Phenothiazines are potent inhibitors of osteoclastic bone resorption

• 1.1. We have previously shown that promethazine inhibits osteoclastic bone resorption in the in vitro bone slice assay (IC₅₀=0.8 μM), but the mechanism(s) involved are unclear.
• 2.2. We have now tested the effects on osteoclast activity of five other structurally related compounds. Phenothiazine, chlorpromazine, amitriptyline, phenazine, and phenoxazine had IC₅₀ values of 0.8, 0.9, 6, 7, and > 10 μM, respectively, in the bone slice assay, indicating that the basic phenothiazine structural element itself is important for osteoclast inhibitory activity.
• 3.3. The results are discussed in terms of the known effects of phenothiazines on plasma membrane fluidity, blocking of ion channels, and inhibition of calmodulin.

     

The mechanism of action of KBT-3022, a new antiplatelet agent

• 1.1. The mechanism of action of a new antiplatelet agent, KBT-3022 (ethyl 2-[4,5-bis(4-methoxyphenyl)thiazol-2-yl]pyrrol-1-ylacetate) and its active main metabolite, desethyl KBT-3022, was investigated.
• 2.2. KBT-3022 and desethyl KBT-3022 inhibited cyclooxygenase from ovine seminal gland with IC₅₀ values of 0.69 and 0.43 μM, respectively.
• 3.3. At concentrations higher than those required for cyclooxygenase inhibition, desethyl KBT-3022 inhibited cAMP-phosphodiesterase, specific binding of U46619, and release of phosphatidic acid from thrombin-stimulated platelets.
• 4.4. Oral administration of KBT-3022 inhibited the production of thromboxane B₂ during blood coagulation more potently than the production of 6-keto-prostaglandin F_1α from aortic strips in guinea pigs.
• 5.5. These findings suggest that KBT-3022 may inhibit platelet activation principally via the inhibition of cyclooxygenase by desethyl KBT-3022.

     

Peroxidative xenobiotic oxidation by partially purified peroxidase and lipoxygenase from human fetal tissues at 10 weeks of gestation

• 1.1. Present study reports the ability of partially purified peroxidase and lipoxygenase from human fetal tissues at 10 weeks of gestation to oxidize selected xenobiotics in vitro.
• 2.2. Peroxidase was found to oxidize four different chemicals in the presence of H₂O₂. Sodium azide and potassium cyanide inhibited peroxidase activity towards guaiacol in a concentration-dependent manner.
• 3.3. The dioxygenase and co-oxidase activities of lipoxygenase towards linoleic acid and four model xenobiotics, respectively, were observed. Both the catalytic activities of lipoxygenase were significantly inhibited by < 1.0 μM nordihydroguaiaretic acid.
• 4.4. These findings suggest that peroxidase and lipoxygenase may be important pathways for peroxidative xenobiotic oxidation in human fetal tissues.

     

Pharmacological properties of MM-706, a new prostacyclin derivative

• 1.1. In human platelet-rich plasma, platelet aggregation induced in vitro by collagen (10 μg/ml) or thrombin (50 mU/ml) was dose-dependently inhibited by increasing concentrations of prostacyclin or of the new derivative (±)(5E)-13,14-didehydro-ω-hexanor(1-hydroxycyclohexyl)-9a-carbaprostacyclin (MM-706) with an IC₅₀ of 20–50 nM and 250–500 nM, respectively. In human platelets loaded with fura-2, the intracellular rise of [Ca²⁺] induced by thrombin was dose-dependently inhibited by MM-706 with an approximate IC₅₀ of 100 μM.
• 2.2. In rabbit isolated femoral artery, MM-706 (10nM–10μM) was completely ineffective in relaxing the vessel, which was different to prostacyclin which was able to relax vessels at the same concentrations.
• 3.3. In in vitro guinea-pig ileum, prostacyclin produced a contractile effect in the concentration range 1 nM-10μM, but the derivative MM-706 was ineffective at the same concentrations. Preventive addition of MM-706 did not inhibit prostacyclin contraction.
• 4.4. On isolated guinea-pig tracheal preparation, prostacyclin induced a concentration-dependent contraction but the new compound MM-706 showed a lower activity, in the concentration range 10nM–10μM. The activity of prostacyclin was not affected by the contemporary presence of MM-706.
• 5.5. It is concluded that MM-706 is a prostacyclin analogue with antiaggregating properties but without evident effects on smooth muscle of different regions.

     

Synergistic antiplatelet effects of a nipecotamide A-1C and low dose aspirin

• 1.1. The effects of an antithrombotic nipecotamide, A-1, and aspirin were examined separately and in combination, on human platelet aggregation in vitro and on collagen + epinephrine-induced thromboembolic death of mice in vivo.
• 2.2. Concurrent addition of the two agents to a platelet suspension resulted in a supraadditive inhibition. Racemic A-1 and its meso diastereomer A-1C behaved similarly in this respect. The IC₅₀ value of rac. A-1 declined from 46.25 to 18.4 μM in the presence of aspirin.
• 3.3. In vivo, concurrent administration of A-1C and aspirin produced significant potentiation of antithrombotic activity. A 2-fold reduction in the ED₅₀ of A-1C occurred when it was coadministered with aspirin to mice; also, the toxicity reduced slightly, increasing the therapeutic index by a factor of 2.2.
• 4.4. The design and synthesis of new compounds possessing the structural features of the two molecules appears to provide superior antithrombotic agents.

     

The role of cyclic nucleotides in the action of peripheral-type benzodiazepine receptor ligands in rat aorta

• 1.1. Peripheral-type benzodiazepine ligands (Ro 5-4864, AHN-086, PK 11195 and PK 14105) inhibit, in a concentration-dependent and non-competitive manner, noradrenaline-induced contractions in isolated rat aortic rings (IC₅₀ values: 24 ± 1.8, 49 ± 2.5, 15 ± 1.2, 49 ± 3.2 μM, respectively).
• 2.2. This effect is probably not mediated by peripheral-type benzodiazepine receptors and is not related to the presence of endothelium.
• 3.3. All compounds inhibited phosphodiesterase activity in vitro.
• 4.4. From the results obtained with nucleotide analogs, calcium antagonists and specific inhibitors of PDE isoenzymes, it can be concluded that the actions of AHN-086 and PK 11195 are related to effects on PDE I, III and IV.

     

N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) impairs neurotransmission in the vas deferens of the rat

• 1.1. The in vitro effects of N-(2-chloroethyl)-N-ethyl-bromobenzylamine (DSP4) were studied in the rat vas deferens.
• 2.2. DSP4 inhibited the biphasic motor response induced by field stimulation in a concentration-dependent manner. The concentration of DSP4 that elicited 50% of the maximal inhibition of the twitch response induced by 3 Hz was 10 μM.
• 3.3. DSP4 10 μM abolished the motor response induced by exogenously applied noradrenaline and 0.1 mM ATP. Phentolamine (an α-adrenoceptor blocker) prevented DSP4 inhibitory effect.
• 4.4. DSP4 inhibitory effect was no due to the activation of α₂-presynaptic adrenoceptor mechanisms.
• 5.5. DSP4 impairs neurotransmission in the rat vas deferens by a postsynaptic α₁-adrenoceptor blockade and by an inhibition of the purinergic response.

     

Inhibition of NO synthase induction by an anticancer drug 4′-epi-doxorubicin in rats

• 1.1. Nitric oxide (NO) plays various physiological roles in tumour tissues. Herein, we examined the effects of an anticancer drug 4′-epi-doxorubicin on NO synthase and the related responses in rat thoracic aorta, rat cerebellum and lung homogenates.
• 2.2. Treatment with an anticancer drug 4′-epi-doxorubicin in vitro or in vivo had little effect on the relaxation response to acetylcholine or nitroprusside in rat thoracic aorta.
• 3.3. Treatment with 4′-epi-doxorubicin in vitro or in vivo did not alter the constitutive NO synthase activity of rat cerebellum ([³H]-citrulline production from [³H]-arginine).
• 4.4. After inducible NO synthase had been induced by lipopolysaccharide, 4′-epi-doxorubicin also neither affected the relaxation response to L-arginine in rat thoracic aorta nor the enzyme activity of rat lung.
• 5.5. Coincubation with lipopolysaccharide and 4′-epi-doxorubicin in vitro prevented the development of relaxation response to L-arginine in rat thoracic aorta. Pretreatment with 4′-epi-doxorubicin in vivo also prevented the induction of inducible NO synthase by lipopolysaccharide in rat thoracic aorta and lung.
• 6.6. These results suggest that 4′-epi-doxorubicin selectively inhibits the induction of NO synthase without affecting constitutive and inducible NO synthase activities. This effect was discussed in relation to the anticancer and side effects of the drug.

     

Hepatoprotective reactivity of a copper-di-Schiffbase active centre analogue of Cu2Zn2 superoxide dismutase

• 1.1. The anti-inflammatory and hepatoprotective efficacy of CuPu(Py)₂ ({[N,N′-bis(2-pyridyl-methylene)-1,4-butanediamine](N,N′,N″,N′″)}-Cu²⁺), a serum-stable, copper-di-Schiffbase active centre analogue of Cu₂Zn₂superoxide dismutase was tested in male NMNR mice suffering from endotoxin/galactosamine-induced hepatitis.
• 2.2. Parameters including the activities of serum transaminases and sorbitol-dehydrogenase as well as the levels of reactive oxygen and nitrogen intermediates which were used to quantify the disease activity.
• 3.3. A dose-dependent inhibition of hepatic enzyme release was noted in the presence of 0.1–10 mg/kg of CuPu(Py)₂.
• 4.4. The release of transaminases from damaged liver cells was reduced by 68% and paralleled the reduction of serum levels of nitric oxides.
• 5.5. Elevated levels of reactive oxygen species were normalized to those healthy controls.
• 6.6. The copper-free apochelate Pu(Py)₂, which is unable to dismutate superoxide, did not display any anti-inflammatory reactivity.

     

Characterization of GABAB ligands in vivo

• 1.1. While GABA_B antagonists have been examined in vitro, very few have been tested in vivo. A range of GABA_B antagonists were tested against baclofen-induced muscle relaxation and hypothermia.
• 2.2. The GABA_B antagonists exhibited a range of in vivo activity profiles.
• 3.3. CGP 35348 showed clear antagonist effects, while BPBA and 4-ABPA appeared to have agonist properties.
• 4.4. Phaclofen, 2-hydroxysaclofen, 3-APPA and 9G seemed to have little effect in this system at the doses tested.
• 5.5. Differences between in vivo and in vitro activity could be explained by differences in blood-brain barrier permeability, or possible differences in affinities for the sub-classes of GABA_B receptors.

     

The relationship between erythrocyte superoxide dismutase activity and plasma levels of some trace elements (Al,Cu, Zn) of dialysis patients

• 1.1. The effect of erythropoietin and some trace elements on superoxide dismutase (SOD) activity of dialysis patients have been studied.
• 2.2. SOD activity of dialysis patients was found to be decreased.
• 3.3. The effect of erythropoietin on SOD activity was not found in vitro.
• 4.4. Plasma and erythrocyte aluminum increased in dialysis patients, but no significant change in plasma copper was found.
• 5.5. Plasma zinc levels of dialysis patients were found to be decreased.
• 6.6. These results suggest that inhibition of erythrocyte SOD activity of dialysis patients may contribute to their anemia.

     

Blockade of cardiac nicotinic responses by anticholinesterases

• 1.1. Tacrine (10 μM) and physostigmine (10 μM) completely inhibited the positive chronotropic and inotropic actions of acetylcholine (ACh) or nicotine in the atropinized guinea pig right atria.
• 2.2. Edrophonium (6 μM) and soman (0.1 μM) completely inhibited these nicotinic responses, as well as the associated increase in pyridine nucleotide fluorescence and vasodilation induced by ACh in the atropinized guinea pig perfused heart.
• 3.3. The 200-fold increase in noradrenaline release induced by ACh in the perfused heart was blocked by 10 μM tacrine and 6 μM edrophonium.
• 4.4. Tacrine (10 μM) significantly (16–32%) reduced the basal heart rate of both preparations.
• 5.5. Edrophonium (6 μM) induced a five- to sixfold increase in basal 3,4-dihydroxyphenyl-(ethylene) glycol (DOPEG) release.
• 6.6. The inhibition of nicotinic receptor activation in the atria by the anticholinesterases appears mainly non-competitive. IC₅₀ values range from 0.1 to 10 μM in the perfused heart to 1 to 100 μM in atria (in either case tacrine about 2 μM).
• 7.7. The possibility that these compounds have a direct action at nicotinic receptors is discussed.

     

Influence of diethylcarbamazine and mefloquine on PGI2 synthesis by the rat thoracic aorta and myometrial tissues

• 1.1. The influence of the antifilarial drug diethylcarbamazine citrate (D) and dl-erythro mefloquine hydrochloride (Mf) on PGI₂ synthesis by the male rat thoracic aorta and day-20 pregnant rat myometrium was investigated in vitro using a rat platelet antiaggregatory bioassay method.
• 2.2. Pretreatment of the tissues with D (25.5–204 μM) or Mf (24–192 μM) for 30 min at 37°C significantly inhibited PGI₂ synthesis in a concentration-dependent manner.
• 3.3. D exhibited its inhibitory effect even in presence of exogenous arachidonic acid (AA) (16.6 μM) whereas Mf lost its inhibitory effect in presence of AA.
• 4.4. Pretreatment of urethane-anaesthetized rats with D (32 μmol kg⁻¹) but not Mf (7.5 μmol kg⁻¹) for 30 min significantly antagonized AA (4 nmol kg⁻¹)-induced hypotension
• 5.5. Furthermore, D (0.25–0.5 μM) antagonized AA-induced aggregation in rabbit platelet-rich plasma without affecting that of ADP.
• 6.6. D seemed to interfere with the action of the PG endoperoxide synthase (PG cyclooxygenase) whereas Mf seemed to interfere with the action of phospholipase A₂ (PLA₂) enzyme.
• 7.7. D may have exerted its effect via release of toxic O₂ radicals whereas Mf effect may have been due to an interaction with PLA₂ substrate phospholipids.
• 8.8. The demonstrated inherent property of these two drugs to inhibit the synthesis of the potent vasodilator, platelet antiaggregatory, anticonvulsant and antiinflammatory mediator PGI₂ may partly contribute towards better understanding of the biochemical mechanisms that underly some of the previously known but poorly understood actions of these drugs.

     

Effect of bunazosin, α1-adrenoceptor blocker,on multidirectional contractile response and localization of bunazosin binding sites in human hypertrophied prostate

• 1.1. Effects of bunazosin, an α₁-adrenoceptor blocker, on the contraction induced by norepinephrine in human hypertrophied prostate were examined in vitro.
• 2.2. Prostatic specimens showed maximum contraction at 10⁻⁴ M norepinephrine in longitudinal and circumferential directions to the urethra.
• 3.3. Bunazosin (10⁻⁷ M) blocked norepinephrine-induced contraction with a parallel shift of the dose-response curve in both directions (pA₂: 8.76 ± 0.15; pA₂: 8.90 ± 0.08, respectively).
• 4.4. Serial sections of prostates were also evaluated by autoradiography. The binding sites were diffusely distributed in the interstitium.
• 5.5. We concluded that bunazosin affects multidirectional contraction in prostates.

     

The effect of N6-cyclohexyladenosine and 5′-N-ethylcarboxamidoadenosine on body temperature in normothermic rabbits.

• 1.1. Thermal responses to IV administration of N⁶-cyclohexyladenosine (CHA; 0.15 mg/ kg), A₁ adenosine receptor agonist, or 5′-N-ethylcarboxamidoadenosine (NECA; 0.15 mg/kg), A₂ adenosine receptor agonist, were investigated in normothermic rabbits at an ambient temperature (Ta) of 20.0±1.0°C.
• 2.2. Although both compounds inhibited metabolic heat production, only NECA produced hypothermia.
• 3.3. NECA showed strong hypotensive activity.
• 4.4. Both compounds produced vasoconstriction of the ear skin vessels and CHA, in addition, slowed down the respiratory rate.
• 5.5. The role of A₁ or A₂ adenosine receptors in the thermoregulatory activity of these compounds is discussed.

     

The effect of Lithium on endothelial-dependent relaxation in rat isolated aorta

• 1.1. In endothelium-containing rings of rat aorta, precontracted by phenylephrine, addition of acetylcholine (Ach), resulted in a concentration-dependent relaxation through the release of endothelial dependent relaxing factors, including nitric oxide (IC₅₀ = 8.41 μM).
• 2.2. Pretreatment of the tissues with 20 μM indomethacin, significantly decreased the relaxation.
• 3.3. Preincubation of the preparations in medium solution in which sodium has been partially replaced by 0.5 mM lithium, significantly reduced Ach-induced endothelial dependent relaxation (EDR).
• 4.4. Lithium (2 mM) in medium, significantly increased Ach-induced relaxation.
• 5.5. As is shown in this study, lithium has two opposite actions on EDR, with the dose of 0.5 mM inhibiting, while the dose of 2 mM potentiates EDR. Thus it seems that the action of lithium on EDR is mediated through two separate mechanisms.

     

Vasoinhibitory effect of leminoprazole,a H+,K+-atpase inhibitor,on rat aortic rings

• 1.1. In isolated rat aortic rings, leminoprazole (2-[2-N-methyl-N-(2-methylpropyl)amino] benzylsulfinyl benzimidazole) (10⁻⁶-10⁻⁴ M) inhibited contractile responses to phenylephrine (PE), KCl and Ca²⁺ in KCl-depolarized tissues in a Ca²⁺ free medium. Leminoprazole also relaxed the aorta contracted by PE and KCI.
• 2.2. The relaxing effect of leminoprazole was markedly inhibited by nifedipine and verapamil (inhibitors of voltage operated Ca²⁺ channels). Relaxation induced by verapamil, but not by nifedipine, was inhibited by pre-treatment by leminoprazole.
• 3.3. The relaxing effect of leminoprazole was also inhibited by N^G-monomethyl-l-arginine (a nitric oxide synthase inhibitor), methylene blue (a guanylate cyclase inhibitor) or endothelium removal but not by indomethacin (a cyclooxygenase inhibitor), glyburide (a K_ATP channel inhibitor) or iberiotoxin (a K_Ca channel inhibitor).
• 4.4. Zaprinast (a cGMP-phosphodiesterase inhibitor) also inhibited the relaxing action of leminoprazole. In addition, relaxation induced by nitroglycerin was potentiated by leminoprazole.
• 5.5. Further, in the presence of methylene blue, residual relaxation induced by leminoprazole was still potentiated by verapamil.
• 6.6. These results suggest that the vasoinhibitory effect of leminoprazole in rat aortic rings is due to the increased level of cGMP through inhibition of cGMP-phosphodiesterase and also due to inhibition of voltage operated Ca²⁺ channels.

     

Clonidine-induced rhythmic activity in rabbit anococcygeus muscle

• 1.1. Clonidine 0.5 mM induced an extremely regular rhythmic activity in isolated rabbit anococcygeus muscle. The movements were resistant to tetrodotoxin effect.
• 2.2. Prazosin (5 × 10⁻⁸M-5 × 10⁻⁶M) and yohimbine (1.5 × 10⁻⁷M-5 × 10⁻⁴M) showed no remarkable effect on clonidine-induced rhythmic activity.
• 3.3. The clonidine-induced contractions were dependent on extracellular calcium and could be inhibited by the omission of calcium from medium or the introduction of verapamil (IC₅₀=1.3 × 10⁻⁷M) or nifedipine (IC₅₀=7.5 × 10⁻⁸M).
• 4.4. Pretreatment of animals with reserpine made the preparations 2800-fold more sensitive to this action of clonidine.
• 5.5. It can be concluded from this study that clonidine is able to induce rhythmic activity in rabbit anococcygeus muscle through a mechanism that increases intracellular concentration of Ca ⁺⁺ via membrane calcium channels.

     

The effects of benzamil on in vitro contracture responses of human skeletal muscle to halothane

• 1.1. Inhibition of sodium-calcium exchange using 100 μM benzamil caused contracture development of in vitro skeletal muscle samples from humans susceptible to malignant hyperthermia, but not of samples from normal individuals.
• 2.2. This dose of benzamil increased the contracture response of both types of muscle to halothane.
• 3.3. At a concentration of 1 μM, benzamil significantly reduced the contracture response to halothane of muscle from malignant hyperthermia individuals.
• 4.4. The implications for the role of sodium-calcium exchange in skeletal muscle calcium homeostasis and the pathophysiology of malignant hyperthermia are discussed.