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Article, 信州医学雑誌 51(2): 79-86(2003)

Idarubicin (IDA) is a member of an important class of anticancer agents, the anthracycline antibiotics. Although the clinical efficacy of anthracyclines is limited by a high incidence of severe cardiac toxicity, our understanding of IDA transport into the heart is still limited. In a previous study, we demonstrated that IDA is transported into the heart by a saturable mechanism. Based on in vitro data suggesting an enhancement by methylxanthines of IDA influx in leukemia cells, this study was designed to test the hypothesis that a commonly used methylxanthine, caffeine, might influence the myocardial uptake of IDA. In the Langendorff rat heart, after infusion of 0.5 mg IDA during 10 min, the presence of caffeine (1 µM) in perfusate enhanced the residual amount of IDA in the heart by 30% due to a 2.7-fold increase in the maximal uptake rate V max . Theophylline (3 µM), in contrast, did not influence the uptake process but caused a slight decrease of fractional myocardial sequestration rate (19% reduction). Caffeine reversed the cardiodepressive action of IDA (49% decrease in left ventricular developed pressure at the end of infusion) to a positive inotropic effect (18% increase of basal level). Theophylline significantly attenuated the negative inotropic effect of IDA (only 21% decrease) and led to positive inotropism in the washout phase (21% increase at the end of experiment). We speculate that co-administration of caffeine may enhance the chronic cardiotoxicity of IDA by increasing its accumulation in the heart.

Oxidative metabolism of blood-borne fuels provides myocardium the energy required to sustain its contractile performance. Recent research has revealed that, in addition to supplying energy, certain fuels are able to detoxify harmful oxidants and bolster the myocardium's endogenous antioxidant defenses. These antioxidant capabilities could potentially protect the myocardium from the ravages of reactive oxygen and nitrogen intermediates generated upon reperfusion of ischemic myocardium. This article reviews experimental evidence that two fuels, pyruvate and acetoacetate, provide such antioxidant protection. Pyruvate's antioxidant properties stem in part from its α-keto carboxylate structure, which enables it to directly, non-enzymatically neutralize peroxides and peroxynitrite. Also, citrate, which accumulates in pyruvate-perfused myocardium following anaplerotic pyruvate carboxylation, supports NADPH production to maintain glutathione:glutathione disulfide (GSH/GSSG) redox potential, the central component of the myocardial antioxidant system. Like pyruvate, acetoacetate restores GSH/GSSG and increases contractile function of post-ischemic stunned myocardium, although some of its antioxidant mechanisms may differ from pyruvate's. Both compounds restore β-adrenergic signaling and inotropism, which are compromised in stunned myocardium. N-acetylcysteine, a pharmacological antioxidant that does not provide energy, duplicated the salutary effects of pyruvate and acetoacetate on post-ischemic β-adrenergic signaling and GSH/GSSG. These findings reveal novel, energy-independent mechanisms for enhancement of post-ischemic cardiac performance by metabolic fuels.

Vagus Nerve Stimulation (VNS) has been shown to be useful in heart failure patients, including antiarrhythmic effects, improvement of cardiac function and reduction of the mortality. However, the optimal configuration of VNS can be a difficult task, since there are several adjustable parameters, such as current amplitude (mA), pulse width (ms), burst frequency (Hz), number of pulses and, in the case of cardiac-triggered VNS, the delay (ms) between the R-wave and the beginning of the stimulation. The objective of this paper is to analyse the effect of these parameters, and their interaction, on the chronotropic and inotropic responses to vagal stimulation. 306 VNS sequences were tested on 12 sheep with induced heart failure. Autonomic markers of the chronotropic (changes in RR interval) and inotropic (changes in dP/dtmax) effects were extracted from the observed data. In order to analyse the influence of stimulation parameters on these markers, a sensitivity analysis method was applied. Results illustrate the strong interaction between the delay and the others parameters. The number of pulses, the current and the frequency seem to be particularly influent on chronotropism and inotropism although the effect of the frequency is highly non-linear or it depends on other parameters.

Coronary by-pass on a beating heart may provide a safer form of surgical revascularization by avoiding the well-documented side effects of cardiopulmonary by-pass. In addition, off-pump bypass is suggested to be a good alternative to on-pump especially in high risk patients. This study reviews the feasibility of coronary by-pass on the beating heart in all patients referred to surgery. Two hundred and ninety-four patients operated on the beating heart were prospectively followed and compared to the control group of 100 consecutive patients operated with the conventional method. There were no significant differences between the groups with respect to risk factors, except the incidence of chronic obstructive pulmonary disease and ejection fraction which were higher in the conventional group, whereas peripheral vascular disease was higher in the beating heart group. There was more distal anastomosis in the conventional group. Postoperative inotrope requirement, peak creatine phosphokinase—MB, ventilation time, blood loss in the first 24 h, transfusion needs, new atrial fibrillation and length of hospital stay were significantly lower in the beating heart operations. However, there were no significant differences between the groups in terms of neurological complications, chest infection, intraaortic balloon pump usage and mortality. In conclusion, multivessel off pump coronary by-pass is feasible with the same or better results as it is observed in the conventional technique when postoperative bleeding, neurogenic complications, arrythmias. hospital stay, overall morbidity and mortality are compared.

β1- and β2-adrenoceptors (AR) are polymorphic. β1-AR: There is a Gly389Arg polymorphism of the β1-AR with the Gly389 exhibiting reduced in vitro responsiveness upon agonist-induced stimulation. To study this in vivo we assessed exercise-induced increase in heart rate and shortening of heart rate-corrected duration of electromechanical systole (QS2c—a measure of inotropism) in 12 volunteers homozygous for Gly389 and 12 volunteers homozygous for Arg389. In both groups, exercise caused nearly identical increases in heart rate and shortening of QS2c, indicating that the differential responsiveness observed in vitro is not of major functional importance in vivo. β2-AR: There are at least three polymorphisms of the β2-AR: the Arg16Gly and the Gln27Glu polymorphisms differ from the wild-type (WT, Arg16, Gln27) β2-AR in vitro in their susceptibility to agonist-induced downregulation. We studied in 16 WT-volunteers, 6 volunteers homozygous for Glu27 and 6 volunteers homozygous for Gly16, the effects of 2-week treatment with 3×5 mg/day p.o. terbutaline on terbutaline infusion-induced increases in heart rate and shortening of QS2c. In all three groups, oral terbutaline treatment reduced terbutaline infusion-induced increases in heart rate and shortening of QS2c to a similar extent, indicating that the differential susceptibility to agonist-induced downregulation of the Gly16 and Glu27 polymorphism of the β2-AR observed in vitro is not of major functional importance in vivo. Finally, there is a Thr164Ile polymorphism of the β2-AR with Ile164 exhibiting reduced in vitro responsiveness upon agonist-induced stimulation. We studied in 12 WT-volunteers and in 6 volunteers heterozygous for the Ile164 polymorphism the effects of terbutaline infusion on heart rate and QS2c. In the Ile164 volunteers increases in heart rate and shortening of QS2c induced by the terbutaline infusion were significantly (p

The in vivo and in vitro cardiac responses of Lepidosiren paradoxa were analyzed during temperature variations from 25°C (acclimation temperature) to 15°C and 35°C, and subsequent return to 25°C. Chronotropic (heart frequency) and inotropic (twitch force) responses varied directly with temperature, decreasing from 25°C to 15°C and increasing from 25°C to 35°C. However, time to peak tension (TPT) and time to half relaxation (THR) showed an inverse tendency. The results indicate that the myocardium of L. paradoxa responds more appropriately to acute elevations in temperature, which results in an increased cardiac performance due to both positive chronotropism and inotropism, in spite of the temperature-induced curtailment of TPT and THR.

In the present work the effect of dioclein, a new flavonoid from Dioclea grandiflora, was investigated in rat hearts. The experiments were performed using the classic method of Langendorff, where flow, inotropic, chronotropic and electric parameters were analyzed. Bolus administration of Dioclein (1-100 microg) induced a sustained and dose-dependent increase in coronary flow with no modification in inotropic, chronotropic and electrical parameters. The duration of increase in coronary flow induced by dioclein (10 microg) was approximately 4-fold higher than that observed in the presence of sodium nitroprusside (NPS; 10 microg). Besides, the effect of dioclein measured as the area-under-the-curve was approximately 4.5-folds higher than that observed with NPS. Pre-treatment with L-NAME (100 microM) and indomethacin (10 microM) alone did not modify the effect of dioclein (10 microg), suggesting that nitric oxide (NO) and cyclooxygenase-derived factors were not involved. However, association of L-NAME plus indomethacin inhibited the duration of the effect of dioclein (10 microg) without changing its increase in the coronary flow. Furthermore, the absence of alteration in inotropism and chronotropism of the heart associated with its coronary effect suggest that dioclein could be an interesting lead compound for the development of drugs for the treatment coronary heart diseases.

International audience; RATIONALE: TRPM4 is a non-selective Ca2+-activated cation channel expressed in the heart, particularly in the atria or conduction tissue. Mutations in the Trpm4 gene were recently associated with several human conduction disorders such as Brugada syndrome. TRPM4 channel has also been implicated at the ventricular level, in inotropism or in arrhythmia genesis due to stresses such as ß-adrenergic stimulation, ischemia-reperfusion, and hypoxia re-oxygenation. However, the physiological role of the TRPM4 channel in the healthy heart remains unclear.OBJECTIVES: We aimed to investigate the role of the TRPM4 channel on whole cardiac function with a Trpm4 gene knock-out mouse (Trpm4-/-) model.METHODS AND RESULTS: Morpho-functional analysis revealed left ventricular (LV) eccentric hypertrophy in Trpm4-/- mice, with an increase in both wall thickness and chamber size in the adult mouse (aged 32 weeks) when compared to Trpm4+/+ littermate controls. Immunofluorescence on frozen heart cryosections and qPCR analysis showed no fibrosis or cellular hypertrophy. Instead, cardiomyocytes in Trpm4-/- mice were smaller than Trpm4+/+with a higher density. Immunofluorescent labeling for phospho-histone H3, a mitosis marker, showed that the number of mitotic myocytes was increased 3-fold in the Trpm4-/-neonatal stage, suggesting hyperplasia. Adult Trpm4-/- mice presented multilevel conduction blocks, as attested by PR and QRS lengthening in surface ECGs and confirmed by intracardiac exploration. Trpm4-/-mice also exhibited Luciani-Wenckebach atrioventricular blocks, which were reduced following atropine infusion, suggesting paroxysmal parasympathetic overdrive. In addition, Trpm4-/- mice exhibited shorter action potentials in atrial cells. This shortening was unrelated to modifications of the voltage-gated Ca2+ or K+ currents involved in the repolarizing phase.CONCLUSIONS: TRPM4 has pleiotropic roles in the heart, including the regulation of conduction and cellular electrical activity which impact heart development.

M. I. Tejero-Taldo ,J . L. Caffrey ,J . Sun and R. T. Mallet. Antioxidant Properties of Pyruvate Mediate its Potentiation of b-Adrenergic Inotropism in Stunned Myocardium. Journal of Molecular and Cellular Cardiology (1999) 31, 1863‐1872. This study tested the hypothesis that pyruvate’s antioxidant actions, particularly its enhancement of the endogenous glutathione system, mediate its potentiation of b-adrenergic inotropism in stunned myocardium. Isolated working guinea pig hearts, metabolizing 10 mm glucose and stunned by 45 min of low flow ischemia, were treated with 5 mm pyruvate, 5 mm N-acetylcysteine (NAC) and/or 2 nm isoproterenol beginning 15 min after reperfusion. The antioxidant NAC alone did not increase cardiac power (mJ/min/g wet: 11‐1 in untreated and 15‐2 in NAC treated stunned hearts), but NAC potentiated the increase in power produced by 2 nm isoproterenol (isoproterenol alone: 50‐10; NAC plus isoproterenol: 133‐24). Addition of NAC doubled cyclic AMP content but lowered cytosolic phosphorylation potential by 32% in isoproterenolstimulated hearts. Stunning decreased the glutathione antioxidant ratio (GSH/GSSG) by 68%. The antioxidant ratio was completely restored by pyruvate alone or in combination with isoproterenol, but only partially restored by isoproterenol alone. Combining isoproterenol and NAC increased the GSH/GSSG ratio by an additional 36%. The combined treatment of pyruvate and isoproterenol increased the NADPH/NADP + ratio almost three-fold, and produced the greatest accumulation of glucose-6-phosphate of any treatment. Conclusions: like pyruvate, the antioxidant NAC potentiated b-adrenergic inotropism of stunned myocardium. Unlike pyruvate, NAC did not increase cellular energy reserves, thus effectively limiting its potentiation of b-adrenergic stimulation. Thus, pyruvate’s potentiation of b-adrenergic stimulation in stunned myocardium is most likely the result of the combined effects of its antioxidant and energetic properties. ” 1999 Academic Press

S1319 (4-hydroxy-7-[1-(1-hydroxy-2-methylamino)ethyl]-1,3-benzothiazol-2(3H)-one acetate), a novel non-catecholamine β-adrenoceptor agonist, has been compared with isoprenaline, salbutamol and formoterol for activity in vitro on a range of β-adrenoceptor containing preparations from guinea-pig. S1319, like isoprenaline, salbutamol and formoterol, relaxed preparations of guinea-pig trachea (contracted by histamine) in a concentration-dependent manner. The relaxing activity of S1319 appeared to be more potent than that of isoprenaline and salbutamol, and similar to that of formoterol (pD2 values of 10.58±0.03 vs 7.60±0.01, 7.50±0.01 and 10.52±0.04, respectively), and was blocked by the β2-adrenoceptor selective antagonist (ICI 118,551). The intrinsic activity of S1319 was close to 1.0. In the β1-adrenoceptor containing preparations, guinea-pig right and left atria, a monophasic inotropic response of S1319 was observed. The pD2 value of S1319 for left atrial and right atrial inotropism was 6.70±0.15 and 7.81±0.01, respectively. The selectivity ratio (trachea/left atrial inotropism) of S1319, formoterol, salbutamol and isoprenaline was 8523, 284, 4.8 and 0.45, respectively. The relative selectivity ratio of S1319 was 18743, 1858 and 30 times greater than that of isoprenaline, salbutamol and formoterol, respectively. Relaxant responses of guinea-pig trachea to S1319 declined rapidly when the agonist was washed from the tissues, with complete recovery within 30 min. The duration of action of S1319 was similar to that of isoprenaline and less than that of salbutamol and formoterol. In summary, S1319, a sponge-derived β-adrenoceptor agonist, is a potent and selective β2-adrenoceptor agonist with a short-duration of action in isolated guinea-pig tracheas. British Journal of Pharmacology (1999) 128, 716–720; doi:10.1038/sj.bjp.0702839

We investigated whether the adenosine triphosphate (ATP)-sensitive K + (K ATP ) channel activation by bimakalim, at concentrations devoid of both negative inotropic and action-potential duration (APD) shortening effects, might exhibit myocardial protection after hypoxia and reoxygenation in human atrial myocardium by using 112 preparations. The recovery of contractility of human atrial trabeculae, subjected either to short-duration (5 min) or to long-duration (60 min) and severe (high pacing rate) hypoxia followed by reoxygenation, was assessed by challenging with dobutamine. Treated preparations were exposed to 10 or 100 nM bimakalim, I μM glibenclamide, or both before hypoxia. Variations of isometric developed tension (%DT) or APD 90 were studied. At concentrations

Steroid hormones exert their biological actions via intracellular receptors modulation of transcription. In addition, a number of molecular interactions, and the existence of membrane receptors in several tissues, support the hypothesis of nongenomic action of steroids. The androgens, 5alpha- and 5beta-dihydrotestosterone (0.1 to 100 microM), induce a rapid positive inotropism in the isolated left atrium of male Wistar rats whose time course of response might suggest that it is a non-genomic effect. However, the fact that the facilitation of contractility was inhibited by actinomycin D (5 microg/ml) and cycloheximide (10 microg/ml) indicates that a transcriptional component might play a role. The existence of a rapid functional genomic role would be somewhat surprising. However, rapid transcriptional mechanisms were also observed in certain cAMP-dependent responses. In the left atrium of rat, Rp-cAMPS (10 microM), a cAMP-dependent protein kinase inhibitor, antagonized 5alpha- but not 5beta-dihydrotestosterone-induced positive inotropism. The inhibition by Rp-cAMPS of isoproterenol- and forskolin-induced positive inotropism, and the fact that these cAMP-dependent effects were also inhibited by actinomycin D and cycloheximide, suggest that a cAMP-dependent transcriptional component may be partly involved in the positive inotropism induced by 5alpha-dihydrotestosterone. In addition, 5alpha-dihydrotestosterone might increase the basal adenylyl cyclase activity by acting on unoccupied beta-adrenoceptor-G-protein-adenylyl cyclase complexes, since the elicited inotropism was inhibited by a beta-blocker, atenolol (1 microM), a G-protein inhibitor, pertussis toxin (2 microg/ml, 3 h), and an adenylyl cyclase inhibitor, dideoxy-adenosine (10 microM).

It is well known that beta-adrenoceptor stimulation induces positive inotropism by cAMP-dependent phosphorylation of cardiac calcium channels. Furthermore, hypertrophy of different tissues including the heart have been related to the stimulation of these adrenoceptors via mechanisms coupled to activation of transcription and protein synthesis. Early effects of isoproterenol mediated via this pathway has also been associated to the stimulation of beta-adrenoceptors. However, the effects on the inotropism through genomic mechanisms have not yet been described. Isoproterenol (3 nM to 3 microM) induced a concentration-dependent positive inotropism, in isolated left atrium of male Wistar rats electrically stimulated (0.5 Hz, 5 ms, 30-50% above the threshold voltage), which was antagonized by atenolol (1 microM) and inhibited by a protein kinase A inhibitor, (R)p-cAMPS (10 microM). The inhibitor of transcription, actinomycin D (4 microM), and the protein synthesis inhibitor, cycloheximide (35.5 microM), significantly decreased the positive inotropism induced by isoproterenol. Forskolin (0.1 to 3 microM), an activator of adenylyl cyclase, induced a concentration-dependent positive inotropism which was also inhibited by (R)p-cAMPS, actinomycin D and cycloheximide. In the left atrium of rat, isoproterenol induced a positive inotropism which seems, at least in part, dependent upon intact transcription and protein synthesis, as suggested by the fact that the response was inhibited by the incubation with actinomycin D and cycloheximide. In addition, this genomic effect seems to be mediated by a cAMP-dependent mechanism. As it was inhibited by a protein kinase A inhibitor ((R)p-cAMPS) and similarly to isoproterenol, the positive inotropism induced by forskolin, which increases cytosolic cAMP, was also inhibited by actinomycin D and cycloheximide.

The effects of arachidonic acid (AA) and indomethacin (IM) on performance, oxygen consumption and lactate release of the trout heart were studied in vitro TPa s m−3 using a perfusion system, which allowed the evaluation of the integrated function of ventricle and coronary system by continuously setting the input coronary flow and pressure proportional to the pressure and flow output of the heart. The heart was working against a fixed resistance. A reduction of input oxygen partial pressure (PO2) from 175 torr (high PO2) to 76 torr (low PO2) increased the coronary flow (from 0.51 ml min−1 kg−1 to 1.21 ml min−1 kg−1, respectively) due to a strong reduction in coronary resistance (from 0.60 TPa s m−3 to 0.19 TPa s m−3, respectively). Oxygen consumption by the heart was significantly reduced from 20.7 ml min−1 g−1 at high PO2 to 4.6 ml min−1 g−1 at low PO2, while lactate production was increased from 24 μmol h−1 g−1 to 42 μmol h−1 g−1, indicating a higher contribution of anaerobic respiration to mechanical work. Mechanical efficiency was significantly higher at low than at high PO2. Exogenous AA caused a depression of inotropism and a reduction in the aerobic metabolic rate (by 25–35%), which was not accompanied by increased lactate production. IM enhanced the depression of both inotropism and aerobic metabolism. The effect of AA and IM on the heart were amplified at low PO2.

We have reported that, in canine hearts, cardiac cooling to 29°C enhanced left ventricular contractility but changed neither the contractile efficiency of cross-bridge (CB) cycling nor the excitation-contraction coupling energy. The mechanism of this intriguing energetics remained unknown. To get insights into this mechanism, we simulated myocardial cooling mechanoenergetics using basic Ca2+and CB kinetics. We assumed that both adenosinetriphosphatase (ATPase)-dependent sarcoplasmic reticulum (SR) Ca2+uptake and CB detachment decelerated with cooling. We also assumed that all the ATPase-independent SR Ca2+release, Ca2+binding to and dissociation from troponin, and CB attachment remained unchanged. The simulated cooling shifted the CB force-free Ca2+concentration curve to a lower Ca2+concentration, increasing the Ca2+responsiveness of CB force generation, and increased the maximum Ca2+-activated force. The simulation most importantly showed that these cooling effects combined led to a constant contractile efficiency when Ca2+uptake and CB detachment rate constants changed appropriately. This result seems to account for our experimentally observed constant contractile efficiency under cooling inotropy.

Background The mechanisms underlying the negative inotropic effects of isoflurane are incompletely understood. One suggested mechanism is that isoflurane may decrease Ca2+ sensitivity of contractile proteins. If so, more free calcium would be needed to activate contractile proteins to the same degree, which would impose a greater requirement for myocardial oxygen consumption used in the cycling of calcium. In this study, the authors use the excised, cross-circulated, canine heart model and the volume servopump technique to measure the effects of isoflurane on Emax (a contractile index) and on the relationship between pressure-volume area (PVA, a measure of total mechanical energy) and myocardial oxygen consumption per beat (VO2). Methods Effects of intracoronary isoflurane infused via a precoronary oxygenator on myocardial mechanoenergetics were studied during isovolumic contractions. The authors measured left ventricular (LV) pressure, LV volume, coronary flow, and arteriovenous oxygen content difference and computed Emax, VO2 and PVA at 0, 1.0, 1.5, and 2.0% isoflurane. From these data, the authors obtained oxygen costs of PVA and Emax in control subjects and in those receiving 2.0% isoflurane. Results Emax, PVA, and VO2 dose-dependently decreased by similar degrees (P < 0.05). Isoflurane did not change the oxygen costs at 1.5% and 2.0% concentration (P < 0.05). Conclusions These mechanoenergetic findings suggest that the primary method by which isoflurane decreases contractility is not by decreasing Ca2+ sensitivity of contractile proteins but mainly by decreasing Ca2+ handling in the excitation-contraction coupling without myocardial oxygen wasting effect.

Dynamic positron emission tomography (PET) with [11C]acetate allows noninvasive assessment of myocardial oxygen consumption. In combination with echocardiography, PET enables determination of cardiac efficiency (defined as useful cardiac work per unit of oxygen consumption). We used this approach to compare the effects of levosimendan, a Ca(2+)-dependent calcium sensitizer, with dobutamine and sodium nitroprusside in healthy male volunteers. The effects of levosimendan on k(mono), an index of oxygen consumption, and cardiac efficiency were neutral, whereas the hemodynamic profile was consistent with balanced inotropism and vasodilatation. Dobutamine enhanced cardiac efficiency at the expense of increased oxygen requirement, but the effects of nitroprusside on k(mono) and cardiac efficiency were neutral. This study shows the feasibility of PET in phase 1 pharmacodynamic studies and suggests potential energetical advantages of calcium sensitization with levosimendan.

The negative inotropism of 2,3-butanedione monoxime (BDM) < or = 5 mmol/l has been attributed primarily to directly suppressed crossbridge force development without much suppressed intracellular Ca2+ handling. However, there is evidence that BDM simultaneously or even primarily suppresses myocardial excitation-contraction (E-C) coupling. We therefore studied the mechanoenergetic effects of intracoronary BDM in the left ventricle (LV) of 11 canine excised cross-circulated hearts. We fully utilized the VO2-PVA-Emax framework that we have developed, where VO2 is myocardial O2 consumption, PVA is the systolic pressure-volume area as a measure of the total mechanical energy, and Emax is a contractility index. We gradually depressed Emax from 5.9 to 3.4 mmHg/(ml/100 g) on average by increasing intracoronary BDM to 2.6 +/- 2.1 mmol/l, and then gradually restored Emax to the pre-BDM level by increasing intracoronary CaCl2. We compared the O2 cost of Emax between BDM and Ca2+. We found that BDM and Ca2+ had a similar O2 cost of Emax. BDM did not affect the concentrations of blood-borne catecholamines. We therefore conclude that the negative inotropism of BDM is primarily due to suppressed E-C coupling in canine blood-perfused hearts.

This study supports a mathematical model and previous findings indicating that , the time from onset of contraction to , reflects the time-dependent aspects of contraction and hence decreases with increasing contractility. Combined data from 20 conscious instrumented dogs create a highly significant inverse and linear - HR (heart rate) relation. Both norepinephrine and isoproterenol decreased values, but norepinephrine, in contrast to isoproterenol, decreased the heart rate by a reflex response. Despite the remarkable decline in heart rate (25.8%) was decreased (16.5%). During wide spontaneous R - R variations longer preceding intervals gave shorter values. The latter two facts indicate the dependence of on the contractile state rather than it being merely interval dependent. Keywords: heart contractility, myocardial contraction, left ventricular function, cardiac inotropism, cardiac chronotropism

Cardiac function improvement seen with hemofiltration may be attributable to "cardiac depressant factor(s)" removal. The authors have attempted "factor" isolation. Initial 12 hr hemofiltrate was obtained from: 4 patients with acute congestive heart failure (cardiac index: 2.02 +/- 0.48) and acute renal failure (blood urea nitrogen [BUN] 97.7 +/- 32.7; serum creatinine [SCr] 6.2 +/- 3.4 mg%) (Group I); 8 patients with chronic congestive heart failure (CI: 2.69 +/- 1.3) and mild renal failure (BUN 48.8 +/- 31.4; SCr 3.5 +/- 2.4 mg%) (Group II); and 8 patients with end-stage renal disease and no congestive heart failure (Group III). Crude samples were passed through C18Sep-Pak, and eluted with methanol/water mixtures, and 50% methanol samples were fractionated by high pressure liquid chromatography. Inotropic response was studied by injecting samples (in Krebs-Hensleit buffer) into a Langendorff rat heart preparation. The effect of pH, acetate, salts, and adding propranolol on the inotropic response also was tested. Myocardial depression followed all vehicle and preparatory elements: 0.1 M HCl (-47%); 0.08 M acetic acid (-75%); Na acetate (-25%); 0.1 M NaHCO3 (-11%); Na citrate (-84%); and Na glutarate (-14%). Group I had biphasic responses, the positive inotropism accorded to catecholamines, whereas negative inotropism was equal in each patient (-40.3%). Group II had a biphasic response with negative (-15%) inotropism noted. Group III was weakly biphasic. The data indicate there was myocardial depressive activity, most pronounced in Groups I and II, after method interference was corrected.

The isolation and identification of two cardioactive compounds from two Eremophila species (Myoporaceae) considered important in the pharmacopoeia of the Australian Aboriginal people is described. Verbascoside, isolated from the methanol and water extracts of E. alternifolia leaves, mediated significant increases in chronotropism, inotropism and coronary perfusion rate (CPR) in the Langendorff rat heart. Geniposidic acid, isolated from the methanol extract of E. longifolia leaves, mediated an inhibitory effect with significant negative chronotropism, negative inotropism and CPR.

Mechanical vibration depresses cardiac contractility. We studied the mechanoenergetic effects of this negative inotropism in the left ventricle (LV) of an isolated, cross-circulated dog heart preparation. We took full advantage of the mechanoenergetic relationship among the LV end-systolic elastance (Emax, contractility index), systolic pressure-volume area (PVA), and myocardial oxygen consumption (VO2). PVA is a measure of the total mechanical energy that cardiac contraction generates. PVA correlates closely with VO2. The VO2 intercept of the VO2-PVA relation reflects the VO2 component for excitation-contraction (E-C) coupling plus basal metabolism (PVA-independent VO2). VO2 above the PVA-independent VO2 reflects the VO2 component for mechanical contraction (PVA-dependent VO2). When we applied 70-Hz vibration of 2-mm amplitude to a LV wall region, it instantly decreased Emax and PVA by 20%, followed by a 10% decrease in VO2 at a fixed volume. However, the vibration neither lowered the VO2-PVA relation obtained at different LV volumes, unlike ordinary negative inotropism, nor changed its slope (1.88 +/- 0.23 vs. 1.86 +/- 0.23 x 10(-5) ml O2.mmHg-1.ml-1). The virtually zero delta PVA-independent VO2/delta Emax with vibration indicates a much smaller O2 cost of Emax than that seen with calcium and propranolol inotropism. These mechanoenergetics support the hypothesis that mechanical vibration primarily suppresses cardiac contractility without suppressing E-C coupling.

S-nitrosylation of several Ca2+ regulating proteins in response to β-adrenergic stimulation was recently described in the heart; however the specific nitric oxide synthase (NOS) isoform and signaling pathways responsible for this modification have not been elucidated. NOS-1 activity increases inotropism, therefore, we tested whether β-adrenergic stimulation induces NOS-1-dependent S-nitrosylation of total proteins, the ryanodine receptor (RyR2), SERCA2 and the L-Type Ca2+ channel (LTCC). In the isolated rat heart, isoproterenol (10 nM, 3-min) increased S-nitrosylation of total cardiac proteins (+46±14%) and RyR2 (+146±77%), without affecting S-nitrosylation of SERCA2 and LTCC. Selective NOS-1 blockade with S-methyl-L-thiocitrulline (SMTC) and Nω-propyl-l-arginine decreased basal contractility and relaxation (-25-30%) and basal S-nitrosylation of total proteins (-25-60%), RyR2, SERCA2 and LTCC (-60-75%). NOS-1 inhibition reduced (-25-40%) the inotropic response and protein S-nitrosylation induced by isoproterenol, particularly that of RyR2 (-85±7%). Tempol, a superoxide scavenger, mimicked the effects of NOS-1 inhibition on inotropism and protein S-nitrosylation; whereas selective NOS-3 inhibitor L-N5-(1-Iminoethyl)ornithine had no effect. Inhibition of NOS-1 did not affect phospholamban phosphorylation, but reduced its oligomerization. Attenuation of contractility was abolished by PKA blockade and unaffected by guanylate cyclase inhibition. Additionally, in isolated mouse cardiomyocytes, NOS-1 inhibition or removal reduced the Ca2+-transient amplitude and sarcomere shortening induced by isoproterenol or by direct PKA activation. We conclude that 1) normal cardiac performance requires basal NOS-1 activity and S-nitrosylation of the calcium-cycling machinery; 2) β-adrenergic stimulation induces rapid and reversible NOS-1 dependent, PKA and ROS-dependent, S-nitrosylation of RyR2 and other proteins, accounting for about one third of its inotropic effect.

A question whether phosphorylation is involved in adrenergic effects on cardiac tissues has long been a matter of dispute. We examined whether phosphorylation is involved in adrenergic chronotropism and inotropism in excised cardiac muscles from guinea pigs. KT5720, a specific inhibitor of A-kinase, abolished the late phase of adrenergic chronotropism. Okadaic acid, an inhibitor of phosphoprotein phosphatases, and IBMX (1-methyl, 3-isobutylxanthine), a phosphodiesterase inhibitor, potentiated the chronotropism. The adrenergic inotropism was influenced neither by KT5720, okadaic acid, nor by IBMX. The specific beta 1 -adrenergic agonist, denopamine, showed actions similar to adrenaline and susceptibility to the inhibitors. Adrenaline of 10 microM showed a chronotropic time course consisting of early and late components. We concluded that only the late component results from phosphorylation, and its early one and the inotropism is entirely independent of phosphorylation.

SUMMARY 1. Inhibition of If or Ica by zatebradine has been reported in mammalian SA nodal cells. We thus investigated whether zatebradine differentially attenuates the positive chronotropic and inotropic responses to norepinephrine, isoproterenol, NKH 477 (an adenylyl cyclase activator), 3-isobutyl-1-methylxanthine (IBMX) and Bay k 8644 (a calcium channel agonist) in the isolated, blood-perfused dog atrium. 2. When zatebradine (0.03–1 μmol) decreased sinus rate from 104 ± 4.5 to 73 ± 4.9 beats/min dose-dependently, it selectively attenuated the positive chronotropic but not inotropic responses to norepinephrine in a dose-related manner. Zatebradine decreased the norepinephrine-induced tachycardia (by approximately 80% from the control) more effectively than the spontaneous sinus rate (by approximately 30% from the control). 3. Zatebradine similarly attenuated the positive chronotropic but not inotropic responses to isoproterenol, NKH 477 and IBMX. Fifty per cent inhibition doses of zatebradine (0.10–0.18 μmol) for the chronotropic responses to each substance were not significantly different. 4. On the other hand, zatebradine attenuated neither positive chronotropic nor inotropic responses to Bay k 8644. 5. We therefore suggest that zatebradine selectively attenuates the positive chronotropic but not inotropic responses to cyclic AMP-related substances due to inhibition of If but not Ica in the dog heart.

This study developed an evidence-based, goal-directed haemodynamic management algorithm to standardize intraoperative haemodynamic therapy. A systematic literature search identified three haemodynamic management goals: stroke volume optimization by fluid therapy; maintenance of a target mean arterial pressure by vasopressor therapy; maintenance of a target cardiac index ≥ 2.5 l/min per m2by inotropic therapy. The algorithm was adapted to international standards and consensus was reached through a modified Delphi method at international meetings. Implementation of the algorithm into routine intraoperative management in noncardiac surgery was shown to be feasible. Compared with conventional haemodynamic management, use of the algorithm significantly reduced length of hospital stay, requirement for ventilation and incidence of prolonged hospital stay, thereby resulting in reduced hospital costs.

We tested the hypothesis that NOS-1 activity regulates basal and β-adrenergic-stimulated cardiac contractility by S-nitrosylation of Ca2+-handling proteins. We used the isolated rat heart preparati...

Background and aims The anorexigenic glucagon-like peptide (GLP)-2 is produced by intestinal L cells and released in response to food intake. It affects intestinal function involving G-protein-coupled receptors. To verify whether GLP-2 acts as a cardiac modulator in mammals, we analysed, in the rat heart, the expression of GLP-2 receptors and the myocardial and coronary responses to GLP-2. Methods and results GLP-2 receptors were detected on ventricular extracts by quantitative real-time polymerase chain reaction (Q-RT-PCR) and Western blotting. Cardiac GLP-2 effects were analysed on Langendorff perfused hearts. Intracellular GLP-2 signalling was investigated on Langendorff perfused hearts and by Western blotting and enzyme-linked immunosorbent assay (ELISA) on ventricular extracts. By immunoblotting and Q-RT-PCR, we revealed the expression of ventricular GLP-2 receptors. Perfusion analyses showed that GLP-2 induces positive inotropism at low concentration (10–12 mol l −1 ), and negative inotropism and lusitropism from 10 to 10 mol l −1 . It dose-dependently constricts coronaries. The negative effects of GLP-2 were independent from GLP-1 receptors, being unaffected by exendin-3 (9–39) amide. GLP-2-dependent negative action involves Gi/o proteins, associates with a reduction of intracellular cyclic adenosine monophosphate (cAMP), an increase in extracellular signal regulated kinases 1 and 2 (ERK1/2) and a decrease in phospholamban phosphorylation, but is independent from endothelial nitric oxide synthase (eNOS) and protein kinase G (PKG). Finally, GLP-2 competitively antagonised β-adrenergic stimulation. Conclusions For the first time, to our knowledge, we found that: (1) the rat heart expresses functional GLP-2 receptors; (2) GLP-2 acts on both myocardium and coronaries, negatively modulating both basal and β-adrenergic stimulated cardiac performance; and (3) GLP-2 effects are mediated by G-proteins and involve ERK1/2.

1. We have characterized alpha 1-adrenoceptor in the conduction systems of the rat heart by quantitative autoradiography. 2. Consecutive 20 micron thick sections from a single rat heart containing the sinoatrial (SA) node and atrioventricular (AV) node were incubated with increasing concentrations of [3H]-prazosin with or without 10 microM phentolamine. After exposure to 3H-Ultrofilm, optical densities corresponding to the SA node and AV node were determined by computerized densitometry after comparison with 3H standards. 3. The SA node and AV node were stained heavily for cholinesterase and they contained a higher concentration of alpha 1-adrenoceptors than the adjacent myocardium without a significant change in the affinity. 4. These results support the hypothesis that alpha 1-adrenoceptors may play an important role not only in inotropism but also in chronotropism of rat hearts.

This study compared the positive inotropic actions of milrinone in isolated rabbit myocardium with that of the conventional positive inotropic drug, dobutamine, and a cardiac glycoside, ouabain. Maximal increase in developed tension (g/mm2) was significantly (p0.05) greater with ouabain (from 2.0 to 4.4; 132 +/- 11%) than with dobutamine (from 3.9 to 6.0; 77.8 +/- 22.4%) or milrinone (from 2.4 to 3.6; 54.0 +/- 12.0%). Maximal augmentation of the rate of tension development (g/s/mm2), however, was similar with ouabain (from 14.3 to 39.7; 187 +/- 20%) and dobutamine (from 25.9 to 64.4; 174 +/- 35%), and both were significantly (p0.05) greater than with milrinone (from 18.2 to 30; 73.1 +/- 14.7%). In combination with dobutamine, however, the dose-response curve of milrinone was shifted to the left, and its ED10 was significantly (p0.001) reduced by 100-fold to 1.6 x 10(-7) M. Thus, milrinone is significantly less potent than dobutamine or ouabain in vitro and is without contractile effect at clinically relevant concentrations. However, data from the combined application of a catecholamine and milrinone in isolated myocardium suggest that milrinone may induce a direct positive inotropic effect at clinical concentrations in the presence of augmented sympathetic neurohumoral stimulation.

Teas and infusions from C. spiralis leaf have largely been used by folk medicine as diuretic, hypotensor, cytotoxic, immunomodulator, antilithiasic, antidiarrheic, antispasmodic, antiurolitic, antimicrobian, antifungic, antioxidant, antileishmania activity, antiinflamatory, and antiedematogenic activity. In spite of these biological effects attributed to the extracts of C. spiralis, nothing so far could be found in the scientific literature dealing with its effects on the mammalian myocardium.The present study aimed to describe the inotropic effects produced by extracts from the C. spiralis leaf on isolated guinea pig atrium, as well as to contribute for a better understanding about its mechanism of action in that tissue. In isolated mouse cardiomyocytes, the effect produced by those extracts on the intracellular calcium transient and on the sarcolemal L-type calcium current were also measured. Experiments performed to evaluate the contractile effects were carried out on isolated atrium from guinea pig (Cavia porcellus). Firstly, our purpose was to determine the most potent fraction obtained from the C. spiralis leaf. This was done by comparing the hydroalchoolic crude extract with the following ones: aqueous, chloroform, and ethyl acetate. A phytochemical analysis was performed on the fraction exhibiting the greater potency. This evaluation followed the procedures proposed by Matos (1997). The content of sodium and potassium in the most potent fraction was determined by flame photometry. In the contractile experiments, the atrial force was measured isometrically. Biological signals were captured, amplified, and then stored in computer to be processed off line. Intracellular calcium transients were studied by confocal microscopy with laser scanning by using the fluorescent dye FLUO 4AM. Calcium inward currents were measured in mouse cardiomyocytes by using patch clamp technique in the whole cell configuration. Yield percentage of the aqueous fraction (AqF) was 69,40%. This fraction showed the most potent depressor effect on the myocardial contractility (EC50 = 305 ± 41,00 mg/L, Hill constant = 1,46 ± 0,19). The following metabolites were found in the AqF: tannins, saponins, and polifenols (flavonol, flavononol, flavone, xanthone, phenol, and flavonoid). The potassium and sodium contents in 1 g/L of AqF were 1,91 and 0,15 mM, respectively. This was not enough to change the myocardial inotropism, even in the highest concentration of AqF used in the experiments. The contraction and the relaxation time, as well as the time related to the excitation-contraction coupling (stimulus-response) were not modified by adding AqF to the organ bath. However, AqF reduced the Efficiency Index for the contraction and relaxation phases. The Neyler & Merrillees protocol was employed to evaluate the AqF effect on the calcium inward current in myocardial cells. Our results showed that AqF is able to completely abolish the Bowditch phenomenon, suggesting that it could be acting by reducing the sarcolemal calcium current. Supported by those experimental evidences, experiments were proposed to better understand the relationship between AqF and calcium mechanisms in cardiac cells. The following results were obtained with 1,5 g/L AqF: 1) AqF completely abolished the positive inotropic effect induced by isoproterenol (10-1 to 103 pM); 2) AqF shifted rightwardly the concentration-effect curve for CaCl2 (0.5 to 7.0 mM) and increased the EC50 from 1.12 ± 0.07 (Hill = 1.5) to 7.23 ± 0.47 mM (Hill = 7.4) (n = 3; p < 0.05); 3) AqF completely abolished the positive inotropic effect of (-) BAY K8644 (5 to 2000 nM); 4) AqF reduced the intracellular fluorescence from 4.66 ±1.17 to 3.74 ± 1.0 a.u. (n = 30 cells, 4 mice, p < 0.05); 5) AqF did not modify the decay rate of the fluorescent signal (892 ± 37 to 930 ± 30 ms, n = 30 cells, 4 mice, p > 0.05), indicating that it does not interfiere with the calcium removal from the sarcoplasm; 6) AqF reduced the calcium inward current through L-type calcium channels from 6,29 ± 0,34 to 4,9 ± 0,2 A/F (23% , n = 5 animals, p < 0,05). This study brought us unto the following conclusions: 1) AqF is the most potent fraction obtained from C. spirallis leaves; 2) AqF contains the following secondary metabolites: tannins, saponins, and poliphenols; 3) AqF reduces the contraction force of the guinea pig left atrium; 4) AqF acts on the myocardium contractility by reducing the calcium entry in myocardial cells during contraction. Preparados de Costus spiralis têm sido usados pela medicina popular (diurético, hipotensor, citotóxico, imunomodulador, antilitiásico, antidiarréico, antiespasmódico, antiurolítico, antimicrobiano, antifúngico, antioxidante, antileishmânia, anti-inflamatório e antiedematogênico). Apesar da gama de ações a eles atribuídas, nada pôde ser encontrado na literatura científica com respeito ao possível efeito dos Este trabalho visou determinar os efeitos inotrópicos obtidos das folhas de C. spiralis, que apresentava maior potência, bem como contribuir para o mecanismo de ação desse preparado no miocárdio de mamíferos. Os experimentos sobre contração foram realizados em átrio esquerdo de cobaia (Cavia porcellus), enquanto que as medidas de transiente de cálcio intracelular e de corrente de membrana foram feitas em cardiomiócitos de camundongo. A investigação fitoquímica do preparado mais ativo foi conduzida segundo Matos (1997). Os teores de sódio e de potássio presentes na fração mais potente, foram determinados por fotometria de chama. A força de contração atrial foi captada isometricamente e, depois amplificada, foi armazenada em computador. O transiente de cálcio intracelular foi avaliado com microscopia confocal de varredura a laser. As correntes de cálcio sarcolemais foram medidas em cardiomiócitos submetidos à técnica do patch clamp ( whole cell ). A fração aquosa (FAq) foi a que apresentou maior rendimento (69,40%) e a que exerceu maior efeito inotrópico negativo (CE50 = 305 ± 41,00 mg/L, Hill = 1,46 ± 0,19). Na sua constituição foram detectadas as seguintes classes de metabólitos secundários: taninos e saponinas, com reação fortemente positiva, e os polifenóis, com reação positiva (flavonóis, flavononóis, flavonas, xantonas, fenóis e flavonóides). Em 1 g/L de FAq foram encontrados 1,91 mM de potássio e 0,15 mM de sódio. A adição de FAq ao Tyrode não modificou significativamente a concentração desses íons. Os tempos de contração e de relaxamento, bem como o tempo de acoplamento eletromecânico não foram alterados pela FAq. Contudo, ela reduziu os Índices de Eficiência da contração e do relaxamento. A FAq aboliu completamente o fenômeno de Bowditch induzido por alta frequência de estimulação, indicando que ela reduz a entrada desse íon nas células. Com base nessa evidência, foram realizados protocolos para aprofundar o conhecimento sobre a participação das correntes de cálcio no mecanismo cardiodepressor da FAq. Esta fração produziu os seguintes resultados: 1) aboliu completamente o efeito inotrópico positivo do isoproterenol (10-1 a 103 pM); 2) deslocou para a direita a curva concentração-efeito para o CaCl2 (0,5 a 7,0 mM), aumentando a CE50 de 1,12 ± 0,07 (Hill = 1,5) para 7,23 ± 0,47 mM (Hill = 7,4) (n = 3; p < 0,05); 3) aboliu completamente o efeito inotrópico positivo do (-) BAY K8644 (5 a 2000 nM); 4) reduziu em cerca de 20% o pico da fluorescência intracelular correspondente ao transiente de cálcio citoplasmático (controle: n = 30 células; teste: n = 27 células; 4 animais); 5) não modificou a velocidade de decaimento do sinal de fluorescência, o que significa que ela não interfere com o funcionamento da bomba de cálcio do retículo sarcoplasmático; 6) reduziu em 23% a densidade de corrente de cálcio tipo-L que variou de -6,29 ± 0,34 para -4,9 ± 0,2 A/F (n = 5 animais, p < 0,05). 1) a FAq foi a fração com maior potência inotrópica; 2) os principais metabólitos secundários presentes na FAq foram taninos, saponinas e polifenóis; 3) a FAq reduz a força de contração do átrio; 4) o mecanismo da ação cardiodepressora da FAq sobre a contratilidade miocárdica se deve à diminuição da disponibilização do cálcio durante a contração.

Background and Aims: Moderate red wine consumption associates with lower incidence of cardiovascular diseases. Attention to the source of this cardioprotection was focused on flavonoids, the non-alcoholic component of the red wine, whose intake inversely correlates with adverse cardiovascular events. We analysed whether two red wine flavonoids, quercetin and myricetin, affect mammalian basal myocardial and coronary function. Methods and results: Quercetin and myricetin effects were evaluated on isolated and Langendorff perfused rat hearts under both basal conditions and a- and b-adrenergic stimulation. The intracellular signalling involved in the effects of these flavonoids was analysed on perfused hearts and by western blotting on cardiac and HUVEC extracts. Quercetin induced biphasic inotropic and lusitropic effects, positive at lower concentrations and negative at higher concentrations. Contrarily, Myricetin elicits coronary dilation, without affecting contractility and relaxation. Simultaneous administration of the two flavonoids only induced vasodilation. Quercetin-elicited positive inotropism and lusitropism depend on b1/b2-adrenergic receptors and associate with increased intracellular cAMP, while the negative inotropism and lusitropism observed at higher concentrations were a-adrenergic-dependent. NOS inhibition abolished Myricetin-elicited vasodilation, also inducing Akt, ERK1/2 and eNOS phosphorylation in both ventricles and HUVEC. Myricetin-dependent vasodilation increases intracellular cGMP and is abolished by triton X-100. Abstract BACKGROUND AND AIMS: Moderate red wine consumption associates with lower incidence of cardiovascular diseases. Attention to the source of this cardioprotection was focused on flavonoids, the non-alcoholic component of the red wine, whose intake inversely correlates with adverse cardiovascular events. We analysed whether two red wine flavonoids, quercetin and myricetin, affect mammalian basal myocardial and coronary function. METHODS AND RESULTS: Quercetin and myricetin effects were evaluated on isolated and Langendorff perfused rat hearts under both basal conditions and alpha- and beta-adrenergic stimulation. The intracellular signalling involved in the effects of these flavonoids was analysed on perfused hearts and by western blotting on cardiac and HUVEC extracts. Quercetin induced biphasic inotropic and lusitropic effects, positive at lower concentrations and negative at higher concentrations. Contrarily, Myricetin elicits coronary dilation, without affecting contractility and relaxation. Simultaneous administration of the two flavonoids only induced vasodilation. Quercetin-elicited positive inotropism and lusitropism depend on beta1/beta2-adrenergic receptors and associate with increased intracellular cAMP, while the negative inotropism and lusitropism observed at higher concentrations were alpha-adrenergic-dependent. NOS inhibition abolished Myricetin-elicited vasodilation, also inducing Akt, ERK1/2 and eNOS phosphorylation in both ventricles and HUVEC. Myricetin-dependent vasodilation increases intracellular cGMP and is abolished by triton X-100. CONCLUSIONS: The cardiomodulation elicited on basal mechanical performance by quercetin and the selective vasodilation induced by myricetin point to these flavonoids as potent cardioactive principles, able to protect the heart in the presence of cardiovascular diseases.

Acute myocardial dysfunction is a typical manifestation of septic shock. Experimentally, the administration of endotoxin [lipopolysacharride (LPS)] to laboratory animals is frequently used to study such dysfunction. However, a majority of studies used load-dependent indexes of cardiac function [including ejection fraction (EF) and maximal systolic pressure increment (dP/d tmax)], which do not directly explore cardiac inotropism. Therefore, we evaluated the direct effects of LPS on myocardial contractility, using left ventricular (LV) pressure-volume catheters in mice. Male BALB/c mice received an intraperitoneal injection of E. coli LPS (1, 5, 10, or 20 mg/kg). After 2, 6, or 20 h, cardiac function was analyzed in anesthetized, mechanically ventilated mice. All doses of LPS induced a significant drop in LV stroke volume and a trend toward reduced cardiac output after 6 h. Concomitantly, there was a significant decrease of LV preload (LV end-diastolic volume), with no apparent change in LV afterload (evaluated by effective arterial elastance and systemic vascular resistance). Load-dependent indexes of LV function were markedly reduced at 6 h, including EF, stroke work, and dP/d tmax. In contrast, there was no reduction of load-independent indexes of LV contractility, including end-systolic elastance (ejection phase measure of contractility) and the ratio dP/d tmax/end-diastolic volume (isovolumic phase measure of contractility), the latter showing instead a significant increase after 6 h. All changes were transient, returning to baseline values after 20 h. Therefore, the alterations of cardiac function induced by LPS are entirely due to altered loading conditions, but not to reduced contractility, which may instead be slightly increased.

In the present study, we examined the inotropic effect of Mn 2+ on adult and neonatal rat myocardia, eontraction of which is known to he highly dependent on Ca 2+ release from the sarcoplasmic reticulum and trans-sarcolemmal Ca 2+ influx, respectively. Mn 2+ produced an initial negative inotropic effect followed by a late augmentation of contractile force in both neonatal and adult preparations, accompanied by marked prolongation of the contraction duration. The attenuation of the late augmentation by ryanodine was greater in the adult while the effect of nicardipine was greater in the neonate, which was similar to the effects of the two drugs in the absence of Mn 2+ . We tentatively concluded that Mn 2+ produces late augmentation of the contractile force in neonatal and adult rat myocardia through some action on the general mechanism of force development, rather than by acting specifically on the sarcoplasmic reticulum.

The cardiac in vitro effects of R 80122, a novel phosphodiesterase (PDE) inhibitor, were investigated and compared with those of the reference compound milrinone and of the calcium-sensitizer adibendan. In guinea pig left atria, both milrinone and R 80122 increased contractile force; 10 μM milrinone was equieffective to 1 μM R 80122. The rate of spontaneously beating atria was not altered by R 80122 in the concentration range of 0.01- 0.3 μM. Higher concentrations (1-10 μM) led to a statistically insignificant increase of 20%. Milrinone's effect on frequency was more pronounced and amounted to 21% at 10 μM and to 40% at 100 μM. Adibendan increased heart rate (HR) by 10% at a concentration of only 0.03 μM. This effect was not enhanced any further by increasing the concentration. In papillary muscle, the positive inotropic effects of both milrinone and R 80122 were inhibited by carbachol, indicating involvement of cyclic AMP. Further indications for a cyclic AMP-dependent action were obtained by induction of slow action potentials and synergism with isoprenaline. In electrophysiologic measurements, milrinone reduced action potential duration (APD) in a high concentration whereas R 80122 had no effect. Action potential changes elicited by a toxic concentration of ouabain were reduced by R 80122. Relaxation of rat aortic rings contracted by KCl and relaxation of guineapig aortic rings contracted by norepinephrine (NE) was comparable for both milrinone and R 80122. R 80122 also caused relaxation of canine coronary arteries constricted with prostaglandin F(2α) (PGF(2α)) both with and without endothelium. NE-induced contractions in canine gastrosplenic arteries were not affected by R 80122. Cardiac contractility that had been impaired to various degrees by pentobarbital or by aging was restored to control values by both milrinone and R 80122. R 80122 enhanced cardiac contractility at lower concentrations than milrinone with no concomitant increase in frequency or shortening of the action potential, which may be advantageous for treatment of heart failure.

We compared the oxygen cost of increasing ventricular contractility using Emax (slope of the ventricular end-systolic pressure-volume relation) as the index of ventricular contractility. Contractility was enhanced by calcium and epinephrine in paired experiments on dog left ventricles. Firstly, we obtained left ventricular oxygen consumption (VO2) and systolic pressure-volume area (PVA, a measure of total mechanical energy) of contractions at different volumes in the control contractile state to determine a reference VO2-PVA relation. PVA was obtained as the area in the pressure-volume (P-V) diagram which was bounded by the end-systolic P-V line, end-diastolic P-V curve and systolic P-V trajectory of individual contractions. Secondly, we gradually enhanced Emax with calcium and epinephrine in two consecutive runs at a fixed ventricular volume. Both VO2 and PVA increased with enhanced Emax. From these VO2-PVA data, we calculated the PVA-independent VO2 values at the respective enhanced Emax levels and determined the oxygen cost of Emax as the slope of the relation between the PVA-independent VO2 and Emax. The cost per beat and per 100 g was 0.00158 ml O2/(mmHg/ml) for calcium and 0.00166 ml O2/(mmHg/ml) for epinephrine on average, values not significantly different from each other (P less than 0.05). We conclude that epinephrine and calcium have similar oxygen costs of contractility over a wide range of Emax despite their different pharmacological mechanisms of positive inotropism.

Summary: The propyl derivative of ajmaline, N-n-propylajmaline (prajmalium), is an antiarrhythmic compound that lacks the commonly reported negative inotropic effects of all others under clinical use. The present study was undertaken to establish and understand its effects at the cellular level in mammalian preparations. Electrical and mechanical activities were recorded from right ventricular strips and Na and L-type Ca currents (INa and ICaL, respectively) were recorded with the whole-cell patch-clamp technique in right ventricular myocytes freshly dissociated from rabbit hearts. Prajmalium decreased the maximal rate of depolarization of the action potential in a dose-dependent manner with an EC50 of 3 μM. This effect was use and frequency dependent. Action potential duration was increased by 1 μM prajmalium but decreased on applying higher concentrations. The force of contraction was slightly (15%) increased at 0.1 μM, not affected at all at 1 μ M and depressed by 30% at 20 μM. In single cardiomyocytes maintained at negative holding potentials, INa was slightly depressed by prajmalium at 10 nM and reduced by 75% at 10 μM. ICaL was increased by 30 and 20% on applying prajmalium at 1 and 10 μM, respectively; on the other hand, ICaL was reduced by these two concentrations of prajmalium at less negative holding potentials. A higher prajmalium concentration (100 μM) decreased ICaL at all holding potentials studied and this effect was enhanced with depolarization. The increase in ICaLinduced by prajmalium (1μM) was also observed after ICaL had been fully β-adre-nergic and P2-purinergic stimulated by isoproterenol (1μM) in the presence of IBMX (100 μM) and ATP (10 μM). It is concluded that prajmalium is able to increase ICaLin rabbit ventricular cells in a voltage-dependent manner, an effect that could account in part for the observed lack of negative inotropism of this antiarrhythmic in clinics.

We propose new indexes to evaluate the effects of ventricular inotropism and lusitropism on stroke volume. The end-systolic pressure-volume relationship (ESPVR) or its slope (Emax) has been employed to assess ventricular inotropism. The end-diastolic pressure-volume relationship (EDPVR) or compliance has been used to express ventricular diastolic properties or lusitropism. However, their net effect on stroke volume under a given set of preload and afterload pressures has not quantitatively been evaluated. Ejecting volume gain (Ge) was proposed to quantify the inotropic effect on stroke volume by the change in end-systolic volume between the two ESPVR curves obtained before and during an inotropic intervention at a specified ejecting pressure. Ge is a function of afterload pressure. Filling volume gain (Gf) was proposed to quantify the lusitropic effect on stroke volume by the change in end-diastolic volume between the two EDPVR curves before and during a lusitropic intervention at a specified filling pressure. Gf is a function of preload pressure. The net effect of these inotropic and lusitropic effects on stroke volume at these specified preload and afterload pressures can be expressed by the sum of Ge and Gf. We call this sum stroke volume gain (Gsv). Gsv is a function of preload and afterload pressures. Using representative examples, we demonstrate that these new indexes are conceptually useful to quantitatively understand changes in the pumping ability of the heart under simultaneous inotropic and lusitropic effects as a function of ejecting and filling pressures.

The cardiac in vitro effects of R 80122, a novel phosphodiesterase (PDE) inhibitor, were investigated and compared with those of the reference compound milrinone and of the calcium-sensitizer adibendan. In guinea pig left atria, both milrinone and R 80122 increased contractile force; 10 muM milrinone was equieffective to 1 muM R 80122. The rate of spontaneously beating atria was not altered by R 80122 in the concentration range of 0.01-0.3 muM. Higher concentrations (1-10 muM) led to a statistically insignificant increase of 20%. Milrinone's effect on frequency was more pronounced and amounted to 21% at 10 muM and to 40% at 100 muM. Adibendan increased heart rate (HR) by 10% at a concentration of only 0.03 muM. This effect was not enhanced any further by increasing the concentration. In papillary muscle, the positive inotropic effects of both milrinone and R 80122 were inhibited by carbachol, indicating involvement of cyclic AMP. Further indications for a cyclic AMP-dependent action were obtained by induction of slow action potentials and synergism with isoprenaline. In electrophysiologic measurements, milrinone reduced action potential duration (APD) in a high concentration whereas R 80122 had no effect. Action potential changes elicited by a toxic concentration of ouabain were reduced by R 80122. Relaxation of rat aortic rings contracted by KCl and relaxation of guineapig aortic rings contracted by norepinephrine (NE) was comparable for both milrinone and R 80122. R 80122 also caused relaxation of canine coronary arteries constricted with prostaglandin F2alpha (PGF2alpha) both with and without endothelium. NE-induced contractions in canine gastrosplenic arteries were not affected by R 80122. Cardiac contractility that had been impaired to various degrees by pentobarbital or by aging was restored to control values by both milrinone and R 80122. R80122 enhanced cardiac contractility at lower concentrations than milrinone with no concomitant increase in frequency or shortening of the action potential, which may be advantageous for treatment of heart failure.

We studied effects of hydrolysable tannins on rat papillary muscle contractions induced by propranolol. The developed force of papillary muscle was measured isometrically with an inductive force transducer. The IC 50 values for digallic acid, gallic acid, germin D, praecoxin A and 1-desgalloyl rugosin F were 4.2 × 10 − 5 M, 1.3 × 10 − 4 M, 1,4 × 10 − 4 M, 1.5 × 10 − 4 and 1.7 × 10 − 4 M, respectively. Incubation with tannins significantly attenuated the propranolol-induced negative inotropic contractile response. These results show that hydrolysable tannins depress muscle contractions and potentiate the activities of β-adrenergic blocker.

Chromogranin A (CgA) is the major soluble protein co-stored and co-released with catecholamines (CAs) from secretory vesicles in the adrenal medulla chromaffin cells. Present in the diffuse neuroendocrine system, it has also been detected in rat and human cardiac secretory granules where it co-stores with natriuretic peptide hormones (NPs). Mounting evidence shows that CgA is a marker of cardiovascular dysfunctions (essential hypertension, hypertrophic and dilatative cardiomyopathy, heart failure) and precursor of the cardioactive peptides vasostatin-1 (VS-1) and catestatin (Cts). This review focuses on recent knowledge regarding the myocardial, coronary and anti-adrenergic actions of VS-1. In particular, the negative inotropism, lusitropism and coronary dilation effects of rat CgA1-64 (rCgA) and human recombinant STACgA1-78 (hrSTACgA1-78) are summarized with attention on their counteracting isoproterenol- and endothelin-1-induced positive inotropism, as well as ET-1-dependent coronary constriction. The interactions between vasostatins (VSs), NPs and CA receptors are proposed as a paradigm of the heart capacity to organize complex connection-integration processes for maintaining homeostasis under intense cardio-excitatory stimuli (myocardial stress).

Propofol is a widely used intravenous general anesthetic. The negative inotropic effect of propofol has been best explained by inhibition of the L-type Ca2+ current (ICa). Using guinea-pig cardiac preparations, however, we found that the propofol concentration producing a 50% decrease in force of contraction was more than 10 times higher than that producing a 50% inhibition of ICa, implying that a compensatory mechanism may be present to counteract the negative inotropic effect associated with the ICa inhibition. Consistent with ICa inhibition, propofol produced a shortening of action potential duration (APD) in single cardiomyocytes. Yet, the concentrations necessary to shorten APD were greater than that for 50% inhibition of ICa. This was associated with the potent and effective inhibition of the slowly activating component of the delayed rectifier K+ current (IKs). Thus, the IKs blockade with propofol may counterbalance the APD shortening evoked by its ICa inhibition. Taken together, the negative inotropic effect of propofol is detectable only at supratherapeutic concentrations. At clinically relevant concentrations, the action potential prolongation mechanism due to IKs inhibition appears to alleviate the reduction in transsarcolemmal Ca2+ influx through L-type Ca2+ channels, which may help to counteract the net negative inotropism of propofol. Keywords:: propofol, cardiac contractility, L-type Ca2+ current, delayed rectifier K+ current, cardiac action potential

Introduction The ICH S7A and S7B guidelines require that effects of test substances on the cardiovascular system be assessed with respect to blood pressure, heart rate and electrocardiogram intervals. Where adverse effects are identified additional supplemental studies, including ventricular contractility, should be conducted as deemed appropriate. However, there is an absence of definitive guidance regarding when to pursue supplementary studies, in part due to ill-defined criteria of what constitutes an adverse effect and to surgical/technical monitoring limitations of study designs. However with advances in technology it is now feasible to develop models for assessing LVP and contractility in conjunction with standard assessments. The objectives of this study were to 1) develop a model for chronic evaluation of LVP and contractility, 2) illustrate changes in LV contractility without concurrent proportional changes in heart rate and/or systemic blood pressure and 3) determine if the QA interval, the time between the Q on the ECG and the beginning of the upstroke on the arterial blood pressure, can be used as a indicator of altered LV contractility. Methods Dogs (N = 4) were implanted with a telemetry transmitter. LVP, contractility, ECG and BP were assessed prior to and up to 24 h following administration of Atenolol (10 mg/kg) and Pimobendan (0.45 mg/kg). Results Atenolol caused an ~ 30% decrease in HR, followed by a sustained decrease in maximum left ventricular contractility (+ dP/dt mmHg/s). No effects were noted on blood pressure. Pimobendan caused a 100% increase in contractility (+ dP/dt mmHg/s) which remained elevated for ~ 4 h. No effects were noted on blood pressure. Heart rate was highly variable initial decreasing, followed by a highly variable increase until 4 h postdose. Following administration of both compounds changes in maximum left ventricular contractility correlated with reverse changes in QA interval duration. Discussion This model demonstrates that evaluation of LV contractility complements measurements of heart rate and blood pressure as part of a more complete cardiovascular safety assessment strategy. Furthermore, we demonstrate an apparent correlation between dP/dt and QA interval and concluded that QA interval can be utilized as an indicator of a potential inotropic effect. However further confirmation should be assessed through additional in-vivo measurements of LVP and contractility.

We assessed alpha-adrenoceptor-mediated inotropism in comparison with beta-adrenoceptor-mediated inotropism in whole left ventricle. We used an isolated perfused isovolumic rabbit heart preparation, which enables one to assess contractility and time course of contraction as well as energetic efficiency. Left ventricular pressure (LVP) and volume were measured with an intraventricular fluid-filled balloon. Myocardial oxygen consumption was assessed from the oxygen tension of coronary effluent. Both isoproterenol (n = 7) and phenylephrine (n = 7) increased LV developed pressure (LVDP). Isoproterenol shortened the time to peak pressure (Tmax) from 171 +/- 6 to 142 +/- 7 ms (p less than 0.01) and the time constant of LV pressure decay (TBF) from 44.8 +/- 2.7 to 32.8 +/- 1.9 ms (p less than 0.01). In contrast, phenylephrine slightly but significantly prolonged Tmax from 178 +/- 4 to 184 +/- 4 (p less than 0.05) and did not alter TBF. Both isoproterenol and phenylephrine increased O2 consumption, whereas only phenylephrine increased the force-time integral from 14.0 +/- 1.5 to 17.2 +/- 2.1 g.s (p less than 0.01). These results confirmed in the whole heart preparation that alpha- and beta-adrenoceptor-mediated inotropisms had qualitatively different effects on the time course of contraction and energetic efficiency.

1. 1. Contractile amplitude in the flounder auricle, ventricle and gut fell in response to temperature increase above the normal ambient temperature of 10°C. 2. 2. In whole heart and gut, the preparations were seen to hyperpolarize as temperature increased above 10°C, followed by a secondary depolarization. 3. 3. The amplitude of the cardiac action potential was not affected by temperature increase but the duration of the plateau phase was reduced. The amplitude of ileal muscle slow waves was reduced as temperature increased and above 30°C slow wave generation ceased. 4. 4. Radiocalcium flux studies showed that calcium influx into isolated ventricular and ileal strips fell as temperature was raised above ambient. 5. 5. Radiocalcium efflux from isolated ventricular and ileal muscle microsomes declined as temperature was raised above ambient. 6. 6. The negative inotropism and chronotropism seen with increasing temperature suggests a dysfunction in oscillatory slow wave cycles possibly related to denaturation of the electrogenic Na+/K+ ATPase pump.