Ranolazine Prevents Levosimendan-Induced Atrial Fibrillation.

OBJECTIVES: Levosimendan is a calcium sensitizer that is used as positive inotropic drug in acute decompensated heart failure. An increased incidence of atrial fibrillation after levosimendan-treatment was observed in clinical and experimental studies. Due to the limited range of antiarrhythmic drugs, the aim of the present study was to assess potential antiarrhythmic effects of ranolazine in levosimendan-pretreated isolated rabbit hearts. METHODS: Twelve rabbit hearts were excised and retrogradely perfused employing the Langendorff setup. Left and right atrial catheters were used to record monophasic action potentials and to obtain cycle length-dependent atrial action potential durations (aAPD90) and effective refractory periods (aERP). After obtaining baseline data, 0.5 µmol/L levosimendan was infused. Subsequently, 10 µmol/L ranolazine was administered. RESULTS: Infusion of levosimendan led to a reduction of aAPD90 (-9 ms, p < 0.05) and aERP (-13 ms, p < 0.05). Additional treatment with ranolazine prolonged aAPD90 (+23 ms, p < 0.01) and aERP (+30 ms, p < 0.05). Under baseline conditions, a predefined pacing protocol induced 77 episodes of atrial fibrillation. Infusion of levosimendan enhanced the vulnerability to atrial fibrillation (132 episodes, p = 0.14). Further treatment with ranolazine had a significant antiarrhythmic effect (61 episodes, p < 0.05). CONCLUSIONS: In this study, ranolazine seems to prevent atrial fibrillation in levosimendan-pretreated hearts. Underlying mechanism is a prolongation of atrial repolarization and aERP.

Warhead biosynthesis and the origin of structural diversity in hydroxamate metalloproteinase inhibitors.

Metalloproteinase inhibitors often feature hydroxamate moieties to facilitate the chelation of metal ions in the catalytic center of target enzymes. Actinonin and matlystatins are  potent metalloproteinase inhibitors that comprise rare N-hydroxy-2-pentyl-succinamic acid warheads. Here we report the identification and characterization of their biosynthetic pathways. By gene cluster comparison and a combination of precursor feeding studies, heterologous pathway expression and gene deletion experiments we are able to show that the N-hydroxy-alkyl-succinamic acid warhead is generated by an unprecedented variation of the ethylmalonyl-CoA pathway. Moreover, we present evidence that the remarkable structural diversity of matlystatin congeners originates from the activity of a decarboxylase-dehydrogenase enzyme with high similarity to enzymes that form epoxyketones. We further exploit this mechanism to direct the biosynthesis of non-natural matlystatin derivatives. Our work paves the way for follow-up studies on these fascinating pathways and allows the identification of new protease inhibitors by genome mining.

The BCR-ABL inhibitor ponatinib inhibits platelet immunoreceptor tyrosine-based activation motif (ITAM) signaling, platelet activation and aggregate formation under shear.

BACKGROUND: Treatment of chronic myelogenous leukemia (CML) with the BCR-ABL tyrosine kinase inhibitor (TKI) imatinib significantly improves patient outcomes. As some patients are unresponsive to imatinib, next generation BCR-ABL inhibitors such as nilotinib have been developed to treat patients with imatinib-resistant CML. The use of some BCR-ABL inhibitors has been associated with bleeding diathesis, and these inhibitors have been shown to inhibit platelet functions, which may explain the hemostasis impairment. Surprisingly, a new TKI, ponatinib, has been associated with a high incidence of severe acute ischemic cardiovascular events. The mechanism of this unexpected adverse effect remains undefined. OBJECTIVE AND METHODS: This study used biochemical and functional assays to evaluate whether ponatinib was different from the other BCR-ABL inhibitors with respect to platelet activation, spreading, and aggregation. RESULTS AND CONCLUSIONS: Our results show that ponatinib, similar to other TKIs, acts as a platelet antagonist. Ponatinib inhibited platelet activation, spreading, granule secretion, and aggregation, likely through broad spectrum inhibition of platelet tyrosine kinase signaling, and also inhibited platelet aggregate formation in whole blood under shear. As our results indicate that pobatinib inhibits platelet function, the adverse cardiovascular events observed in patients taking ponatinib may be the result of the effect of ponatinib on other organs or cell types, or disease-specific processes, such as BCR-ABL+cells undergoing apoptosis in response to chemotherapy, or drug-induced adverse effects on the integrity of the vascular endothelium in ponatinib-treated patients.

The gender differences in the relaxation to levosimendan of human internal mammary artery.

PURPOSE: The mechanism of the vasorelaxation to levosimendan varies depending on the vascular bed and species studied. Here, we examined the vasorelaxation to levosimendan as well as its modification by various potassium channel antagonists in human internal mammary artery (IMA) obtained from male and female patients. METHODS: IMA grafts were supplied from 27 male and 19 age-matched female patients undergoing coronary bypass operation. The contraction to noradrenaline and relaxation to levosimendan were studied in IMA rings obtained from both gender. The relaxations to levosimendan were also assessed in the presence of glibenclamide (10 microM), an adenosine triphosphate-sensitive potassium channel (K(ATP)) blocker, or charybdotoxin (100 nM), a calcium-activated potassium channel (K(Ca)) blocker, or 4-aminopyridine(1 mM), a voltage-sensitive potassium channel (K(v)) inhibitor. RESULTS: Concentration-response curves to noradrenaline were not different in IMA rings from either gender. Pretreatment with levosimendan (3 x 10(-7) M) slightly modified the contractions to noradrenaline in both gender. Levosimendan (10(-9)-10(-5) M) produced concentration-dependent relaxation in IMA rings, contracted by noradrenaline (5 x 10(-6) M), from males and females. The vasodilatory effects of levosimendan were more pronounced in the arteries from males (83%) than females (69%), in term of the maximal relaxation (E (max)). Charybdotoxin and glibenclamide significantly inhibited the relaxation to levosimendan in the arteries from males but not in those of females. CONCLUSIONS: The vasodilating efficacy of levosimendan and its relaxation mechanism differs between the arteries from males and females, which may have clinical consequences in the treatment of heart failure.

The role of potassium channels in the vasodilatory effect of levosimendan in human internal thoracic arteries.

OBJECTIVE: We investigated the role of potassium channels in vasodilatory effect of levosimendan in human internal thoracic arteries. METHODS: Samples of redundant internal thoracic arteries obtained from patients undergoing a coronary artery bypass graft surgery were cut into 3 mm wide rings and suspended in 20 ml organ baths. Isometric tension was continuously measured with an isometric force transducer connected to a computer-based data acquisition system. RESULTS: Levosimendan (10(-8)-10(-5) M) or cromakalim (10(-8)-10(-5) M) produced concentration-dependent relaxation responses in human internal thoracic arteries precontracted by 10(-6) M phenylephrine. The relaxant responses to levosimendan did not differ significantly between endothelium-intact and endothelium-denuded preparations. Incubation of human internal thoracic artery rings with adenosine 3',5'-triphosphate (ATP)-dependent potassium channel blocker glibenclamide (10(-6) M) for 30 min significantly inhibited the relaxant responses to both levosimendan and cromakalim. The Ca2+-activated potassium channel blocker iberiotoxin (10(-7) M) also caused a significant but smaller inhibition on relaxant responses to levosimendan. Incubation of the rings with the voltage-dependent potassium channel blocker 4-aminopyridine (5 mM) for 10 min did not cause significant alterations in relaxant responses to levosimendan. CONCLUSIONS: The findings of this study suggested that levosimendan-induced relaxation responses in human internal thoracic arteries were depended on the activation of ATP-dependent and Ca2+-activated potassium channels.

Potassium channel-related relaxation by levosimendan in the human internal mammary artery.

BACKGROUND: Levosimendan is a potent inotropic and vasodilator drug used in the treatment of decompensated heart failure. There is no study on in vitro effects of levosimendan in human isolated arteries. METHODS: We investigated the effect of levosimendan on contractile tone of human isolated internal mammary artery (IMA). The responses in IMA were recorded isometrically by a force-displacement transducer in isolated organ baths. Levosimendan was added to organ baths either at rest or after precontraction with phenylephrine (1 micromol/L). Levosimendan-induced relaxations were tested in the presence of cyclooxygenase inhibitor indomethacin (10 micromol/L), nitric oxide synthase inhibitor N122-nitro-L-arginine methyl ester (100 micromol/L), large-conductance calcium-activated potassium-channel inhibitor tetraethylammonium (1 mmol/L), adenosine triphosphate-sensitive potassium-channel inhibitor glibenclamide (10 micromol/L), and voltage-sensitive potassium-channel inhibitor 4-aminopyridine (1 mmol/L). RESULTS: Levosimendan (10 nmol/L to 3 micromol/L) produced potent relaxation in human IMA (maximal effect, 75.3% +/- 4.9% of phenylephrine maximum contraction, 6.8 +/- 0.1, n = 15; -log10 of 50% effective concentration). Vehicle had no significant relaxant effect. The relaxation to levosimendan is not affected by either potassium-channel inhibitors (tetraethylammonium and 4-aminopyridine) or cyclooxygenase and nitric oxide synthase inhibitors. Glibenclamide (10 micromol/L) inhibited levosimendan-induced relaxation significantly (p < 0.01). CONCLUSIONS: Levosimendan effectively and directly decreases the tone of IMA. The mechanism of levosimendan-induced relaxation in IMA appears in part to be adenosine triphosphate-sensitive potassium-channel opening action. Levosimendan may be a cardiovascular protective agent by its relaxing action on the major arterial graft, IMA.

Levosimendan, a novel Ca2+ sensitizer, activates the glibenclamide-sensitive K+ channel in rat arterial myocytes.

The electrophysiological effect of levosimendan, a novel Ca(2+)-sensitizing positive inotropic agent and vasodilator, was examined on rat mesenteric arterial myocytes using the patch clamp technique. Resting potential was significantly hyperpolarized with levosimendan, with an EC50 of 2.9 microM and maximal effect (19.5 +/- 3.5 mV; n = 12) at 10 microM. Levosimendan (10 microM) significantly increased the whole-cell outward current. The currents intersected close to the calculated EK (-84 mV), suggesting that the activated current was a K+ current. Hyperpolarization and stimulation of K+ current by levosimendan were not prevented by 30 microM H-7 (a non-specific inhibitor of protein kinases) and 100 nM charybdotoxin (a blocker of Ca(2+)-activated K+ channels), but were abolished by 10 microM glibenclamide. In single-channel current recording in open cell-attached patches, two types of K+ channels were observed having conductances of 26 and 154 pS. The 154 pS channels were not affected by levosimendan and glibenclamide. The 26 pS channels were evoked in one-fourth of the patches when 10 microM levosimendan (and 0.1 mM UDP) was added (at -60 mV) and channel activity was abolished by glibenclamide. The mean open probability of the 26 pS channels was 0.094 +/- 0.017 (n = 9), and the mean open time (at -60 mV) was 6.6 ms in the presence of UDP and levosimendan. Although significant hyperpolarization (4.7 +/- 1.5 mV, n = 8) was observed at 1 microM levosimendan, the same concentration did not affect Ca2+ channel currents (n = 10). In summary, levosimendan hyperpolarized the arterial myocytes, probably through activation of a glibenclamide-sensitive K+ channel. This mechanism may contribute to the vasodilating action of levosimendan.

Steroid inhibition of [3H]SR 95531 binding to the GABAA recognition site.

The interaction of three types of steroids with the GABAA recognition site labeled by the antagonist ligand [3H]SR 95531 was evaluated in rat brain cortical membranes. The first type is the GABA site antagonist RU 5135, which potently (IC50 7 nM) but also incompletely (Imax 82%) displaced [3H]SR 95531. RU 5135 probably binds only to high affinity [3H]SR 9553] sites recognized by GABA and unlabelled SR 95531. The second type are the neuroactive steroids which act as positive allosteric modulators, including 3 alpha-hydroxy-5 beta-pregnan-20-one (3 alpha, 5 beta-P) and 5 beta-tetrahydrodeoxycorticosterone (5 beta-THDOC), which inhibited [3H]SR 95531 binding with limited efficacy (IC50 460 nM and 1.4 microM, Imax 41 and 31%, respectively). In contrast, 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha, 5 alpha-P) was inactive. The third type are the neurosteroids acting as negative allosteric modulators, such as pregnenolone sulfate, which inhibited [3H]SR 95531 binding with limited efficacy (IC50 10 microM, Imax 23%). In the presence of a saturating concentration of pregnenolone sulfate, 3 alpha, 5 beta-P further inhibited [3H]SR 95531 binding suggesting that these two steroids act through different sites or, possibly, at different populations of GABAA receptors. The allosteric modulation was selective for steroids since benzodiazepines and barbiturates were inactive up to 100 microM. Taken together, these data suggest that 3 alpha, 5 beta-P and 5 beta-THDOC modulate [3H]SR 95531 binding by interacting with a unique site on the GABAA receptor complex distinct from the sites for 3 alpha, 5 alpha-P, pregnenolone sulfate, GABA, benzodiazepines, and barbiturates.

F 2692: flumazenil-reversible anxiolytic effects but inactive on [3H]-Ro 15-4513 binding.

F 2692, a pyridazine derivative, has little affinity for benzodiazepine receptors, yet in two animal tests its anxiolytic effects have been reported to be reversed by benzodiazepine antagonists. In the rat social interaction test, after 5 days of IP treatment, F 2692 (3, 10, or 30 mg/kg) produced greater increases in social interaction than diazepam (0.3, 1, or 3 mg/kg). A comparison of acute and 5 day administration of F 2692 showed rapidly developing tolerance at all doses. The acute anxiolytic effects of F 2692 (1 mg/kg) were reversed by the benzodiazepine antagonists flumazenil (4 mg/kg) and ZK 93426 (4 mg/kg). We, therefore, examined whether F 2692 was active at a benzodiazepine binding site (the diazepam-insensitive portion of [3H]-Ro 15-4513) to which flumazenil but not flunitrazepam binds. However, F 2692 (10(-9) to 10(-4) M) was without effect on this binding. Thus, F 2692 has anxiolytic actions in the social interaction test, that are greater than those of diazepam, and which can be reversed by benzodiazepine antagonists. However, the site of action of the compound remains unknown.

Post-training minaprine enhances memory storage in mice: involvement of D1 and D2 dopamine receptors.

Post-training administration of minaprine (2.5, 5 and 10 mg/kg) dose-dependently improved retention of an inhibitory avoidance response in mice. Animals receiving nine daily injections of 5 mg/kg and administered a challenge dose post-training showed an improvement in memory consolidation similar to that produced by acute injection of 10 mg/kg. The effects on retention performance induced by the drug appear to be due to an effect on memory consolidation. They were observed when drugs were given at short, but not long, periods of time after training, i.e. when the memory trace was susceptible to modulation. Moreover, these effects are not to be ascribed to an aversive or a rewarding or non-specific action of the drugs on retention performance, as the latencies during the retention test of those mice that had not received a footshock during training were not affected by post-training drug administration. The effects of an acutely injected dose (10 mg/kg) of minaprine as well as those of a challenge dose (5 mg/kg) of the drug administered to repeatedly treated animals were reversed by pretreatment with either selective D1 or D2 dopamine receptor antagonists SCH 23390 and (-)-sulpiride administered at per se non-effective doses (0.025 and 6 mg/kg, respectively), thus suggesting that D1 and D2 receptor types are similarly involved in the effects of minaprine on memory consolidation. These results show that minaprine improves memory consolidation and that repeated drug administration leads to potentiation of this effect. Moreover, the effects of minaprine on memory consolidation are related to its dopaminergic action.

Neuropharmacology of a new potential anxiolytic compound, F 2692, 1-(3'-trifluoromethyl phenyl) 1,4-dihydro 3-amino 4-oxo 6-methyl pyridazine. 1. Acute and in vitro effects.

F 2692 [1-(3'-trifluoromethyl phenyl) 1,4-dihydro 3-amino 4-oxo 6-methyl pyridazine] exhibited dose-dependent "anxiolytic" properties in the elevated plus-maze and the punished drinking tests in rats. It was also active in the two-compartment test in mice. The "anxiolytic" effects were antagonised by the benzodiazepine antagonists, flumazenil and ZK 93426. The compound exhibited anticonvulsant, sedative, myorelaxant and amnesic effects at doses 3-30 times higher than those required for "anxiolytic" activity. F 2692 has a very low affinity for benzodiazepine binding sites in vitro and in vivo (about 1000 and 160 fold lower than diazepam respectively). In addition it displayed no affinity for GABAA, alpha 2-adrenergic, 5-HT1A or 5-HT2 receptors. These data suggest that F 2692 may be a potential anxiolytic compound with an unusual mechanism of action.

Cholinomimetic activity of minaprine is related to the amelioration of delayed neuronal death in gerbils.

We attempted to determine if the cholinomimetic activity of the psychotropic drug minaprine was related to the amelioration of the delayed neuronal death induced by cerebral ischemia in Mongolian gerbils. Minaprine improved the passive avoidance deficit induced by cerebral ischemia, and the histopathological ischemic neuronal changes in the hippocampal CA1 neurons were diminished. These effects were completely inhibited by treatment with the cholinergic blocker scopolamine. Rectal temperature fell about 1.5 degrees C immediately after cerebral ischemia and hyperthermia occurred 30 and 60 min after recirculation. Minaprine had no effect on body temperature before or after ischemia. Physostigmine and tetrahydroaminoacridine (THA), drugs which stimulate the cholinergic system, improved passive avoidance deficits and prevented the delayed neuronal death. These effects of physostigmine and THA were completely inhibited by scopolamine. Pentobarbital and diazepam also improved the passive avoidance deficit and prevented the destruction of CA1 neurons. In contrast with minaprine, these effects of pentobarbital and diazepam were not inhibited by scopolamine. As the protective effect of minaprine against ischemia-induced delayed neuronal death is related to cholinomimetic activities, these events differ from those seen with pentobarbital and diazepam.

Like diazepam, CL 218,872, a selective ligand for the benzodiazepine omega 1 receptor subtype, impairs place learning in the Morris water maze.

The sedative, anxiolytic, and amnesic effects of diazepam were compared to those of CL 218,872, a triazolopyridazine that has a preferential affinity for the benzodiazepine omega 1 receptor subtype. Spontaneous locomotion was assessed using a running wheel, anxiety was assessed using an open-field divided into central and peripheral areas (thigmotaxis), and amnesia was assessed using the Morris water maze. It was found that CL 218,872, like diazepam, depressed spontaneous locomotion, reduced anxiety, and impaired place learning in a dose-dependent manner. Flumazenil, a benzodiazepine receptor antagonist with a similar affinity for both omega 1 and omega 2 subtypes, reversed all of the effects of diazepam and antagonized the anxiolytic and amnesic effects, and some but not all of the sedative effects of CL 218,872. These results suggest that the selective activation of the omega 1 receptor subtype by CL 218,872 is sufficient to produce sedation, anxiolysis, and amnesia in a manner similar to that produced by the coactivation of both the omega 1 and omega 2 receptor subtypes with diazepam.

Role of the endocardium in the inotropic action of UD-CG-212 CL.

UD-CG-212 CL is a metabolite of pimobendan (UD-CG-115 BS), a non-glycosidic, non-adrenergic positive inotropic agent. In the present study we investigated the effect of UD-CG-212 CL on cat papillary muscles in the presence or absence of an intact endocardial endothelium. The endocardium was damaged by a very short detergent treatment. We demonstrated that, in muscles with an intact endocardial endothelium, UD-CG-212 CL induced a moderate, but significant inotropic effect resembling the changes induced by adrenoceptor agonists. Addition of an alpha- and or beta-blocker reduced this positive inotropic effect. The effect induced by UD-CG-212 CL, was completely abolished after the endocardial endothelium was damaged. We conclude that the endocardium played a modulatory role in the action of UD-CG-212 CL through the release of various factors with inotropic activity.

Antihypertensive and renal effects of cilazapril and their reversal by angiotensin in renovascular hypertensive rats.

1. The antihypertensive and renal effects of cilazapril, a new angiotensin converting enzyme inhibitor, were evaluated in both two-kidney, one-clip Goldblatt hypertensive rats (n = 11) and normotensive rats (n = 6). 2. Intravenous infusion of cilazapril (1 mg/kg followed by 25 micrograms min-1 kg-1) caused significant reductions of blood pressure from 163 +/- 3 to 122 +/- 4 mmHg and from 157 +/- 2 to 113 +/- 3 mmHg in two separate groups of hypertensive rats and from 124 +/- 1 to 105 +/- 2 mmHg in normotensive rats. The hypotensive effect in terms of absolute value of percentage change was greater in hypertensive rats than in normotensive rats (41 +/- 6 vs 20 +/- 3 mmHg or 25 +/- 4% vs 16 +/- 2%, respectively). 3. Cilazapril increased glomerular filtration rate, urine flow, and absolute and fractional excretion rates of sodium and potassium in the non-clipped kidney of hypertensive rats. In contrast, the clipped kidney exhibited a depressed renal function during cilazapril infusion. 4. In normotensive rats, the hypotensive and enhanced renal function responses to cilazapril were much less than those of the non-clipped kidney of hypertensive rats. 5. Superimposed administration of either angiotensin II or angiotensin III during cilazapril infusion completely reversed the blood pressure and bilateral renal responses of cilazapril in both hypertensive and normotensive rats. 6. These results indicate that cilazapril reduces arterial pressure and enhances renal excretion mainly via inhibition of angiotensin II and angiotensin III formation.

Behavioral effects of zopiclone, CL 218,872 and diazepam in squirrel monkeys: antagonism by Ro 15-1788 and CGS 8216.

The effects of zopiclone, CL 218,872 and diazepam were compared in squirrel monkeys trained to respond under a fixed-interval (FI) schedule of food presentation. Dose-response curves were determined for each drug by administering cumulative doses i.v. during timeout periods that preceded sequential components of the FI schedule. Low and intermediate doses of zopiclone (0.03-1.0 mg/kg), CL 218,872 (0.3-3.0 mg/kg) or diazepam (0.1-1.0 mg/kg) produced dose-related increases in the rate of FI responding. The highest doses of diazepam (10.0 mg/kg) and CL 218,872 (30.0 mg/kg), but not of zopiclone (30.0 mg/kg), decreased FI responding markedly. Doses of zopiclone, CL 218,872 and diazepam that were effective in increasing FI responding were similar to the doses reported previously to increase suppressed (punished) responding in squirrel monkeys. Pretreatment with the benzodiazepine antagonists Ro 15-1788 or CGS 8216 (1.0 or 3.0 mg/kg) reduced or eliminated the increases in FI responding produced normally by intermediate doses of zopiclone, CL 218,872 or diazepam, suggesting that the rate-increasing effects of the three agonists reflect similar actions at benzodiazepine recognition sites. In contrast, Ro 15-1788 and CGS 8216 were less effective or ineffective in attenuating the marked decreases in FI responding produced by the highest doses of CL 218,872 or diazepam, suggesting that the rate-decreasing effects of these agonists are mediated differently from their rate-increasing effects.

The sedative effects of CL 218,872, like those of chlordiazepoxide, are reversed by benzodiazepine antagonists.

The effects of CL 218,872, initially classified as a non-sedative anxiolytic, were investigated and compared with those of chlordiazepoxide in the holeboard. The ability of two drugs that antagonise the effects of benzodiazepines, CGS 8216 and Ro 15-1788, to reverse the effects of CL 218,872 and chlordiazepoxide were also investigated, to see whether their effects might be mediated via benzodiazepine receptors. CL 218,872 (10 mg/kg) was found to be significantly sedative in both mice and rats (i.e., both locomotor activity and head-dipping were significantly decreased). In mice, the effects of CL 218,872 and of chlordiazepoxide were very similar over a range of doses, except that the stimulatory effect seen with low doses of chlordiazepoxide on head-dipping just failed to reach significance with CL 218,872. This study is in agreement with recently published results from different tests showing that sedative effects can be obtained with doses of CL 218,872 that are low and not much higher than those leading to anxiolysis. The sedative effects of both CL 218,872 (10 mg/kg) and chlordiazepoxide (20 mg/kg) were significantly reversed by RO 15-1788 (10 and 20 mg/kg) and CGS 8216 (10 mg/kg), suggesting that their effects are mediated via benzodiazepine receptors. The increase in head-dipping seen with chlordiazepoxide (2.5 mg/kg) was also reversed by RO 15-1788 and CGS 8216.

UD-CG 115--a cardiotonic pyridazinone which elevates cyclic AMP and prolongs the action potential in guinea-pig papillary muscle.

The mechanism of the positive inotropic effect of a benzimidazole-pyridazinone, UD-CG 115, was analysed in the isolated guinea-pig papillary muscle contracting isometrically at a frequency of 0.2 Hz. UD-CG 115 produced a slowly developing and poorly reversible positive inotropic effect increasing with concentration (3-300 mumol/l). The effect amounted to 30 and 74% of the maximum inotropic effect of a standard, dihydroouabain, at 34 and 300 mumol/l, respectively. Low concentrations shortened and 300 mumol/l UD-CG 115 significantly prolonged the duration of contraction. The enhancement of the maximum rate of relaxation, S2, was intermediate between those produced by isoprenaline and dihydroouabain, respectively. UD-CG 115 prolonged the duration of the transmembrane action potential (90% repol .) by up to 22% at 300 mumol/l, whereas an equieffective concentration of isoprenaline did not consistently alter action potential duration. UD-CG 115 increased Vmax and overshoot, and prolonged the duration, of slow action potentials elicited at 24 mmol/l [K]0. The inotropic potency of UD-CG 115 was not significantly changed by reserpine pretreatment of the guinea pig or by the presence of 1 mumol/l(-)-propranolol, 3 mumol/l phentolamine or 10 mumol/l cimetidine. Neither was it reduced by 10 mumol/l TTX. The inotropic effect of 100 mumol/l UD-CG 115 remained unchanged when [K]0 was elevated from 3.2 to 12.0 mmol/l. A sarcolemmal preparation of guinea- pig ventricular Na,K-ATPase was only slightly inhibited by the highest concentration of UD-CG 115.(ABSTRACT TRUNCATED AT 250 WORDS)

Antioxidation theory of non-steroidal anti-inflammatory drugs based upon the inhibition of luminol-enhanced chemiluminescence from the myeloperoxidase reaction.

The action of non-steroidal anti-inflammatory drugs (NSAIDS) has been ascribed to their ability to block the reaction of arachidonate with cyclooxygenase/peroxidase, thus inhibiting the cellular production of inflammation mediators such as prostaglandins and leukotrienes. However, this and other polymorphonuclear leukocyte (PMN) peroxidases such as myeloperoxidase (MPO) would still be capable of producing destructive oxidants which contribute to inflammation. Sulindac sulfide (Clinoril sulfide) has recently been shown to scavenge oxidant products of prostaglandin cyclooxygenase/peroxidase and MPO. The MPO-H2O2-Cl- reaction is a potent antimicrobial/cytotoxic system which produces HOCl, a strong oxidant. MPO itself has the ability to oxidize drugs and cellular components, and may be the main oxidant in PMN defenses. An antioxidant/free radical scavenger action of NSAIDs against the MPO system could be a primary mechanism of their anti-inflammatory effects. Other antioxidant/free radical scavengers have anti-inflammatory effects. MPO activity has previously been quantified using chemiluminescence (CL). In this study, NSAIDs from various classes were tested for their ability to inhibit luminol-enhanced CL from MPO. The most potent NSAIDs against MPO-CL were BW755C, phenylbutazone, indomethacin and sulindac sulfide. Salicylates and arylacetic acid derivatives, such as naproxen, also decreased MPO-CL. These drugs are also effective against CL from PMNs, of which MPO may be a main source. This effect of NSAIDs on MPO suggests that NSAIDs may impair the killing mechanism of the PMN, preventing cell destruction and release of inflammation mediators. PMN MPO appears to be a target for the antioxidant/free radical scavenging effects of NSAIDs.