Effect of acute and chronic simvastatin treatment on post-ischemic contractile dysfunction in isolated rat heart

Statins are powerful lipid-lowering drugs, widely used in patients with hyperlipidemia and coronary artery disease. It was found, however, that statins appear to have a pleiotropic effect beyond their lipid-lowering ability. They exert anti-inflammatory, antithrombotic and antioxidant effects, increase nitric oxide production and improve endothelial dysfunction. The aim of our study was to examine the effect of chronic and acute treatment with simvastatin on the contractile function of the isolated perfused rat heart after ischemia/reperfusion injury. Contractile function was measured on isolated rat hearts, perfused according to Langendorff under constant pressure. The hearts were subjected to 20 min of global ischemia, followed by 40 min of reperfusion. To investigate the acute effect, simvastatin at a concentration of 10 micromol/l was added to the perfusion solution during reperfusion. In chronic experiments the rats were fed simvastatin at a concentration of 10 mg/kg for two weeks before the measurement of the contractile function. Acute simvastatin administration significantly increased reparation of the peak of pressure development [(+dP/dt)(max)] (52.9+/-8.2 %) after global ischemia, as compared with the control group (28.8+/-5.2 %). Similar differences were also observed in the time course of the recovery of [(+dP/dt)(max)]. Chronic simvastatin was without any protective effect. Our results reveal that the acute administration of simvastatin during reperfusion, unlike the chronic treatment, significantly reduced contractile dysfunction induced by ischemia/reperfusion injury. This supports the idea of possible cardioprotective effect of statin administration in the first-line therapy of the acute coronary syndrome.     

Myocardial function in rat genetic models of low and high aerobic running capacity

We recently evaluated treadmill aerobic running capacity in 11 inbred strains of rats and found that isolated working left ventricular function correlated (r = 0.86) with aerobic running capacity. Among these 11 strains the Buffalo (BUF) hearts produced the lowest and the DA hearts the highest isolated cardiac output. The goal of this study was to investigate the components of cardiac function (i.e., coronary flow, heart rates, stroke volume, contractile dynamics, and cross-bridge cycling) to characterize further the BUF and DA inbred strains as potential models of contrasting myocardial performance. Cardiac performance was assessed using the Langendorff-Neely working heart preparation. Isolated DA hearts were superior (P < 0.05) to the BUF hearts for cardiac output (63%), stroke volume (60%), aortic +dP/dt (47%), and aortic -dP/dt (46%). The mean alpha/beta-myosin heavy chain (MHC) isoform ratio for DA hearts was 21-fold higher relative to BUF hearts. At the steady-state mRNA level, DA hearts had a fivefold higher alpha/beta-ratio than the BUF hearts. The mean rate of ATP hydrolysis by MHCs was 64% greater in DA compared with BUF ventricles. These data demonstrate that the BUF and DA strains can serve as genetic models of contrasting low and high cardiac function.     

Changes in biomechanical parameters during heart perfusion and after midazolam pre-medication--experimental pilot study

Background: Midazolam is a frequently used benzodiazepine in anaesthesiology and intensive care. Aim: The aim of pilot study was to monitor its effect during heart perfusion in the laboratory rat. Methods: The same groups of animals (n = 10). The 1(st) group was treated with midazolam in a dose of 0.5mg/kg i.p. The 2(nd) group was a placebo. After i.p. administration of heparine injection of 500 IU dose, the hearts were excised and perfused (modified Langendorf's method). Working schedule: stabilization/ischaemia/reperfusion proceed at intervals of 20/30/60 min. Monitored parameters in isolated heart: left ventricle pressure (LVP), end-diastolic pressure (LVEDP), contractility (+dP/dt(max)). Results: The treated hearts showed improved postischemic recovery, reaching LVP values of 92 +/- 6 % at the end of the reperfusion, placebo only 61 +/- 7 %. In placebo hearts LVEDP rose from 10.0 +/- 0.5 mmHg to 43 +/- 4 mmHg after, in treated animals only about 25 mmHg. The treated hearts improved +dP/dt(max) recovery during reperfusion to 91 +/- 8 %. These values were significantly greater than those obtained from the placebo hearts. Conclusions: Positive changes in monitored parameters were found in this experimental pilot study. We conclude that the administration of midazolam in laboratory rats has a cardioprotective potential against ischemia-reperfusion induced injury.     

The effect of changes in cardiac frequency on left and right ventricular dP/dt max at different contractile states of the myocardium

In 17 canine heart-lung preparations the dependence of frequency potentiation of the right and left ventricular myocardium on the basic inotropic state of the heart was investigated. The effect of unipolar stimulation of the right atrium on dP/dt max in both ventricles was measured. The aortic pressure was maintained constant. Shortly after isolation of the heart, a stepwise increase of rate from 140 to 200 beats/min only had a very weak influence on left ventricular dP/dt max. With deterioration of the myocardium the frequency potentiation of dP/dt max increased considerably. End-diastolic pressure regularly decreased with rising cardiac frequency. Since the real positive inotropic effect is masked by the concomitant fall in diastolic loading, the end-diastolic pressure was maintained constant in a second group of 8 hearts during rate variation. The most pronounced inotropic effect was now found shortly after isolation of the heart. A rate increase of 30 beats/min resulted in a 20% rise of dP/dt max. The frequency potentiation decreased with deterioration of the heart resulting in a 12% dP/dt max increase at an estimated inotropic state of 50% of control. When the contractile state of the heart was improved above the control state by calcium application the frequency potentiation of the myocardium decreased. In the right ventricle similar results were obtained except for the fact that no significant correlation between the steepness of the frequency characteristics and the contractile state of the heart could be found when the end-diastolic pressure was kept constant.     

Cardiac pump function of the isolated rat heart at two modes of energy deprivation and effect of adrenergic stimulation

The contractile function of the isolated rat heart and high energy phosphate content were evaluated under conditions of depressed energy supply caused by disturbances either in mitochondrial ATP production or ATP-phosphocreatine transformation. Amytal (0.3 mM), an inhibitor of mitochondrial respiration, or iodoacetamide (IAA, 0.1 mM) reducing in this dose creatine kinase activity to 19% of the initial level, were used, respectively. Myocardial ATP content remained unaffected in both groups and PCr content decreased to 37% only in amytal-treated group. Very similar alterations in cardiac pump function during volume load were observed in both treated groups; maximal cardiac output was significantly less by 30%, cardiac pressure-volume work by 38–40%, left ventricular (LV) systolic pressure by 24–29%, and LV +dP/dt by 36–39%. In contrast, the extent of decreased LV distensibility was different, a curve relating LV filling volume and end-diastolic pressure was shifted up and to the left much more prominently after IAA treatment. Heart rate was decreased by 24% only in amytal-treated group. Results indicate that a decreased myocardial distensibility is a dominating feature in the acute cardiac pump failure caused by an inhibition of myocardial creatine kinase. Isoproterenol (0.1 M) substantially increased heart rate and pressure-rate product in IAA-treated hearts but failed to increase cardiac work probably due to its inability to improve myocardial distensibility.     

Effect of thyroid hormone treatment on responses of the isolated working rat heart

Hearts from rats pretreated either with L-triiodothyronine (T3) or with L-thyroxine (T4) exhibited changed function curve characteristics on the working heart apparatus compared with hearts from vehicle-treated rats. There was no supersensitivity of the hyperthyroid myocardium to the inotropic effect of isoproterenol as estimated by pD2 values. There were significant increases in +dP/dt and -dP/dt in hyperthyroid working hearts over the entire range of the function curve. T3 hearts showed much shorter relaxation times and total contraction times throughout the function curve. T4 hearts showed significantly reduced relaxation times and total contraction times as compared with control at all left atrial filling pressures under 15 cm of water. At high filling pressures T4 heart relaxation times and total contraction times were not different from control, but were however, significantly increased from those of T3 hearts. Area under the left ventricular pressure curve was unchanged by thyroid hormone pretreatment. Heart weight increased about 15% following either T3 or T4 treatment while the increases in (+) or (-) dP/dt and the left ventricular developed pressure (LVDP) were about 20-30%. The increase in cardiac mass certainly played a role in the increased cardiac function. Potency of isoproterenol in hyperthyroid working heart preparations was unchanged from control. The pD2 values, as determined from +dP/dt data, were 8.8 +/- 0.15 for T3-treated hearts, 8.25 +/- 0.40 for T4-treated hearts, and 8.18 +/- 0.12 for euthyroid hearts. While the mechanism(s) for the altered performance of the hyperthyroid working heart are not absolutely known, possible biochemical and physiological changes which may be implicated are discussed.     

Impaired in vivo myocardial reactivity to norepinephrine in diabetic rats

The effects of long-term diabetes with and without insulin treatment on in vivo myocardial contractile activity were studied under basal conditions and as a function of intravenously infused norepinephrine. Diabetes was induced by iv injection of streptozotocin (50 mg/kg). Insulin-treated diabetic rats received 5 units per day of isophane insulin suspension. The duration of the study was 8 weeks. In vivo myocardial contractility measurements were performed in ketamine-xylazine-anesthetized rats using a miniature catheter-tip pressure transducer advanced through the right carotid artery into the left ventricle. Peak positive dP/dt and intraventricular developed pressure were comparable among the groups when measured under basal conditions; however, the magnitude of the response to variable doses of norepinephrine (6 X 10(-12) to 6 X 10(-8) mole/kg body wt) were significantly diminished in diabetic rats, but the sensitivity was unchanged. Negative dP/dt was decreased under basal conditions and in response to norepinephrine in diabetic rats. Insulin treatment to diabetic rats prevented these changes, but heart rate was elevated. These results demonstrate that the in vivo cardiovascular reactivity of diabetic rats to norepinephrine is significantly attenuated.     

Depressor effect of diabetes in the spontaneously hypertensive rat: associated changes in heart performance

Effects of streptozotocin-induced diabetes (8 weeks) on the performance of perfused hearts from spontaneously hypertensive (SH) rats were compared with effects on normotensive Wistar-Kyoto (WK) and Sprague-Dawley (SD) rat hearts. Diabetes markedly decreased systolic arterial pressure (SAP) of SH rats in vivo but did not affect SAP of either of the normotensive strains. Diabetes also reduced heart size of SH and normotensive rats and reversed absolute left ventricular hypertrophy (wall-to-lumen ratios and left-to-right ventricular weight ratios) of SH rats. Heart perfusion at the end of the 8-week period revealed that diabetes (i) reduced hydraulic work at high pressure loads and efficiency of contraction (work/mu LO2 consumed) of SH rat hearts but not of WK or SD hearts, and (ii) depressed left ventricular pulse pressure development (LVPP) and contractility (LV + dP/dt) of SH hearts more extensively than it reduced these variables in either of the normotensive control groups. Effects of diabetes which were similar in hypertensive and normotensive hearts were reductions in stroke work at high volume loads and depressions in LV-dP/dt. Attendant hypothyroidism probably contributed to the reductions in SAP, heart size, LVPP, LV+ and -dP/dt, and stroke work but not to the decreased efficiency or reversal of hypertrophy of SH rat hearts. Malnutrition of SH rats, like hypothyroidism, also decreased heart size without reversing hypertrophy but had no effect on SAP and only reduced LV-dP/dt. The results show that diabetes reversed hypertrophy and selectively reduced contraction efficiency, contractility, and LVPP of SH hearts, but otherwise the effects of diabetes in hypertensive and normotensive rat strains were similar to each other.(ABSTRACT TRUNCATED AT 250 WORDS)     

Analysis of postextrasystolic relaxation response in the human heart

Postextrasystolic potentiation is the phenomenon in which ventricular contractile force is strengthened by a preceding premature beat. However, the response of diastolic function after an extrasystole is unknown. We studied 58 patients with chronic heart failure (CHF) and two control subjects to evaluate the response of relaxation following extrasystole. At cardiac catheterization, from the derivative of the left ventricular (LV) pressure, the ratio of LV peak negative dP/dt (–dP/dt) of a postextrasystole to a basal beat was calculated and defined as the postextrasystolic relaxation response (PRR). PRR was compared with parameters of left ventriculography: LV end-diastolic volume index (EDVI), LV end-systolic volume index (ESVI), and LV ejection fraction (EF). The PRRs of the two control subjects were 0.80 and 0.84. The mean PRR of the CHF patients was 0.99 ± 0.15. In all subjects, including patients and controls, correlation analysis between (EDVI, ESVI, and EF) and PRR yielded the following: (a) EDVI vs. PRR: R = 0.273, p = 0.036; (b) ESVI vs. PRR: R = 0.446, p < 0.001; and (c) EF vs. PRR: R = –0.520, p < 0.001. Thus, normal or non-failing human hearts showed a decline of –dP/dt in postextrasystole compared with the basal beats, but failing hearts had potentiated relaxation following an extrasystole.     

Quinapril inhibits progression of heart failure and fibrosis in rats with dilated cardiomyopathy after myocarditis

The cardioprotective properties of quinapril, an angiotensin-converting enzyme inhibitor, were studied in a rat model of dilated cardiomyopathy. Twenty-eight days after immunization of pig cardiac myosin, four groups rats were given 0.2 mg/kg (Q0.2, n = 11), 2 mg/kg (Q2, n = 11) or 20 mg/kg (Q20, n = 11) of quinapril or vehicle (V, n = 15) orally once a day. After 1 month, left ventricular end-diastolic pressure (LVEDP), ±dP/dt, area of myocardial fibrosis, and myocardial mRNA expression of transforming growth factor (TGF)-1, collagen-III and fibronectin were measured. Four of 15 (27%) rats in V and two of 11 (18%) in Q0.2 died. None of the animals in Q2 or Q20 died. The LVEDP was higher and ±dP/dt was lower in V (14.1 ± 2.0 mmHg and +2409 ± 150/–2318 ± 235 mmHg/sec) than in age-matched normal rats (5.0 ± 0.6 mmHg and +6173 ± 191/–7120 ± 74 mmHg/sec; all p < 0.01). After quinapril treatment, LVEDP was decreased and ±dP/dt was increased in a dose-dependent manner (10.8 ± 1.8 mmHg and +3211 ± 307/–2928 ± 390 mmHg/sec in Q0.2, 9.4 ± 1.5 mmHg and +2871 ± 270/–2966 ± 366 mmHg/sec in Q2, and 6.6 ± 1.5 mmHg, and +3569 ± 169/–3960 ± 203 mmHg/sec in Q20). Increased expression levels of TGF-1, collagen-III and fibronectin mRNA in V were reduced in Q20. Quinapril improved survival rate and cardiac function in rats with dilated cardiomyopathy after myocarditis. Furthermore, myocardial fibrosis was regressed and myocardial structure returned to nearly normal in animals treated with quinapril.     

The cardiotonic effects of levosimendan in guinea pig hearts are modulated by beta-adrenergic stimulation

The effects of the Ca2+-sensitiser levosimendan alone or in combination with beta-adrenergic stimulation on the contractile function were studied in various guinea pig cardiac preparations. Echocardiography in narcotised animals indicated that a maximal dose of levosimendan (50 microg x kg(-1)) increased the left ventricular posterior wall movement velocity during systoles and diastoles by 25 +/- 3% (mean +/- S.E.M.) and 17 +/- 2%, respectively. In Langendorff hearts, a saturating concentration of levosimendan (0.3 micromol x l(-1) for 5 min) increased +dP/dt(max) and dP/dt(max) by 28 +/- 3% and 14 +/- 2%, respectively. Further, the Ca2+-sensitising potential of levosimendan in Triton-skinned cardiomyocytes (EC50: 5 +/- 3 nmol x l(-1)) was illustrated by a maximal increase in the isometric force production by 51 +/- 5% (at pCa 6.2). However, following stimulation by isoproterenol, when the level of troponin I phosphorylation was elevated, no significant additional increase in the contractile parameters could be demonstrated upon levosimendan administration. Moreover, the levosimendan-induced increase in force production in isolated skinned myocytes could be prevented by incubation with the catalytic subunit of protein kinase A (100 U x ml(-1) for 40 min). These data indicate that thin filament-targeted Ca2+-sensitisation by levosimendan is modulated by phosphorylation of the contractile filaments, an effect that should be considered during combination therapy with levosimendan.     

The effect of chronic alloxan- and streptozotocin-induced diabetes on isolated rat heart performance

Cardiac disease is a common secondary complication appearing in chronic diabetics. Isolated perfused working hearts obtained from both acute and chronic diabetic rats have also been shown to exhibit cardiac functional abnormalities when exposed to high work loads. We studied cardiac performance at various time points after induction of diabetes in rats to determine exactly when functional alterations appeared and whether these alterations progressed with the disease state. Female Wistar rats were made diabetic by a single i.v. injection of either alloxan (65 mg/kg) or streptozotocin (STZ 60 mg/kg). Cardiac performance was assessed at 7, 30, 100, 180, 240, and 360 days after induction of diabetes using the isolated perfused working heart technique. No changes were observed in the positive and negative dP/dt development at various atrial filling pressures in the diabetic hearts 7 days after treatment. Alloxan diabetic rat hearts exhibited depressed left ventricular pressure and positive and negative dP/dt development when perfused at high atrial filling pressures, at 30, 100, and 240 days after treatment. STZ diabetic rat hearts exhibited depressed cardiac performance at high atrial filling pressures, at 100, 180, and 360 days after treatment, but not at 30 days after treatment. Control hearts exhibited slight but significant depressions in cardiac function with age. These results suggest that cardiac functional alterations appear in diabetic rats about 30 days after induction and progress with the disease. These alterations may indicate the development of a cardiomyopathy.     

Divergent changes in the rate of development of pressure in the left ventricle and in the performance of the heart as a pump.

Dog hearts were prepared in situ so that heart rate (HR), left ventricular end diastolic pressure (LVEDP) and mean aortic pressure (MAP) could be controlled separately during computation of left ventricular dP/dt max and external stroke work (SW). Progressive increases in HR consistently raised dP/dt max over a wide range, and consistently lowered SW except at low rates. Progressive increases in LVEDP or MAP consistently raised both dP/dt max and SW. Infusion of noradrenaline consistently raided both dP/dt max and SW, except at very high HR when only dP/dt max was consistently raised. Our results lead us to question the validity of equating changes in pre-ejection measurements with changes in performance of the heart as a pump under abnormal conditions and in the assessment of inotropic agents.     

Inhibition of PKC phosphorylation of cTnI improves cardiac performance in vivo

Protein kinase C (PKC) modulates cardiomyocyte function by phosphorylation of intracellular targets including myofilament proteins. Data generated from studies on in vitro heart preparations indicate that PKC phosphorylation of troponin I (TnI), primarily via PKC-epsilon, may slow the rates of cardiac contraction and relaxation (+dP/dt and -dP/dt). To explore this issue in vivo, we employed transgenic mice [mutant TnI (mTnI) mice] in which the major PKC phosphorylation sites on cardiac TnI were mutated by alanine substitutions for Ser(43) and Ser(45) and studied in situ hemodynamics at baseline and increased inotropy. Hearts from mTnI mice exhibited increased contractility, as shown by a 30% greater +dP/dt and 18% greater -dP/dt than FVB hearts, and had a negligible response to isoproterenol compared with FVB mice, in which +dP/dt increased by 33% and -dP/dt increased by 26%. Treatment with phenylephrine and propranolol gave a similar result; FVB mouse hearts demonstrated a 20% increase in developed pressure, whereas mTnI mice showed no response. Back phosphorylation of TnI from mTnI hearts demonstrated that the mutation of the PKC sites was associated with an enhanced PKA-dependent phosphorylation independent of a change in basal cAMP levels. Our results demonstrate the important role that PKC-dependent phosphorylation of TnI has on the modulation of cardiac function under basal as well as augmented states and indicate interdependence of the phosphorylation sites of TnI in hearts beating in situ.     

Regulation of cardiac sarcolemmal Ca2+ channels and Ca2+ transporters by thyroid hormone

In order to examine the regulatory role of thyroid hormone on sarcolemmal Ca²⁺-channels, Na⁺–Ca²⁺ exchange and Ca²⁺-pump as well as heart function, the effects of hypothyroidism and hyperthyroidism on rat heart performance and sarcolemmal Ca²⁺-handling were studied. Hyperthyroid rats showed higher values for heart rate (HR), maximal rates of ventricular pressure development+(dP/dt)max and pressure fall–(dP/dt)max, but shorter time to peak ventricular pressure (TPVP) and contraction time (CT) when compared with euthyroid rats. The left ventricular systolic pressure (LVSP) and left ventricular end-diastolic pressure (LVEDP), as well as aortic systolic and diastolic pressures (ASP and ADP, respectively) were not significantly altered. Hypothyroid rats exhibited decreased values of LVSP, HR, ASP, ADP, +(dP/dt)max and –(dP/dt)max but higher CT when compared with euthyroid rats; the values of LVEDP and TPVP were not changed. Studies with isolated-perfused hearts showed that while hypothyroidism did not modulate the inotropic response to extracellular Ca²⁺ and Ca²⁺ channel blocker verapamil, hyperthyroidism increased sensitivity to Ca²⁺ and decreased sensitivity to verapamil in comparison to euthyroid hearts. Studies of [³H]-nitrendipine binding with purified cardiac sarcolemmal membrane revealed decreased number of high affinity binding sites (B_max) without any change in the dissociation constant for receptor-ligand complex (K_d) in the hyperthyroid group when compared with euthyroid sarcolemma; hypothyroidism had no effect on these parameters. The activities of sarcolemmal Ca²⁺-stimulated ATPase, ATP-dependent Ca²⁺ uptake and ouabain-sensitive Na⁺–K⁺ ATPase were decreased whereas the Mg²⁺-ATPase activity was increased in hypothyroid hearts. On the other hand, sarcolemmal membranes from hyperthyroid samples exhibited increased ouabain-sensitive Na⁺–K⁺ ATPase activity, whereas Ca²⁺-stimulated ATPase, ATP-dependent Ca²⁺ uptake, and Mg²⁺-ATPase activities were unchanged. The V_max and K_a for Ca²⁺ of cardiac sarcolemmal Na⁺–Ca²⁺ exchange were not altered in both hyperthyroid and hypothyroid states. These results indicate that the status of sarcolemmal Ca²⁺-transport processes is regulated by thyroid hormones and the modification of Ca²⁺-fluxes across the sarcolemmal membrane may play a crucial role in the development of thyroid state-dependent contractile changes in the heart.     

Proteasome Expression in Ovarian Heterotopic Allografts of Wistar and August Rats under Induction of Donor-Specific Tolerance

Russian Journal of Developmental Biology - The aim of this work is to investigate the dynamics for the ovarian tissue engraftment of inbred August rats transplanted to outbred Wistar rats and vice...     

Short-term exercise training can improve myocardial tolerance to I/R without elevation in heat shock proteins

We examined the effects of 3 days of exercise in a cold environment on the expression of left ventricular (LV) heat shock proteins (HSPs) and contractile performance during in vivo ischemia-reperfusion (I/R). Sprague-Dawley rats were divided into the following three groups (n = 12/group): 1) control, 2) exercise (60 min/day) at 4 degrees C (E-Cold), and 3) exercise (60 min/day) at 25 degrees C (E-Warm). Left anterior descending coronary occlusion was maintained for 20 min, followed by 30 min of reperfusion. Compared with the control group, both the E-Cold and E-Warm groups maintained higher (P < 0.05) LV developed pressure, first derivative of pressure development over time (+dP/dt), and pressure relaxation over time (-dP/dt) throughout I/R. Relative levels of HSP90, HSP72, and HSP40 were higher (P < 0.05) in E-Warm animals compared with both control and E-Cold. HSP10, HSP60, and HSP73 did not differ between groups. Exercise increased manganese superoxide dismutase (MnSOD) activity in both E-Warm and E-Cold hearts (P < 0.05). Protection against I/R-induced lipid peroxidation in the LV paralleled the increase in MnSOD activity whereas lower levels of lipid peroxidation were observed in both E-Warm and E-Cold groups compared with control. We conclude that exercise-induced myocardial protection against a moderate duration I/R insult is not dependent on increases in myocardial HSPs. We postulate that exercise-associated cardioprotection may depend, in part, on increases in myocardial antioxidant defenses.     

The role of NO in ischemia/reperfusion injury in isolated rat heart

Nitric oxide (NO) is an important regulator of myocardial function and vascular tone under physiological conditions. However, its role in the pathological situations, such as myocardial ischemia is not unequivocal, and both positive and negative effects have been demonstrated in different experimental settings including human pathology. The aim of the study was to investigate the role of NO in the rat hearts adapted and non-adapted to ischemia. Isolated Langendorff-perfused hearts were subjected to test ischemic (TI) challenge induced by 25 min global ischemia followed by 35 min reperfusion. Short-term adaptation to ischemia (ischemic preconditioning, IP) was evoked by 2 cycles of 5 min ischemia and 5 min reperfusion, before TI. Recovery of function at the end of reperfusion and reperfusion-induced arrhythmias served as the end-points of injury. Coronary flow (CF), left ventricular developed pressure (LVDP), and dP/dt(max) (index of contraction) were measured at the end of stabilization and throughout the remainder of the protocol until the end of reperfusion. The role of NO was investigated by subjecting the hearts to 15 min perfusion with NO synthase (NOS) inhibitor L-NAME (100 mmol/l), prior to sustained ischemia. At the end of reperfusion, LVDP in the controls recovered to 29.0 +/- 3.9 % of baseline value, whereas preconditioned hearts showed a significantly increased recovery (LVDP 66.4 +/- 5.7 %, p < 0.05). Recovery of both CF and dP/dt(max) after TI was also significantly higher in the adapted hearts (101.5 +/- 5.8 % and 83.64 +/- 3.92 % ) as compared with the controls (71.9 +/- 6.3 % and 35.7 +/- 4.87 %, respectively, p < 0.05). NOS inhibition improved contractile recovery in the non-adapted group (LVDP 53.8 +/- 3.1 %; dP/dt(max) 67.5 +/- 5.92 %) and increased CF to 82.4 +/- 5.2 %. In contrast, in the adapted group, it abolished the protective effect of IP (LVDP 31.8 +/- 3.1 %; CF 70.3 +/- 3.4 % and dP/dt(max) 43.25 +/- 2.19 %). Control group exhibited 100 % occurrence of ventricular tachycardia (VT), 57 % incidence of ventricular fibrillation (VF) - 21 % of them was sustained VF (SVF); application of L-NAME attenuated reperfusion arrhythmias (VT 70 %, VF 20 %, SVF 0 %). Adaptation by IP also reduced arrhythmias, however, L-NAME in the preconditioned hearts increased the incidence of arrhythmias (VT 100 %, VF 58 %, SVF 17 %). In conclusion: our results indicate that administration of L-NAME might be cardioprotective in the normal hearts exposed to ischemia/reperfusion (I/R) alone, suggesting that NO contributes to low ischemic tolerance in the non-adapted hearts. On the other hand, blockade of cardioprotective effect of IP by L-NAME points out to a dual role of NO in the heart: a negative role in the non-adapted myocardium subjected to I/R, and a positive one, due to its involvement in the mechanisms of protection triggered by short-term cardiac adaptation by preconditioning.     

Load-insensitive measurements from an isolated perfused biventricular working rat heart

To determine whether a rat heart model can provide load-insensitive measurements of cardiac function, a recently developed biventricular perfused preparation was tested. Using 29 Sprague-Dawley rat hearts perfused with modified Krebs-Henseleit buffer, ventricles functioned simultaneously with adjustable independent preload (venous reservoirs) and afterload (compliance chambers). Ultrasonic crystal pairs provided continuous left (LV) and right ventricular (RV) short-axis dimensions. LV and RV pressure-length loops (loop area = work) were generated from paired intraventricular pressure and short-axis dimensions. Load-insensitive measurements were obtained from the slopes (elastance) and x-intercepts (L₀) of regression lines generated from the end-systolic coordinates of these pressure-length loops over ranges of RV and LV preloads. Measurements were made after 15 min of stable function and after 20 min of warm (37°C) ischemia. During perturbations in LV afterload, there were linear changes in dP/dt, but loop work remained relatively unchanged. RV dP/dt and work varied little with physiologic ranges of afterload. Increased RV afterload had little effect on LV function. Ischemia affected LV function more than RV function using these measurements. Elastance, however, increased after ischemia with diastolic creep (increased L₀) for both ventricles. Load-insensitive and other sophisticated hemodynamic measurements are possible with this new preparation.