Effects of diltiazem upon globally ischemic rat hearts

Safety pharmacology of sibutramine mesylate, an anti-obesity drug

Sibutramine mesylate is a new anti-obesity drug. It is a crystalline salt of sibutramine developed to improve the solubility of sibutramine hydrochloride. Methanesulfonic acid was used as a salt-forming acid instead of hydrochloric acid, resulting in a greatly improved solubility of 1000 mg/mL in water. Sibutramine mesylate was administered orally to ICR mice, Sprague / respiratory system and the other organ systems. Following administration of sibutramine mesylate, spontaneous locomotor activity was significantly increased from 120 min to 24 hours at 3.45 mg/kg and from 30 min to 24 hours at 11.50 mg/kg. Furthermore, there were a decrease in hexobarbitalinduced sleep time, an increase in respiratory rate at 120 min, increases in intestinal transport capacity and gastric pH at 11.50 mg/kg, and decreases in gastric / Dawley rats, and beagle dogs at dose levels of 1.15, 3.45, and 11.50 mg/kg to measure its effects on the central nervous system (CNS), general behaviour, cardiovascular volume and total acidity at 3.45 and 11.50 mg/kg. However sibutramine mesylate caused no effects on general behaviour, motor coordination, body temperature, analgesia, convulsion, blood pressure, heart rate, electrocardiogram, cardiac functions of the isolated rat heart, isolated smooth muscles and renal function. Based on the above results, it was concluded that sibutramine mesylate caused effects on the spontaneous locomotor activity, hexobarbital-induced sleep time, respiration, gastrointestinal transport, and gastric secretion at a dose level of 3.45 mg/kg or greater but caused no effects on other general pharmacological reactions.

General Pharmacology of Artesunate, a Commonly used Antimalarial Drug:Effects on Central Nervous, Cardiovascular, and Respiratory System

Artesunate, a semi-synthetic derivative of artemisinin, is used primarily as a treatment for malaria. Its effects on the central nervous system, general behavior, and cardiovascular, respiratory, and other organ systems were studied using mice, rats, guinea pigs, and dogs. Artesunate was administered orally to mice at doses of 125, 250, and 500 mg/kg and to rats and guinea pigs at 100, 200, and 400 mg/kg. In dogs, test drugs were administered orally in gelatin capsules at doses of 50, 100, and 150 mg/kg. Artesunate induced insignificant changes in general pharmacological studies, including general behavior, motor coordination, body temperature, analgesia, convulsion modulation, blood pressure, heart rate (HR) , and electrocardiogram (ECG) in dogs in vivo; respiration in guinea pigs; and gut motility or direct effects on isolated guinea pig ileum, contractile responses, and renal function. On the other hand, artesunate decreased the HR and coronary flow rate (CFR) in the rat in vitro; however, the extent of the changes was small and they were not confirmed in in vivo studies in the dog. Artesunate increased hexobarbital-induced sleeping time in a dose-related manner. Artesunate induced dose-related decreases in the volume of gastric secretions and the total acidity of gastric contents, and induced increases in pH at a dose of 400 mg/kg. However, all of these changes were observed at doses much greater than clinical therapeutic doses (2.4 mg/kg in humans, when used as an anti-malarial) . Thus, it can be concluded that artesunate is safe at clinical therapeutic doses.

General Pharmacology of CKD-732, a New Anticancer Agent: Effects on Central Nervous, Cardiovascular, and Respiratory System

CKD-732 [6-O-(4-dimethylaminoethoxy) cinnamoyl fumagillol hemioxalate] is a new fumagillin anticancer drug that belongs to an angiogenesis inhibitor. Its effect on the central nervous system (CNS), general behavior, cardiovascular-respiratory system and the other organ systems were studied. CKD-732 was intravenously administered with the dosages of 10, 30, 40 or 50 mg/kg and the highest dosage of 50 mg/kg prolonged the hexobarbital-induced sleep time. CKD-732 at the dosage of 50 mg/kg, also, caused the decrease of body temperature from 15 to 120 min after the administration, which was recovered at 240 min. In the study of the effects on gastric secretion, CKD-732 induced the increase of pH and decrease of total acidity. However, CKD-732 showed no effect on general behavior, spontaneous locomotor activity, motor coordination, analgesia, convulsion, mean arterial pressure, and cardiac functions except for heart rate of isolated rat heart, respiration, isolated smooth muscle, intestinal charcoal transport and renal function. Based on the results, we suggested that CKD-732 is safe general pharmacologically at clinical supposed dose (1.75 mg/kg) and demonstrated to have much better safety than other fumagillin derivatives.

General Pharmacology of DW-286a, a New Fluoronaphthyridone Antibiotic: Effects on Central Nervous, Cardiovascular, and Respiratory Systems

DW-286a is a new class of fluoronaphthyridone antibiotic. Its effect on the central nervous system, general behavior, and cardiovascular, respiratory, and other organ systems were studied. The doses given were 30, 50, 100, 150, 300, and 1000 mg/kg and drugs were administered orally. DW-286a did not show any effects on general behavior, motor coordination, analgesic action, seizure and mortality, blood pressure and heart rate, contractile response of isolated guinea pig ileums, and renal function. On the other hand, DW-286a decreased spontaneous locomotor activity from 120 to 240 min after administration at the doses of 300 and 1000 mg/kg and the respiration rate from 30 to 240 min after the administration of doses up to 100 mg/kg. The sleeping time and body temperature were increased significantly in mice at the dose of 1000 mg/kg. DW-286a increased the charcoal transport significantly at doses of 300 and 1000 mg/kg. DW-286a inhibited gastric acid secretion, reduced the volume of the gastric juice and total acidity, and increased the pH dose dependently. Based on the above results, it was concluded that DW-286a affects spontaneous locomotor activity, respiration and body temperature, gastrointestinal transport, gastric secretory action, and hexobarbital sleeping time at high doses.

Oxidant stress with hydrogen peroxide attenuates calcium paradox injury: role of protein kinase C and ATP-sensitive potassium channel

OBJECTIVE

We tested the hypotheses that low concentration of H2O2 attenuates the Ca2+ paradox (Ca2+ PD) injury, and that activation of protein kinase C (PKC) and/or ATP-sensitive potassium channel (KATP) are involved in the protective effects of H2O2.

METHODS

Langendorff-perfused rat hearts were subjected to the Ca2+ PD (10 min of Ca2+ depletion followed by 10 min of Ca2+ repletion). Functional and biochemical effects of H2O2 and other interventions on the cell injury induced by the Ca2+ PD were assessed.

RESULTS

In the Ca2+ PD hearts pretreated with 20 mumol/l H2O2, left ventricular end-diastolic pressure and coronary flow were significantly preserved. Furthermore, peak lactate dehydrogenase release was significantly decreased and ATP contents were more preserved, compared with non-treated Ca2+ PD hearts. H2O2-treated hearts also showed remarkable preservation of cell structure. Addition of a specific PKC inhibitor, chelerythrine during H2O2 treatment completely abolished the beneficial effects of H2O2 on the Ca2+ PD. Similarly, an activator of PKC. Phorbol 12-myristate 13 acetate mimicked the protection by H2O2. Furthermore, pretreatment with a KATP opener, cromakalim also provided protection similar to H2O2 against the Ca2+ PD injury. However, a specific KATP inhibitor, glibenclamide was not able to completely block the effects of H2O2.

CONCLUSIONS

These findings suggest that pretreatment with low concentration of H2O2 provides significant protection against the lethal injury of Ca2+ PD in rat hearts. PKC-mediated signaling pathways appear to play a crucial role in the protection against the Ca2+ PD injury.

Cardioprotective effects of KR-30450, a novel K+(ATP) opener, and its major metabolite KR-30818 on isolated rat hearts

The cardiac effects of KR-30450 ((-)-(2R)-2-([1,3]-dioxolan-2-yl)-2-methyl-4-(2-oxopyrrolidin++ +-1-yl)-6-nitro-2H-1-benzopyran), a newly synthesized potassium channel activator, and its major metabolite KR-30818 ((-)-(2R)-2-hydroxymethyl-2-methyl-4-(2-oxopyrrolidin-1-yl)-6-nitr o-2H-1-benzopyran) were compared with those of lemakalim, a prototype of this class, in isolated globally ischemic rat hearts. KR-30450 and KR-30818 significantly improved reperfusion cardiac function (LVDP, left ventricular developed pressure; double product, LVDP x heart rate/1000), their potency being 5.2-fold and 0.7-fold greater than lemakalim (ED50 for recovering predrug double product: 0.10, 0.80 and 0.54 microM, respectively). KR-30450 and KR-30818 significantly attenuated reperfusion contracture and lactate dehydrogenase release with potency greater than and equal to lemakalim, respectively. They significantly increased time to contracture (TTC) during ischemia in a dose-dependent manner with a greater potency than lemakalim (EC25 for increasing TTC: 1.2, 2.1 and 3.2 microM, respectively). The protective effects of three compounds on the measured parameters were reversed by glyburide, a selective K+(ATP) blocker. In non-ischemic hearts, KR-30450 and lemakalim exerted weak negative inotropism at high concentrations and KR-30818 had no effects, whereas the three compounds significantly increased coronary flow at doses studied. Glyburide completely reversed preischemic cardiodepressant effects of these compounds but not their effects on coronary flow. In conclusion, KR-30450, a recently developed K+(ATP) opener, exerted more potent cardioprotective effects than lemakalim, and its major metabolite KR-30818 may play a significant role in its action in vivo.

Protective effect of amiloride against reperfusion damage as evidenced by inhibition of accumulation of free fatty acids in working rat hearts

To examine whether amiloride protects against ischemia-induced or reperfusion-induced damage to the heart, mechanical and metabolic studies were performed in the isolated, working rat heart. Ischemia decreased both mechanical function and the tissue levels of high-energy phosphates and increased the tissue levels of free fatty acids (FFAs). Reperfusion restored the levels of high-energy phosphates but further increased FFA accumulation. For this reason, accumulation of FFAs was used as an indicator of both ischemia-induced and reperfusion-induced damage. Drugs were added to the perfusion solution 5 min before ischemia until the end of ischemia (pre) or until 10 min after reperfusion (pre + post). Diltiazem (1 or 5 mumol/L pre) decreased the mechanical function of the non-ischemic heart and attenuated both ischemia-induced and reperfusion-induced accumulation of FFAs. Amiloride (50 mumol/L pre) did not affect the mechanical function of the non-ischemic heart or attenuate ischemia-induced or reperfusion-induced FFA accumulation effectively. However, amiloride (50 mumol/L pre + post) did markedly attenuate the reperfusion-induced accumulation of FFAs. In conclusion, diltiazem attenuates both ischemia-induced and reperfusion-induced myocardial damage, probably through its energy-sparing effect as a result of a decrease in mechanical function before ischemia. In contrast, amiloride attenuates only the reperfusion-induced myocardial damage through mechanisms other than the energy-sparing effect.

Pharmacological studies on a new antihypertensive agent, S-2150, a benzothiazepine derivative: 1. Antinecrotic and antiarrhythmic effects in reperfused rat hearts

S-2150 is a new 1,5-benzothiazepine derivative that inhibits [3H]diltiazem and [3H]WB4101 bindings to the membrane of rat tissue. The effects of S-2150 on ischemia/ reperfusion injury were studied in anesthetized rats. S-2150 reduced the myocardial infarct size (IS) induced by 20-min coronary artery occlusion followed by reperfusion. To evaluate reperfusion-induced ventricular tachycardia and fibrillation (VT, VF), we occluded the coronary artery for 4 min and then reperfused it. The incidence of arrhythmia was blocked by S-2150, and this effect offered protection against cardiac death. Prazosin did not modify the IS or incidence of reperfusion arrhythmias, but combined treatment with a noneffective dose of diltiazem showed significant cardioprotective effects. We also compared the direct effects of S-2150 and diltiazem on cardiac function and coronary perfusion flow using isolated rat hearts. Both drugs decreased mechanical function and increased coronary flow, with S-2150 being less cardiodepressive and more vasodilatory. S-2150 is cardioprotective at doses comparable to hypotensive doses even though its cardiodepressant effect is much weaker than that of diltiazem. This effectiveness may be partly explained by its dual characteristics: blocking the Ca channel and the alpha 1-adrenoceptor.

Antioxidant properties of dihydropyridines in isolated rat hearts

Isolated Sprague-Dawley rat hearts were perfused under constant flow conditions. Hearts were treated with vehicle or treatment buffers, including nisoldipine, nifedipine, or the optical isomers (+)- or (-)-nisoldipine. H2O2 (500-600 microM) was then added to the treatment buffer for 12 min. H2O2 was removed and perfusion continued with treatment buffers (10 min) followed by control buffer (20 min). Contractile function decreased following perfusion with H2O2. Contractile function was protected was protected in a concentration-dependent manner (nisoldipine=19,26,50,63 and 78%; nifedipine = 23, 37, 55,61, and 63% of pre-peroxide function, 0, 0.1, 0.5 1.0, and 5 microliter, respectively). There were no significant differences between equal concentrations of nisoldipine and nifedipine. Contractile function was equally protected by both (+)- and (-)-nisoldipine compared with vehicle-treated hearts (56, 67, and 16%, of pre-peroxide function, respectively). Biochemical analyses indicated that H2O2 damaged plasma membranes (increased lactate dehydrogenase leak) and caused lipid peroxidation (elevated tissue thiobarbituric acid reactive substances). Biochemical changes were equally reduced by nisoldipine and nifedipine treatments and by (+)- and (-)-nisoldipine. The treatment groups have widely differing IC50 values as calcium channel antagonists, yet they had equal effects in reducing oxidative injury, suggesting that this beneficial effect is not mediated by calcium antagonism.

Effects of K+ channel openers on ischemic dysfunction and metabolic disturbance in isolated perfused rat heart

The effects of two structurally different K+ channel openers, KRN2391 and cromakalim, on cardiac mechanisms during ischemia and reperfusion were studied in isolated perfused rat hearts. Isolated buffer-perfused rat hearts pretreated with KRN2391, cromakalim and vehicle were subjected to 25 min of ischemia followed by 30 min of reperfusion. Before ischemia, KRN2391 (1-10 microM) and cromakalim (1-10 microM) increased coronary flow, but did not modify cardiac function or biochemical parameters (adenine nucleotides, energy charge potential: ECP, lactate). During ischemia, KRN2391 (3, 10 microM) and cromakalim (10 microM) significantly accelerated the reduction in cardiac function and attenuated the decreased levels of ATP and ECP, but did not change the lactate content. After 30 min of reperfusion, pretreatment with KRN2391 and cromakalim resulted in a significant improvement in cardiac function, ischemic contracture and biochemical parameters. Thus, both KRN2391 and cromakalim have beneficial effects on biochemical parameters during ischemia and reperfusion, effects which may be related to cardiodepression during ischemia.

Specific block of the anti-ischemic actions of cromakalim by sodium 5-hydroxydecanoate

The potassium channel activators cromakalim and pinacidil were recently shown to have anti-ischemic properties in isolated globally ischemic rat hearts. The effects of two reported blockers of ATP-sensitive potassium channels, glibenclamide (glyburide) and sodium 5-hydroxydecanoate, on the anti-ischemic efficacy of cromakalim were determined in this model. Buffer-perfused rat hearts were subjected to 25 minutes of ischemia followed by 30 minutes of reperfusion. Pretreatment of these hearts with 60 microM cromakalim significantly decreased indexes of contractile function but caused a significant improvement of postreperfusion function and a significant decrease in release of lactate dehydroxygenase and in end-diastolic pressure. Pretreatment with glibenclamide at concentrations that reversed the preischemic effects of cromakalim (0.05 and 1.0 microM) also significantly reversed its postischemic protective effects. Sodium 5-hydroxydecanoate (100 and 300 microM) had no effect on the preischemic (negative inotropic) effects of cromakalim but completely reversed its cardioprotective effects. Sodium 5-hydroxydecanoate did not reverse the cardioprotective effects of the calcium entry blocker diltiazem. In phenylephrine-contracted rat aorta, glibenclamide (0.1-10 microM) inhibited cromakalim-induced relaxation, whereas sodium 5-hydroxydecanoate (10-1,000 microM) had no effect. Similarly, the ability of cromakalim to shorten cardiac action potential duration in guinea pig papillary muscle and to increase outward whole-cell potassium currents in isolated myocytes was inhibited by glibenclamide, whereas sodium 5-hydroxydecanoate was without effect. Thus, both glibenclamide and sodium 5-hydroxydecanoate inhibited the effects of cromakalim after reperfusion; however, sodium 5-hydroxydecanoate, unlike glibenclamide, had no effect in nonischemic preparations. These results suggest that sodium 5-hydroxydecanoate is an ischemia-selective inhibitor of ATP-sensitive potassium channels.

Anti-ischaemic and vasospasmolytic effects of a novel Ca2+ channel blocker, SD-3211, in vitro

1. The present study was undertaken to determine the vasospasmolytic activity of a novel non-dihydropyridine type of Ca2+ channel blocker, SD-3211, in isolated canine coronary arteries and its ability to reduce myocardial ischaemic damage in isolated perfused rabbit hearts. 2. The vasospasmolytic effect of SD-3211 was investigated using 3,4-diaminopyridine-induced rhythmic contraction, in comparison with its enantiomer (SD-3212), nicardipine and diltiazem. SD-3211 was shown to reduce the peak tension and increase the contraction frequency. The order of potency for the relaxation of the peak tension was as follows: nicardipine greater than SD-3211 greater than diltiazem greater than SD-3212 and being compatible with that for the relaxant effects of these compounds on KCl-induced contraction in the same specimen. 3. Furthermore, the effect of SD-3211 on myocardial damage due to global ischaemia for 60 min followed by 60 min of reperfusion was examined. SD-3211 at a concentration of 2 X 10(-8) mol/L was given for 40 min before and again for 60 min after the ischaemia. SD-3211 attenuated the increase in leakage of creatine phosphokinase from the hearts and the decrease in pH of perfusate during reperfusion, while concomitantly providing a significant improvement in the post-ischaemic recovery of developed tension. 4. These results suggest that SD-3211 has properties to reduce coronary vasospasm and to provide protection against ischaemic damage, both of which may have beneficial actions in the treatment of ischaemic heart disease.

The protective effects of cromakalim and pinacidil on reperfusion function and infarct size in isolated perfused rat hearts and anesthetized dogs

The direct myocardial protective effects of intracoronary infusions of cromakalim and pinacidil were determined in an anesthetized canine model of coronary occlusion and reperfusion. The left circumflex coronary artery was occluded for 90 minutes and reperfused for 5 hours, at which time the infarct size was determined. Cromakalim (0.1 micrograms/kg/min) or pinacidil (0.09 micrograms/kg/min) were infused into the left circumflex coronary artery starting 10 minutes preischemia. Cromakalim significantly reduced infarct size as a percent of the left ventricular area at risk (25 +/- 5%) compared with vehicle controls (55 +/- 7%). Pinacidil did not reduce infarct size at an equimolar dose, but at the higher dose also significantly reduced infarct size. Collateral blood flow was not significantly altered by either drug, though reperfusion flow was significantly higher in cromakalim-treated animals, particularly in the subepicardial region. When the same dose of cromakalim was given starting 2 minutes before the initiation of reperfusion, no significant beneficial effect of cromakalim was observed. In another study, isolated buffer-perfused rat hearts were subjected to 25 minutes of global ischemia and 30 minutes of reperfusion. These hearts were treated with 7 microM cromakalim, either starting 10 minutes before ischemia or only during reperfusion, and its effect on reperfusion function and LDH release were determined. Cromakalim pretreatment (both when given throughout the experiment and when not present in the reperfusion buffer) resulted in significant improvements in the reperfusion function. Reperfusion contracture and LDH were also significantly reduced with this treatment. When given only during reperfusion, cromakalim did not reduce the severity of ischemia when compared with vehicle controls. Thus, both cromakalim and pinacidil reduce ischemic/reperfusion injury, though the timing of treatment may be important.

Effect of amlodipine on myocardial functional and metabolic recovery following coronary occlusion and reperfusion in dogs

The effects of the dihydropyridine calcium-channel blocker, amlodipine, on subendocardial segment shortening (%SS), regional myocardial blood flow, myocardial high-energy phosphate levels and tissue water content were compared to those of a saline-treated group of barbital-anesthetized dogs subjected to a 45-minute coronary artery occlusion followed by 60 minutes of reperfusion. Saline or amlodipine (200 micrograms/kg, IV) were administered 15 minutes prior to coronary occlusion. There were no significant differences between groups in ischemic bed size or hemodynamics, although dP/dt was higher following amlodipine. Subepicardial collateral blood flow was higher in the amlodipine group during coronary occlusion. Following occlusion, %SS in the ischemic region was markedly decreased in both series and passive systolic lengthening resulted. In spite of similar decreases in %SS during occlusion, the amlodipine- treated dogs showed a marked improvement in myocardial segment function (%SS) of the ischemic-reperfused region throughout 60 minutes of reperfusion as compared to saline-treated animals. In addition, amlodipine prevented the rebound increase in phosphocreatine and attenuated the loss of adenine nucleotides and the increase in tissue water in the ischemic-reperfused area at 60 minutes of reperfusion. These results suggest that amlodipine has a favorable effect on the functional and metabolic recovery of the ischemic-reperfused myocardium, and may have potential as a therapeutic agent for the treatment of coronary artery disease. The mechanism of action of amlodipine in this model is unknown but may be partially related to a drug-induced increase in coronary collateral blood flow.

Protection of cardiac membrane phospholipid against oxidative injury by calcium antagonists

Calcium antagonists representative of the four major chemical classes were assessed for their abilities to prevent peroxidation of rat heart membrane lipids through xanthine oxidase-dependent, superoxide-driven, iron-promoted oxygen radical chemistry. The dihydropyridines nifedipine and nitrendipine did not affect peroxidation, even at a concentration (500 microM) approaching their solubility limit. The benzothiazepine diltiazem did protect the cardiac lipids against oxidative injury, but at high micromolar concentrations: 50% inhibition of peroxidation (antiperoxidant IC50) required 510 microM diltiazem. The phenylalkylamines verapamil and gallopamil (D-600) were likewise weak antiperoxidants (approximately 35% inhibition of peroxidation at 500 microM). In contrast, two other alkylamines, bepridil and prenylamine, were very effective membrane lipid protectants with respective antiperoxidant IC50 values of 55 and 75 microM. The diphenylpiperazines flunarizine (IC50 = 190 microM) and cinnarizine (IC50 = 180 microM) displayed moderate antiperoxidant activity. No Ca2+ antagonist inhibited xanthine oxidase under conditions whereby 10 microM allopurinol inhibited enzyme activity by 50%. The effects of the Ca2+ antagonist-antiperoxidants on the kinetics of cardiac membrane lipid peroxidation indicate that they inhibit peroxidation by intercepting oxy- and/or lipid free radical intermediates. These data raise the possibility that antiperoxidant action may contribute to the spectrum of pharmacologic and therapeutic activities of certain Ca2+ antagonists.