Inhibition of calcium entry induced by cularines and isocrasifoline in uterine smooth muscle

Traditional Chinese medicine for the treatment of primary dysmenorrhea: how do Yuanhu painkillers effectively treat dysmenorrhea?

AIM

To examine the efficacy of YuanHu painkillers (YHP) as a treatment for primary dysmenorrhea and to reveal YHP's principle formula.

METHODS

A Wistar rat uterine contraction model was utilized in this study. Rats were given 0.698g/kg YHP, 0.07g/kg tetrahydropalmatine (THP; YHP's main component), 0.02g/kg imperatorin (IMP), or THP+IMP (0.07+0.02g/kg) as polypharmacy (PG) by gavage. H&E staining and histopathological examination of the uteri tissue samples were performed. We then detected superoxide dismutase (SOD) and malondialdehyde (MDA), nitric oxide (NO), as well as inducible nitric oxide synthase (iNOS), i-κB, nuclear factor-κB (NF-κB), and cyclooxygenase-2 (COX-2) indices.

RESULTS

PG significantly inhibited the uterine contraction of the primary dysmenorrhea rat model (p<0.05), and was significantly different than single-agent therapy (p<0.05). Histopathological examination showed inflammation in the uteri of the control group which YHP and its main constitutes alleviated. THP significantly inhibited the contraction of isolated uteri caused by Ach, PGF2α and oxytocin in a concentration-dependent fashion. THP and IMP both significantly affected the levels of NO, activation of NF-κB, up-regulated the expression of i-κB and down-regulated the expression of both iNOS and COX-2. IMP obviously decreased the level of MDA and increased the activation of SOD (p<0.05). PG obviously improved all the parameters mentioned above (p<0.05).

CONCLUSIONS

YHP exerted protective effects on primary dysmenorrhea in rats and remarkably alleviated the severity of experimental primary dysmenorrhea. The combined strategy proved to be more effective than either THP or IMP alone and may have synergistic effects in combination in primary dysmenorrhea. Mechanisms that might account for the beneficial effects include abating oxidative stress, inhibiting over-inflammatory reaction, and alleviating the contraction of isolated rat uteri by inhibiting the influx of extracellular Ca(2+). Broad potential for future clinical practice is foreseeable.

Relaxative effect of core licorice aqueous extract on mouse isolated uterine horns

CONTEXT

Primary dysmenorrhea is one of the most frequent gynecological disorders in young women. Chinese herbal medicine has the advantage in terms of multi-targeting efficacy, lower toxicity, as well as lower cost. Core licorice is the hard and atropurpureus heart part in root and rootstock of Glycyrrhiza uralensis Fisch (Leguminosae), having a therapeutic effect on dysmenorrhea.

OBJECTIVE

This experiment indicated the spasmolytic effect of core licorice aqueous extract (CLE) on spontaneous rhythmic contractions and spasmogen-provoked contractions of stilbestrol primed, estrogen-dominated, non-pregnant mouse isolated uterine horns and its spasmolytic mechanism.

MATERIALS AND METHODS

We investigated the spasmolytic effect of CLE (0.025-0.1 mg/mL) on spontaneous contractions and potassium chloride (KCl, 40 mM), acetylcholine (ACh, 5 μg/mL), carbachol (CCh, 5 μg/mL), oxytocin (OT, 2 U/L) or bradykinin (5 ng/mL)-provoked contractions of mouse isolated uterine horns. Contractions were recorded by tension force transducers using Biolap 420F software on a PC.

RESULTS

Our present study showed that graded, escalated concentrations of CLE (0.025-0.1 mg/mL) significantly inhibited the amplitude of spontaneous phasic contractions (15.03-55.10%), as well as the contractions produced by KCl (40 mM; 20.16-53.99%), ACh (5 μg/mL; 14.65-48.32%), CCh (5 μg/mL; 38.40-76.70%), OT (2 U/L; 21.53-58.49%) or bradykinin (5 ng/mL; 58.01-79.44%) of the estrogen-dominated isolated mice uterine horn preparations in a concentration-related manner.

DISCUSSION AND CONCLUSION

The spasmolytic effect of CLE observed in the present study lends pharmacological support to the traditional use of core licorice in the management, control and treatment of primary dysmenorrhea.

Relaxant effect induced by wogonin from Scutellaria baicalensis on rat isolated uterine smooth muscle

CONTEXT

Wogonin is a flavone derivative isolated from Scutellaria baicalensis Georgi (Labiatae) root, which is a traditional Chinese drug used as an anti-inflammatory and for management of dysmenorrhea.

OBJECTIVE

The effect of wogonin on the uterus has not yet been examined. We investigated the relaxant effects of wogonin on contractile activity of isolated uterine strips of rats.

MATERIALS AND METHODS

The effect of wogonin on spontaneous uterine contraction, and uterine contraction induced by agonists, K⁺-depolarization and oxytocin in Ca²⁺-free solution was observed. To clarify the type of potassium channel, we tested the effects of 4-aminopyridine, tetraethylammonium and glibenclamide.

RESULTS

Wogonin reduced the contractile amplitude of uterine strip smooth muscle of rats in a dose-dependent manner. The concentration of wogonin for reducing the contraction amplitude by 50% (IC₅₀) on spontaneous contractions was 60.5 μM. Wogonin also inhibited the contraction induced by three agonists (oxytocin, prostaglandin F(2α) and acetylcholine). For the uterine strips pretreated with oxytocin in Ca²⁺-free solution or K⁺-depolarization, wogonin showed relaxant effect on the induced uterine contractions. In addition, whereas the inhibitive effect of wogonin on the contraction of uterine smooth muscle in rats could be partly blocked by 4-aminopyridine and tetraethylammonium, it was not influenced by glibenclamide.

DISCUSSION AND CONCLUSION

Wogonin significantly inhibited the contraction of rat uterine smooth muscle probably through the inhibition of the inflow of extracellular calcium into cells via cell membrane, and intracellular release of calcium ions. In addition, the relaxant effect induced by wogonin might be due in part to the opening of voltage-dependent and large conductance Ca²⁺-activated K⁺ channels.

Tetrandrine and Isotetrandrine, Two Bisbenzyltetrahydroisoquinoline Alkaloids from Menispermaceae, with Rat Uterine Smooth Muscle Relaxant Activity

The effects of two bisbenzyltetrahydroisoquinoline alkaloids, 1S, 1′S tetrandrine and its isomer 1R, 1′S isotetrandrine, were investigated in rat isolated uterus in order to identify the mechanism of relaxant action and to study the influence of the absolute configuration on the activity of these alkaloids. Both inhibited the uterine contraction induced by high K+, acetylcholine and oxytocin. In Ca2+-free medium, isotetrandrine relaxed the sustained contraction induced by oxytocin but tetrandrine did not. The relaxant effects of the alkaloids may be due to blockade of calcium influx through specific channels. Tetrandrine and isotetrandrine modify the calcium channel in a nonreversible manner whilst only isotetrandrine acts intracellularly. Tetrandrine shows a more specific relaxant activity as a calcium entry blocker.

Selective Inhibition of Calcium Entry Induced by Benzylisoquinolines in Rat Smooth Muscle

The mechanism of relaxant activity of six benzylisoquinolines was examined in order to determine the minimal structural requirements that enable these compounds to have either a non-specific action like papaverine or an inhibitory activity on calcium entry via potential-operated channels. All the alkaloids tested totally or partially relaxed KCl-depolarized rat uterus and inhibited oxytocin-induced rhythmic contractions. Only glaucine and laudanosine inhibited K+-induced uterine contractions more than oxytocin-induced uterine contractions. In Ca+-free medium, sustained contractions induced by oxytocin or vanadate were relaxed by the alkaloids tested except for glaucine and laudanosine indicating no inhibitory effect on intracellular calcium release. Those alkaloids containing an unsaturated heterocyclic ring (papaverine, papaverinol, papaveraldine, N-methylpapaverine and dehydropapaverine) exhibited a more specific activity than those with a tetrahydroisoquinoline ring.

In vitro myometrial inhibition by the partitioned aqueous fraction of Anthocleista djalonensis leaves

This study investigated the effect on the uterus of the aqueous fraction of the partitioned methanol crude extract of the leaves of Anthocleista djalonensis (AD) and the possible mechanism of AD activity. AD inhibited the concentration-response curves induced by oxytocin and CaCl2 on the rat uterus in vitro and significantly reduced the EC50 in a concentration-dependent manner (p < 0.05). A similar effect was observed with salbutamol and verapamil on the concentration-response curves obtained for oxytocin and CaCl2. The inhibitory effect of AD was not attenuated in the presence of propranolol. AD, salbutamol, and verapamil also produced a concentration-dependent relaxation on K+-induced sustained uterine contraction. In Ca2+-free medium, AD and salbutamol similarly inhibited oxytocin-induced contraction, but verapamil failed to produce this effect. The present results suggest that AD, being a mixture of phytochemicals, probably exerts inhibitory activity on in vitro uterine contractions of the nonpregnant, diethylstilboestrol-treated rat by multiple mechanisms that do not involve interaction with &beta;-adrenergic receptors and do not solely depend on inhibition of calcium influx.

Chemical composition and antispasmodic effect of Casimiroa pringlei essential oil on rat uterus

The Casimiroa pringlei essential oil was analyzed to determine its chemical composition. Its effect on rat uterine smooth muscle was studied and compared with verapamil. Pure commercial piperitone, eucalyptol, and alpha-terpineol, the major constituents of C. pringlei essential oil, were tested on the uterine tonic contraction induced by high-potassium depolarizing solution (KCl 60 mM).

Spasmolytic effect of constituents from Lepechinia caulescens on rat uterus

Lepechinia caulescens Ortega Epling (Lamiaceae) is a perennial herb used in Mexican folk medicine to treat diabetes, hypertension, gastrointestinal infections, dysmenorrhea and as abortifacient. In this study, a bioassay-guided fractionation of the hexanes extract of the leaves, evaluating the capacity to relax contraction of rat uterus rings induced by KCl (60mM), was made. The results indicated that, from the four isolated terpenes, spathulenol (1) was the most potent spasmolytic agent, followed by methyl 9alpha,13alpha-epidioxyabiet-8(14)-en-18-oate (2), 9alpha-hydroxydehydroabietyl alcohol (4) and dehydroabietic acid (3) studied at 10 and 30 microg/mL. The spasmolytic activity of 1 was totally reverted by addition of increasing extracellular Ca2+ concentrations ([Ca2+]o), while incubation of uterus rings with 1 in calcium free solutions reduced the contraction produced by [Ca2+]o in a concentration-dependent manner. Moreover, the presence of L-NAME (100 microM) or propranolol (10 microM) did not block the spasmolytic effect. These results suggest that 1 induces a greater blocking action on voltage-operated calcium channels. EtOAc and MeOH extracts of the leaves, which showed slight relaxing activity, led to 4 and rosmarinic acid (5).

Ligustilide inhibits spontaneous and agonists- or K+ depolarization-induced contraction of rat uterus

In the present study, the effects of ligustilide (LIG) on uterine contraction in vitro were investigated. In isolated rat uterine, LIG (2-8 microg/ml) inhibited the spontaneous periodic contraction in a concentration-dependent manner (EC(50)=4.4 microg/ml, 95% confidence interval 2.7-6.1 microg/ml), and attenuated prostaglandin F2alpha (PGF(2)alpha)- or acetylcholine chloride (Ach)-induced uterine contractions. At 8 microg/ml, LIG nearly completely blocked the PGF(2)alpha-induced contractions (95.3%). In the case of Ach-induced contraction, about 73.9% was inhibited by LIG at this dosage. It was also observed that LIG affected significantly oxytocin-induced increase in the contraction of uterine horns that were incubated not only in the Locke solution but also in a Ca(2+)-free solution. In addition, LIG caused concentration-dependent inhibition of uterine contraction induced by K(+) (56.3 Mm) depolarization, reaching the significant level at 2 microg/ml (EC(50)=3.3 microg/ml, 95% confidence interval 2.5-4.1 microg/ml). The findings clearly show that LIG has multiple effects on the uterine smooth muscles, suggesting that LIG possesses a non-specific antispasmodic function. The data also imply strongly that LIG is one of active ingredients of Danggui and has the potential to be developed into an effective drug for the prevention and treatment of primary dysmenorrhoea.

Effect of "Dang-Qui-Shao-Yao-San" a Chinese medicinal prescription for dysmenorrhea on uterus contractility in vitro

Dysmenorrhea is directly related to elevated level of prostaglandin F(2)alpha (PGF(2)alpha), and is treated with nonsteroid anti-inflammatory drugs. Though efficacy of the latter is rapid, the effect is temporary, and they cause many side effects to the liver, kidney and digestive system. Because of this, Chinese medicinal therapy is being considered as a feasible alternative medicine. In this study, Dang-Qui-Shao-Yao-San (DQSYS), one of Chinese medicinal prescriptions was selected. A 50% alcohol solution was used to extract the active ingredients and create a freeze-dried product. Using rat uterine smooth muscle in vitro, DQSYS was used to suppress spontaneous contractions and PGF(2)alpha induced contractions. Then acetylcholine, ergonovine, propranolol, oxytocin and KCl were used to analyze the physiological mechanisms. The results show that DQSYS has the antagonistic action on both PGF(2)alpha and Ach induced uterine contraction. Furthermore, it has the antagonistic effect on contraction caused by KCl-depolarization. These actions may be the major mechanism of the beneficial effect of Chinese prescription in treating dysmenorrhea.

Identification and quantification of isoquinoline alkaloids in the genus Sarcocapnos by GC-MS

Six cularine alkaloids, cularicine, O-methylcularicine, celtisine, cularidine, cularine and celtine, three isocularine alkaloids, sarcophylline, sarcocapnine and sarcocapnidine, and five non-cularine alkaloids, glaucine, protopine, ribasine, dihydrosanguinarine and chelidonine, were identified and quantified by GC-MS in nine taxa of the genus Sarcocapnos (Fumariaceae). The chemotaxonomic significance of the results is discussed.

Diastereoselective Synthesis of Cularine Alkaloids via Enium Ions and an Easy Entry to Isoquinolines by Aza-Wittig Electrocyclic Ring Closure

In preliminary communications, we reported the diastereoselective synthesis of cularine and sarcocapnine via the intramolecular ring closure of nitrenium and oxenium ions, a new highly diastereoselective reductive methylation with (+)-8-phenylmenthyl chloroacetate followed by reduction with sodium borohydride, and a facile entry to the isoquinoline precursors by aza-Wittig electrocyclic ring closure. We now report the full details of the syntheses of (+)-O-demethylcularine, (+)-cularine, (+)-sarcocapnidine, (+)-sarcocapnine, and (+)-crassifoline and describe different methods of synthesis of their precursors.

Antiplatelet activity of benzylisoquinoline derivatives oxidized by cerium(IV) ammonium nitrate

Oxidation of 1-benzyl-3,4-dihydroisoquinolines with cerium(IV) ammonium nitrate (CAN) under mild condition yielded the mixture of corresponding 1-benzylisoquinolines (b-type) and 1-benzoylisoquinolines (a- or c-type) in an equal yields. The selective oxidation products (c-type) can be prepared by using MeCN instead of MeOH. In the antiplatelet assays, four inducers were employed, including AA, Col, PAF, and Thr. In the PAF or Col induced platelet aggregation, compounds belonging to a- and b-type showed stronger inhibitory effects than aspirin.

Nantenine blocks muscle contraction and Ca2+ transient induced by noradrenaline and K+ in rat vas deferens

The effect of nantenine, an aporphine alkaloid isolated from Ocotea macrophylla H.B.K., was studied on contractions and Ca(2+) translocation induced by noradrenaline, Ca(2+), or K(+) in the isolated rat vas deferens from reserpinized animals. Concentration-response curves of calcium chloride (CaCl(2)) were performed in the vas deferens, in a Ca(2+)-free nutrient solution, using potassium chloride (KCl, 80 mM) as a depolarizing agent. In these conditions, nantenine (2.35 x 10(-4) and 4.7 x 10(-4) M) significantly reduced the maximum contractions (E(max)) of Ca(2+) (IC(50)=2.6 x 10(-4) M) and noradrenaline (IC(50)=2.9 x 10(-4) M). The contractile responses were totally recovered after the withdrawal of nantenine. In addition, experiments performed to measure simultaneously the contraction and the increase of intracellular Ca(2+) induced by noradrenaline (10(-5) M) or KCl (80 mM) showed that nantenine (2.35 x 10(-4) and 4.7 x 10(-4) M) significantly decreased both effects. The results suggest that a reversible block of Ca(2+) entry could be involved on the non-competitive-like antagonism of nantenine in rat vas deferens.

Relationships between structure and vascular activity in a series of benzylisoquinolines

1. In the present work, the properties of 3-methyl isoquinoline, 3,4-dihydropapaverine, tetrahydropapaverine and tetrahydropapaveroline were compared with those of papaverine and laudanosine. The work includes functional studies on rat isolated aorta contracted with noradrenaline, caffeine or KCl, and a determination of the affinity of the compounds for alpha1-adrenoceptors and calcium channel binding sites, with [3H]-prazosin, [3H]-nitrendipine and [3H]-(+)-cis-diltiazem binding to rat cerebral cortical membranes. The effects of papaverine derivatives on the different molecular forms of cyclic nucleotide phosphodiesterases (PDE) isolated from bovine aorta were also determined. 2. The three papaverine derivatives show greater affinity than papaverine for the [3H]-prazosin binding site. They are therefore more selective as inhibitors of [3H]-prazosin binding as opposed to [3H]-(+)-cis-diltiazem, while papaverine appears to have approximately equal affinity for both. [3H]-nitrendipine binding was not affected by either papaverine or papaverine derivatives in concentrations up to 100 microM. 3-Methylisoquinoline had no effect on any of the binding sites assayed. 3. Contractions evoked by noradrenaline (1 microM) in rat aorta were inhibited in a concentration-dependent manner by 3,4-dihydropapaverine, tetrahydropapaverine and with a lower potency, by tetrahydropapaveroline. In Ca2+-free solution, tetrahydropapaverine and to a lesser extent, tetrahydropapaveroline, inhibited the noradrenaline (1 microM) evoked contraction in a concentration-dependent manner and did not modify the phasic contractile response evoked by caffeine (10 mM). This suggests that these alkaloids do not act at the intracellular level, unlike papaverine which inhibits the contractile response to caffeine and noradrenaline. 4. Inositol phosphates formation induced by noradrenaline (1 microM) in rat aorta was inhibited by tetrahydropapaverine (100 microM) and tetrahydropapaveroline (300 microM), thus suggesting that alpha1D-adrenoceptors are coupled to phosphoinositide metabolism in rat aorta. 5. Unlike papaverine, which has a significant effect on all the PDE isoforms, the three alkaloids assayed did not have an inhibitory effect on the different forms of PDE isolated from bovine aorta. 6. These results provide evidence that papaverine derivatives with a partially or totally reduced isoquinoline ring have a greater affinity for alpha1-adrenoceptors and a lower affinity for benzothiazepine sites in the Ca2+-channel than papaverine. This structural feature also implies a loss of the inhibitory activity on PDE isoforms. The planarity of the isoquinoline ring (papaverine) impairs the interaction with the alpha1-adrenoceptor site and facilitates it with the Ca2+-channels and PDEs, whereas the more flexible tetrahydroisoquinoline ring increases the binding to alpha1-adrenoceptors.

Inhibitory effects of okadaic acid on rat uterine contractile responses to different spasmogens

In the present study, we examined the effects of okadaic acid, a selective inhibitor of type 1 and 2A protein phosphatases, on the mechanical responses evoked by oxytocin, K(+)- and Na(+)-modified solutions and ouabain in estrogen-primed rat myometrium. Oxytocin elicited a rapid, phasic contraction followed by rhythmic oscillations. The phasic response was partially resistant to the absence of external Ca2+. Okadaic acid (1 microM) and the L-type calcium channel blocker nifedipine (1 microM) abolished the oscillatory component and reduced the initial, phasic response to about 80% of the control response. High K+ (60 mM) solution, ouabain (1 mM), K(+)-free medium and low Na+ (25 mM) solution induced extracellular Ca(2+)-dependent biphasic responses composed by an early rapid (KCl, ouabain and K(+)-free solution) or slower developed (25 mM Na+ solution) phasic contraction followed by a sustained increase in tension. Okadaic acid and nifedipine, alone or in combination, abolished or decreased similarly the contractile response evoked by these stimulants. The okadaic acid- and nifedipine-insensitive responses to ouabain, K(+)-free and low Na+ solution were enhanced by increasing the extracellular concentration of Ca2+ in the medium and were inhibited in a dose-dependent manner by amiloride (0.05-0.5 mM). These data suggest that, in estrogen-primed rat uterus, dephosphorylating mechanisms by OA-sensitive protein phosphatases play an important role in regulating myometrial contractions elicited by Ca2+ entry through voltage-sensitive Ca2+ channels.

Ca(2+)-independent contraction induced by hyperosmolar K(+)-rich solutions in rat uterus

The present experiments were designed to investigate the mechanisms involved in the contractile responses evoked by KCl, added either isoosmotically or hyperosmotically, in the rat uterus. Exposure of uterine strips to a Ca(2+)-free, 3 mM EGTA-containing solution abolished the responses induced by isoosmotic KCl solutions. Conversely, addition of hyperosmolar KCl induced concentration-dependent tonic responses in a Ca(2+)-free, 3 mM EGTA-containing solution. The maximum increase in tension was reached with 210 mM K+. The response to hyperosmotic K+ was unaffected by previous depletion of intracellular Ca2+ stores with oxytocin (1 microM), by inhibition of refilling of the intracellular Ca2+ stores using cyclopiazonic acid (10 microM) or by increasing the concentration of EGTA in the medium to 10 mM. Sucrose and mannitol (60-420 mM) induced concentration-dependent sustained contractions which were not reproducible and were significantly smaller in size than those evoked by the maximally effective concentration of hyperosmotic K+ (210 mM). The contraction induced by hyperosmotic K+ in Ca(2+)-free solution was not altered by the calmodulin inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7, 100 microM), the Ca2+/calmodulin protein kinase II inhibitor 1-[N,O-bis(1,5-isoquinolinesulphonyl)-N-methyl-L-tyrosyl]-4-phenyl piperazine (KN-62, 10 microM) or the tyrosine kinase inhibitor genistein (10 microM). The protein kinase C inhibitor calphostin C (1-3 microM) failed to modify the K(+)-effect curve, which was however partially inhibited in the presence of the non-selective protein kinase inhibitor 1-(5-isoquinolinylsulphonyl)-2 methylpiperazine dihydrochloride (H-7, 3-100 microM). The protein kinase inhibitor staurosporine (30-300 nM) depressed the contraction induced by hyperosmolar K+ in a concentration-dependent manner. The contraction induced by sucrose in Ca(2+)-free solution was unaffected by W-7 (100 microM) and KN-62 (10 microM) but was partially reduced by calphostin C (1 microM), H-7 (30 microM), staurosporine (100 nM) and genistein (10 microM). These results suggest that different mechanisms are involved in the responses evoked by isoosmotic and hyperosmotic KCl in the rat uterus. A component of the contraction induced by hypertonic KCl seems mainly independent of both external and internal Ca2+ and of hyperosmolar stress. This contraction is not mediated by protein kinase C, Ca2+/calmodulin-dependent kinases or protein tyrosine kinases but involves activation of other, at the present unknown, staurosporine-sensitive protein kinase(s).

Effect of inhibition of the electrogenic Na+/K+ pump on the mechanical activity in the rat uterus

The effects of ouabain and K(+)-free solution were studied in estrogen-primed rat uterine strips under resting tone or repeatedly stimulated with KCl, acetylcholine or oxytocin applied for 20 minutes at 60 minute intervals. These effects were compared with those of the K+ channel opener cromakalim. In preparations under resting tone, ouabain (0.1 mM and 0.3 mM) induced rhythmic contractions which disappeared after 20-30 minutes whereas at a higher concentration (1 mM) it evoked a rapid, phasic response followed by a small tonic contraction. Exposure of the strip to a K(+)-free solution induced either rhythmic waves, which ceased after 8-10 minutes, or a single phasic contraction which was followed by a small and slow increase in the resting tone (54 +/- 10 mg after 180 min exposure). Nifedipine (0.3 microM) abolished the rhythmic or phasic component of these responses but failed to modify the late small tonic contraction induced by ouabain 1 mM or by K(+)-free solution. Ouabain (0.1-1 mM) or K(+)-free-evoked responses disappeared after short (4 min) or prolonged (60 min) exposure to a Ca(2+)-free, 3 mM EGTA-containing solution. Cromakalim (10 nM-0.1 mM) did not induce any variation in the resting tone either in the presence or in the absence of Ca2+ in the medium. In strips repeatedly stimulated with acetylcholine (0.1 mM) or oxytocin (1 microM), ouabain (0.3 mM), K(+)-free-solution and cromakalim (10 microM) reduced the amplitude of the initial, phasic response and progressively decreased the oscillatory component of the response to these agonists. Conversely, the successive responses evoked by KCl 60 mM in similar experimental conditions were not affected by ouabain or cromakalim. Ouabain (0.3 mM), K(+)-free solution and cromakalim (10 microM) decreased the Ca(2+)-independent, maintained contractions induced by acetylcholine or oxytocin after prolonged exposure to a Ca(2+)-free, EGTA-containing medium. These inhibitory effects were partially or completely reversed in the presence of the non-selective potassium channel blocker tetraethylammonium (10 mM) or in a Ca(2+)-free solution containing 60 mM K+. In conclusion, these results suggest that the response induced by ouabain or K(+)-free solution in estrogen-primed rat myometrium involves Ca2+ influx through potential-operated calcium channels but not Ca2+ release from intracellular stores. In addition, our results show that prolonged exposure to ouabain or K(+)-free medium decreases membrane receptor-mediated responses in rat uterus. This inhibitory effect seems to be the result, at least in part, of a decrease in the cytosolic level of K+, due to the inhibition of the electrogenic Na+ pump.

Mechanism of the cardiovascular activity of laudanosine: comparison with papaverine and other benzylisoquinolines

1. The activity of (+/-)-laudanosine, a benzyltetrahydroisoquinoline alkaloid, was investigated in pithed rats and rat isolated aorta. Its effects on [3H]-(+)-cis-diltiazem and [3H]-nitrendipine binding to rat cerebral cortical membranes, and on the different molecular forms of cyclic nucleotide phosphodiesterases (PDE) isolated from bovine aorta were investigated. 2. The dose-response curve to methoxamine (3-300 micrograms kg-1, i.v.) in normotensive pithed rats was shifted to the right by (+/-)-laudanosine, 3 and 6 mg kg-1. 3. (+/-)-Laudanosine inhibited in a concentration-dependent manner the contractile responses evoked by noradrenaline (NA 1 microM), depolarizing solution (KCl 80 mM) or depolarizing solution plus phentolamine (10 microM) in rat isolated aorta. The alkaloid appeared to be more potent against NA-induced contractions. 4. In Ca(2+)-free solution, (+/-)-laudanosine (100 microM) inhibited the contraction evoked by NA and did not modify the phasic contractile response evoked by caffeine. The alkaloid did not modify the refilling of the intracellular Ca(2+)-sotres sensitive to NA or caffeine. 5. (+/-)-Laudanosine inhibited [3H]-prazosin binding to cortical membranes and also inhibited [3H]-(+)-cis-diltiazem but with a lower potency. [3H]-nitrendipine binding was not affected by laudanosine. 6. (+/-)-Laudanosine does not have a significant effect on the different forms of PDEs isolated from bovine aorta. In contrast, compounds structurally related to this alkaloid such as papaverine and its derivatives, had a non-selective or more specific inhibitory effect on these PDE forms. These differences can be explained on the basis of their structural features: the planarity of the isoquinoline ring(papaverine) facilitates the interaction with receptor sites, and the different position of the benzyl group does not modify the activity unless this position leads to the presence of a chiral centre (laudanosine).7. These results suggest that (+/-)-laudanosine has a selective activity as an alpha1-adrenoceptor blocker. Its lack of action on different PDE forms provides us with information about a group of benzylisoquinolines that with small structural changes show a different effect on PDE-forms isolated from vascular smooth muscle.

Cardiovascular effect of a naphthylmethyl substituted tetrahydroisoquinoline, YS 49, in rat and rabbit

A novel tetrahydroisoquinoline, 1-alpha-naphthylmethyl-6,7-dihydroxy-1,2,3,4- tetrahydroisoquinoline (YS 49) 1) increased heart rate and force in isolated rat atria; 2) relaxed PE- and KCl-contracted rat aorta, and 3) decreased blood pressure and increased heart rate in anesthetized rabbit. These effects were blocked by propranolol, a nonselective beta-antagonist, but not by phentolamine, an alpha-blocker, and/or depletion of catecholamine by reserpine. These results suggest that the mechanism of action of YS 49 is due, at least in part, to beta-adrenergic receptor stimulation.

Different mechanism of relaxation induced by aporphine alkaloids in rat uterus

We have examined the uterine relaxant action of three aporphine molecules (S-glaucine, S-boldine and R-apomorphine) in two experimental conditions, with and without calcium in the bathing solution, and compared these effects with those obtained with the calcium antagonists verapamil and diltiazem. The present study shows that the alkaloids relax the uterine muscle but with different mechanisms of action. In Ca(2+)-containing solution all three alkaloids relaxed the uterus previously contracted by KCl or acetylcholine, but in Ca(2+)-free medium only R-apomorphine was able to relax oxytocin-induced contraction. The calcium antagonists, verapamil and diltiazem, relaxed KCl- or acetylcholine-induced contraction in Ca(2+)-containing solution, whereas they only relaxed oxytocin-induced contraction in Ca(2+)-free medium at much higher doses. These results suggest that glaucine and boldine behave as specific calcium entry blockers without affecting the contractile machinery or intracellular Ca2+ levels as apomorphine does. The absolute configuration (S-glaucine and S-boldine vs R-apomorphine) may account for this different action.

Selective action of two aporphines at alpha 1-adrenoceptors and potential-operated Ca2+ channels

Contractions evoked by noradrenaline (1 microM) or a depolarizing solution of 60 mM KCl were concentration dependently depressed by the aporphine alkaloids (S)-boldine and (R)-apomorphine in rat aorta. Both drugs had a greater inhibitory potency on the contraction elicited by noradrenaline. Dose-response curves for noradrenaline were shifted to the right in presence of (S)-boldine. (R)-Apomorphine acted by a complex mechanism at alpha 1-adrenoceptors and its inhibitory effect was irreversible. The conformational features of these alkaloids may explain their different behaviour at alpha 1-adrenoceptors. In Ca(2+)-free solution, the alkaloids inhibited the contraction evoked by noradrenaline but did not modify (apomorphine) or increase (boldine) the contractile response induced by caffeine. Both alkaloids interacted with [3H]prazosin binding and with the benzothiazepine binding site of the Ca2+ entry receptor complex but had no effect at the dihydropyridine binding site in the rat cerebral cortex. Both drugs showed some selectivity as inhibitors of [3H]prazosin binding as opposed to [3H]d-cis diltiazem binding. (R)-Apomorphine slightly inhibited one of the two forms of the Ca(2+)-independent, low Km cyclic AMP-phosphodiesterase (type IV), whereas it did not have a significant effect on the other phosphodiesterase forms. (S)-Boldine had negligible inhibitory effects on all phosphodiesterase forms. The present study provides evidence that (S)-boldine and (R)-apomorphine have interesting properties as Ca2+ entry blockers (through the benzothiazepine receptor site in the Ca2+ channel) and at alpha 1-adrenoceptors.

New synthetic ligands for L-type voltage-gated calcium channels

The pharmacology of the L-type Ca2+ channel has been the subject of considerable basic and clinical investigation over the past two decades primarily because of the clinical activities of nifedipine, verapamil and diltiazem. However, it is quite clear that this Ca2+ channel is, in common with other pharmacologic receptors, a multiple drug receptor. There are probably as many as six or more discrete drug binding sites associated with this Ca2+ channel. Continued investigation of these sites may yield both new therapeutic agents, structural clues to ligands active at other classes of Ca2+ channel and structures active at other classes of ion channel.

Inhibitory and contractile effects of okadaic acid on rat uterine muscle

The effects of okadaic acid and its interactions with various agents known to increase, by different mechanisms, the intracellular levels of cyclic AMP and/or cyclic GMP were investigated in isolated strips of rat myometrium. Okadaic acid showed inhibitory effects at concentrations between 10(-7) M and 3 x 10(-6) M. At higher concentrations, a biphasic, contractile and then relaxant response was observed. The results obtained suggest that, in rat uterine smooth muscle, the inhibitory effects of okadaic acid are not entirely mediated by the activation of cyclic AMP- and/or cyclic GMP-dependent pathways. The data also point to the existence of a clear interaction between okadaic acid and methylxanthines, although further studies are needed to clarify the mechanisms involved in this interaction.

Selective chiral inhibition of Ca2+ entry promoted by bisbenzyltetrahydroisoquinolines in rat uterus

The effects of diltiazem and six bisbenzyltetrahydroisoquinoline alkaloids (antioquine, 7-O-methylantioquine, dimethylantioquine, monterine, granjine and cordobimine) were studied in rat isolated uterus in order to clarify the mechanisms of their relaxant actions. All the compounds tested completely relaxed KCl-induced contractions and totally or partially inhibited oxytocin-induced rhythmic contractions. Only alkaloids with absolute configurations (1R,1'S or 1R,1'R) acted intracellularly, promoting relaxation of contractile responses induced by oxytocin in a Ca(2+)-free medium, as does papaverine. Alkaloids of the antioquine series (1S,1'R) selectively inhibited Ca2+ entry. The great rigidity of these structures and their stereoselective action make these alkaloids useful in studies of the conformational features of the Ca2+ channel.

Multiple actions of glaucine on cyclic nucleotide phosphodiesterases, alpha 1-adrenoceptor and benzothiazepine binding site at the calcium channel

1. In the present study, the properties of glaucine (an aporphine structurally related to papaverine) were compared with those of papaverine, diltiazem, nifedipine and prazosin. The work includes functional studies on rat isolated aorta contracted with noradrenaline, caffeine or KCl, and a determination of the affinity of glaucine at calcium channel binding sites of alpha-adrenoceptors, by use of [3H]-(+)-cis-diltiazem, [3H]-nitrendipine and [3H]-prazosin binding to cerebral cortical membranes. The effects of glaucine on the different molecular forms of cyclic nucleotide phosphodiesterases (PDE) isolated from bovine aorta were also determined. 2. Contraction evoked by noradrenaline (1 microM) or depolarizing solution (60 mM KCl) were inhibited in a concentration-dependent manner by all the compounds tested. As expected, prazosin showed a greater selectivity of action on NA-induced contraction, whereas nifedipine and diltiazem appeared more potent on KCl-induced contraction. Glaucine had a greater potency on the contraction elicited by noradrenaline whereas papaverine acted non specifically. 3. In Ca(2+)-free solution, prazosin (0.1 microM) and glaucine (0.1 mM) inhibited the contraction evoked by NA; diltiazem (0.1 mM) diminished this contraction whereas nifedipine (1 microM) had no effect. Preincubation of tissues with glaucine, diltiazem, nifedipine and prazosin did not modify the contractile response induced by caffeine. In contrast, papaverine (0.1 mM) significantly inhibited the contractions evoked by NA or caffeine in Ca(2+)-free medium. 4. Glaucine and papaverine show affinity at the [3H]-prazosin binding site and at the benzothiazepine binding site of the Ca(2+)-channel receptor complex, but have no effect at the dihydropyridine binding site in rat cerebral cortex. Glaucine exerts some selectivity as an inhibitor of [3H]-prazosin binding as opposed to [3H]-(+ )-cis-diltiazem binding while papaverine appears to have approximately equal affinity in this respect.5. This study confirms the presence of four phosphodiesterase (PDE) activities in bovine aorta: a calmodulin-activated PDE (CaM-PDE type I) which hydrolyzed preferentially guanosine 3':5'-cyclic monophosphate (cyclic GMP); a cyclic GMP selective form (cGMP-PDE type V); and two low Km adenosine 3':5'-cyclic monophosphate (cyclic AMP) PDEs that are insensitive to the stimulatory effect of CaM, one of which was inhibited by cyclic GMP (CGI-PDE, type III) and the other by rolipram (cAMP-PDE, type IV). Glaucine selectively inhibits one of the two forms of Ca2+-independent low Km cAMP-PDE, the type IV. In contrast, papaverine exerts a non-selective inhibitory effect upon all PDE forms.6. The present work provides evidence that glaucine, a benzyltetrahydroisoquinoline alkaloid, has interesting properties as an alpha l-adrenoceptor antagonist, calcium entry blocker (through the benzothiazepine recognition site in the calcium channel) and as a selective inhibitor of the rolipram-sensitive cAMP-PDE, type IV PDE.