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.

     

Possible Stimulation of Na+-K+-ATPase by NO Produced from Sodium Nitrite by Ultraviolet Light in Mouse Gastric Fundal Strip

• 1.In the present study, we investigated the roles of Na⁺-K⁺-ATPase and extracellular Na⁺ or Ca²⁺ ions in ultraviolet (UV) light-induced photorelaxation of methacholine-contracted mouse isolated gastric fundus in the presence of NaNO₂ (50 μM).
• 2.Ouabain (1–500 μM), sodium vanadate (10 μM to 3 mM) and amiloride (1–100 μM) completely inhibited the photorelaxation in a concentration-dependent manner.
• 3.Metabolic inhibitors, sodium azide (10–100 μM), 2,4-dinitrophenol (100 μM to 1 mM) and sodium fluoride (100 μM to 1 mM) significantly reduced photorelaxation.
• 4.Substitution of sucrose, lithium or KCl with extracellular Na⁺ completely abolished the photorelaxant responses.
• 5.Replacement of all extracellular CaCl₂ with BaCl₂ also completely inhibited UV-induced relaxation.
• 6.Verapamil (1–10 μM) decreased UV-induced relaxation significantly.
• 7.These results suggest that nitric oxide produced from NaNO₂ by UV-light in mouse gastric fundus probably stimulates Na⁺-K⁺-ATPase activity, and photorelaxation of gastric smooth muscle is dependent on extracellular Na⁺ and Ca²⁺ ions.

     

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.

     

H-7, A protein kinase C inhibitor,inhibits spontaneous tone and spasmogenic responses in normal and sensitized guinea pig trachea

• 1.1. H-7, a protein kinase C inhibitor, fully inhibited the spontaneous and stimulated (KC120 mM or histamine 0.5 mM) tone of trachea from normal and sensitized guinea pig.
• 2.2. H-7 depressed the concentration-contraction curves to KCI, histamine or 5-hydroxytryptamine in epithelium-denuded, indomethacin-treated, trachea from normal and sensitized guinea pigs while responses to CaCI₂ (in Ca²⁺-free, K⁺-depolarized tissues) and acetylcholine were not affected.
• 3.3. H-7 (100 gM) did not depress Ca²⁺ (20 μM)-induced contraction of Triton X-100 skinned trachea.
• 4.4. These results suggest the involvement of PKC in the maintenance of spontaneous tone and spasmogenic responses of guinea pig trachea.

     

Sodium nonivamide acetate: A non-pungently antinociceptive capsaicin derivative with unusual anti-inflammatory properties

• 1.1. Bradykinin-induced vascular pain in conscious rats, hyperalgesia in the rat hind paw, rat hind paw edema induced by compound 48/80 and carrageenin and dye exudation induced by intraperitoneal injection of 0.7% acetic acid in mice were all inhibited by sodium nonivamide acetate (SNA).
• 2.2. Collagen and arachidonic acid-induced rabbit platelet aggregations were inhibited by SNA and capsaicin. In human platelet microsomes, prostaglandin E₂ formation in arachidonic acid metabolite was not inhibited by SNA but was inhibited by capsaicin and indomethacin; thromboxane B₂ formation and its synthetase activity were inhibited by SNA and capsaicin.
• 3.3. In the extracellular recording, SNA could not decrease the action potential amplitude of the vagus nerve.
• 4.4. The motor activity of mice induced by caffeine (1.0 mg/kg) was inhibited by SNA and capsaicin.

     

Effects of diltiazem and verapamil on ADP-induced rabbit platelet shape change and aggregation

• 1.1. The effects of diltiazem and verapamil (two structurally different calcium channel blockers) were examined on the rabbit platelets shape change and aggregation induced by adenosine-5′-diphosphate (ADP).
• 2.2. ADP was a much more potent stimulator on inducing platelet shape change (ED₅₀ = 1 × 10⁻⁷) than platelet aggregation (ED₅₀ = 1.78 × 10⁻⁶).
• 3.3. Both drugs similarly inhibited ADP-induced platelet shape change and aggregation at concentrations more than 300 μM.
• 4.4. There were no significant differences in inhibitory effects of either diltiazem or verapamil on ADP-induced platelet shape change and aggregation.
• 5.5. The inhibitory effects of diltiazem and verapamil on ADP-induced platelet shape change and aggregation at high concentrations may be due to their non specific properties.

     

Xanthonolol: A calcium channel and beta-adrenoceptor blocker with vasodilating properties

• 1.1. Xanthonolol (0.1–0.5 mg/kg, i.v.) reduced the blood pressure, heart rate, and l-isoproterenol (0.05 μg/kg, i.v.)-induced tachycardia in rats.
• 2.2. In the isolated guinea-pig right atrium, xanthonolol (10⁻⁶−3 × 10⁻⁴ M) produced long-lasting negative, inhibited l-isoproterenol-induced positive chronotropic effects, prevented the rate-increasing effects of increased extracellular Ca²⁺ (3.0–9.0 mM), and inhibited Ca²⁺ (3.0–9.0 mM)-induced heart rate-increase.
• 3.3. In the isolated guinea-pig thoracic aorta, the contractions induced by CaCl₂ (0.1–5.0 mM) were inhibited by xanthonolol (10⁻⁶–10⁻⁴ M).
• 4.4. Xanthonolol is suggested to have a calcium channel and beta adrenergic blocking effect with vasodilating properties.

     

Modulatory effect of 8-iso-PGE2 on platelets

• 1.1. 8-Iso-PGE₂ induced either reversible or irreversible aggregation of platelets in human platelet-rich plasma (PRP) or in the suspension of washed platelets (WP). The values of EC₅₀ for irreversible aggregation in PRP and WP were 4 and 2 μM, respectively.
• 2.2. In rabbit PRP, 8-iso-PGE₂ (0.1-100 μM) itself did not induce or induced only reversible aggregation.
• 3.3. 8-Iso-PGE₂ (0.1-20μM) potentiated adenosine diphosphate-(ADP) induced platelet aggregation in both human and rabbit. The same effect also was found for adrenaline-induced platelet aggregation in rabbit.
• 4.4. The lower concentrations (0.2-0.5 μM) of 8-iso-PGE₂ decreased, and higher concentrations (1–2 μM) increased platelet aggregating factor- (PAF) induced aggregation in human PRP. In rabbit PRP, 8-iso-PGE₂ (0.02–200 μM) had only a decreasing effect on PAF-induced aggregation.
• 5.5. The results suggest that low concentrations of 8-iso-PGE₂ can amplify or weaken platelet aggregation induced by various aggregatory agents.

     

Comparative effects of the Dihydropyridine-type calcium-agonists (−)-S-Bay K 8644, (±)-Bay-W 5035 and (±)-Bay-T 5006 on human platelet aggregability

• 1.1. Human platelet aggregation induced by collagen is concentration-dependently inhibited by dihydropyridine (DHP)-type calcium(Ca)-agonists.
• 2.2. There was no significant difference between the maximal anti-aggregatory effects or the anti-aggregatory potencies of (−)-S-Bay-K 8644 (EC₅₀: 5.3 ± 1.5 × 10^-5 M), (±)-Bay-W 5035 (EC₅₀: 14.9 ± 8.8 × 10^-5 M) or (±)-Bay-T 5006 (EC₅₀: 2.7 ± ± 10^-5 M) (P > 0.05).
• 3.3. Antiaggregatory effects of DHP-type Ca-agonists seem to be independent of Ca-channel activation.

     

Effect of TYB-2285 on lung anaphylaxis in actively sensitized rats

• 1.1. We examined the effect of TYB-2285 on the acute phase and the late phase of lung anaphylaxis in rats.
• 2.2. TYB-2285 (3-30 mg/kg PO) inhibited antigen-induced bronchoconstriction and TxB₂ production during the acute phase of lung anaphylaxis in a dose-dependent manner.
• 3.3. Ketotifen fumarate (30 mg/kg PO) inhibted bronchoconstriction and TxB₂ production less potently than TYB-2285.
• 4.4. TYB-2285 (30 mg/kg PO) inhibited the accumulation of neutrophils during the late phase of lung anaphylaxis significantly without a significant change in total cells.
• 5.5. Hydrocortisone acetate (100 mg/kg PO) inhibited the accumulation of total cells as potent as neutrophils.

     

Propionate regulates lymphocyte proliferation and metabolism

• 1.1. The effect of propionate on lymphocyte proliferation and metabolism was investigated. Lymphocytes obtained from human blood and rat mesenteric lymph nodes were utilized.
• 2.2. Propionate at concentrations of 0.04 and 1.0 mmol/1 stimulated the amount of [³H]thymidine incorporated either in cultured human T lymphocytes or rat T and B lymphocytes.
• 3.3. Concentrations of propionate between 2 and 5 mmol/1 caused a marked inhibition of lymphocyte proliferation.
• 4.4. This short-chain fatty acid was metabolized by these cells and produced succinate in significant amounts; however, its oxidation was low.
• 5.5. Propionate did not alter glucose, glutamine and pyruvate utilization and oxidation in incubated rat lymphocytes but increased the formation of lactate and aspartate.
• 6.6. In contrast, propionate inhibited by 50% the synthesis of lymphocyte lipid from [1-¹⁴C]acetate at concentrations of 0.5 and I mmol/1 and reduced by half the incorporation of ³H₂O into lipids at 1 and 5 mmol/1.
• 7.7. The results suggest that inhibition of lipid synthesis is a possible mechanism leading to reduction of lymphocytes proliferation.

     

Caffeine depression of spontaneous activity in rabbit sino-atrial node cells

• 1.1. Effects of caffeine on the action potentials and the membrane currents in spontaneously beating rabbit sino-atrial (SA) node cells were examined using a two-microelectrode technique.
• 2.2. Cumulative administrations of caffeine (1–10 mM) caused a negative chronotropic effect in a concentration-dependent manner, which was not modified by atropine (0.1 μM). At 10 mM, caffeine increased the amplitude and prolonged the duration of action potentials significantly; the other parameters were unaffected.
• 3.3. In 3 of 16 preparations, caffeine (5 mM) elicited arrhythmia. At high Ca²⁺ (8.1 mM), caffeine (5 mM) increased the incidence of arrhythmia.
• 4.4. Caffeine (0.5–10 mM) enhanced the slow inward current, but at 10 mM decreased the enhanced peak current by 5 mM. The hyperpolarization-activated inward current was also enhanced by caffeine, but 10 mM caffeine decreased the current peak as compared with that at 5 mM. In addition, caffeine inhibited the delayed rectifying outward current in a concentration-dependent manner, accompanied by a depressed activation curve without any shift in the half-maximum activation voltage.
• 5.5. Caffeine elevated the cytoplasmic Ca²⁺ level in the SA node cells loaded with Ca²⁺-sensitive fluorescent dye (fura-2).
• 6.6. These results suggest that caffeine enhances and/or inhibits the ionic currents and elicits arrhythmia due to the induction of cellular calcium overload.

     

Involvement of sodium/calcium exchange in the diclofenac-induced spasmolytic effect on rat uterus

• 1.1. The effect of diclofenac (10–100 μM) on rat uterus contraction and its modification by ouabain (0.1 mM), amiloride (0.1 and 1 mM), ouabain (0.1 mM) plus amiloride (1 mM) and the replacement of sodium by choline have been assayed.
• 2.2. Diclofenac produces dose-dependent relaxation of vanadate (0.3 mM)-induced contraction (EC₅₀, 17.3 ± 1.8 μM). This effect is significantly reduced in choline medium (EC₅₀, 49.1 ± 4.5 μM) and by ouabain in sodium-medium (EC₅₀, 52 ± 7 μM).
• 3.3. Amiloride displaces, in a dose-dependent way, the diclofenac-induced relaxant effect. However, ouabain plus amiloride did not produce a sinergic effect.
• 4.4. Our results suggest that diclofenac produces relaxation of vanadate-induced contraction by activation of Na⁺/Ca²⁺-exchange.

     

Protection by selective amino acid solutions against doxorubicin induced growth inhibition of Escherichia coli

• 1.1. Incubation of Escherichia coli with 0.7 mM doxorubicin in MBS-glucose medium resulted in complete growth inhibition, an inhibition that was blocked by placing specific amino acids (AA) in the medium.
• 2.2. The mechanism of protection by AA was similar to that reported previously for cells poisoned by hyperoxia and by paraquat, e.g. of 20 common AA, ten protect, ten do not and the branched-chair AA are among those required for inhibition.
• 3.3. Unlike hyperoxia and paraquot stringency which caused elevation of intracellular concentrations of guanosine tetraphosphate (ppGpp), doxorubicin inhibition did not elevate ppGpp.
• 4.4. Concentrations of ppGpp were increased by isoleucine starvation as expected, and the subsequent addition of doxorubicin did not abolish that increase; however, pretreatment with doxorubicin prevented the induction of stringency by isoleucine starvation.
• 5.5. This suggests that doxorubicin directly inhibits ppGpp synthesis or protein biosynthesis to leave tRNA loaded as is the case with chloramphenicol.

     

Cardiac mechanical and electrophysiologic modulations of guinea-pig by caffeine and thapsigargin

• 1.1. The effects of caffeine and thapsigargin on the contractile force and the action potential in guinea-pig papillary muscles were examined.
• 2.2. Caffeine (1 to 10 mM) initially increased contractile force in a concentration-dependent manner. Subsequently, 1 mM caffeine decreased it as compared with precaffeine level (but not significantly). At 5 mM or 10 mM, caffeine also decreased contractile force, but the decrease was still positive as compared with control level.
• 3.3. Exchange to low [Ca]_o(0.9 mM) or high[k]_o(8 mM) decreased steady-state value during exposure to 1 mM caffeine. Addition of 1 μM thapsigargin (TG) decreased the steady-state value during exposure to 1 mM caffeine, but enhanced it with 5 mM and 10 mM caffeine. TG (1 μM) alone increased the force.
• 4.4. In electrophysiologic studies, caffeine shortened the action potential duration (APD) in a concentration-dependent manner. In the presence of caffeine (1 mM), high[K]_o shortened APD and decreased the action potential amplitude and resting potential.
• 5.5. These results suggest that in the presence of caffeine and/or thapsigargin calcium overload might not occur in the left ventricular papillary muscles of the guinea-pig heart.

     

High potassium-evoked release of ATP from rabbit pulmonary artery via endogenous noradrenaline

• 1.1. High potassium 30 mM and noradrenaline at 10 μM significantly evoked the release of ATP and produced remarkable vasoconstriction in the rabbit pulmonary artery.
• 2.2. Phentolamine and prazosin at 0.1 μM inhibited ATP release but not vasoconstriction by 30 mM potassium.
• 3.3. 30 mM potassium significantly evoked the release of noradrenaline.
• 4.4. There was a significant positive correlation between the amounts of release of total purines, sum of ATP, ADP, AMP and adenosine, and noradrenaline evoked by 30 mM potassium.
• 5.5. 30 mM potassium-evoked ATP release was significantly reduced by denudation of endothelium.

     

Effect of potassium on the contractile response of the rat detrusor muscle to field stimulation at increasing calcium concentrations

• 1.1. At 0.6 and 1.8 mM calcium, increasing the potassium concentration from 2.5 to both 7.5 and 12.5 mM significantly increased the contractile response to field stimulation at 0.5, 1, 2 and 4 Hz. There were no effects on the contractile responses to 8, 16, 32 and 64 Hz. 22.5 mM potassium significantly reduced the contractile response to all frequencies of stimulation.
• 2.2. At 5.4 mM calcium, the contractile responses to all frequencies in the presence of 2.5, 7.5 and 12.5 mM potassium were similar. The responses to all frequencies of stimulation in the presence of 22.5 mM potassium were significantly reduced.
• 3.3. In general, the relative responses to low frequencies of stimulation were significantly greater in the presence of 5.4 mM calcium than in the presence of 0.6 or 1.8 mM calcium.
• 4.4. The magnitude of the inhibition in the presence of 22.5 mM potassium was inversely proportional to the extracellular calcium concentration, i.e. the lower the calcium concentration, the greater the inhibition.
• 5.5. The bladder base responded to alterations in the potassium and calcium concentrations similarly to the bladder body.
• 6.6. In conclusion, increasing the potassium concentration from 2.5 mM (normal bath concentration) to 7.5 and 12.5 mM significantly enhanced the contractile response to low frequency stimulation at both 0.6 and 1.8 mM (normal bath concentration) calcium.

     

Phorbol esters impair endothelium-dependent and independent relaxation in rat aortic rings

• 1.1. This study examined the ability of various nitro-vasodilators, 8-bromo cyclic guanosine 3′:5′ monophosphate (8-BrcGMP) and forskolin to relax rings of rat thoracic aorta pre-contracted with either noradrenaline (0.1 μM) or the protein kinase C activators, phorbol 12,13-dibutyrate (PDB, 0.1 μM) or phorbol 12-myristate 13-acetate (PMA, 0.5 μM).
• 2.2. In noradrenaline pre-contracted rings, acetylcholine (10 nM−10 μM), sodium nitroprusside (1 nM−0.5 μM), the calcium ionophore A23187 (10 nM−10 μM) and 8-BrcGMP (10 mM) totally reversed the smooth muscle contraction. In PDB-contracted aortic rings acetylcholine, sodium nitroprusside and 8-BrcGMP-induced relaxation was reduced compared to that in noradrenaline-contracted aortic rings, but A23187 and forskolin-induced relaxations were unaffected. Both acetylcholine and A23187-induced relaxations in PDB-contracted rings were abolished in the presence of the nitric oxide synthesis inhibitor Nω-nitro-l-arginine (NOLA, 100 μM).
• 3.3. Acetylcholine and sodium nitroprusside were even less potent in their ability to relax PMA-contracted aortic rings compared with noradrenaline and PDB-contracted rings. A23187-induced relaxation was also inhibited in PMA-contracted rings.
• 4.4. These results show that protein kinase C activation reduces the ability of agents which liberate nitric oxide to induce smooth muscle relaxation, and also inhibits the biochemical pathways which are subsequently activated by nitric oxide and lead to vascular smooth muscle relaxation.

     

Modulation of Ca2+-activated K+ current by isoprenaline,carbachol, and phorbol ester in cultured (and fresh) rat aortic vascular smooth muscle cells

• 1.1. Effects of isoprenaline (ISO), carbachol, and phorbol ester on the outward K⁺ currents in single cultured (or fresh) rat aortic vascular smooth muscle (A7r5 and A-10) cells were examined using a whole-cell voltage-clamp (at room temperature 22°C).
• 2.2. With 10 mM EGTA in the pipette solution, the delayed rectifier K⁺ current (I_K) was activated by Ca²⁺ at pCa 7 more than at pCa 10, and was TEA (10 mM) and apamin (200 nM) sensitive, which represents a Ca²⁺-activated K⁺ current (I_KCa).
• 3.3. In cultured A7r5 cells, isoprenaline (1 and 5 μM) and carbachol (0.1 and 1 μM) inhibited I_KCa. Phorbol ester, 4-β-phorbol-12, 13-dibutyrate (PDB), at 0.1 and 1 μM also inhibited I_KCa and increased the inhibitory effects induced by isoprenaline (1 μM).
• 4.4. In fresh aortic cells, these drugs, at the same concentrations, also produced the similar effects.
• 5.5. In A-10 cells, PDB (1 μM) enhanced the transient outward current (4-AP-sensitive), but ISO (1 μM) inhibited the current.
• 6.6. These results suggest that the I_KCa current would be inhibited by cyclic nucleotides (cAMP and cGMP) and also by PK-C stimulation, and thereby be directly contributed to excitation-contraction coupling of the vascular smooth muscle cells.

     

Taurine-induced hyperpolarizing shift of the reversal potential of the fast Na+ current in embryonic chick cardiomyocytes

• 1.1. Effects of taurine on the reversal potential of Na⁺ channel (I_Na) in isolated 17-day-old embryonic chick ventricular cardiomyocytes were examined using whole-cell voltage clamp technique. Experiments were performed at room temperature (22°C).
• 2.2. Test pulses were applied between -60 and +50 mV from a holding potential of -90 mV. Addition of taurine (1–20mM) to the bath solution inhibited the I_Na at -30mV in a concentration-dependent manner; by 38.8 ± 3.7% (n = 14, P < 0.01) at 10 mM and by 49.5 ± 4.6% (n = 12, P < 0.001) at 20 mM.
• 3.3. Simultaneously, the reversal potential was shifted in the hyperpolarizing direction by 10.6 ± 2.9 mV (n =10, P < 0.05) at 10mM and by 12.6 ± 2.2mV (n = 9, P <0.01) at 20mM. The shift was also produced concentration-dependently. Even when taurine at low concentrations (1 and 5 mM) enhanced I_Na, the shift occurred.
• 4.4. Intracellular taurine level decreased in Langendorff perfused guinea-pig hearts with Ca²⁺- and Mg²⁺-free solution, but not with Ca²⁺-free and 20 mM Mg²⁺ solution.
• 5.5. These results indicate that taurine shifts the reversal potential of the I_Na due to Na²⁺-taurine cotransport, which might play an important role for the cell functions.