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Ethanol lock therapy (ELT) is effective in reducing rates of catheter-related-bloodstream infections (CRBSI) in the pediatric intestinal failure (IF) population; however, ELT may increase the risk of line occlusion and breakage, significantly impacting preservation of vascular access. During a period of ethanol shortage, Health Canada temporarily approved the use of taurolidine lock therapy (TLT) in pediatric iF patients previously utilizing ELT. This provided a unique opportunity to directly compare rates of central venous catheter (CVC) complications, including CRBSi, breaks, occlusions, repairs and replacements in patients who utilized both ELT and TLT.A retrospective study of pediatric IF patients managed by three Western Canadian intestinal rehabilitation programs was performed. Event rates in patients who used both ELT and TLT during the study period were compared using Poisson regression analysis.In 13 patients with 10,187 catheter days (CDs), TLT (vs ELT) had lower rates of CVC breaks (1.11 vs 5.19/1000 CDs, P 0.001), occlusions (0.83 vs 4.06/1000 CDs, P = 0.01) and repairs (1.94 vs 5.64/1000 CDs, P = 0.01). There was no difference in CRBSI rates (0.83 vs 2.03/1000 CDs, P = 0.25) or rates of CVC replacements due to mechanical events (0.28 vs 1.81/1000 CDs, P = 0.08).Although there was no difference in CRBSI rates, TLT was associated with lower rates of mechanical complications compared to ELT in this study. Taurolidine may be a suitable alternative to ethanol in preventing CRBSI and may be associated with improved preservation of central lines in children with IF.

Choosing the best catheter for renal replacement therapy (RRT) is not an easy task. Beyond catheter length, many of its properties can influence effectiveness of the RRT session. Maintenance between sessions, particularly the locking solution, also impacts catheter lifespan and infection rates.Many innovations in dialysis catheters have been proposed by the industry over the past decade, including the material used, the shape of the lumens and the position of the inflow and outflow holes. Impregnated catheters have also been developed to prevent catheter-related infections. Many locking solutions are available, either for maintaining catheter patency or for preventing infections.Although studies conducted in the specific context of the ICU are still scarce, some conclusions can be drawn. Catheter length must be adapted to the insertion site to reach an area of high blood flow. Kidney-shape lumens appear to be less thrombogenic and seem to prevent catheter dysfunction. Catheter tip and lumen holes also affect catheter function. For catheter locking, 4% citrate appears nowadays as one of the best options, but taurolidine-based solutions are also interesting.

This study describes a successful, targeted intervention in central venous access device routine care to decrease central line-associated bloodstream infection. Taurolidine-citrate locks significantly reduced the rate of central line-associated bloodstream infection, particularly Gram-negative organisms without adverse events.

Background Neuroblastoma is a common pediatric solid tumor with poor outcome for metastatic disease. Thus, novel therapeutic options are of main interest. The anti-neoplastic properties of taurolidine have been demonstrated on a variety of human cancer cells. However, data on neuroblastoma is lacking. Therefore, our aim was to evaluate the effect of taurolidine on growth of neuroblastoma cell lines. Materials and methods Neuroblastoma SK-N-BE(2)-M17 and SK-N-SH cells and nonmalignant human umbilical vein endothelial cells as controls were incubated with increasing concentrations of taurolidine (100, 250, 500 µM). Cell growth was examined after 12, 24, and 48 hours of exposure. Results Inhibition of cell growth by taurolidine was seen in both malignant cell lines. When compared with human umbilical vein endothelial cells, the neuroblastoma cell lines were significantly more responsive to taurolidine. Conclusions The observed negative impact on cell growth, highly distinctive in SK-N-BE(2)-M17 and SK-N-SH, implies a taurolidine-specific mode of action that appears dependent on differences on cellular and molecular level. Further investigations are warranted to evaluate its mechanism and probable clinical use.

Rationale: The Ca 2+ sensitivity of the myofilaments is increased in hypertrophic cardiomyopathy and other heart diseases and may contribute to a higher risk for sudden cardiac death. Ca 2+ sensitization increases susceptibility to reentrant ventricular tachycardia in animal models, but the underlying mechanism is unknown. Objective: To investigate how myofilament Ca 2+ sensitization creates reentrant arrhythmia susceptibility. Methods and Results: Using hypertrophic cardiomyopathy mouse models (troponinT-I79N) and a Ca 2+ sensitizing drug (EMD57033), here we identify focal energy deprivation as a direct consequence of myofilament Ca 2+ sensitization. To detect ATP depletion and thus energy deprivation, we measured accumulation of dephosphorylated Connexin 43 (Cx43) isoform P0 and AMP kinase activation by Western blotting and immunostaining. No differences were detected between groups at baseline, but regional accumulation of Connexin 43 isoform P0 occurred within minutes in all Ca 2+ -sensitized hearts, in vivo after isoproterenol challenge and in isolated hearts after rapid pacing. Lucifer yellow dye spread demonstrated reduced gap junctional coupling in areas with Connexin 43 isoform P0 accumulation. Optical mapping revealed that selectively the transverse conduction velocity was slowed and anisotropy increased. Myofilament Ca 2+ desensitization with blebbistatin prevented focal energy deprivation, transverse conduction velocity slowing, and the reentrant ventricular arrhythmias. Conclusions: Myofilament Ca 2+ sensitization rapidly leads to focal energy deprivation and reduced intercellular coupling during conditions that raise arrhythmia susceptibility. This is a novel proarrhythmic mechanism that can increase arrhythmia susceptibility in structurally normal hearts within minutes and may, therefore, contribute to sudden cardiac death in diseases with increased myofilament Ca 2+ sensitivity.

The aim of this study was to review the incidence and type of central venous catheter-related bloodstream infection in children on treatment with home parenteral nutrition (PN) before and after the introduction of taurolidine. Taurolidine is a catheter lock solution that prevents biofilm formation and has broad-spectrum bactericidal and antifungal action. Its use in pediatric patients on PN has only been reported in case studies.A total of 19 children were reviewed, with the diagnoses of enteropathy (8 cases), short bowel syndrome (7 cases), and gastrointestinal dysmotility (4 cases). Incidence and type of sepsis were reviewed for 8 to 12 months pre- (when heparin was used) and 2 to 33 months postintroduction of the taurolidine catheter lock.There were 8.6 episodes of catheter-related bloodstream infections per 1000 catheter days with heparin and 1.1 episodes per 1000 catheter days with taurolidine (P=0.002). A total of 14 of the 19 patients (74%) had no infections for up to 33 months after changing to taurolidine. No reports of multiresistant organisms or adverse effects with taurolidine were found.Taurolidine line lock was associated with a decreased incidence of catheter-related bloodstream infections. This finding supports its use in patients with a history of septicemia on treatment with cyclical PN.

BACKGROUND:: Sometimes, a temporary increase in alkaline phosphatase level is found in healthy infants and toddlers without evidence of liver or bone disease. The condition is customarily termed transient benign hyperphosphatasemia of infancy and early childhood. Most textbooks do not refer to the condition. METHODS:: We completed a systematic review of the literature using the principles underlying the UK Economic and Social Research Council guidance on the conduct of narrative synthesis and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. RESULTS:: The 142 reports retained for analysis included 813 cases (male:female ratio = 1.1:1.0): 80 in subjects >18 years and 733 in subjects ≤18 years of age. The alkaline phosphatase ratio, calculated by dividing the measured level by the upper normal limit, was ≥5.0 in ≈70% and the duration of the elevation ≤4 months in 80% of the cases. Transient benign hyperphosphatasemia often followed a benign infection but available data fail to demonstrate a causal link. The prevalence of transient benign hyperphosphatasemia ranged 1.1-3.5% in infants 2 to 24 months of age. CONCLUSIONS:: Transient benign hyperphosphatasemia is likely the most common cause of hyperphosphatasemia among healthy infants and toddlers. Sometimes, it also occurs in older children and adults, indicating that the traditional term transient benign hyperphosphatasemia of infancy and early childhood might not be correct. The elevation in alkaline phosphatase persists for >4 months in ≈20% of the cases. Recognition of this benign condition is crucial to avoid unnecessary investigations.

The annual incidence of malignant melanoma is estimated at 10-12 per 100000 inhabitants in countries of Central Europe and the US, with more recent estimates showing a dramatic upward trend. Taurolidine (Carter/Wallace, Cranberry, NJ) is a novel, potentially effective, antitumor chemotherapeutic agent. We hypothesized that Taurolidine could inhibit the growth, induce apoptosis, affect the cell cycle and change morphology of melanoma cells. We expected this process to be different in adherent and floating subpopulations that may be reflective of solid tumors and their metastases. Analysis of MNT-1 human and B16F10 murine melanoma cells showed that at 72 h the IC(50) of Taurolidine was 25.4+/-3.3 microM for MNT-1 human melanoma cells and 30.9+/-3.6 microM for B16F10 murine melanoma cells. Taurolidine induced DNA fragmentation of melanoma cells in a dose-dependent manner. Taurolidine (75 and 100 microM) induced 52-97% Annexin-V binding (apoptosis), respectively. Evaluation of cell cycle after 72 h exposure to Taurolidine (0-100 microM) revealed that the percentage of melanoma cells in S phase increased from 27 to 40% in the adherent subpopulation and from 33 to 49% in the floating subpopulation. Phase contrast microscopy revealed a marked swelling of melanoma cells and decreasing cell numbers in adherent subpopulation starting at 24 h with 25 microM Taurolidine. Shrinkage of cells dominated at 75-100 microM Taurolidine. Using Cytospin assay in the floating population, we observed swelling of melanoma cells induced by 25-100 micro Taurolidine and appearance of giant (multinuclear) forms resulting from exposure to 75-100 micro Taurolidine. Some floating cells with normal morphology were observed with low concentrations of Taurolidine (0-25 microM). These data show that effects of Taurolidine may be different in adherent and floating subpopulations of melanoma cells. More importantly, floating subpopulations that may contain some viable melanoma cells, may be reflective of potential metastasis after treatment of solid tumors in vivo.

The purpose of this study was to determine if prereatment with taurolidine, a known anti-endotoxin agent, would attenuate the hemodynamic and respiratory responses associated with endotoxin induced lung injury in a large animal model in a randomized controlled study under license from the Department of Health. All animals underwent a general anesthetic. Vascular catheters were placed in the femoral artery and in the femoral vein. A Swan-Ganz Catheter was inserted for measurement of pulmonary artery pressure. Animals were randomized into three groups: Control, with measurements taken at baseline and half hourly up to 90 min; Endotoxin, receiving 5microg/Kg E. coli endotoxin intravenously after baseline measurements; and Endotoxin + Taurolidine, receiving 5g of taurolidine via intraperitoneal infusion 1 h before endotoxin administration. Main outcome measures were mean systemic arterial pressure (MAP), mean pulmonary arterial pressure (MPAP), arterial oxygen tension (pO2), serum endotoxin concentration, and pulmonary myeloperoxidase. Endotoxin induced a significant lung injury characterized by an increase in pulmonary artery pressure, hypoxia, and systemic hypotension. Pretreatment with intraperitoneal taurolidine significantly attenuated these hemodynamic and respiratory changes. Serum endotoxin concentration was also significantly reduced as was lung myeloperoxidase. The data suggest that taurolidine may have a therapeutic role in preventing the lung injury seen in endotoxemia.

The thiadiazinone derivatives EMD 60417, EMD 66430, and EMD 66398 were developed as class III antiarrhythmic agents. Their chemical structure is closely related to that of their calcium-sensitizing congener |+|-EMD 60263, and EMD 66398 possesses the methylsulfonylaminobenzoyl moiety present in the prototypical I Kr blocker E-4031, We compared the electrophysiologic effects of these compounds with standard drugs (almokalant, E-4031, quinidine) in cardiac myocytes from guinea-pig ventricle and human atrium by whole-cell patch-clamp technique. The test compounds' class III action, which is related to impairment of K + channel function, was confirmed by action potential measurements. EMD 60417, EMD 66430, EMD 66398, and almokalant (1 μM each) reversibly prolonged the action potential duration in guinea-pig myocytes. In the same cells, the rapidly activating component I Kr of the delayed rectifier K + current, which has been defined by its sensitivity to E-4031, was reduced by EMD 60417, EMD 66430, EMD 66398, and almokalant. Inhibition of I Kr was concentration-dependent as determined by attenuation of tail currents. The slowly activating component I Ks of the delayed rectifier K + current was not affected. The inward rectifier K + current I K1 was not influenced at potentials close to the reversal potential. Transient and sustained outward K + currents (I to , I so ) measured in human atrial myocytes were not altered by any EMD compound. L-type Ca 2+ current was hardly affected at concentrations of 1-10 μM, but sodium current was decreased. Action potential prolongation by EMD 60417, EMD 66430, and EMD 66398 is due to block of I Kr . I Na is inhibited at higher concentrations by EMD 66430 and EMD 60417. EMD 66398 is more potent and selective for I Kr than EMD 60417 and EMD 66430, and thus resembles E-4031 in structure and function.

Calcium sensitizers increase myocardial contractile function without affecting Ca2+ homeostasis, which might be beneficial in the treatment of patients with heart failure. However, it remains uncertain whether Ca sensitizers induce quantitatively similar inotropic responses in control and failing hearts. To compare their effects in normal versus failing hearts at the cellular level, shortening mechanics and intracellular calcium ([Ca2+]i) transient were simultaneously measured in the left ventricular myocytes isolated from normal dogs (n = 8) and dogs with rapid pacing-induced heart failure (n = 7). CGP 48506 and EMD 57033 exerted a positive inotropic effect in a dose (0.1-3 microM)-dependent manner in both normal and heart failure myocytes. The percent increase of cell shortening magnitude was comparable between the two groups. CGP 48506 and EMD 57033 did not affect the diastolic cell length and resting [Ca2+]i level. They did not affect the duration of [Ca2+]i transient dynamics. Thus Ca2+ sensitizers exerted comparable positive inotropic effects without affecting the rest cell length and rest [Ca2+]i in normal and heart failure myocytes.

Objective : To assess the benefit gained from administration of the antiendotoxic drug, taurolidine, on outcome in critically ill patients with sepsis syndrome. Design : A prospective, randomized, double-blind trial Setting : The general intensive therapy unit in a university teaching hospital. Patients : One hundred patients admitted with sepsis syndrome over a 2-yr period. Interventions : Patients were randomized to receive the amino-acid derivative, taurolidine, or an identically presented placebo. Measurements and Main Results : Acute Physiology and Chronic Health Evaluation II (APACHE II), sepsis, and organ failure scores were measured daily. Blood for culture and endotoxin assay (using the limulus amoebocyte lysate assay) was sampled every 12 hrs for up to 5 days. Hemodynamic variables were recorded every 4 hrs. Forty-nine patients received taurolidine and 51 patients received placebo. There was no difference in APACHE II score, Sepsis Score, or presence of infections between the groups. The frequency of Gram-negative bacteremia was low at 12%. There was no difference in endotoxin activity, clinical or bacteriologic outcome, resolution of organ failure, or mortality rate between groups. Predicted risk of death for patients receiving taurolidine was 45%, and the actual mortality rate was 44%. In the group that received placebo, the predicted mortality rate was 38% and the actual mortality rate was 39%. Conclusion : Taurolidine had no beneficial therapeutic effect on the outcome of patients admitted to the intensive therapy unit with sepsis syndrome, using clinical, bacteriologic outcomes, progression of endotoxemia, resolution of organ failure, and 28-day mortality rate as end points. (Crit Care Med 1995 ; 23 :1033-1039)

Levosimendan is a novel positive inotropic drug targeted to increase contraction force of the heart through its calcium-dependent binding to troponin C (cTnC). We investigated the calcium-sensitizing effect of levosimendan on contractile proteins as well as its positive inotropic and lusitropic effects in paced guinea pig papillary muscle. We also studied the effect on energy consumption of myosin-actin crossbridges in a myosin ATPase assay. The calcium sensitization induced by levosimendan in fibers skinned with saponin was dependent on the perforation velocity of cell membranes. Levosimendan was almost ineffective in slowly perforated fibers, but was the most potent calcium sensitizer in fibers with rapidly perforated cells. The perforation-dependent calcium sensitization was probably due to changes in phosphorylation state of contractile proteins during the slow dissection of fibers. It is noteworthy that the calcium-sensitizing effect of levosimendan was not affected by acidic pH. Levosimendan at therapeutically relevant (0.3-10 microM) concentrations markedly increased calcium sensitivity both at pH 6.7 and 7.0, being more potent than EMD 53998, pimobendan, and MCI-154. The lack of effect of levosimendan on maximum tension supports the hypothesis that levosimendan increases calcium sensitivity through its action on cTnC. Unlike EMD 53998, levosimendan did not increase myosin ATPase activity, indicating that it did not increase the cycling rate of myosinactin crossbridges. In paced papillary muscles, levosimendan induced positive inotropic effect without changing relaxation time. Thus, levosimendan was devoid of the main negative factors described for calcium sensitizers.

In papillary muscles from reserpinized guinea pigs, EMD 57033, the most potent Ca 2+ -sensitizer known, effectively increased force of contraction (FOC) and concomitantly increased duration of contraction. In isolated 32 P-labeled guinea pig ventricular cardiomyocytes, EMD 57033 increased the phosphorylation state of phospholamban as well as the inhibitory subunit of troponin, which are usually linked to reductions in contraction time. Therefore, EMD 57033 dissociates phospholamban-phosphorylation and effects on contractile parameters, probably owing to its strong Ca 2+ -sensitizing properties

Calcium sensitizers may influence myocardial energetics by their action on calcium turnover and on crossbridge behavior. Using a myothermal method, the effects of the Ca2+ sensitizer EMD-53998 on calcium cycling, crossbridge behavior, and myocardial energy turnover were compared with the effects of an increase in extracellular calcium from 1.25 to 7.5 mM and with the effects of the catecholamine isoproterenol. All three inotropic interventions increased isometric force development in right ventricular rabbit papillary muscles. Relaxation time was decreased with isoproterenol, unchanged with high calcium, and increased with EMD 53998. Calcium cycling-related energy consumption, as measured by tension-independent heat, increased by 234% with high calcium, by 439% with isoproterenol, and by 77% with EMD 53998. In contrast to high calcium and isoproterenol, EMD 53998 increased economy of crossbridge cycling by increasing the force-time integral of the individual crossbridge cycle. The data indicate that EMD 53998 acts by phosphodiesterase inhibition and myofilament calcium sensitization. The latter effect is in part mediated by alteration of crossbridge behavior. Because of its effects on calcium cycling and crossbridge function myocardial energy turnover was reduced significantly with EMD 53998, whereas energy turnover was unchanged with high calcium and was increased with isoproterenol. The new calcium sensitizer levosimendan was investigated in isolated failing human myocardium. Levosimendan dose-dependently increased isometric tension. The inotropic effect was associated with increased rate of relaxation and reduced relaxation time. Measurements of intracellular calcium using the photoprotein aequorin suggest that levosimendan acts by increasing myofilament calcium sensitivity and by increasing cAMP due to phosphodiesterase inhibition. However, the contribution of the cAMP system to the action of levosimendan appears to be rather small. Therefore, the finding of a positive lusitropic effect of levosimendan may be consistent with the notion that levosimendan binds to troponin-C and increases calcium sensitivity only at high (systolic) intracellular calcium concentrations.

The two isomers of the positive inotropic compound EMD 53998, (+)EMD 57033 and (-)EMD 57439, possess selective calcium sensitizing and phosphodiesterase (PDE) inhibitory properties, respectively. We measured the pharmacological responses to both enantiomers in isolated rat cardiac and vascular tissues and in muscles from severely failing human hearts. We also measured positive inotropic and chronotropic responses to EMD 57033 in cardiac tissues from rats with thyroid dysfunction, diabetes, or hypertension. Both compounds increased force of contraction in isolated rat cardiac tissues, although the ventricular response to EMD 57439 was only approximately 10% that of calcium chloride. Forskolin pretreatment potentiated responses to both compounds in atria but only to EMD 57439 in ventricles. Hyperthyroidism increased ventricular responses to EMD 57033 relative to calcium chloride; hypothyroidism and diabetes decreased these responses. Ventricular responses were unchanged in hypertensive rats. Both enantiomers produced positive inotropy in human isolated right atrial trabeculae, although the maximal increases were only 14% (EMD 57033) and 26% (EMD 57439) that of calcium chloride. In rat thoracic aortic rings, both enantiomers produced relaxation; the responses due to EMD 57033 were endothelium dependent. Thus, calcium sensitization produces positive inotropy and vascular relaxation in rats. Positive chronotropic responses to EMD 57033 are most likely due to PDE inhibition. The limited inotropic response in severely failing human myocardium, together with possible vasorelaxation, may provide cardiac support in heart failure without an excessive increase in cardiac O2 demand.

BACKGROUND Most positive inotropic agents increase cardiac contractility by increasing the amount of Ca2+ cycled with each beat. The additional amount of oxygen that is consumed by the heart to cycle this additional Ca2+ is believed to reduce myocardial efficiency. On the other hand, it has been suggested that the agent EMD-53998 increases the Ca2+ sensitivity of the contractile proteins without affecting the intracellular Ca2+ transient in cardiac muscle. Therefore, application of this agent may increase cardiac contractility without decreasing myocardial efficiency. The purpose of the present study was to test this hypothesis. METHODS AND RESULTS We measured myocardial oxygen consumption (MVO2) in six isolated, isovolumically beating blood-perfused canine hearts. The hearts were paced at 120 beats per minute. Contractility was varied in each heart by infusion of either CaCl2 or EMD-53998. With infusion of either agent, MVO2 was a linearly proportional function of contractility. No significant difference between CaCl2 and EMD-53998 could be detected in the interrelation between contractility and MVO2. CONCLUSIONS We conclude that the "calcium-sensitizing agent" EMD-53998 is a potent positive inotropic agent in the isolated, blood-perfused canine heart. However, EMD-53998 does not provide an energetic advantage over currently used positive inotropic agents.

The inotropic state of the myocardium can be enhanced via an increase in cell Ca2+ loading or in myofilament responsiveness to Ca2+. Although different pharmacological agents combine these properties, no presently available drug acts predominantly as a myofilament sensitizer in situ. We have investigated the effects and the mechanism of action of novel diazinone derivatives, EMD 54622, EMD 53998, and EMD 54650 (developed by E. Merck, Darmstadt), on guinea pig myocardial preparations. Force- and ATPase-pCa relations in skinned fibers show differing potencies of these agents on myofilament sensitization: EMD 54622 greater than EMD 53998 much greater than EMD 54650. This is in contrast to their relative potencies to inhibit isolated myocardial phosphodiesterase III: EMD 54650 greater than EMD 53998 greater than EMD 54622. In isolated hearts studied at constant coronary flow, each of the three diazinone derivatives had a positive inotropic effect. In enzymatically dissociated left ventricular myocytes loaded with the Ca2+ probe indo-1, the positive inotropic effect of EMD 54622 occurred with no change in the amplitude of the cytosolic [Ca2+] (Cai) transient. In contrast, both EMD 53998 and EMD 54650 enhanced Cai transient and twitch contraction amplitudes. Length-indo-1 fluorescence relations were analyzed to determine the effects of the three substances on myofilament responsiveness to Ca2+. EMD 54622 enhanced and EMD 54650 had no effect on myofilament responsiveness to Ca2+. Less uniform results were obtained with EMD 53998 (in two of five cells the myofilament responsiveness to Ca2+ was increased, whereas in three other cells it was unaltered). Our results indicate that structural changes in the diazinone molecule shift the mechanism of action for the positive inotropic effect of the diazinone derivatives in the intact cell from a predominant myofilament sensitization (EMD 54622) to an enhancement in cell Ca2+ loading and an augmentation in the Cai transient (EMD 54650).

The effect of a new cardiotonic agent Y-20487 [6-(3,6-dihydro-2-oxo-2H-1,3,4-thiadiazin-5-yl)-3,4-dihydro-2(1H)- quinolinone] on cyclic AMP levels of rat ventricular cardiomyocytes and the contractile force of papillary muscles was investigated in comparison with selective cyclic AMP phosphodiesterase (PDE) inhibitors, milrinone (PDE-III selective), rolipram and Ro 20-1724 (PDE-IV selective), and a nonselective inhibitor 3-isobutyl-1-methylxanthine (IBMX). Rolipram and Ro 20-1724 did not elicit cyclic AMP accumulation and positive inotropy, but they potentiated the isoproterenol (ISO)-induced cyclic AMP accumulation more effectively than IBMX. Rolipram was more effective than Ro 20-1724 in enhancing ISO-induced cyclic AMP accumulation but was less effective in enhancing the ISO-induced positive inotropic effect, indicating that these agents produce a differential action on cyclic AMP metabolism and inotropy. Milrinone and Y-20487 elicited cyclic AMP accumulation and positive inotropy by themselves. Whereas milrinone scarcely affected the ISO-induced effects, Y-20487 shifted the concentration-response curve for the positive inotropic effect of ISO to the left to the same extent that IBMX did. Y-20487, however, was much less effective than IBMX in enhancing the ISO-induced cyclic AMP accumulation. The present results indicate that in rat ventricular myocardium, PDE-IV may play a crucial role in breakdown of cyclic AMP generated by beta-adrenoceptor stimulation, whereas other types of PDE isoenzymes, including PDE-III, may be responsible for the cyclic AMP accumulation and direct positive inotropic effect induced by PDE inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

EMD 53998 (a thiadiazinone) is an inotropic drug that produces a pronounced increase in the Ca2+ sensitivity of the contractile proteins in skinned cardiac fibers. The present study was undertaken to determine whether this effect on Ca2+ sensitivity could explain the increase in tension observed in intact ventricular muscle. The experiments were performed on isolated ferret papillary muscles that had been microinjected with aequorin to measure the intracellular Ca2+ concentration. Force and intracellular Ca2+ concentration were monitored before, during, and after application of EMD 53998. EMD 53998 (5 microM) increased developed tension by 230%; aequorin light transients increased by only 85%, and this increase was reduced and became insignificant in the presence of agents that prevent catecholamine release. When a similar increase in developed tension was produced by elevation of extracellular calcium, the aequorin light transients increased by 240%. Thus, EMD 53998 produces a substantial Ca2+ sensitization in intact ventricular muscle, and this can explain most of its inotropic effect. In addition, EMD 53998 caused a small prolongation of the time course of contraction and a small reduction of the time course of the aequorin light transient. A computer model is described that shows that both these effects can be explained by the effect of EMD 53998 on Ca2+ sensitivity. At much higher concentrations, EMD 53998 also caused an increase in resting tension. EMD 53998 is the first agent for which much of the inotropic effect in intact cardiac muscle can be accounted for by increased Ca2+ sensitivity of the contractile proteins. Inotropic agents with this mechanism of action cause increased force production with much less increase in the intracellular Ca2+ transients than conventional agents and, therefore, increase the energy efficiency of the myocardium and are less likely to cause Ca(2+)-activated arrhythmias.

EMD 53 998, a novel thiadiazinone derivative, increases the contractile force of cardiac tissue in vitro through both an inhibition of phosphodiesterase III (PDE III) and a sensitization of cardiac contractile proteins to Ca2+. Guinea pig ventricular PDE III is selectively inhibited by EMD 53 998 (IC50 = 60 nM) without major effects on other PDE isoenzymes. Consonant with this is an increase in cAMP content of rat ventricular cells and a potentiation by EMD 53 998 of the cAMP-elevating action of isoprenaline (increase by 50% at 1.3 microM). Sensitization to Ca2+ by EMD 53 998 (3-30 microM) finds its expression in a leftward shift of the Ca2+ response curve for force generation in skinned fibers from porcine ventricular muscle and failing human heart as well as for activation of bovine cardiac myofibrillar actomyosin ATPase. Interestingly, EMD 53 998 elevates the maximum of the Ca(2+)-response curve for both parameters. Pimobendan studied under identical conditions was 100 times less potent than EMD 53 998. EMD 53 998 increases force development of guinea pig papillary muscle in a concentration-dependent manner with an EC50 of 3.6 microM, thus being 10 times more potent than pimobendan. In contrast to pimobendan, the positive inotropic effect of EMD 53 998 is barely affected by carbachol. Further evidence for a Ca(2+)-sensitizing effect of EMD 53 998 is provided by an additional increase in force generation in the presence of supramaximal isoprenaline concentrations. It is concluded that the positive inotropic action of EMD 53 998 is mediated through both cAMP-independent and cAMP-dependent mechanisms, with the former probably prevailing. We are not aware of other compounds with a similarly high Ca(2+)-sensitizing potency. On these grounds. EMD 53 998 appears to be a promising inotropic agent.