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

Repurposing of US-FDA approved drugs against SARS-CoV-2 main protease (Mpro) by using STD-NMR spectroscopy, in silico studies and antiviral assays

SARS-CoV-2 Main protease (M^pro) is a well-known drug target against SARS-CoV-2 infection. Identification of M^pro inhibitors is vigorously pursued due to its crucial role in viral replication. The present study was aimed to identify M^pro inhibitors via repurposing of US-FDA approved drugs by STD-NMR spectroscopy. In this study, 156 drugs and natural compounds were evaluated against M^pro. Among them, 10 drugs were found to be interacting with M^pro, including diltiazem HCl (1), mefenamic acid (2), losartan potassium (3), mexiletine HCl (4), glaucine HBr (5), trimebutine maleate (6), flurbiprofen (7), amantadine HCl (8), dextromethorphan (9), and lobeline HCl (10) in STD-NMR spectroscopy. Their interactions were compared with three standards (Repurposed anti-viral drugs), dexamethasone, chloroquine phosphate, and remdesivir. Thermal stability of M^pro and dissociation constant (K_d) of six interacting drugs were also determined using DSF. RMSD plots in MD simulation studies showed the formation of stable protein-ligand complexes. They were further examined for their antiviral activity by plaque reduction assay against SARS-CoV-2, which showed 55-100% reduction in viral plaques. This study demonstrates the importance of drug repurposing against emerging and neglected diseases. This study also exhibits successful application of STD-NMR spectroscopy combined with plaque reduction assay in rapid identification of potential anti-viral agents.

Oxoglaucine mediates Ca2+ influx and activates autophagy to alleviate osteoarthritis through the TRPV5/calmodulin/CAMK-II pathway

BACKGROUND AND PURPOSE

Stimulation of calcium influx and suppression of autophagy play important roles in the pathogenesis of osteoarthritis (OA). In this study, we used a novel inhibitor of TRPV5 cation channels - oxoglaucine to attenuate progression of deterioration and pathological changes in OA patient-derived chondrocytes and OA animal model, by activating autophagy.

EXPERIMENTAL APPROACH

Inhibition by oxoglaucine of calcium influx was assessed in cells.. Analyses were also carried out to investigate the effect of oxoglaucine on OA by detection of anti-inflammatory response, TRPV5/CAMK-II/calmodulin pathway, autophagy, and cartilage protection both in vitro and in vivo. demonstrated by macroscopic evaluation and histological findings.

KEY RESULTS

Oxoglaucine suppressed expression of proinflammatory and apoptosis-related proteins, including TNF-α, IL-6, IL-1β, MMP-13, CASP-3, and BAX, and prevented matrix degradation in OA chondrocytes. It also successfully blocked Ca²⁺ influx, activating autophagy dose-dependently asshown by up-regulated expression of LC-3II/I, Beclin-1, ATG5, ATG7, higher autophagic influx and formation of autophagic vesicles. It also decreased expression of mRNA and protein of TRPV5, CAMK-II, and calmodulin. Conversely, 1,25-dihydroxyvitamin D3, anagonist of TRPV5 channels, reversed the oxoglaucine-induced calcium influx inhibition and autophagy activation, demonstrating the association of oxoglaucine with TRPV5. Further, oxoglaucine prevented the apoptosis and matrix degradation of articular cartilage in a rat model of OA.

CONCLUSION AND IMPLICATIONS

Oxoglaucine protects against cartilage damage by blocking the TRPV5/CAMK-II/calmodulin pathway to inhibit Ca²⁺ influx and activate autophagy. Our results indicate that oxoglaucine has the potential to become a candidate drug for treatment of OA.

Arterialized collateral capillaries progress from nonreactive to capable of increasing perfusion in an ischemic arteriolar tree

OBJECTIVE

CCA, outward remodeling of capillaries that anastomose 2 arteriolar trees with different parent feed arteries, may represent a therapeutic target for patients who lack collaterals. ACCs can reperfuse an ischemic tree, but their functional capacity is unknown. Therefore, we determined whether ACCs mature into resistance vessels that regulate blood flow following arterial occlusion.

METHODS

We ligated the lateral spinotrapezius feed artery in Balb/C mice, which induces CCA. At days 7 and 21 following occlusion, we measured vasodilation of ACCs using intravital microscopy and blood flow in the ischemic tree using LSF. We determined the presence of ACCs and neurovascular alignment with immunofluorescence.

RESULTS

At day 7, ACCs do not vasodilate following muscle contraction and have reduced responses to endothelial- and smooth muscle-dependent agents. By day 21, ACCs exhibit normal vasodilation, accompanied by normalized increases in relative blood flow to the ischemic zone. Although functioning as resistance vessels by regulating blood flow, ACCs do not appear to be innervated.

CONCLUSIONS

ACCs mature into resistance vessels that regulate blood flow to the downstream tissue. Therefore, induction of mature ACCs may be a target for reducing ischemia in patients who lack collateral networks.

In vitro functional evaluation of isolaureline, dicentrine and glaucine enantiomers at 5-HT2 and α1 receptors

Compounds with activity at serotonin (5-hydroxytryptamine) 5-HT₂ and α₁ adrenergic receptors have potential for the treatment of central nervous system disorders, drug addiction or overdose. Isolaureline, dicentrine and glaucine enantiomers were synthesized, and their in vitro functional activities at human 5-HT₂ and adrenergic α₁ receptor subtypes were evaluated. The enantiomers of isolaureline and dicentrine acted as antagonists at 5-HT₂ and α₁ receptors with (R)-isolaureline showing the greatest potency (pK_b  = 8.14 at the 5-HT_2C receptor). Both (R)- and (S)-glaucine also antagonized α₁ receptors, but they behaved very differently to the other compounds at 5-HT₂ receptors: (S)-glaucine acted as a partial agonist at all three 5-HT₂ receptor subtypes, whereas (R)-glaucine appeared to act as a positive allosteric modulator at the 5-HT_2A receptor.

Therapeutic potentials of natural compounds acting on cyclic nucleotide phosphodiesterase families

Intracellular cyclic AMP and/or cyclic GMP are characterized in the 1960th. These second messengers, hydrolysed specifically by cyclic nucleotide phosphodiesterase (PDE), play a major role in intracellular signalling. Natural products have been a rich source of drug discovery, Theophylline and Methylxanthine originated from tea leaves used for asthma treatment, whereas, Papaverine, a natural isoquinolein originated from Papaver somniferum traditionally used in impotency, altogether as caffeine where firstly described as PDE-inhibiting compounds. Since that time, the knowledge in PDE field has been drastically increased, allowing the design and development of new therapeutic drugs acting against different pathologies in the nanomolar range. During this period some natural compounds have been identified as PDE inhibitors and used in that context to investigate their therapeutic potential effects. The aim of this literature review is to point out the reported data and demonstrating the contribution of natural characterized molecules as PDE inhibitors in various pathologies that can open new fields of research for drug discovery, notably in epigenetic regulation.

Monoaminergic, Ion Channel and Enzyme Inhibitory Activities of Natural Aporphines, their Analogues and Derivatives

The aporphine alkaloids constitute the second-largest group of isoquinoline alkaloids. Nevertheless, only a relatively small number of natural aporphines and their derivatives have been studied from a pharmacological viewpoint. Here we review the pharmacological data available for these compounds as related to their dopaminergic, noradrenergic and serotonergic activities, and also some results pertaining to their effects on ion channels and enzymes.

(+)-Nantenine isolated from Nandina domestica Thunb. inhibits adrenergic pressor responses in pithed rats

The effects of (+)-nantenine on various pressor responses, recently reported exerting competitive antagonistic activity at the alpha1-adrenoceptor/5-hydroxytryptamine (5-HT)2A receptor, were examined in vivo. (+)-Nantenine (0.03-3 mg/kg) caused a dose-dependent inhibition of the pressor response to phenylephrine (alpha1-adrenoceptor agonist) or 5-HT (5-HT receptor agonist) in both anesthetized and pithed rats. The pressor response to UK 14304 (5-Bromo-N-[2-imidazolin-2-yl]-6-quinoxalinamine) (an alpha2-adrenoceptor agonist) was inhibited by (+)-nantenine (0.003-3 mg/kg) in pithed rats in a dose-dependent manner without affecting the angiotensin II-induced pressor response in anesthetized rats. The pressor response to sympathetic nerve stimulation was also inhibited by (+)-nantenine (0.3-3 mg/kg) in a dose-dependent manner. (+)-Nantenine (3 mg/kg) facilitated the norepinephrine release induced by sympathetic nerve stimulation in pithed rats. In the guinea pig vas deferens, the initial component of contractions induced by electrical field stimulation was enhanced by (+)-nantenine (1-30 microM) in a concentration-dependent manner, while the later component was inhibited by it. These data suggest that (+)-nantenine has antagonistic activities on alpha1-adrenoceptors, alpha2-adrenoceptors and 5-HT2A receptors in pithed rats.

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.

Functional characterization of alpha 1-adrenoceptor subtypes in vascular tissues using different experimental approaches: a comparative study

1. The alpha(1)-adrenergic responses of rat aorta and tail artery have been analysed measuring the contractility and the inositol phosphate (IP) formation induced by noradrenaline. Three antagonists, prazosin, 5-methylurapidil (alpha(1A) selective) and BMY 7378 (alpha(1D) selective) have been used in different experimental procedures. 2. Noradrenaline possesses a greater potency inducing contraction and IP accumulation in aorta (pEC(50)-contraction=7.32+/-0.04; pEC(50)-IPs=6.03+/-0.08) than in the tail artery (pEC(50)-contraction=5.71+/-0.07; pEC(50)-IPs=5.51+/-0.10). Although the maximum contraction was similar in both tissues (E(max)-tail=619.1+/-55.6 mg; E(max)-aorta-698.2+/-40.8 mg), there were marked differences in the ability of these tissues to generate intracellular second messengers the tail artery being more efficient (E(max)-tail=1060+/-147%; E(max)-aorta=108.1+/-16.9%). 3. Concentration response curves of noradrenaline in presence of antagonist together with concentration inhibition curves for antagonists added before (CICb) or after (CICa) noradrenaline-induced maximal response in Ca(2+)-containing or Ca(2+)-free medium have been performed. A comparative analysis of the different procedures as well as the mathematical approaches used in each case to calculate the antagonist potencies, were completed. 4. The CICa was the simplest method to characterize the predominant alpha(1)-adrenoceptor subtype involved in the functional response of a tissue. 5. In aorta, where constitutively active alpha(1D)-adrenoeptors are present, the use of different experimental procedures evidenced a complex equilibrium between alpha(1D)- and alpha(1A)-adrenoceptor subtypes. 6. The appropriate management of LiCl in IP accumulation studies allowed us to reproduce the different experimental procedures performed in contractile experiments giving more technical possibilities to this methodology.

Nantenine alkaloid presents anticonvulsant effect on two classical animal models

The present study investigated the anticonvulsant and convulsant profiles of nantenine, an aporphine alkaloid found in several vegetal species. At lower doses (20-50 mg/kg, i.p.) the alkaloid proved to be effective in inhibiting pentylenotetrazol- (PTZ 100 mg/kg, s.c.) and maximal electroshock-induced seizures (80 mA, 50 pulses/s, 0.2 s), suggesting its potential as an anticonvulsant drug. However, at higher doses (> or = 75 mg/kg, i.p.) a convulsant activity was observed. Comparing the present in vivo nantenine effects on seizures with previous in vitro biphasic action on Na+, K+-ATPase activity, the convulsant effect appears to be related to inhibition of these phosphatase at high doses whereas anticonvulsant effect, observed at low doses, seems attributable to its stimulation and the resultant decrease of Ca2+-influx into the cell.

(+/-)-Domesticine, a novel and selective alpha1D-adrenoceptor antagonist in animal tissues and human alpha 1-adrenoceptors

The pharmacological profile of (+/-)-domesticine, a novel alpha(1)-adrenoceptor antagonist, was examined in animal tissues and Chinese hamster ovary (CHO) cells expressing cloned human alpha(1)-adrenoceptor subtypes and compared with the properties of BMY-7378 ([8-(2-[4-(2-methoxy-phenyl)-1-piperazinyl]ethyl)-8-azaspirol [4.5]decane-7,9-dione dihydrochloride], the prototypical alpha(1D)-adrenoceptor antagonist. Both (+/-)-domesticine and BMY-7378 were more potent in inhibiting the phenylephrine-induced contraction in rat thoracic aorta than tail artery or spleen. The selectivity of (+/-)-domesticine to inhibit phenylephrine-induced contraction in rat thoracic aorta was 32- and 17-fold higher than that in tail artery and spleen, respectively, while that of BMY-7378 it was 125- and 11-fold, respectively. The functional affinity profiles of these compounds for the alpha(1)-adrenoceptor subtypes in animal tissues were consistent with the respective binding affinity profiles in cloned human alpha(1)-adrenoceptor subtypes. (+/-)-Domesticine displayed a 34- and 9-fold higher selectivity for alpha(1d)-adrenoceptor than for alpha(1a)- and alpha(1b)-adrenoceptor, respectively, while BMY-7378 showed a selectivity for alpha(1d)-adrenoceptor of 102-fold higher than that of alpha(1a)-adrenoceptor and 21-fold higher than that of alpha(1b)-adrenoceptor. Interestingly, in [3H]8-OH-DPAT (8-hidroxy-2-(di-n-propyl-amino)tetraline hidrobromide) binding to 5-HT(1A) receptors of rat cerebral cortex, (+/-)-domesticine showed a 183-fold higher selectivity for alpha(1D)-adrenoceptor relative to 5-HT(1A) receptor, whereas BMY-7378 displayed a similar affinity at this receptor with respect to the alpha(1D)-adrenoceptor (0.89-fold). Both compounds, however, showed a weak affinity for 5-HT(2A)/5-HT(2C) receptors in rat frontal cortex. These results suggest that (+/-)-domesticine is more potent for alpha(1D)-adrenoceptor than for alpha(1A)- or alpha(1B)-adrenoceptor subtypes and it is highly selective compared to 5-HT(1A) and other receptors.

Structure-activity relationship studies with (+/-)-nantenine derivatives for alpha1-adrenoceptor antagonist activity

A series of (+/-)-nantenine derivatives of the natural aporphine alkaloids was synthesized and examined for a blocking action on alpha1-adrenoceptors in rat aorta and A10-cells. The potency of these derivatives was compared with that of an aporphine-related compounds (+)-boldine, an alpha1-adrenoceptor antagonist. Among nine (+/-)-nantenine derivatives having different substituents at N-6, C-1, or C-4 of the aporphine skeleton, (+/-)-domesticine had the most powerful alpha1-adrenoceptor-blocking action. The order of pA2 values was (+/-)-domesticine (8.06+/-0.06)>(+/-)-nordomesticine (7.34+/-0.03)>(+/-)-nantenine (7.03+/-0.03)>(+)-boldine (6.91+/-0.02)>other derivatives. Study of the structure-activity relationships showed that the replacement of a methoxy moiety at C-1 position of (plus minus)-nantenine with a hydroxyl group increased affinity for the receptor. In contrast, replacement of a methyl group with a hydrogen atom or an ethyl group at N-6 position in the (+/-)-nantenine structure decreased affinity for the receptor. These results suggest that a hydroxyl group at the C-1 position and a methyl group at the N-6 position in the (+/-)-nantenine structure are essential for the enhancement of affinity for the alpha1-adrenoceptor.

Effect of in vitro and in vivo aerosolized treatment with geniposide on tracheal permeability in ovalbumin-induced guinea pigs

The primary objective of this study was to investigate the effect of geniposide, a potent anti-inflammatory, on ovalbumin-antigen-induced tracheal permeability and transepithelial electrical resistance in guinea pigs. Two weeks after sensitization with ovalbumin (100 mg/ml), the permeability of guinea-pig tracheas was evaluated by flux measurements using the transcellular tracer, [(14)C]estradiol, and the paracellular tracer, [(14)C]mannitol. The effect of extracellular Ca(2+) with geniposide was also studied, using deletion of Ca(2+) in the donor chamber. The in vivo treatment effect of aerosolized geniposide on tracheal permeability in the ovalbumin-sensitized guinea pigs was also evaluated. The results indicate that tight junction permeability of ovalbumin-sensitized trachea was significantly dose dependent and decreased by geniposide (1-10 mM), as evidenced by substantial recovery of transepithelial electrical resistance and decreased transepithelial permeability of [(14)C]mannitol at (1.32+/-0.12) x 10(-5) cm/s. The effect of combination of the removal of extracellular Ca(2+) with geniposide had no effect on tight junction permeability of ovalbumin-sensitized trachea and revealed that transepithelial electrical resistance and junction permeability did not recover. In addition, the cAMP levels and phosphodiesterase activity were not significantly influenced in ovalbumin-sensitized tracheal tissues after geniposide treatment. Inhaled geniposide (50 mM, 30 min after ovalbumin sensitization) significantly restored junction permeability induced by ovalbumin (100 mg/ml, 2 min). Junction permeability did not recover on pretreatment with geniposide (50 mM for 30 min over 16 days consecutive before ovalbumin sensitization) after exposure of conscious guinea pigs to aerosol ovalbumin. In conclusion, geniposide has inhibitory effects on ovalbumin-induced junction permeability and recovery of transepithelial electrical resistance in guinea pig trachea, showing its potential as anti-asthma therapy.

Nantenine and papaverine differentially modify synaptosomal membrane enzymes

Papaverine (1-[(3,4-Dimethoxyphenyl) methyl]-6,7-dimethoxyisoquinoline) and nantenine (O-methyldomesticine) are chemically related isoquinoline alkaloids displaying similar dose-dependent sedative or convulsant effects, but seem to act differentially on synaptosomal membrane enzymes. Na+, K+-, Mg2+- and Ca2+-ATPase activities were inhibited by nantenine but not by papaverine, whereas acetylcholinesterase activity remained unchanged by nantenine but slightly enhanced by papaverine. Nantenine inhibited roughly both 20-50% Ca2+- and Mg2+-ATPase activities but 40-90% Na+, K+-ATPase activity. Kinetic analysis indicated that nantenine interacts with the substrate ATP for Ca2+-ATPase activity but that it competes with K+ for Na+, K+-ATPase activity. Given the roles of Na+, K+-ATPase and Ca2+-ATPase in cation transport and [Ca2+]i regulation, respectively, the inhibitory effect of nantenine upon these enzymes may explain its convulsant effect though not its sedative activity. The sedative action of both nantenine and papaverine is hardly attributable to an effect on the synaptosomal membrane enzymes assayed.

Effects of inhaled glaucine on pulmonary responses to antigen in sensitized guinea pigs

The alkaloid (S)-(+)-1,2,9,10-tetramethoxyaporphine (glaucine) is a phosphodiesterase 4 inhibitor with bronchodilator and anti-inflammatory activity in vitro. In this study, we examined the in vivo effects of glaucine on an animal model of asthma. In ovalbumin sensitized guinea pigs, inhaled glaucine (10 mg ml(-1), 3 min) inhibited the acute bronchoconstriction produced by aerosol antigen (antigen response was 256+/-42 and 95+/-14 cm H(2)O l(-1) s(-1) in control and glaucine-treated animals, respectively; P<0.05). Pretreatment with glaucine (10 mg ml(-1), 10 min inhalation, 30 min pre- and 3 h post-antigen exposure) markedly reduced airway hyperreactivity to histamine, eosinophil lung accumulation, and increased eosinophil peroxidase activity in bronchoalveolar lavage fluid 24 h after exposure of conscious guinea pigs to aerosol antigen. In addition, inhaled glaucine (5-10 mg ml(-1), 3 min) inhibited the microvascular leakage produced after inhaled antigen at all airway levels. These data support the potential interest of phosphodiesterase 4 inhibitors in asthma treatment.

Molecular modeling study of diltiazem mimics at L-type calcium channels

PURPOSE

A theoretical study was performed to generate a pharmacophore model for chemically diverse structures that specifically interact with the diltiazem binding site of L-type calcium channels.

METHODS

Via molecular mechanics and quantum chemical methods solvation energies, logP values, conformational and electronic features of classical 1,5-benzothiazepin-4(5H)-one (BTZ, e.g., diltiazem), 1-benzazepin-2-one (BZ), pyrrolo[2,1-d][1,5]benzothiazepine, pyrrolo[2,1-c][1,4]benzothiazine, and benzobicyclo[2.2.2]octyl amines derivatives were determined. Furthermore, the molecular electrostatic potentials (MEPs) and common interaction fields derived from use of the GRID programme were compared.

RESULTS

This yielded a pharmacophore model with three crucial pharmacophoric characteristics, (1) two aromatic ring systems in a distance of about 6.7 A, (2) a basic side chain with pKa in the physiological range, and (3) a 4'-methoxy moiety. In addition, a strong negative MEP in 4-position (carbonyl oxygen) and hydrophobic electron-rich features in the position equivalent to the sulphur atom of BTZ derivatives were explored to be favourable for receptor binding and calcium antagonistic effect. Moreover, the stabilizing effect of substituents in 3-position of BZs on the bioactive "M" twist-boat conformation of the heptagonal ring could be demonstrated by molecular dynamics simulations.

CONCLUSIONS

Based on these molecular descriptors, the quinazolinone derivative MCI-176 is predicted to be a potential ligand of the diltiazem binding site.

Bronchodilator and anti-inflammatory activities of glaucine: In vitro studies in human airway smooth muscle and polymorphonuclear leukocytes

1. Selective phosphodiesterase 4 (PDE4) inhibitors are of potential interest in the treatment of asthma. We examined the effects of the alkaloid S-(+)-glaucine, a PDE4 inhibitor, on human isolated bronchus and granulocyte function. 2. Glaucine selectively inhibited PDE4 from human bronchus and polymorphonuclear leukocytes (PMN) in a non-competitive manner (Ki=3.4 microM). Glaucine displaced [3H]-rolipram from its high-affinity binding sites in rat brain cortex membranes (IC50 approximately 100 microM). 3. Glaucine inhibited the spontaneous and histamine-induced tone in human isolated bronchus (pD2 approximately 4.5). Glaucine (10 microM) did not potentiate the isoprenaline-induced relaxation but augmented cyclic AMP accumulation by isoprenaline. The glaucine-induced relaxation was resistant to H-89, a protein kinase A inhibitor. Glaucine depressed the contractile responses to Ca2+ (pD'2 approximately 3.62) and reduced the sustained rise of [Ca2+]i produced by histamine in cultured human airway smooth muscle cells (-log IC50 approximately 4.3). 4. Glaucine augmented cyclic AMP levels in human polymorphonuclear leukocytes challenged with N-formyl-Met-Leu-Phe (FMLP) or isoprenaline, and inhibited FMLP-induced superoxide generation, elastase release, leukotriene B4 production, [Ca2+]i signal and platelet aggregation as well as opsonized zymosan-, phorbol myristate acetate-, and A23187-induced superoxide release. The inhibitory effect of glaucine on superoxide generation by FMLP was reduced by H-89. 5. In conclusion, Ca2+ channel antagonism by glaucine appears mainly responsible for the relaxant effect of glaucine in human isolated bronchus while PDE4 inhibition contributes to the inhibitory effects of glaucine in human granulocytes. The very low PDE4/binding site ratio found for glaucine makes this compound attractive for further structure-activity studies.

Contractile effect of (+)-glaucine in the isolated guinea-pig ileum

The intestinal effects of (+)-glaucine [(S)-1,2,9,10-tetramethoxyaporphine] were studied using the guinea-pig ileum. (+)-Glaucine (10-300 microM) induced ileal contractions. The contraction was not affected by tetrodotoxin, atropine, hexamethonium, propranolol, naloxone, methysergide, N(G)-nitro-L-arginine methyl ester, SR141716A (a cannabinoid CB1 receptor antagonist) or SR140333 (a tackykinin NK1 receptor antagonist) plus SR48968 (a tackykinin NK2 antagonist). (+)-Glaucine-induced contraction was reduced by indomethacin, nordihydroguaiaretic acid or bisindolylmaleimide I and abolished by verapamil and nifedipine. These results suggest that (+)-glaucine-induced contraction involves activation of voltage-dependent Ca2+ channels and protein kinase C and could be mediated by the release of arachidonic acid metabolites.

Halogenated derivatives of boldine with high selectivity for alpha1A-adrenoceptors in rat cerebral cortex

The selectivity of 3-nitrosoboldine and different halogenated derivatives of boldine (3-bromoboldine, 3,8-dibromoboldine and 3-chloroboldine) for alpha1-adrenoceptor subtypes was studied by examining [3H]-prazosin competition binding in rat cerebral cortex. In the competition experiments [3H]-prazosin binding was inhibited completely by all the compounds tested. The inhibition curves displayed shallow slopes which could be subdivided into high and low affinity components. The relative order of affinity and selectivity for alpha1A-adrenoceptors was 3-bromoboldine = 3,8-dibromoboldine = 3-chloroboldine > boldine > 3-nitrosoboldine. The competition curves for 3-bromoboldine remained shallow and biphasic following chloroethylclonidine treatment. Whereas the relative contribution of the high affinity sites increased, the 3-bromoboldine affinities at its high and low affinity sites remained similar to those obtained in untreated membranes. 3-Bromoboldine, 3,8-dibromoboldine, 3-chloroboldine and 3-nitrosoboldine did not significantly displace [3H]-(+)-cis-diltiazem binding to rat cerebral cortex membranes. This activity was lower than that shown by boldine. Compared to boldine, halogen (bromine or chlorine) substitution at position 3 increases the alpha1A-adrenoceptor subtype selectivity and decreases the affinity for the benzothiazepine binding site at the calcium channel. Further halogen substitution at position 8 did not significantly improve this activity with respect to 3-bromoboldine. In contrast, the NO substitution at position 3 of boldine (3-nitrosoboldine) gives a loss of affinity and selectivity for alpha1-adrenoceptor subtypes.

Mechanisms involved in the vasorelaxant effect of (-)-stepholidine in rat mesenteric small arteries

The purpose of the present investigation was to clarify whether the hypotensive action of the protoberberine alkaloid, and dopamine receptor antagonist, (-)-stepholidine, can be ascribed to an effect on peripheral small arteries. For this purpose isolated mesenteric small arteries were suspended in microvascular myographs for isometric tension recording. Relaxations mediated by dopamine D1 receptors were antagonized by (-)-stepholidine. (-)-Stepholidine inhibited in a concentration-dependent manner the contractile responses evoked by noradrenaline (10(-6) M), but not the contractile responses evoked by depolarizing solution (KCl, 60 mM) or 9,11-dideoxy-11alpha,9alpha-epoxymethano prostaglandin F2alpha (U46619, 10(-7) M). Mechanical endothelial cell removal, blockade of K+ channels, muscarinic receptors or adrenoceptors did not influence the inhibitory effect of (-)-stepholidine on the contractile response evoked with noradrenaline in the segments. (-)-Stepholidine caused rightward shifts of the concentration-response curves for noradrenaline and phenylephrine. The pA2 values for (-)-stepholidine were 6.05 and 5.94 against noradrenaline and phenylephrine, respectively. Electrical field stimulation induced prazosin-sensitive frequency-dependent contractions in mesenteric small arteries. These contractions were significantly inhibited by 10(-6) and 10(-5) M (-)-stepholidine. In membranes from the rat cerebral cortex labelled with [3H]prazosin, (-)-stepholidine (10(-7)-10(-4) M) completely inhibited the specific binding of the ligand with a pKi of 5.6. The present investigation suggests the inhibitory effect of (-)-stepholidine on the alpha1-adrenoceptor-mediated contractions induced by exogenously added and nerve-released noradrenaline in peripheral small arteries might contribute to a hypotensive effect of the drug.

The 5-HT and alpha-adrenoceptor antagonist effect of four benzylisoquinoline alkaloids on rat aorta

The action of four benzylisoquinoline alkaloids (two aporphines-glaucine and apomorphine, a benzylisoquinoline-papaverine and a bisbenzyltetrahydroisoquinoline-antioquine) on 5-HT-induced contraction in rat thoracic aorta has been examined and compared with that of the control drugs: ketanserin, nifedipine, prazosin and phentolamine. The relaxant action on 5-HT-induced contraction was contrasted with that on the contraction induced by noradrenaline and KCl. The results obtained with control drugs show that ketanserin has clear selectivity for 5-HT receptors, whereas prazosin and phentolamine have high selectivity for the alpha1-adrenoceptor and nifedipine seems to have a more potent effect on KCl-induced contraction than on that induced by 5-HT or noradrenaline. The contraction evoked by 5-HT (10 microM) was inhibited in a concentration-dependent manner by all the alkaloids. The order of potency was: papaverine = glaucine > apomorphine > antioquine. Papaverine had a non-specific relaxant action on 5-HT-, noradrenaline- and KCl-induced contraction, antioquine had a weak relaxant action on the agonist assays, and glaucine and apomorphine inhibited noradrenaline- and 5-HT-induced contraction more potently than they inhibited the K+-depolarized response. These results indicate that the aporphines assayed, S-glaucine and R-aporphine, had selective action against agonist (noradrenaline or 5-HT)-induced contraction rather than against KCl-depolarization of rat aorta. In contrast papaverine, a benzylisoquinoline alkaloid, relaxes all agents used non-selectively as could be expected from the lack of specificity that characterizes this alkaloid.

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.

Immunopharmacological activity of aporphinoid alkaloid oxoglaucine

The ability of aporphinoid alkaloid oxoglaucine to influence T- and B-cell immune response was studied in mice models. The substance inhibited in vitro mitogen-induced lymphocyte proliferation and suppressed antibody response to sheep red blood cells (SRBC) and lipopolysaccharide (LPS) in vivo effectively. The action depended on the relative timing of antigen and oxoglaucine administration. The substance manifested stimulatory effect in popliteal lymph node (PLN) reaction and LPS-induced B-cell activation. In the chronic inflammatory model of adjuvant arthritis oxoglaucine exhibited stimulatory or suppressive action related to the kinetics of the process. At low doses (1 or 2 mg kg-1) oxoglaucine improved the outcome of Klebsiella pneumoniae infection, while at higher doses (10 or 20 mg kg-1) the substance caused an impairment of host resistance to infectious agent. The comparison with cyclophosphamide in some tests showed that oxoglaucine was effective in manifold lower doses. In conclusion, oxoglaucine exerted immunomodulatory effects in vivo in a dose-dependent and protocol-dependent manner. Yet, its overall action might be attributed to the different sensitivity of the cells involved in the developing immune response.

A possible structural determinant of selectivity of boldine and derivatives for the alpha 1A-adrenoceptor subtype

1. The selectivity of action of boldine and the related aporphine alkaloids, predicentrine (9-O-methylboldine) and glaucine (2,9-O-dimethylboldine) and alpha 1-adrenoceptor subtypes was studied by examining [3H]-prazosin competition binding in rat cerebral cortex. WB 4101 and benoxathian were used as selective alpha 1A-adrenoceptor antagonists. 2. In the competition experiments [3H]-prazosin (0.2 nM) binding was inhibited by WB 4101 and benoxathian. The inhibition curves displayed shallow slopes which could be subdivided into high and low affinity components (pKi = 9.92 and 8.29 for WB 4101, 9.35 and 7.94 for benoxathian). The two antagonists recognized approximately 37% of the sites with high affinity from among the total [3H]-prazosin specific binding sites. 3. Boldine, predicentrine and glaucine also competed for [3H]-prazosin (0.2 nM) binding with shallow and biphasic curves recognizing 30-40% of the sites with high affinity. Drug affinities (pKi) at the high and low affinity sites were, 8.31 and 6.50, respectively, for boldine, 8.13 and 6.39 for predicentrine, and 7.12 and 5.92 for glaucine. The relative order of selectivity for alpha 1A-adrenoceptors was boldine (70 fold alpha 1A-selective) = predicentrine (60 fold, alpha 1A-selective) > glaucine (15 fold, alpha 1A-selective). 4. Pretreatment of rat cerebral cortex membranes with chloroethylclonidine (CEC, 10 microM) for 30 min at 37 degrees C followed by thorough washing out reduced specific [3H]-prazosin binding by approximately 70%. The CEC-insensitive [3H]-prazosin binding was inhibited by boldine monophasically (Hill slope = 0.93) with a single pKi value (7.76). 5. These results suggest that whereas the aporphine structure shared by these alkaloids is responsible for their selectively of action for the alpha 1A-adrenoceptor subtype in rat cerebral cortex, defined functional groups, namely the 2-hydroxy function, induces a significant increase in alpha 1A-subtype selectivity and affinity.

The effect of S-(+)-boldine on the alpha 1-adrenoceptor of the guinea-pig aorta

1. The cardiovascular activity of S-(+)-boldine, an aporphine alkaloid structurally related to papaverine, was determined. The work includes functional studies on guinea-pig isolated aorta contracted with noradrenaline, caffeine, KCl or Ca2+, and on guinea-pig trachea contracted with acetylcholine or histamine. 2. S-(+)-boldine inhibited in a concentration-dependent manner the contractile response evoked by noradrenaline (10 microM) in guinea-pig aorta (IC50 = 1.4 +/- 0.2 microM) while the KCl depolarizing solution (60 mM)- or the Ca2+ (1 mM)-induced contractions were only partially affected by boldine up to 300 microM. In contrast, papaverine relaxed noradrenaline (NA), KCl or Ca2+ induced contractions showing similar IC50 values in all cases. S-(+)-boldine had a greater potency on the contraction elicited by NA whereas papaverine acted in a non-selective manner. 3. S-(+)-boldine was found to be an alpha 1-adrenoceptor blocking agent in guinea-pig aorta as revealed by its competitive antagonism of noradrenaline-induced vasoconstriction (pA2 = 5.64 +/- 0.08), and its potency was compared with that of prazosin (pA2 = 8.56 +/- 0.24), a known potent alpha 1-adrenoceptor antagonist. In contrast, papaverine caused rightward shifts of the NA concentration-response curves with depression of maximal response indicating that it acts as a non-competitive antagonist. 4. Contraction of guinea-pig aorta induced by caffeine (60 mM) in a Ca(2+)-containing Krebs solution was not affected by a 60 min incubation period with different doses of S-(+)-boldine (1-300 microM). Papaverine inhibited partially this caffeine-induced contraction at the maximal dose used (100 microM). 5. Inositol phosphates formation induced by noradrenaline (10 microM) in guinea-pig thoracic aorta was inhibited by S-(+)-boldine (30 microM) but not by papaverine (10 microM). 6. Contractions of guinea-pig trachea caused by acetylcholine (100 microM) or histamine (10 microM) were not modified by S-(+)-boldine (0.1-100 microM). 7. These results provide evidence that S-(+)-boldine, an aporphine alkaloid, has interesting properties as an alpha 1-adrenoceptor blocker in vascular smooth muscle, and acts as a competitive antagonist of the alpha 1-adrenoceptor present in the guinea pig aorta.

Relaxant activity of three aporphine alkaloids from Annona cherimolia on isolated aorta of rat

In the present study we tested the relaxant effect of three aporphine alkaloids--roemerine, anonaine and dehydroroemerine--isolated from the roots of Annona cherimolia, on isolated strips of rat thoracic aorta. All compounds completely relaxed KCl- and noradrenaline-induced contractions with different potencies depending on their structural characteristics. The experiments, carried out in Ca(2+)-free medium using two different agonists (noradrenaline and caffeine) which mobilize calcium intracellularly by different mechanisms of action, showed that the alkaloids made no contribution to intracellular calcium processes. The present study provides evidence that the relaxant effects produced by aporphine alkaloids may be due to the blockade of calcium movements across the cell membrane, mainly through voltage-operated channels, and to the disruption of alpha 1-adrenoceptors connected to receptor-operated channels.

Study of the in vivo and in vitro cardiovascular effects of (+)-glaucine and N-carbethoxysecoglaucine in rats

1. The cardiovascular and vasorelaxant effects of (+)-glaucine and of a semisynthetic derivative (N-carbethoxysecoglaucine) were studied in rats. 2. N-carbethoxysecoglaucine did not modify either systolic arterial pressure or heart rate values in conscious (25 mg kg-1, p.o.) and anaesthetized normotensive rats (5 mg kg-1, i.v.). Furthermore, this compound showed no activity in the experiments carried out on rat isolated aorta [contractility and 45Ca2+ influx assays (5 microM)] and did not modify the rate and force of contraction in rat isolated atria (5 microM). 3. In conscious normotensive rats, oral administration of (+)-glaucine (25 mg kg-1) did not modify either systolic arterial pressure or heart rate. 4. In anaesthetized normotensive rats, (+)-glaucine (5 mg kg-1, i.v.) produced a remarkable fall in mean arterial pressure (MAP) accompanied by a significant decrease in heart rate. In the same preparation, (+)-glaucine (5 mg kg-1, i.v.) did not modify the cardiovascular effects induced by noradrenaline (NA) (5 micrograms kg-1) and 5-hydroxytryptamine (5-HT) (300 micrograms kg-1) but markedly inhibited those induced by nicotine (200 micrograms kg-1). 5. In isolated intact aorta of rat, (+)-glaucine (0.15-5 microM) competitively inhibited the contractions induced by NA (with a pA2 value of 7.14) and non-competitively those induced by 5-HT (in normal Krebs solution) and Ca2+ (in depolarizing Ca(2+)-free high-K+ 50 mM solution), with depression of the maximal response and with pD2 values of 5.56 and 5.26, respectively. 6. In experiments in Ca2+-free medium, (+)-glaucine (3 microM) inhibited the contractions induced by NA and had no effect on either 5-HT- or caffeine-induced contractions.7. Furthermore, in the experiments with radioactive Ca2+, (+)-glaucine (3 microM) did not modify the basal uptake of 45Ca2+ but strongly inhibited the influx of 45Ca2+ induced by NA, 5-HT and K+.8. (+)-Glaucine (5microM) had no effect on rate and force of contraction in rat isolated atria.9. These results indicate that: (a) the cardiovascular effects (hypotension and bradycardia) of (+)-glaucine in anaesthetized normotensive rats (5 mg kg-1) may be due, at least in part, to a ganglioplexic effect; (b) the vasorelaxant action of ( + )-glaucine (0.15-5 microM) in rat isolated aorta can be attributed to an alpha1-adrenoceptor blocking property (which may explain its inhibition of noradrenaline-induced 45Ca2+influx and contractions in normal Krebs solution and noradrenaline-induced contractions in Ca2+-free medium) and to a Ca2+-antagonist activity (which may be responsible, at least in part, for the inhibition of 45Ca2+ uptake induced by NA, 5-HT and K+ and the contractions induced by both NA and 5-HT in normal Krebs solution and by Ca2+ in Ca2+-free high-K+ medium) and (c) there is no correlation between the mechanisms of action observed for (+ )-glaucine in vivo and in vitro, which suggests that the vasorelaxant activity of this alkaloid does not contribute to its hypotensive activity.

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.

Study of the mechanism of the relaxant action of (+)-glaucine in rat vas deferens

1. Effects of the aporphinoid alkaloid, (+)-glaucine, on rat vas deferens were investigated. 2. (+)-Glaucine (2-18 microM) competitively inhibited contractions induced by noradrenaline and methoxamine with a pA2 value of about 6. 3. (+)-Glaucine (2 and 18 microM) did not change the accumulation of tritium during incubation of the vas deferens with [3H]-noradrenaline. 4. (+)-Glaucine (0.3 nM-0.1 mM) inhibited specific [3H]-prazosin binding to membranes from rat vas deferens with a pKi value of 6.63, which is close to the pA2 value obtained against noradrenaline and methoxamine in functional studies. 5. In electrically-stimulated rat vas deferens, (+)-glaucine (0.3-10 microM) enhanced twitch contractions and competitively antagonized the inhibitory effect of clonidine with a pA2 value of 5.91. 6. In tissues incubated in depolarizing calcium-free high-potassium medium, (+)-glaucine (30-80 microM) inhibited Ca(2+)-induced contractions with depression of the maximal response at higher doses and with a pD'2 value of 3.65. Furthermore, (+)-glaucine (50 microM) did not modify basal 45Ca uptake but strongly inhibited the influx of 45Ca induced by K+. 7. These results suggest that (+)-glaucine has non-selective alpha 1- and alpha 2-adrenoceptor blocking properties. At higher doses, (+)-glaucine shows calcium antagonist activity which may be responsible, at least in part, for the inhibition of the contractions induced by Ca2+ in calcium-free high-potassium medium.

Investigations of the dual contractile/relaxant properties showed by antioquine in rat aorta

1. In the present study we assessed the activity of antioquine, a bisbenzyltetrahydroisoquinoline alkaloid isolated from Pseudoxandra sclerocarpa, by examining its effects on the contractile activity of rat isolated aorta, specific binding of [3H]-(+)-cis-diltiazem, [3H]-nitrendipine and [3H]-prazosin to cerebral cortical membranes and the different molecular forms of cyclic nucleotide phosphodiesterases (PDE) isolated from bovine aorta. 2. Contractions in rat aorta induced by high concentrations of KCl (80 mM) and noradrenaline (1 microM) were inhibited by antioquine in a concentration-dependent manner (0.1 microM- 300 microM). The alkaloid appeared more potent against KCl-induced contractions. This inhibitory effect was observed at both 37 degrees C and 25 degrees C. 3. Paradoxically, at the highest concentration tested (300 microM) antioquine induced a contractile response of similar magnitude in the presence and absence of extracellular calcium, at 37 degrees C. This activity was greatly attenuated at 25 degrees C. Antioquine-induced contractions were not inhibited by prazosin (0.1 microM), nifedipine (1 microM) or diltiazem (100 microM). On the contrary, prazosin and nifedipine slightly increased the contractions in the presence of extracellular calcium. Papaverine (100 microM) partially inhibited the contractile response to antioquine both in the presence and absence of extracellular calcium. 4. At 25 degrees C, in Ca(2+)-free solution, antioquine (300 microM) did not modify the contractile response (phasic and tonic) evoked by noradrenaline, but increased the phasic contraction induced by caffeine. At 37 degrees C, the contraction elicited by antioquine made it impossible to observe the noradrenaline-induced one. 5. Antioquine showed affinity for the [3H]-prazosin binding site and for the [3H]-(+)-cis-diltiazembinding site of the Ca2+-channel receptor complex, but had no effect at the dihydropyridine binding site in rat cerebral cortex.6. Antioquine weakly inhibited some PDE forms isolated from bovine aorta: a CaM-PDE (PDE I)which preferentially hydrolyzes cyclic GMP and is activated by calmodulin, and a rolipram-sensitive cyclic AMP-PDE (PDE IV) which hydrolyzed cyclic AMP. Antioquine did not exert any inhibitory effect on the other forms of PDE, a cyclic GMP selective form (PDE V) and a low Km cyclic AMP-PDEthat is inhibited by cyclic GMP (CGI-PDE, PDE III).7. The present work provides evidence that antioquine has properties both as a calcium entry blocker(possibly through the benzothiazepine recognition site in the calcium channel) and as a contractile agent.Its mechanism of action as a contractile agent is not related to Ca2+-entry and is hypothetically similar to that of calyculin-A or okadaic acid. The possible involvement of a-adrenoceptors in this paradoxical effect cannot be excluded. The rigidity of the molecule provides an interesting model for analyzing this contractile mechanism and the intracellular processes involved.

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.