Inhibitory effects of d-nicotine on the responses evoked by 1-isomer in trachea and bronchus isolated from guinea-pig and rabbit

• 1.1. The effects of d-nicotine on the responses induced by 1-isomer were studied in tracheae and bronchi isolated from guinea-pigs and rabbits. In guinea-pig trachea 1-nicotine produced a biphasic response consisting of initial contraction and following relaxation. In other airway preparations 1-nicotine produced only contraction.
• 2.2. d-Nicotine did not produce any responses except for the case of guinea-pig trachea. d-isomer produced only relaxation and relative potency was approximately 0.44 in guinea-pig trachea.
• 3.3. Pretreatment with d-nicotine (30 ∼ 300 μM) reduced concentration response curves for 1-isomer in a non-competitive manner in all preparations used in this study.
• 4.4. 1-nicotine at the concentration of 3 μM, which did not produce any response itself, reduced the concentration response curve of 1-nicotine in guinea-pig trachea.
• 5.5. Inhibition by d-nicotine or 1-nicotine (3 μM) of the concentration-response curve of 1-nicotine may be due to desensitization of nicotine receptors.

     

A comparison of the relaxant effects of pinacidil in rabbit renal and mesenteric artery

• 1.1. The relaxant effects of pinacidil were compared in isolated rabbit renal and mesenteric artery.
• 2.2. Pinacidil (10 nm–300 μM) relaxed renal and mesenteric arterial rings precontracted with phenylephrine with pD₂ values of 5.11 ± 0.03 and 6.27 ± 0.04, respectively.
• 3.3. The inhibitory effect of pinacidil on the rabbit mesenteric artery was competitively antagonized by glibenclamide (1–10 μM). The calculated pK_B value was 6.37 ± 0.04. On the renal artery, glibenclamide (2–20 μM) did not significantly affect pinacidil-induced relaxation (P > 0.05).
• 4.4. Tetraethylammonium (TEA, 1–10 mM) competitively antagonized the pinacaidil induced relaxation of the rabbit renal artery. The pK_B value was 3.22 ± 0.08. On the mesenteric artery TEA antagonized the effect of pinacidil in a noncompetitive manner.
• 5.5. The concentration-response curves for pinacidil on the rabbit renal and mesenteric artery were not affected by apamin (0.1 μM).
• 6.6. It is concluded that ATP-sensitivie K⁺ channels (K_ATP) are not involved in pinacidil action on the rabbit renal artery. On the contrary, K_ATP are probably major sites of pinacidil action on the rabbit mesenteric artery.

     

Insulin-activated amiloride-blockable nonselective cation and Na+ channels in the fetal distal lung epithelium

• 1.1. The apical membrane of fetal distal lung epithelium had two types of amiloride-blockable Na⁺-permeant cation channels; (1) nonselective cation (NSC) channel with a single channel conductance of 27 pS and (2) Na⁺ channel with a single channel conductance of 12 pS around resting membrane potential.
• 2.2. The IC₅₀ of amiloride to the Na⁺ channel was 1–2 μM, while the IC₅₀ of amiloride to the NSC channel was less 1μM. The open probability of the Na⁺ channel was about 10-fold larger than that of the NSC channel.
• 3.3. Insulin (100 nM) increased the open probability of both channels.

     

Alterations in antioxidant/oxidant gene expression and proteins following treatment of transformed and normal colon cells with tellurium compounds

The current study evaluated the potential of TeCl₄ and DPDT to accumulate within cells and cause oxidative stress. HO-1, antioxidant gene expression and protein alterations were studied.

• •Significant Te accumulation was observed in HT-29 cells (500–1000 μM DPDT; 125–1000 μM TeCl₄) and CCD-18Co cells (500 μM DPDT and TeCl₄).
• •Significant increases in HO-1 were observed with 250–1000 μM DPDT and 62.5–1000 μM TeCl₄ in HT-29 cells and in 500–1000 μM DPDT and 62.5–1000 μM TeCl₄ in CCD-18Co cells.
• •In CCD-18Co cells, a significant increase in COX-2 was observed at 500–1000 μM DPDT and 125–1000 μM TeCl₄.
• •Significant increase in NQO1 was observed with exposure to 500–1000 μM DPDT and TeCl₄.
• •In HT-29 cells, increased CYGB was noted at concentrations of 500–1000 μM DPDT and TeCl₄, while significant increases were noted in NCF-1at 1000 μM DPDT and TeCl₄.
• •No change in MT-3 and GSR were observed in either cell line.

     

Mechanisms involved in the spasmolytic effect of extracts from sabal serrulata fruit on smooth muscle

• 1.1. The effects of two extracts from Sabal serrulata fruits [total lipidic (L) and saponifiable (S)] on smooth muscle contractions have been assayed.
• 2.2. Both extracts (0.1–1 mg/ml) relaxed the tonic contraction induced by norepinefrine (30 nM) on rat aorta [EC₅₀, 0.53 ± 0.05 mg/ml (L) and 0.5 ± 0.04 mg/ml (S)] and by KCl (60 mM) on rat uterus. The Sabal extracts (0.3–1 mg/ml) also antagonized the dose-response curve of contractions induced by acetylcholine (0.1–100 μM) on urinary bladder.
• 3.3. dL-Propranolol (1 μM) but not the inactive (R)-(+)-propranolol (1 μM) potentiated the Sabal extracts relaxant effect by lowering the EC₅₀ (0.35 ± 0.2 vs 0.20 ± 0.01 mg/ml for L and 0.43 ± 0.02 vs 0.19 ± 0.02 mg/ml, P < 0.01, for S extract).
• 4.4. Cycloheximide (10 μg/ml) antagonized the effect of extracts from Sabal. However, actinomycin D (5 μg/ml) significantly (P ≤ 0.01) antagonized the effect of the total lipidic extract without modifying that of the saponifiable extract.
• 5.5. The relaxant effect of both extracts was not modified by the tyrosine kinase inhibitor genistein (10 μM) or the ornithine decarboxylase inhibitor α-difluoromethyl-ornithine (10 mM).

     

5-HT3 receptor blocking properties of the antiparkinsonian agent,talipexole

• 1.1. Talipexole showed moderate displacement activity of ³H-GR 65630 binding to 5-HT₃ receptors in both rat cortical and intestinal membrane fractions with Ki values of 0.35 μM and 0.22 μM, respectively.
• 2.2. Bromocriptine failed to displace the binding activity in either experimental system even at a concentration of 10 μM.
• 3.3. Both talipexole and tropisetron were found to significantly inhibit 5-HT₃ receptor-mediated effects of 5-HT in isolated guinea-pig ileum or atrium; however, the effect of talipexole was weaker than that of tropisetron.
• 4.4. Bromocriptine, in contrast, had no antagonistic effects on 5-HT₃ receptor-mediated activity in guinea-pig ileum or atrium.
• 5.5. It was concluded that talipexole might act as an antagonist on 5-HT₃ receptors in both brain and intestinal tissues.

     

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.

     

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.

     

Calcium and depolarization-dependent effect of pregnenolone derivatives on uterine smooth muscle

• 1.1. The effects of several gestagens (pregnenolone [1 to 30 μm], 20α-hydroxypregnenolone [1 to 30 μM]), and 20β-hydroxypregnenolone [1 to 30 μm]) on rat uterine contraction induced by KC1 (60 mM) and CaCl₂ (30 μM to 6 mM) have been assayed.
• 2.2. The three drugs relaxed the tonic contraction induced by KCI in a concentration-dependent way. The respective EC₅₀ values were: 27.6±1.58 μM (pregnenolone), 4.1±0.12 μM (20α-hydroxypregnenolone), and 11.2±1.04 μM (20β-hydroxypregnenolone). CaCl₂ (1 to 10 mM) totally counteracted the relaxing effect of pregnenolone but only partially compared to that of 20α- or 20β-hydroxy-pregnenolone.
• 3.3. CaC1₂ (30 μM to 6 mM) produced concentration-dependent contraction of rat uterus in medium lacking calcium plus 30, 60, or 90 mM of KC1. The EC₅₀ values of CaCl₂ were: 0.38±0.072, 0.183±0.015, and 0.183±0.015 μM in a medium with 30, 60, or 90 mM of KCI, respectively.
• 4.4. Pregnenolone (10 μM) did not significantly modify the EC₅₀ of CaC1₂ in a medium with 30, 60, or 90 mM of KCI. However, 20β-hydroxypregnenolone (10 μM) antagonized, in a noncompetitive manner, the concentration-response curve to CaC1₂.
• 5.5. 20α-Hydroxypregnenolone (4 μM) antagonized the concentration-response curve to CaCl₂ in a competitive manner. This antagonism was directly related to the concentration of KCI in the medium.
• 6.6. Our results suggest a different calcium antagonist effect of the three gestagens assayed.

     

Comparison of various calcium channel blockers on guinea-pig isolated common bile duct

• 1.1. The inhibitory effects of various calcium channel blockers; nifedipine, verapamil, diltiazem and a heterogenous compound, dantrolene, have been investigated on isolated common bile duct from guinea-pig.
• 2.2. All the compounds tested induced a concentration-dependent reduction of the amplitude of contractile response to electrical stimulation or increasing the calcium concentration of the bathing media.
• 3.3. Nifedipine was the most potent compound whereas the least potent was dantrolene; verapamil and diltiazem had intermediate potency.
• 4.4. The IC₅₀ values for these compounds were calculated as: nifedipine 3.68 × 10⁻⁹M; verapamil, 4.93 × 10⁻⁸M; diltiazem, 4.2 × 10⁻⁷M; and dantrolene 5.51 × 10⁻⁵M.
• 5.5. All the compounds displaced the concentration-response curve of calcium chloride to the right in a concentration-dependent manner. Among the compounds studied, nifedipine had the highest and dantrolene had the lowest potency.
• 6.6. These results indicate the striking pharmacological effects of the calcium channel blockers on the common bile duct and may indicate a possible role for these compounds in the treatment of biliary colic.

     

The activity of flavonoids extracted from Tanacetum microphyllum DC. (Compositae) on soybean lipoxygenase and prostaglandin synthetase

• 1.1. The in vitro effects of centaureidin and 5,3′-dihydroxy-4′-methoxy-7-carbomethoxyflavonol (Fig. 1), two anti-inflammatory flavonoids extracted from Tanacetum microphyllum DC., have been examined on both cyclooxygenase and lipoxygenase activity.
• 2.2. These flavonoids produced an inhibition of soybean lipoxygenase activity in a dose-dependent manner, with IC₅₀ values (20 and 29 μM respectively) similar to the reference drug.
• 3.3. The IC₅₀ values for the in vitro inhibition of cyclooxygenase activity by these flavonoids, were higher than those that produced lipoxygenase activity (318 and 60μM respectively).
• 4.4. These results suggest that the anti-inflammatory activity of our flavonoids may, at least in part, be due to the inhibition of leukotriene synthesis.
• 5.5. This is the first report of the biological activity in vitro of these compounds.

     

Characterization of muscarinic receptors on the isolated guinea pig ileum at pharmacologically low concentrations

• 1.1. Several selective and non-selective muscarinic agonists (McN-A-343, RS-86, arecoline, oxotremorine-M, pilocarpine, cis-dioxolane, and acetylcholine) were examined for relaxant activity in the isolated guinea-pig ileum at pharmacologically low concentrations.
• 2.2. The concentrations studied include: 1 × 10⁻¹²M, 3 × 10⁻¹²M, 1 × 10⁻¹¹M, 3 × 10⁻¹¹M and 1 × 10⁻¹⁰M.
• 3.3. None of the compounds exhibited relaxant activity in both the field and non-field stimulated ileum.
• 4.4. All of the above compounds exert muscarinic agonist activity in a concentration range of 1 × 10⁻⁹M to 1 × 10⁻⁶M (Williams et al., 1992).
• 5.5. Thus, in the isolated guinea-pig ileum, muscarinic agonists do not exert relaxant activity of the gastrointestinal tract at low concentrations.

     

Comparison of interactions of R(+)- and S(−)-isomers of β-adrenergic partial agonists,befunolol and carteolol,with high affinity site of β-adrenoceptors in the microsomal fractions from guinea-pig ciliary body,right atria and trachea

• 1.1. The stereoselectivities of β-adrenergic partial agonists for the high affinity binding site of β-adrenoceptors in the guinea-pig ciliary body, right atria and trachea were studied.
• 2.2. The inhibition curves by the S(−)-isomers of befunolol and carteolol were not significantly different from that by the R(+)-isomers in the guinea-pig ciliary body.
• 3.3. The inhibition curves by the S(−)-isomers of befunolol and carteolol were about 10 times as potent as the R(+)-isomers in the guinea-pig atria and trachea.
• 4.4. The pK_i values of the S(−)-isomers of befunolol and carteolol were significantly larger than those of R(+)-isomers in the guinea-pig atria and trachea but not larger than those of the R(+)-isomers in the guinea-pig ciliary body.
• 5.5. These results suggest that the high affinity binding site of β-adrenoceptors in ciliary body cannot discriminate stereoselectively between the R(+)- and S(−)-isomers, while in other tissues there is stereoselectivity between the two enantiomers.

     

Effects of non-opioid antitussives on hypoxia-induced electrical changes in rat hippocampal slices: A comparative study with anticonvulsant drugs

• 1.1. The effects of the non-opioid antitussives caramiphen and carbetapentane and of the anticonvulsants 5,5-diphenylhydantoin and MK 801 were tested towards hypoxia-induced electrical changes in rat hippocampal slices.
• 2.2. The incidence of appearance of hypoxia-induced epileptiform bursting was significantly decreased (P < 0.05) by carbetapentane (50–100 μM), caramiphen (50–100 μM), 5,5-diphenylhydantoin (25–50 μM), and the glutamate antagonist dizocilpine (MK 801, 25–50 μM).
• 3.3. The incidence of reappearance of the CA1 population spike after hypoxia was significantly increased (P < 0.05) by carbentapentane (50–100 μM), caramiphen (50–100 μM), 5,5-diphenylhydantoin (25–50 μM), and MK 801 (25–50 μM).
• 4.4. The results suggest a useful role for non-opioid antitussives and some anticonvulsants in the treatment of hypoxia-induced functional disturbances.

     

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.

     

Electrophysiological effects of tiracizin and its metabolites in dog cardiac purkinje fibers

• 1.1. Conventional microelectrode technique was used to study the effects of tiracizin and its two main metabolites on the action potential parameters in dog cardiac Purkinje fibers.
• 2.2. Tiracizin induced a use-dependent depression of the maximal rate of depolarization during the upstroke of the action potential (EC₅₀ = 0.323 ± 0.059μM, n = 5) and decreased the action potential duration (EC₅₀ = 0.230 ± 0.024 μM, n = 5).
• 3.3. The two main metabolites exerted similar effects, but only at concentrations about one order of magnitude higher than tiracizin.
• 4.4. It was concluded that the electrophysiological effects of tiracizin in dog Purkinje fibers correspond to those of Class I antiarrhythmic drugs also in cardiac Purkinje fibers. The main metabolites are less potent than the parent compound, therefore it is likely that their effects play a less important role in the beneficial effect of tiracizin in cardiac arrhythmias.

     

Vascular smooth muscle reactivity to norepinephrine in ovariectomized rats: Relationship to vascular PGE2/PGF2α ratio

• 1.1. We have recently demonstrated that, in normal female rats, vascular reactivity (VR) and vascular prostaglandin-E₂ (PGE₂) and prostacyclin production are influenced by the ovarian cycle.
• 2.2. In this study, we investigated the vascular reactivity (VR) of isolated rat thoracic aorta to norepinephrine (NE 10⁻¹²-10⁻⁶M) in ovariectomized rats (OVX-rats), 48 hr and 8 days after surgical removal of the ovaries and in normally cycling rats (NR) at the proestrus stage of the estrous cycle, when the level of circulating estrogen was higher.
• 3.3. In addition, we determined the vascular synthesis of PGE₂ and protaglandin-F_2α (PGF_2α) in both groups of OVX-rats, and in NR during the proestrous stage.
• 4.4. The results showed that VR to NE 10⁻¹²-10⁻¹⁰ M was similar between OVX-rats and normal rats.
• 5.5. However, aortic rings obtained from both groups of OVX-rats showed a significant increase of the contraction response induced by NE 10⁻⁹-10⁻⁶ M.
• 6.6. Furthermore, the contractile response to NE 10⁻⁷-10⁻⁶ M was greater in the aortic rings from OVX-rats 8 days after ovariectomy compared to OVX-rats 48 hr (p < 0.001).
• 7.7. Vascular PGE₂ and PGF_2α synthesis (ng/mg protein/hr) was significantly higher in both groups of OVX-rats than NR. But the vascular PGF_2α synthesis increased more than PGE₂ in these OVX-rats, thus the ratio PGE₂/PGF_2α was decreased significantly in both groups of OVX-rats (p < 0.01 and p < 0.001 OVX-rats 48 hr and 8 days after surgery, respectively) compared to NR-ratio.

     

Adenosine selectively depresses muscarinic compared with non-muscarinic receptor mediated depolarisation of the rat superior cervical ganglion

• 1.1. A grease gap d.c. recording technique was used to measure electrophysiological responses of the isolated rat superior cervical ganglion.
• 2.2. Adenosine at 100 μM depressed depolarisations to the muscarinic agonists carbachol, muscarine and methylfurmethide. In contrast adenosine (100μM) did not alter depolarisations to 1,1-dimethyl-4-phenylpiperazinium, 2-methyl-5-hydroxytryptamine and potassium and enhanced depolarisations to 5-hydroxytryptamine and gamma-aminobutyric acid.
• 3.3. Adenosine-induced depressions of the depolarisations to carbachol, muscarine, and methylfurmethide tended to be increased in the presence of 0.3 μM methoctramine (a muscarinic receptor antagonist with slight selectivity for M₂ receptors). The increase was statistically significant (P < 0.01) for carbachol.
• 4.4. Medium containing 0.1 mM Ca²⁺ and 0.3 μM pirenzepine augmented the hyperpolarising phase of the response to carbachol. Adenosine (10–300μM) hyperpolarised ganglia and did not significantly alter the hyperpolarisation to 0.3 or 1 μM carbachol but selectively reduced the depolarisation response to 3 μM carbachol.
• 5.5. Adenosine-induced hyperpolarisations (100 μM) were enhanced when applied during depolarisations to muscarinic agonists (muscarine, pilocarpine, N-methyl-N-(1-methyl-4-pyrrolidine-2-butynyl)acetamide (BM-5)), and other M-current inhibitors, barium and eledoisin-related-peptide. Adenosine induced hyperpolarisations were not affected by d-Ala⁶-luteinizing-hormone-releasing-hormone or uridine 5′-triphosphate which produced small depolarisations.
• 6.6. It is concluded that adenosine acts selectively in opposing mechanisms of depolarisation of the rat SCG that are due to the action of muscarinic agonists (acting via M₁-receptors) and by other M-current inhibitors.

     

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.