis tested was that release of endogenous endothelin plays a role in events associated with or leading to myocardial ischaemia and/or post-ischaemic reperfusion damage. Release of endogenous endothelin into the coronary perfusate of isolated perfused rat hearts during ischaemia and reperfusion was measured with a sensitive radioimmunoassay using a polyclonal antibody with 100% cross-reactivity for all three endothelin isomers. Basal endothelin release was 0.69 ± 0.02 pg/min/g wet heart weight ( n = 35) and was constant up to 180 min. During low-flow hypoxic ischaemia for 180 min ( PO 2 ≈ 250 mmHg) and in the presence of 1% foetal calf serum, the release rate was reduced to below 10% of controls ( P < 0.01) and increased four-fold on reperfusion ( P < 0.05). The influence of endothelin on vascular and myocardial reperfusion damage was studied with exogenous endothelin-2. After 1 h of low-flow ischaemia, endothelin-2 increased the coronary perfusion pressure to a similar extent as in non-ischaemic hearts, but with a 30-times higher potency. The threshold dose for the constrictive effect was ≈100 to 300 pg per heart, about ten times more than was recovered in the coronary effluent upon reperfusion. The influence of endothelin on myocardial reperfusion mechanical function (stunning) was assessed with 100 ng endothelin-2, a dose some 3500-fold higher than the amount released during 30 min reperfusion. This dose, given at the onset of reperfusion, improved post-ischaemic aortic output recovery during the first 20 min of reperfusion, but worsened it thereafter (up to 40 min). These data indicate that, in the isolated perfused rat heart model, (1) endothelin is released in measurable amounts into the coronary circulation, (2) the release is much reduced during ischaemia and increased on early reperfusion following prolonged ischaemia, (3) based on the amounts released and the post-ischaemic sensitization of the coronary vasculature to endothelin, the peptide could contribute to reperfusion vascular damage, and (4) endothelin is unlikely to influence stunning owing to the extremely high dose necessary to alter reperfusion mechanical function.