Effect of pretreatment with isoprenaline on functional and metabolic characteristics of isolated rat heart

Mechanical performance and tissue content of high-energy phosphates were studied in working rat hearts, isolated from normal rats, or from daily subcutaneously injected with isoproterenol for one day or seven days (5 mg/kg b.w.) and atrially perfused. Isoproterenol pretreatment led to a significant decrease in myocardial content of ATP, ADP. After 75-min perfusion, the content of ATP, ADP, AMP and CP was significantly lower in pretreated hearts than in untreated. On the other hand, isoproterenol-treated hearts exhibited higher aortic pressure, oxygen consumption, left ventricular systolic pressure and d (L.V.P.) max/dt and heart work. It is suggested from these findings that isoproterenol pretreatment of rats improve cardiac work and decrease efficiency in ISO.24 h group and improve cardiac work and efficiency in ISO.7 days group.     

Dopamine 4-sulfate: effects on isolated perfused rat heart and role of atria

We studied the effects of sulfate conjugate of dopamine on the isolated perfused rat heart (Langendorff preparation). In the experimental group, we removed atria from half number of the hearts. In the hearts with intact atria, dopamine 4-sulfate significantly improved the DT (developed tension), +dT/dt max (maximal rate of contraction), -dT/dt max (maximum rate of relaxation) over baseline values. But when atria were removed, dopamine 4-sulfate had no effect on the mechanical functions of heart. We analysed the effluent perfusate for the free and conjugated catecholamines. In the control group (no drug), and when atria were excised, the free catecholamine levels were negligible. But when the atria were kept intact, the effluent contained significant amount of free dopamine (DA), and norepinephrine (NE). These data suggested that dopamine sulfate had no direct effect on the ventricular muscle of rat heart, but was converted within the atrial tissues into free catecholamines which might be responsible for the positive inotropic actions.     

Metabolic effects of pent-4-enoate in isolated perfused rat heart.

The metabolic effects of the hypoglycaemic agent pent-4-enoate were studied in isolated, beating or potassium-arrested rat hearts. The addition of 0.8mM-pent-4-enoate to the perfusion fluid increased O2 consumption by 76% in the arrested heart and by 14% in the beating heart; the concentration ratio of phosphocreatine/creatine increase concomitantly by 47% and 27% respectively. Perfusion of the heart with pent-4-enoate resulted in a 30-fold increase in the concentration of the pool of tricarboxylic acid-cycle intermediates in the tissue, about 90% of this increase being due to malate. The sum of the concentrations of the myocardial free amino acids remained virtually unchanged during the accumulation of the tricarboxylic acid-cycle intermediates. It was concluded that pent-4-enoate can be effectively metabolized in the myocardium and that its metabolism probably proceeds via propionyl-CoA, since pent-4-enoate reproduces many of the metabolic characteristics of propionate in the cardiac muscle. The accumulation of the tricarboxylic acid-cycle intermediates is probably due to carboxylation of propionyl-CoA. The response pattern of the metabolite concentrations in the cardiac muscle is quite different from that in the liver, in which decrease of the concentrations of the tricarboxylic acid-cycle intermediates has been observed previously [Williamson, Rostand & Peterson (1970) J. Biol. Chem. 245, 3242-3251].     

The effects of high-dose epinephrine combined with isoprenaline on isolated rabbit heart and cardiomyocytes after cardioversion of ventricular fibrillation

The effects of high-dose epinephrine (HDE) combined with isoprenaline (Iso) on myocardial hemodynamics of isolated rabbit heart were studied. The electrophysiology and L-type Ca²⁺ channel of single ventricular myocyte after cardioversion of ventricular fibrillation were determined. The results suggest that parameters of hemodynamics were significantly enhanced by HDE+Iso than that of HDE (p < 0.01). The OS and V_max of HDE+Iso increased 83.7 and 10.15% respectively compared to HDE alone. The APF of HDE+Iso is much more rapid than that of HDE (138.38 ± 9.96 vs. 55.58 ± 8.63 min^-1, p < 0.001). The APD₅₀ and APD₉₀ of HDE+Iso were significantly decreased; HR was increased (134.16 ± 1.48 vs 62.20 ± 6.25 min^-1); and the amplitude current of through L-type Ca²⁺ channel was reduced but was significantly higher than the control. We conclude that HDE+Iso can improve the hemodynamics and improve electrophysiology of cardiomyocytes after cardioversion of ventricular fibrillation which is likely interrelated with ICa. The combined use of epinephine and isoprenaline for cardiopulmonary resuscitation of primary ventricular fibrillation may be beneficial when employed in clinical situations.     

The effects of glycerol treatment on the isolated rat heart

Summary Isolated rat hearts were perfused with a balanced electrolyte solution containing 1000mM glycerol for 15min and then perfused with normal electrolyte solution for up to 32 min. The perfusion with hypertonic glycerol solution and subsequent washout is termed glycerol treatment. Initially, glycerol removal causes swelling and rupture of the T-system in ventricular myocardial cells which correlates temporally with a period of cardiac arrest. Contractility returns during further glycerol removal and concomitant recovery of the T-system is observed. Atomic absorption spectometry and neutron activation analysis were used to measure ventricular sodium, potassium and calcium ion content. There is no apparent correlation between changes in ion content and cardiac arrest or recovery. The water movements were calculated from wet weight, dry weight and inulin space, and confirmed by morphometric analysis of extracellular and intracellular space. It is suggested that the swelling and rupture of the T-system is due to the rapid water movements that were observed during the onset of glycerol removal. Ultrastructural analysis of glycerol-treated atrium from the same hearts shows damage of mitochondria and of the L-system and intracellular edema. The structural changes are correlated with a loss of atrial contraction. As in ventricular myocardium, resumption of contraction is associated with an almost complete recovery from ultrastructural damage.The studies were supported by the German Research Foundation within the SFB 90 Cardiovasculäres System     

The effects of vitamin B6 deprivation with 4-deoxypyridoxine in meal-fed rats

Weanling male rats were trained to consume a control diet in one 4-hr meal a day. Rats were then fed one of three experimental diets for 7 days: (a) control diet minus B6 (-B6); (b) control diet (B6); or (c) control diet restricted to food intake of -B6 (B6R). Xanthurenic acid excretion was greater before and after a tryptophan load in -B6 than in B6R. Body weight gain, food intake, and food efficiency were not different between -B6 and B6. However, in B6R body weight gain, food intake and food efficiency were lower than that in both -B6 and B6. Serum glucose (12-16 hr after meal) and percentage body fat were similar in all three groups. No differences were found in organ size between the -B6 and both control groups indicating that short-term deprivation and deoxypyridoxine did not affect organ size. No significant differences were observed for serum growth hormone (GH), pituitary GH, serum prolactin (PRL), or pituitary PRL among the three groups. When meal fed, differences were minimized between B6 deprived and unrestricted control (B6) rats in body weight gain, food intake, food efficiency, and body composition.     

Norepinephrine amplifies effects of vasopressin on the isolated rat heart.

We compared effects of perfusion of norepinephrine (NE, 10(-9) mol l-1 and of unchanged Krebs-Henseleit solution on the cardiac response to bolus injection of arginine vasopressin (AVP, 2 ng). 14 isolated rat working heart preparations were used in a balanced cross-over design. Coronary flow, oxygen consumption and extraction, heart rate and total flow were continuously recorded. The concentration of NE was below that exerting per se systematic influences on cardiac activity. However, NE changed the cardiac response to AVP: (1) the AVP-induced reduction in coronary flow was greater during NE (mean: 41.7%) than vehicle perfusion (30.5%, P less than 0.005. (2) The AVP-induced decrease in oxygen consumption was stronger on top of the NE (41.5%) than vehicle perfusion (33.6%, P less than 0.005). (3) Following AVP, oxygen extraction during NE was increased compared to oxygen extraction during vehicle perfusion (3.61 +/- 0.03 vs. 3.46 +/- 0.02 microliters O2 ml-1 g-1, P less than 0.005). Results support the view of a potentiating role of catecholamines for direct cardiovascular effects of AVP.     

Glycogen metabolism: a 13C-NMR study on the isolated perfused rat heart

Glycogen synthesis from D-[1-13C]glucose was observed in the perfused rat heart by 13C-NMR spectroscopy at 62.9 MHz. The glycogenogenesis was stimulated by pretreatment of the animals with isoprenaline. Whereas in hearts from control rats the incorporation of D-[1-13C]glucose into the glycogen remained below the detection threshold, 5 min proton-decoupled 13C-NMR spectra revealed, in hearts from treated rats, a significant labelling of the glycogen within the first minutes of the perfusion and a further linear increase of the glycogen resonance for up to 25 min. This model was used to monitor the appearance of 13C-labelled lactate during ischemia.     

Functional and metabolic effects of propionyl-L-carnitine in the isolated perfused hypertrophied rat heart

Aim of this study was to assess the effect of propionyl-L-carnitine (PLC), a naturally occurring derivative of L-carnitine, in cardiac hypertrophy induced by pressure overload in rats. The abdominal aorta was banded and the rats received one daily administration of PLC (50 mg/kg) or saline for four days. The hearts were excised 24 h after the last administration and were perfused retrogradely with oxygenated Krebs-Henseleit buffer containing 1.2 mM palmitate bound to 3% (w/v) albumin, 2.5 M PLC and 25 M L-carnitine. A saline-filled balloon was inserted into the left ventricle and the heart contractility was measured at three volumes of the balloon, corresponding to zero diastolic pressure and to increased volumes (110 and 220 l) over the zero volume. At the end of the perfusion, the hearts were freeze-clamped, weighed and analyzed for adenine nucleotide and phosphocreatine (PCr) content by HPLC methods. No differences in the myocardial performance were found at zero diastolic pressure. In contrast, at high intraventricular volume, the maximal rate of ventricular relaxation was increased in PLC-treated with respect to saline-treated controls (p < 0.05). In addition, the increase of the end-diastolic pressure at increasing balloon volume was more marked in controls than in the PLC-treated hearts (p < 0.02). These data correlate well with the measured higher level of total adenine nucleotides (p < 0.05) and ATP (p < 0.02) in the PLC-treated hearts, while PCr was the same in both groups. Parallel experiments performed in the absence of palmitate in the perfusing media failed to show any effect of PLC. We conclude that PLC improves the diastolic function by increasing the fraction of energy available from fatty acid oxidation in the form of ATP.     

木犀草素改善低温下离体大鼠心脏保存效果的研究

目的:研究木犀草素是否能改善心脏停搏保存液(UW液)对离体大鼠心脏的低温保存效果。方法:将40只成年SD大鼠随机分成4组(n=10):对照组(UW组)、7.5μmol/L木犀草素小剂量组,15μmol/L木犀草素中剂量组及30μmol/L木犀草素大剂量组。利用Langendorff离体心脏灌流法,观察心脏在4℃含或不含木犀草素的UW液中保存12 h复灌60 min后心脏功能及超微结构变化,比较心脏冠脉流量(CF)、心肌含水量及冠脉流出液中磷酸肌酸激酶(CK)的释放量。结果:与对照组比较,添加木犀草素后,复灌期心脏的收缩功能(LVPSP,+dp/dtmax)与心脏舒张功能(-dp/dtmax)、冠脉流量在多个复灌时间点均优于对照组,心率在复灌60 min时也显著优于对照组;复灌过程中磷酸肌酸激酶的漏出量及低温保存后心脏超微结构的损伤也均明显低于对照组;随灌注时间延长木犀草素组心脏结构和功能的改善有剂量依赖性趋势;木犀草素对心肌含水量没有影响。结论:木犀草素能显著改善UW液对离体大鼠心脏的低温保存效果,对心脏有明显的保护作用,以30μmol/L的木犀草素大剂量组作用最显著。     

Protective effects of melatonin against ischemia-reperfusion injury in the isolated rat heart

There has been increased interest in melatonin recently, since it was shown to be a potent scavenger of toxic free radicals. Melatonin has been found to be effective in protecting against pathological states due to reactive oxygen species release. The present study was performed in order to determine whether melatonin or 5-methoxy-carbonylamino-N-acetyl-tryptamine (5-MCA-NAT), a structurally related indole compound, protect against ischemia-reperfusion injury in the isolated rat heart. Wistar rats were treated in vivo with either melatonin (1 or 10 mg/kg, i.p.) or 5-MCA-NAT (10 mg/kg, i.p.) or their vehicle, 30 min before their hearts were excised and perfused according to the Langendorff technique. Two different protocols were then applied. In the first one, a regional ischemia (5 min)-reperfusion (30 min) sequence was performed in order to record incidence and duration of reperfusion arrhythmias. In the second one, infarct size was assessed after a regional ischemia (30 min)-reperfusion (120 min) sequence. Results show a spectacular protection against ischemia-reperfusion injuries (on arrhythmias as well as on infarct size) in rats pre-treated with 10 mg/kg of melatonin or 5-MCA-NAT. In conclusion, both melatonin and its structural analog, 5-MCA-NAT, appear to confer protection against ischemia-reperfusion injury in the isolated rat heart. This observation suggests that melatonin could have a potential clinical application in the treatment of myocardial ischemia, even if the mechanisms underlying this protection remain to be determined.     

Heat acclimation: cardiac performance of isolated rat heart

Cardiac performance was studied in the isolated perfused hearts of rats heat acclimated at 34 degrees C (AC) and their age-matched controls (C). The pressure-volume curves during isovolumetric conditions showed a shift to the right in AC compared with C hearts. At similar left ventricular (LV) volumes end-diastolic and peak systolic pressures of AC hearts were lower, but no difference was observed in the maximal pressure developed at the highest LV volumes measured. In both C and AC hearts the developed force decreased as pacing rate increased. AC and C heart responses were the same up to 250 pulses/min. At higher frequencies the amplitude of the developed force of AC hearts was smaller than that of the controls. In accordance the tension produced by very early premature beat reduced in AC compared with C hearts. Since no hypertrophy was observed in AC hearts, it is concluded that heat acclimation results in a change in the intrinsic properties of the AC hearts exhibited by increased compliance, reduced chamber stiffness, and a decrease in the tension developed for each volume load. It is also suggested that at a high beating rate AC hearts fail to restitute its contractility as quickly as C hearts.     

Comparison of the effects of neuropeptide Y (NPY) and 4-norleucine-NPY on isolated perfused rat hearts; effects of NPY on atrial and ventricular strips of rat heart and on rabbit heart mitochondria

Isolated perfused rat hearts were used to compare the effects of the synthetic neuropeptide Y (NPY) and 4-norleucine-NPY on cardiac function. Each peptide exhibited both negative inotropic and chronotropic effects, and also caused coronary vasoconstriction leading to a reduction in coronary flow. A comparison of the IC50 values from dose-response curves using 10(-14) to 10(-7) M peptides (IC50 is the peptide concentration that produced a 50% decrease of the maximal effect) indicated that NPY was more potent as inhibitor of contractility and less potently inhibited coronary flow and heart rate, whereas 4-norleucine-NPY had more inhibitory influence on coronary flow and heart rate and less on cardiac contractility. This difference in potencies suggests that the inhibitory effects of NPY on contractility, coronary flow and heart rate may be independent of each other. Since NPY also decreased the contractile force of isolated left atrial and right ventricular strips of the rat heart, the coronary flow decrease cannot be the cause of the negative inotropy of isolated heart. Pretreatment of atrial and ventricular strips with NPY did not influence the positive inotropic effect produced by the cardiac glycoside ouabain indicating that sarcolemmal Na+, K+-ATPase was not involved in the inhibitory inotropic effect of NPY. Further studies towards elucidating the mechanism of the negative inotropy of cardiac muscles using isolated heart mitochondria revealed that NPY uncoupled oxidative phosphorylation and blocked mitochondrial calcium uptake; the former event fosters negative inotropy. Since these effects on mitochondria occurred at concentrations 100-fold higher than those required for negative inotropy, the two effects of NPY may not be related.     

Electromechanical effects of menadione on isolated rat heart in relation to oxidative stress

Although Ca2+ overloading has been observed in hepatocytes and in the isolated liver treated with 0.2 mM menadione, it has not been determined if menadione has similar effects on cardiac tissue and, if so, whether Ca2+ overloading leads to cardiac contracture, and if such an event results from plasma membrane peroxidation initiated by oxidative stress. The present study reveals that when the isolated heart is perfused with 0.2 mM menadione for 30 min, it shows Ca2+ overloading, which can not be reversed even after 30 min of drug-free perfusion. The time courses of glutathione, ethane, and LDH release from the hearts do not show a parallel pattern of abnormality between 30 and 60 min, indicating that contractile failure precedes the development of lipid peroxidation or plasma membrane disintegration. The evidence that the plasma membrane of menadione-treated rat cardiac tissue remains intact is supported by the observation that the resting membrane potential of the atrium remains virtually unchanged during the 30 min of drug exposure and then gradually falls (-67 +/- 3.1 vs. -76 +/- 2 mv) only during the last 10 min of the drug washout. Interestingly, even after the atria are treated with menadione for 30 min and followed by washout of 30 min, and have shown calcium overloading, as evidenced by contracture, they are still capable of generating action potentials in response to electrical field stimulation.     

Insulin-like effects of histones H3 and H4 on isolated rat adipocytes

Crude preparations of histones had insulin-like actions in isolated adipocytes. This activity was attributed to the arginine-rich histones, H3 and H4. The metabolic effects of purified H3 and H4 on isolated adipocytes were similar to those of insulin in a number of respects. Like insulin, H3 and H4 stimulated the incorporation of both glucose and pyruvate in isolated cells and stimulated intercellular oxidation of glucose; in contrast, the lipolytic agents ACTH and isoproterenol actually inhibited the incorporation of pyruvate into adipocytes. In contrast to the effects of the lipolytic hormones, the effects of H3 and H4, like insulin, were not blocked by the presence of adenosine deaminase in the medium. The same concentrations of phenylarsine oxide were required to inhibit the stimulation of glucose incorporation whether by insulin or by histones. Furthermore, the addition of H4 or insulin to isolated adipocytes resulted in the increased phosphorylation of 17 kDa phosphoproteins as detected by two-dimensional electrophoresis. The insulin-like effect of the active histones was specific to their structure. Lysine-rich histones (H1, H2A and H2B), various polycations, and proteolytic fragments of purified H3 or H4 were all inactive. It is unknown whether this phenomenon might imply a physiological function for such endogenous molecules; however, a comparison of the detailed effects of insulin and histones might be informative in terms of common intracellular transduction systems.     

The effects of 4-pentenoic and pentanoic acids on the isolated rat atria

The peak developed tension and the pacemaker frequency of the isolated atria from fed and fasted rats, declined progressively during the incubation in a glucose-free medium containing 2-deoxyglucose. The atria from fed rats exhibited a faster decline than those from fasted rats, which was associated to a slower triacylglycerol lipolysis. 4-Pentenoic acid inhibited the lipolysis of both groups of atria but did not alter the atrial contractile performance. However, it enhanced the decline of the pacemaker frequency in the atria from fasted rats whereas, in contrast, it alleviated the decline in the fed atria. n-Pentanoic acid ameliorated the impairment of the contractile and pacemaker activities in both groups of atria, without affecting the lipolysis. It was concluded that, since the inhibition of the intramyocardial lipolysis did not correlate with changes of the atrial functions, 4-pentenoic acid was not appropriate to assess about the contribution of endogenous triacylglycerol to the maintenance of the atrial contractile and pacemaker activities.