Antiplatelet effect of marchantinquinone, isolated from Reboulia hemisphaerica, in rabbit washed platelets.

Platelet activation is involved in serious pathological situations, including atherosclerosis and restenosis. It is important to find efficient antiplatelet medicines to prevent fatal thrombous formation during the course of these diseases. Marchantinquinone, a natural compound isolated from Reboulia hemisphaerica, inhibited platelet aggregation and ATP release stimulated by thrombin (0.1 units mL(-1)), platelet-activating factor (PAF; 2 ng mL(-1)), collagen (10 microg mL(-1)), arachidonic acid (100 microM), or U46619 (1 microM) in rabbit washed platelets. The IC50 values of marchantinquinone on the inhibition of platelet aggregation induced by these five agonists were 62.0 +/- 9.0, 86.0 +/- 7.8, 13.6 +/- 4.7, 20.9 +/- 3.1 and 13.4 +/- 5.3 microM, respectively. Marchantinquinone inhibited thromboxane B2 (TxB2) formation induced by thrombin, PAF or collagen. However, marchantinquinone did not inhibit TxB2 formation induced by arachidonic acid, indicating that marchantinquinone did not affect the activity of cyclooxygenase and thromboxane synthase. Marchantinquinone did inhibit the rising intracellular Ca2+ concentration stimulated by the five platelet-aggregation inducers. The formation of inositol monophosphate induced by thrombin was inhibited by marchantinquinone. Platelet cAMP and cGMP levels were unchanged by marchantinquinone. The results indicate that marchantinquinone exerts antiplatelet effects by inhibiting phosphoinositide turnover.

Aggregation inhibitory activity of minor acetophenones from Paeonia species.

Two minor acetophenones, 2,5-dihydroxy-4-methoxy-acetophenone (2) and 2,5-dihydroxy-4-methylacetophenone (7) from Paeonia species were found to selectively inhibit the aggregation of rabbit platelets induced by arachidonic acid. They were more potent than the major compound, paeonol (1), and 7 also inhibited the formation of TXA2 and PGD2 from arachidonic acid.

Effects of prokinetic agents on contractile responses to electrical field stimulation of isolated guinea pig trachea.

We investigated the effects of two prokinetic agents, metoclopramide and cisapride, on the contractile response of isolated guinea pig tracheal segments exposed to electrical field stimulation (EFS). Tracheal segments were suspended between two platinum electrodes in organ baths. Frequency-response curves were obtained by increasing the frequency of the stimuli on equilibrated tracheal segments, in a stepwise manner. Metoclopramide potentialed the EFS-induced contraction of the tracheal; the potentiation was more prominent at lower stimulation frequencies (< or = 10 Hz). Cisapride significantly inhibited the electrically stimulated contraction in trachea strips when the frequency of the stimulus was higher than 10 Hz. In the presence of both metoclopramide and cisapride, there was a potentiation of the contractile response at lower frequencies, and this potentiation was reduced when the frequency was higher than 10 Hz. These results demonstrate that metoclopramide enhances and cisapride reduces the airway tonicity elicited by EFS in isolated guinea pig trachea segments. Further studies are needed to verify the effects of these prokinetic agents on EFS-induced contraction of isolated guinea pig trachea and to determine the mechanisms involved.

Antiplatelet action of 3',4'-diisovalerylkhellactone diester purified from Peucedanum japonicum Thunb.

3',4'-Diisovalerylkhellactone diester (PJ-1) is a coumarin derivative purified from the medicinal herb Peucedanum japonicum Thunb. We examined its in vitro effects on various aspects of platelet reactivity. PJ-1 inhibited the aggregation and ATP release of rabbit platelets induced by PAF (platelet-activating factor) and collagen. The IC50 values of PJ-1 and BN52021 on PAF (2 ng/ml)-induced platelet aggregation were about 56.3 and 22.0 microM, respectively. And, the IC50 value of PJ-1 toward collagen (10 microg/ml)-induced platelet aggregation was 89.4 microM. Although the platelet aggregation caused by arachidonic acid and thrombin were barely inhibited by PJ-1, the release reactions were partially suppressed. PJ-1 also inhibited the thromboxane B2 formation caused by collagen, while formations of thromboxane B2 and prostaglandin D2 caused by arachidonic acid were not affected. The phosphoinositide breakdown caused by PAF was inhibited by PJ-1, but those by other inducers were not affected significantly. PJ-1 inhibited the intracellular Ca2+ increase caused by PAF in fura-2-loaded platelets. PJ-1 also concentration-dependently inhibited [3H]PAF (3.03 ng/ml) binding to washed platelets with an IC50 value of 3.9 microM. It is concluded that the main antiplatelet effect of PJ-1 may be due to dual activities on the blockade of PAF receptor-induced activation and also the inhibition of phospholipase A2 in rabbit platelets.

Scavenger and antioxidant properties of prenylflavones isolated from Artocarpus heterophyllus.

The antioxidant properties of prenylflavones, isolated from Artocarpus heterophyllus Lam., was evaluated in this study. Among them, artocarpine, artocarpetin, artocarpetin A, and cycloheterophyllin diacetate and peracetate had no effect on iron-induced lipid peroxidation in rat brain homogenate. They also did not scavenge the stable free radical 1,1-diphenyl-2-picrylhydrazyl. In contrast, cycloheterophyllin and artonins A and B inhibited iron-induced lipid peroxidation in rat brain homogenate and scavenged 1,1-diphenyl-2-picrylhydrazyl. They also scavenged peroxyl radicals and hydroxyl radicals that were generated by 2,2'-azobis(2-amidinopropane) dihydrochloride and the Fe3+-ascorbate-EDTA-H2O2 system, respectively. However, they did not inhibit xanthine oxidase activity or scavenge superoxide anion, hydrogen peroxide, carbon radical, or peroxyl radicals derived from 2,2'-azobis(2,4-dimethylvaleronitrile) in hexane. Moreover, cycloheterophyllin and artonins A and B inhibited copper-catalyzed oxidation of human low-density lipoprotein, as measured by fluorescence intensity, thiobarbituric acid-reactive substance and conjugated-diene formations and electrophoretic mobility. It is concluded that cycloheterophyllin and artonins A and B serve as powerful antioxidants against lipid peroxidation when biomembranes are exposed to oxygen radicals.

Antioxidant properties of butein isolated from Dalbergia odorifera.

The antioxidant properties of butein, isolated from Dalbergia odorifera T. Chen, were investigated in this study. Butein inhibited iron-induced lipid peroxidation in rat brain homogenate in a concentration-dependent manner with an IC50, 3.3+/-0.4 microM. It was as potent as alpha-tocopherol in reducing the stable free radical diphenyl-2-picrylhydrazyl (DPPH) with an IC0.200, 9.2+/-1.8 microM. It also inhibited the activity of xanthine oxidase with an IC50, 5.9+/-0.3 microM. Besides, butein scavenged the peroxyl radical derived from 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH) in aqueous phase, but not that from 2,2-azobis(2, 4-dimethylvaleronitrile) (AMVN) in hexane. Furthermore, butein inhibited copper-catalyzed oxidation of human low-density lipoprotein (LDL), as measured by conjugated dienes and thiobarbituric acid-reactive substance (TBARS) formations, and electrophoretic mobility in a concentration-dependent manner. Spectral analysis revealed that butein was a chelator of ferrous and copper ions. It is proposed that butein serves as a powerful antioxidant against lipid and LDL peroxidation by its versatile free radical scavenging actions and metal ion chelation.

Antiproliferative effect in human prostatic smooth muscle cells by nitric oxide donor.

We obtained a primary culture of prostatic cells through explantation from patients with benign prostatic hyperplasia. Structural morphology, immunohistochemical staining, and growth characteristics of these cells demonstrate that they are consistent with the population of smooth muscle cells (SMCs). We examined the influence of a nitric oxide donor, sodium nitroprusside (SNP), on the regulation of human prostatic SMC proliferation. SNP exhibited a concentration-dependent (0.1-10 microM) inhibition of fetal calf serum-induced proliferation in human prostatic SMCs. In addition, growth-inhibitory responses to 8-bromo-cGMP (1-30 muM) were observed. However, the responses to SNP were significantly diminished by the presence of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (3 microM; a selective guanylate cyclase inhibitor). Furthermore, SNP induced an increased concentration-dependent accumulation of intracellular cGMP in human prostatic SMCs. After 48-hr period of deprivation of serum, cells were restimulated with serum to permit cell cycle progression. The addition of SNP (10 microM) at various times after the addition of serum to serum-deprived cells showed maximal inhibition of cell proliferation even when added 6 hr after the serum. This blocking effect of cell cycle progression was lost gradually as the delay from serum to SNP application increased from 6 to 18 hr. The membrane-associated protein kinase C (PKC) activity was studied in human prostatic SMCs; results showed that fetal calf serum (10%, v/v) significantly increased membrane-associated PKC activity. SNP (10 muM), which had little effect on basal kinase activity, completely abolished serum-induced augmentation of PKC activity. Therefore, we suggest that SNP mediates its antiproliferative effect by the inhibition of PKC activity on human prostatic SMCs; furthermore, its antiproliferative effect occurs at the early G1 phase of the cell cycle.

Effect of PP1D-1, a synthetic antiplatelet compound, on rabbit platelets.

The antiplatelet mechanism of a synthetic compound, 2-chloro-3-methoxycarbonylpropionamido-1,4-naphthoquinone (PP1D-1), was studied by employing washed rabbit platelets in vitro. PP1D-1 concentration-dependently inhibited thrombin (0.1 U/ml)-, platelet-activating factor (2 ng/ml)-, collagen (10 microg/ml)-, arachidonic acid (100 microM)- and U46619 (1 microM)-induced aggregation and ATP release in washed rabbit platelets. The IC50 values of PP1D-1 for aggregation induced by the above inducers are 17.9+/-1.7, 9.8+/-1.1, 3.9+/-0.4, 1.8+/-0.3 and 1.7+/-0.3 microM, respectively. PP1D-1 did not affect platelet thromboxane B2 or prostaglandin D2 formation induced by arachidonic acid, indicating that it did not affect cyclooxygenase and thromboxane synthase activities. PP1D-1 significantly inhibited the formation of inositol 1,4,5-trisphosphate caused by these five platelet stimulators. Moreover, PP1D-1 inhibited the increase in intracellular calcium concentration induced by these agents. On the contrary, PP1D-1 did not inhibit thapsigargin-elevated intracellular calcium concentration in indomethacin-pretreated platelets, indicating it did not influence the effect of thapsigargin. According to these data, PP1D-1 exerts antiplatelet effects mainly by inhibiting phosphoinositide turnover.

Isoorientin-6"-O-glucoside, a water-soluble antioxidant isolated from Gentiana arisanensis.

The antioxidant activities of isoorientin-6"-O-glucoside were studied using various models. Isoorientin-6"-O-glucoside was more potent than Trolox, probucol and butylated hydroxytoluene (BHT) in reducing the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH). It also scavenged superoxide anion, peroxyl and hydroxyl radicals that were generated by xanthine/xanthine oxidase, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) and Fe3+-ascorbate-EDTA-H2O2 system, respectively. The IC50 value, stoichiometry factor and second-order rate constant were 9.0+/-0.8 microM, 1.8+/-0.1 and 2.6 X 10(10) M(-1) s(-1) for superoxide generation, peroxyl and hydroxyl radicals. However, isoorientin-6"-O-glucoside did not inhibit xanthine oxidase activity or scavenge hydrogen peroxide (H2O2), carbon radical or 2,2'-azobis(2,4-dimethyl-valeronitrile) (AMVN)-derived peroxyl radical in hexane. Isoorientin-6"-O-glucoside inhibited Cu2+-induced oxidation of human low-density lipoprotein (LDL) as measured by fluorescence intensity, thiobarbituric acid-reactive substance formation and electrophoretic mobility. Since isoorientin-6"-O-glucoside did not possess pro-oxidant activity, it may be an effective water-soluble antioxidant that can prevent LDL against oxidation.

Antiplatelet agents isolated from medicinal plants.

Platelet-vessel wall interaction is an important process in physiological hemostasis and pathological thrombosis. In oriental countries, some medicinal plants have been claimed for uses to improve circulation, induce fibrinolysis or prevent thrombosis. In cooperation with chemists using bioassay-based step-by-step purification, some antiplatelet agents were isolated from plant sources. According to their effects on platelet aggregation, release reaction and signal transductions involved, these antiplatelet agents can be classified into eight groups: 1. platelet-activating factor (PAF) antagonists, 2. collagen-receptor antagonists, 3. thromboxane-receptor antagonists, 4. ADP-receptor agonists, 5. inhibitors of phosphoinositide breakdown, 6. inhibitors of thromboxane formation, 7. agents increasing cyclic nucleotides, and 8. protein kinase C activators. These new pharmacological agents derived from medicinal plant sources may be useful as leads to develop as effective cardiovascular drugs.

Bioactive constituents of Morus australis and Broussonetia papyrifera.

The biological activities of the active principles of two plants in the Moraceae have been investigated. A new prenylflavonoid, australone A (1), and a new triterpenoid, 3 beta-[(m-methoxybenzoyl)oxy]urs-12-en-28-ioc acid (2) were isolated from the root bark of Morus australis, and their structures determined by spectroscopic methods. Also isolated from this plant were seven known compounds, morusin (3), kuwanon C (4), betulinic acid, beta-amyrin, quercetin, ursolic acid, and compound A. Morusin (3) showed significant effects on arachidonic acid-, collagen-, and PAF-induced platelet aggregation, while kuwanon C (4) was active in the arachidonic acid- and PAF-induced platelet aggregation assays. In biological work on a second plant, Broussonetia papyrifera, broussoflavonols F (5) and G (6), broussoflavan A (7), and broussoaurone A (8) potently inhibited Fe(2+)-induced lipid oxidation in rat-brain homogenate. Compounds 5-7 also significantly inhibited the proliferation of rat vascular smooth muscle cells.

A new flavone C-glycoside and antiplatelet and vasorelaxing flavones from Gentiana arisanensis.

A new flavone C-glycoside, isovitexin 6"-O-glucoside (1), and three known flavonoids, quercetin, isovitexin, and luteolin-7-O-beta-D-glucoside, have been further isolated from the whole plant of Gentiana arisanensis Hayata. The new compound was characterized by spectral methods and chemical reactions. The antiplatelet effects of isovitexin 6"-O-glucoside (1), isoorientin (2), 2 peracetate (3), isovitexin (4), luteolin 7-O-beta-D-glucoside (5), luteolin (6), isoorientin 6"-O-glucoside (7), and 7 peracetate (8) were studied using washed rabbit platelets. Of the compounds tested, 6 showed potent antiplatelet effects on arachidonic acid (AA)-induced platelet aggregation (IC50 = 43.5 microM). The effect of 2, 5, and 6 on the contraction of rat thoracic aorta was also studied. Compound 6 depressed markedly the contraction induced by Ca2+ (1.9 mM) in high-K+ (80 mM) medium, with an IC50 of about 156 microM and also inhibited noradrenaline (3 microM)-induced phasic and tonic contractions, with an IC50 of about 68 and 72 microM, respectively.

Antiplatelet effects of some aporphine and phenanthrene alkaloids in rabbits and man.

Two aporphines (boldine and laurolitsine) and five phenanthrene alkaloids (litebamine, secoboldine, N-cyanosecoboldine, N-methylsecoglaucine and N-methylsecopredicentrine) were evaluated in-vitro for their ability to inhibit platelet aggregation. All seven alkaloids inhibited aggregation of rabbit platelets and inhibited the release of ATP induced by arachidonic acid and collagen in rabbit platelets. Those aggregations induced by platelet-activating factor (PAF), thrombin, U46619 and ADP were inhibited by the three N-substituted secoboldine derivatives only. Thromboxane B2 formation caused by arachidonic acid was also suppressed by these compounds. They did not affect the generation of [3H]inositol monophosphate caused by collagen, PAF and thrombin in the presence of indomethacin. Platelet cyclic AMP level was unaffected by litebamine, but was increased by N-methylsecoglaucine. Litebamine suppressed the secondary aggregation, but not the primary aggregation, induced by ADP and adrenaline in platelet-rich plasma from man, whereas N-methylsecoglaucine inhibited both primary and secondary aggregation. It is concluded that the antiplatelet effect of these seven aporphine and phenanthrene alkaloids is mainly a result of inhibition of thromboxane A2 formation; N-methylsecoglaucine has additional antiplatelet activity as a result of increasing the levels of platelet cyclic AMP.

Low-affinity thromboxane receptor mediates proliferation in cultured vascular smooth muscle cells of rats.

We examined the binding properties and mitogenic effects of U46619, using cultured vascular smooth muscle cells (VSMCs), by ligand-binding assay, measuring [3H]thymidine and [3H]leucine incorporation, checking with flow cytometry, and counting the cell number. The U46619-activated mitogenic signal-transduction pathway was assessed by measuring formation of inositol monophosphate (IP); [Ca2+]i; mitogen-activated protein kinase (MAPK), MAPK kinase (MAPKK), and p74raf-1 activities; and GTP-bound Ras. [3H]U46619 bound to cultured VSMCs from Wistar-Kyoto (WKY) rats at a single class of site (Kd: 15.5 +/- 2.6 nmol/L). However, it bound to VSMCs from spontaneously hypertensive rats (SHRs) at two classes of sites (Kd: 2.3 +/- 0.6 nmol/L and 1.4 +/- 0.5 mumol/L). U46619 increased DNA and protein synthesis, cell number, IP formation, [Ca2+]i, and MAPK and MAPKK activities, with EC50 values close to its Kd value for the low-affinity binding site in VSMCs from SHR. Prostaglandin (PG) E2 and PGF2 alpha showed little of such mitogenic effects. All these effects of U46619 were inhibited by SQ29548, staurosporine, or pretreatment of VSMCs with phorbol 12-myristate 13-acetate for 24 hours. However, U46619 stimulation did not lead to a significant increase in the Ras-GTP complex or p74raf-1 activity. In conclusion, the mitogenic effect of U46619 appears to be mediated via the activation of low-affinity thromboxane binding sites that trigger phosphoinositide hydrolysis and activate the MAPK pathway, leading to DNA synthesis and cell proliferation.

Bioactive alkaloids from Illigera luzonensis.

Using antiplatelet aggregation as a guide to fractionation, seven aporphines, actinodaphnine (1), N-methylactinodaphnine (2), launobine (3), dicentrine (4), O-methylbulbocapnine (5), hernovine (7), and bulbocapnine (9), and two oxoaporphines, dicentrinone (6) and liriodenine (8), were isolated from the stems of Illigera luzonensis. Among them, compounds 2, 4, 5, 8, and 9 were isolated for the first time from this species. Moreover, compounds 1-5, and 8 showed significant antiplatelet aggregation and compounds 1 and 6 exhibited significant vasorelaxant activities, respectively.

2',5'-Dihydroxychalcone as a potent chemical mediator and cyclooxygenase inhibitor.

Eleven chalcone derivatives have been tested for their inhibitory effects on platelet aggregation in rabbit platelet suspension and the activation of mast cells and neutrophils. Arachidonic acid-induced platelet aggregation was potently inhibited by almost all the compounds and some also had a potent inhibitory effect on collagen-induced platelet aggregation and cyclooxygenase. Some hydroxychalcone derivatives showed strong inhibitory effects on the release of beta-glucuronidase and lysozyme, and on superoxide formation by rat neutrophils stimulated with the peptide fMet-Leu-Phe (fMLP). We found that the anti-inflammatory effect of 2',5'-dihydroxychalcone was greater than that of trifluoperazine. 2'5'-Dihydroxy and 2',3,4,5'-tetrahydroxyl chalcones, even at low concentration (50 microM), tested in platelet-rich plasma from man almost completely inhibited secondary aggregation induced by adrenaline. These results suggest that the anti-platelet effects of the chalcones are mainly a result of inhibition of thromboxane formation.

Pharmacological evaluation of ocoteine, isolated from Cassytha filiformis, as an alpha 1-adrenoceptor antagonist in rat thoracic aorta.

Ocoteine, isolated from Cassytha filiformis, was found to be an alpha 1-adrenoceptor blocking agent in rat thoracic aorta as revealed by its competitive antagonism of phenylephrine-induced vasoconstriction (pA2 = 7.67 +/- 0.09). Removal of endothelium from the aorta did not affect its antagonistic potency (pA2 = 7.97 +/- 0.07). [3H]-Inositol monophosphate formation caused by noradrenaline (3 microM) was suppressed by ocoteine (10 microM) and prazosin (3 microM). Ocoteine did not affect the contraction induced by U-46619, prostaglandin F2 alpha or angiotensin II, but inhibited slightly those by high K+ and endothelin I. Neither the cyclic AMP nor cyclic GMP content of rat thoracic aorta was changed by ocoteine (10 microM). Comparing the EC50 values, the potency of ocoteine against 5-hydroxytryptamine (5-HT) was about 60 times less than that against phenylephrine. Ocoteine (10 microM) also slightly antagonized the clonidine-induced inhibition of the twitch response evoked by field stimulation in rat vas deferens. In guinea pig trachea, the contraction caused by carbachol, histamine, neurokinin A or leukotriene C4 and beta 2-adrenoceptor-mediated relaxing responses induced by isoprenaline were not affected by ocoteine (10 microM). The voltage clamp study in rat ventricular single myocytes revealed that ocoteine (3, 10 microM) inhibited steady state outward currents, but not transient outward currents or slow inward Ca2+ currents. It is concluded that ocoteine is a selective alpha 1-adrenoceptor antagonist in isolated rat thoracic aorta. At high concentrations, it also blocks 5-HT receptors and Na+ and steady state outward currents in rat ventricular myocytes.

ADP-mimicking platelet aggregation caused by rugosin E, an ellagitannin isolated from Rosa rugosa Thunb.

Among the nine ellagitannins, rugosin E was the most potent platelet aggregating agent with an EC50 of 1.5 +/- 0.1 microM in rabbit platelets and 3.2 +/- 0.1 microM in human platelets. The aggregations caused by rugosin E and ADP were inhibited by EGTA, PGE1, mepacrine, sodium nitroprusside and neomycin, but not by indomethacin, verapamil, TMB-8, BN52021 and GR32191B. Rugosin E-induced thromboxane formation was suppressed by indomethacin, EGTA, PGE1, verapamil, mepacrine, TMB-8 and neomycin. ADP-scavenging agents, such as CP/CPK and apyrase inhibited concentration-dependently ADP (20 microM)-, but not rugosin E (5 microM)-induced platelet aggregation. In thrombin (0.1 U/ml)-treated and degranulated platelets, rugosin E and ADP still caused 63.5 +/- 3.0% and 61.2 +/- 3.5% of platelet aggregation, respectively. Selective ADP receptor antagonists, ATP and FSBA inhibited rugosin E- and ADP-induced platelet aggregations in a concentration-dependent manner. Both rugosin E and ADP did not induce platelet aggregation in ADP (1 mM)-desensitized platelets. In contrast to ADP, rugosin E did not decrease cAMP formation in washed rabbit platelets. Both rugosin E and ADP did not cause phosphoinositide breakdown in [3H]myo-inositol-labeled rabbit platelets. In fura-2/AM-load platelets, both rugosin E and ADP induced increase in intracellular calcium concentration and these responses were inhibited by ATP and PGE1. All these data suggest that rugosin E may be an ADP receptor agonist in rabbit platelets.

The effect of the selective PAF antagonist CIS-19 on PAF- and antigen-induced bronchoconstriction, microvascular leakage and bronchial hyperreactivity in guinea-pigs.

We investigated the effects of a novel platelet-activating factor (PAF) receptor antagonist, CIS-19 [cis-2-(3, 4-dimethoxyphenyl)-6-isopropoxy-7-methoxy-1-(N-methyl-formamido)-1, 2, 3, 4-tetrahydronaphthalene], on PAF-, histamine-, substance P- and antigen-induced bronchoconstriction and microvascular leakage, as well as PAF- and antigen-induced bronchial hyperreactivity to methacholine in urethane-anesthetized guinea-pigs. Administration of CIS-19 (0.5-5 mg/kg, i.v.) inhibited the increase in lung resistance induced by PAF (30 ng/kg, i.v.) in a dose-dependent manner, but failed to inhibit the increase induced by histamine (30 micrograms/kg, i.v.) or substance P (6.5 micrograms/kg, i.v.). CIS-19 (5 mg/kg, i.v.) did not inhibit the increase in lung resistance induced by ovalbumin (2 mg/kg, i.v.) in actively sensitized guinea-pigs. PAF (30 ng/kg, i.v.)-induced microvascular leakage, measured by the extravasation of Evans blue dye, was dose-dependently inhibited by CIS-19 (0.5-5 mg/kg, i.v.) in the trachea, main bronchi and intrapulmonary airways, but it did not affect histamine (30 micrograms/kg, i.v.)- or substance P (6.5 micrograms/kg, i.v.)-induced microvascular leakage at all airway levels. CIS-19 (2.5 and 5 mg/kg) did not affect ovalbumin (2 mg/kg, i.v.)-induced microvascular leakage in all airway levels in actively sensitized guinea-pigs, CIS-19 (2.5 and 5 mg/kg, i.v.) significantly inhibited PAF-induced enhancement of the bronchial response to methacholine, but had no effect on ovalbumin (0.05 mg/kg, i.v.)-induced bronchial hyperreactivity in actively sensitized guinea-pigs. It is concluded that CIS-19 is a potent PAF receptor antagonist which inhibits PAF- but not antigen-induced bronchoconstriction, microvascular leakage and bronchial hyperreactivity. These results suggest that PAF plays little or no role in early airway responses following antigen challenge.

Activation by high potassium of a novel voltage-operated Ca2+ channel in rat spleen.

1. High potassium produced a concentration-dependent contraction in rat isolated spleen. 2. The high potassium-induced contraction of rat spleen was abolished in Ca(2+)-free Krebs solution containing 1 mM EGTA, and the subsequent addition of 3 mM Ca2+ restored the high potassium-induced contraction to the control level. 3. Nifedipine, verapamil, diltiazem, Cd2+, Ni2+, Co2+, R-(+)-Bay K 8644 and pimozide inhibited and relaxed high potassium-induced contraction of rat spleen with IC50 and EC50 values much higher than those values in rat aorta. 4. In addition, high potassium-stimulated contraction of rat spleen was insensitive to omega-conotoxin GVIA, omega-conotoxin MVIIC and omega-agatoxin IVA. 5. The high potassium-induced contraction of rat spleen was also unaffected by tetrodotoxin (TTX), prazosin, chloroethylclonidine (CEC), yohimbine, propranolol, atropine, diphenhydramine, cimetidine, ketanserin, 3-tropanyl-indole-3-carboxylate, saralasin, indomethacin, nordihydroguaiaretic acid, GR32191B, domperidone, naloxone, chlorpromazine, suramin, (+/-)-2-amino-5-phosphonopentanoic acid, 6,7-dinitroquinoxaline-2,3-dione (DNQX), L-659,877, L-703,606, lorglumide, PD 135,158 N-methyl-D-glucamine, benextramine, amiloride, dantrolene, TMB-8, econazole, staurosporine and neomycin. 6. Forskolin and sodium nitroprusside relaxed high potassium-induced contraction of rat spleen with EC50 values of 0.55 +/- 0.04 and 20.0 +/- 2.7 microM, respectively. 7. It is concluded that high potassium may activate a novel, pharmacologically uncharacterized voltage-operated Ca2+ channel in rat spleen.