Blocking properties of terguride at the 5-HT2 receptor subtypes mediating cardiovascular responses in the rat.

In vitro studies have suggested that terguride blocks the contractile and relaxant responses produced by 5-hydroxytryptamine (5-HT) via 5-HT2A/2B receptors. This study has now investigated terguride's blocking properties on central/peripheral 5-HT2 receptors in anaesthetized or pithed rats. Male Wistar anaesthetized/pithed rats were cannulated for recording blood pressure and heart rate and for i.v. administration of several compounds. In both groups of rats, i.v. bolus injections of 5-HT or (±)-DOI (a 5-HT2 receptor agonist; 1-1000 µg/kg) produced dose-dependent increases in diastolic blood pressure and heart rate. These responses were dose-dependently antagonized by terguride (10-3000 µg/kg). In anaesthetized rats, i.v. bolus injections of BW723C86 (a 5-HT2B receptor agonist; 1-1000 µg/kg) produced dose-dependent increases in diastolic blood pressure and not dose-dependent increases in heart rate, while in pithed rats, these responses were attenuated. The vasopressor responses elicited by BW723C86 in anaesthetized rats were dose-dependently blocked by terguride (10-300 µg/kg), whereas its the tachycardic responses were dose-independently blocked. These results, taken together, suggest that terguride behaved as an antagonist at the 5-HT2 receptors located in the central nervous system and (or) the systemic vasculature. This is the first evidence demonstrating that terguride can block central/peripheral 5-HT2 receptors mediating cardiovascular responses in anaesthetized or pithed rats.

Effects of 2-bromoterguride, a dopamine D2 receptor partial agonist, on cognitive dysfunction and social aversion in rats.

RATIONALE: 2-Bromoterguride, a dopamine D2 receptor partial agonist with antagonist properties at serotonin 5-HT2A receptors and α2C-adrenoceptors, meets the prerequisites of a putative atypical antipsychotic drug (APD). We recently showed that 2-bromoterguride is effective in tests of positive symptoms of schizophrenia in rats without inducing extrapyramidal side effects or metabolic changes. OBJECTIVE: In continuation of our recent work, we now investigated the effect of 2-bromoterguride on apomorphine and phencyclidine (PCP)-induced disruptions of prepulse inhibition (PPI) of the acoustic startle response, a measure of sensory gating. In addition, we used subchronic PCP treatment to produce cognitive deficits and social aversion, and assessed the effect of 2-bromoterguride on the performance in the novel object recognition (NOR) task (model for studying cognitive deficit symptoms of schizophrenia) and the social interaction test (model for studying negative symptoms of schizophrenia). Finally, we extended the side effect profile of 2-bromoterguride by measuring the prolactin response to systemic administration of the drug in rats. RESULTS: Treatment with 2-bromoterguride (0.1 and 0.3 mg/kg) reversed PPI deficits induced by apomorphine and PCP, respectively. Subchronic PCP induced impairments in object memory and social interaction behavior which were ameliorated by 2-bromoterguride but not by clozapine and aripiprazole, respectively. Prolactin concentration in blood serum was not elevated at 1, 2, or 4 h post-2-bromoterguride treatment, which further supports the safe and effective use of this drug. CONCLUSIONS: Our data support 2-bromoterguride as a promising APD candidate due to its beneficial effect on cognitive impairments and negative symptoms of schizophrenia.

2-Bromoterguride-a potential atypical antipsychotic drug without metabolic effects in rats.

RATIONALE: Recently, we showed that 2-bromoterguride acted as a dopamine D2 receptor partial agonist, a serotonin 5-HT2A and α2C-adrenergic receptor antagonist, and exhibited antidopaminergic efficacy in amphetamine-induced locomotion (AIL) in rats without inducing catalepsy. OBJECTIVE: To extend our knowledge on the antipsychotic effects of 2-bromoterguride, we used convergent preclinical animal models and tests; i.e., conditioned avoidance response (CAR), predictive of antipsychotic-like effects; Fos protein expression, a molecular marker for (atypical) antipsychotic activity; wet dog shake behavior, a test for the in vivo effects of drugs acting on central 5-HT2A receptors; and investigated metabolic changes as a common side effect of atypical antipsychotic drugs (APDs). RESULTS: Acute treatment with 2-bromoterguride (0.1 and 0.3 mg/kg) decreased the CAR at 30, 90, and 270 min post-injection in rats without inducing escape failures at any time. Fos protein expression, as shown by Western blotting, was enhanced by 2-bromoterguride in the nucleus accumbens (NAc), the dorsolateral striatum (dStr), and the medial prefrontal cortex (mPFC). (±)-2,5-Dimethoxy-4-iodoamphetamine (DOI)-induced wet dog shakes in rats were reduced by 2-bromoterguride. Chronic treatment with 2-bromoterguride did not affect metabolic parameters such as body weight development and body fat composition as well as behavioral parameters such as food intake and locomotor activity. CONCLUSIONS: Our data suggest that 2-bromoterguride is a promising candidate in the treatment of schizophrenia due to its atypical antipsychotic-like activity and its inability to induce weight gain.

A chemically defined 2,3-trans procyanidin fraction from willow bark causes redox-sensitive endothelium-dependent relaxation in porcine coronary arteries.

Extracts of the bark of willow species (Salix spp.) are popular herbal remedies to relieve fever and inflammation. The effects are attributed to salicin and structurally related phenolic metabolites, while polyphenols including procyanidins are suggested to contribute to the overall effect of willow bark. This study aimed at investigating the relaxant response to a highly purified and chemically defined 2,3-trans procyanidin fraction in porcine coronary arteries. The procyanidin sample produced a concentration-dependent relaxation in U46619-precontracted tissues. Relaxation was predominantly mediated through the redox-sensitive activation of the endothelial phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway, leading to the subsequent activation of endothelial nitric oxide synthase (eNOS) by phosphorylation, as evidenced by Western blotting using human umbilical vein endothelial cells (HUVECs). That the relaxant response to Salix procyanidins was reactive oxygen species (ROS)-dependent with O2(-) as the key species followed from densitometric analysis using 2,7-dichlorodihydrofluorescein diacetate (DCFH-DA assay) and employment of various ROS inhibitors, respectively. The data also suggested the modification of intracellular Ca(2+) levels and KCa channel functions. In addition, our organ bath studies showed that Salix procyanidins reversed the abrogation of the relaxant response to bradykinin by oxidized low-density lipoproteins (oxLDL) in coronary arteries, suggesting a vasoprotective effect of willow bark against detrimental oxLDL in pathological conditions. Taken together, our findings suggest for the first time that 2,3-trans procyanidins may contribute not only to the beneficial effects of willow bark but also to health-promoting benefits of diverse natural products of plant origin.

α2-Adrenoceptors are targets for antipsychotic drugs.

RATIONALE: Almost all antipsychotic drugs (APDs), irrespective of whether they belong to the first-generation (e.g. haloperidol) or second-generation (e.g. clozapine), are dopamine D2 receptor antagonists. Second-generation APDs, which differ from first-generation APDs in possessing a lower propensity to induce extrapyramidal side effects, target a variety of monoamine receptors such as serotonin (5-hydroxytryptamine) receptors (e.g. 5-HT1A, 5-HT2A, 5-HT2C, 5-HT6, 5-HT7) and α1- and α2-adrenoceptors in addition to their antagonist effects at D2 receptors. OBJECTIVE: This short review is focussed on the potential role of α2-adrenoceptors in the antipsychotic therapy. RESULTS: Schizophrenia is characterised by three categories of symptoms: positive symptoms, negative symptoms and cognitive deficits. α2-Adrenoceptors are classified into three distinct subtypes in mammals, α2A, α2B and α2C. Whereas the α2B-adrenoceptor seems to play only a minor role in the brain, activation of postsynaptic α2A-adrenoceptors in the prefrontal cortex improves cognitive functions. Preclinical models such as D-amphetamine-induced locomotion, the conditioned avoidance response and the pharmacological N-methyl-D-aspartate receptor hypofunction model have shown that α2C-adrenoceptor blockade or the combination of D2 receptor antagonists with idazoxan (α2A/2C-adrenoceptor antagonist) could be useful in schizophrenia. A potential benefit of a treatment combination of first-generation APDs with the α2A/2C-adrenoceptor antagonists idazoxan or mirtazapine was also demonstrated in patients with schizophrenia. CONCLUSIONS: It is concluded that α2-adrenoceptors may be promising targets in the antipsychotic therapy.

2,3-cis-procyanidins elicit endothelium-dependent relaxation in porcine coronary arteries via activation of the PI3/Akt kinase signaling pathway.

Polyphenols including procyanidins have been reported to reduce the risk of cardiovascular diseases. However, polyphenolic extracts represent complex mixtures, and detailed information on their chemical composition is commonly lacking. The aim of this study was to investigate the potential of a highly purified and chemically defined 2,3-cis-procyanidin sample (di- to hexameric [4ß,8]-linked oligomers) from Nelia meyeri to relax coronary arteries and to get insight into the underlying mechanisms. The procyanidins produced a concentration-dependent relaxation in endothelium-intact vascular rings by activation of the NO and endothelium-derived hyperpolarizing factor (EDHF)-signaling pathway via PI3/Akt kinase in a redox-sensitive manner, with O2(-) as key species predominantly produced by xanthine oxidase and NADPH oxidase. Our observations in tissue bath studies were confirmed by Western blotting; 2,3-cis-procyanidins induced phosphorylation of eNOS and Akt in a ROS-dependent manner. These findings provide a basis for comparing the relaxant response and mode of action with that of structurally related proanthocyanidins. Our results may contribute to a better understanding of the potential link between the beneficial effects of proanthocyanidins on vascular health and their broad distribution in many fruits, natural food sources, and foodstuffs.

Alpha2C-adrenoceptors play a prominent role in sympathetic constriction of porcine pulmonary arteries.

Enhanced pulmonary vasoconstriction in response to injuries of the central nervous system and hypoxia result in pulmonary edema due to increased sympathetic activation. This study aimed to characterize α(2)-adrenoceptor (AR)-mediated responses in porcine pulmonary arteries. α(2)-AR-mediated vasoconstriction was studied using a tissue bath protocol. α(2)-AR protein was determined by Western blotting. UK14304 (α(2)-AR agonist) elicited only a slight contraction in pulmonary arteries compared to veins. Verapamil (voltage-operated Ca(2+) channel blocker), 2-APB (store-operated Ca(2+) channel inhibitor), and P1075 (K(ATP) channel opener) induced a marked decrease of the basal tone in veins, but not in arteries. The UK14304-induced contraction in arteries was enhanced by (S)-(-)-Bay K 8644 (L-type Ca(2+) channel activator), N (ω)-nitro-L: -arginine methyl ester hydrochloride (L-NAME, eNOS inhibitor), and (S)-(-)-Bay K 8644 plus L-NAME to the same extent. Endothelium denudation failed to affect the UK14304 response. (S)-(-)-Bay K 8644 did not increase the maximal noradrenaline (non-selective α-AR agonist) or phenylephrine (α(1)-AR agonist) response. The rightward shift of the concentration-response curve to noradrenaline by prazosin (α(1)-AR antagonist) plus (S)-(-)-Bay K 8644 was smaller and non-parallel compared to that in the presence of prazosin alone. UK14304 responses were inhibited by MK912 (α(2C)-AR antagonist). Affinity of MK912 (pA(2) 9.76) and Western blotting analysis argue for an involvement of α(2C)-ARs in noradrenaline-induced contraction of pulmonary arteries. It is concluded that postjunctional α(2C)-ARs predominantly mediate contraction in porcine pulmonary arteries when the cytosolic Ca(2+) concentration is elevated. α(2C)-AR antagonists may be beneficial in the treatment of pulmonary edema.

Antiserotonergic properties of terguride in blood vessels, platelets, and valvular interstitial cells.

Serotonin (5-hydroxytryptamine; 5-HT) is involved in heart valve tissue fibrosis, pulmonary arterial fibrosis, and pulmonary hypertension. We aimed at characterizing the antiserotonergic properties of the ergot alkaloid derivative terguride [1,1-diethyl-3-(6-methyl-8α-ergolinyl)urea] by using functional receptor assays and valvular interstitial cell culture. Terguride showed no vasoconstrictor effect in porcine coronary arteries (5-HT(2A) receptor bioassay) and no relaxant effect in porcine pulmonary arteries (5-HT(2B) receptor bioassay). Terguride behaved as a potent antagonist at 5-HT(2A) receptors (noncompetitive antagonist parameter pD'2 9.43) and 5-HT(2B) receptors (apparent pA2 8.87). Metabolites of terguride (N″-monodeethylterguride and 6-norterguride) lacked agonism at both sites. N″-monodeethylterguride and 6-norterguride were surmountable antagonists at 5-HT(2A) receptors (pA2 7.82 and 7.85, respectively) and 5-HT(2B) receptors (pA2 7.30 and 7.11, respectively). Kinetic studies on the effects of terguride in pulmonary arteries showed that the rate to reach drug-receptor equilibrium for terguride was fast. Washout experiments showed that terguride easily disappeared from the receptor biophase. Pretreatment with terguride inhibited 5-HT-induced amplification of ADP-stimulated human platelet aggregation (IC50 16 nM). In porcine valvular interstitial cells, 5-HT-induced activation of extracellular signal-regulated kinase (ERK) 1/2, an initiator of cellular proliferation and activity, was blocked by terguride as shown by Western blotting. In these cells, the stimulatory effect of 5-HT on [³H]proline incorporation (index of extracellular matrix collagen) was blocked by terguride. Because of the inhibition of both 5-HT(2A) and 5-HT(2B) receptors, platelet aggregation, and cellular proliferation and activity (ERK1/2 phosphorylation and collagen production) terguride may have therapeutic potential in the treatment of fibrotic disorders.

The bulky N6 substituent of cabergoline is responsible for agonism of this drug at 5-hydroxytryptamine 5-HT2A and 5-HT2B receptors and thus is a determinant of valvular heart disease.

Fibrotic valvular heart disease (VHD) has been observed in patients with Parkinson's disease treated with dopamine receptor agonists such as pergolide and cabergoline. 5-Hydroxytryptamine(2B) receptor (5-HT(2B)R) agonism is the most likely cause, but other 5-HT receptors may also play a role in VHD. We aimed at characterizing the molecular fragment of cabergoline responsible for agonism at 5-HT(2B)R and 5-HT(2A)R. Cabergoline with an allyl substituent at N(6) behaved as a potent 5-HT(2B)R full agonist in relaxation of porcine pulmonary arteries and as a weaker 5-HT(2A)R partial agonist in contraction of coronary arteries. The same was true for cabergoline derivatives with cyclopropylmethyl, propyl, or ethyl at N(6). However, agonism was converted into antagonism, when the N(6) substituent was methyl. 6-Methylcabergoline retained agonism compared with cabergoline at human dopamine D(2LONG) and human dopamine D(2SHORT) receptors as determined by guanosine 5'-O-(3-[(35)S]thio)triphosphate binding. In porcine aortic valve cusps, 5-HT-induced contractions were inhibited by ketanserin (5-HT(2A/2C)R antagonist) but not by N-(1-methyl-1H-5-indolyl)-N'-(3-methyl-5-isothiazolyl)urea (SB204741) (5-HT(2B)R antagonist). In porcine valvular interstitial cells, cabergoline-induced activation of extracellular signal-regulated kinase (ERK) 1/2, an initiator of cellular proliferation and activity, was blocked by (R)-(+)-4-(1-hydroxy-1-(2,3-dimethoxyphenyl)methy1)-N-2-(4-fluorophenylethyl)piperidine (MDL100907) (5-HT(2A)R antagonist) and N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-1,1'-biphenyl-4-carboxamide (GR127935) (5-HT(1B)R antagonist), whereas the stimulatory effect on [(3)H]proline and [(3)H]glucosamine incorporations (indices of extracellular matrix collagen and glycosaminoglycan) was blocked by MDL100907. We conclude that the bulky N(6) substituent of cabergoline is responsible for 5-HT(2A)R and 5-HT(2B)R agonism. The increased ERK1/2 phosphorylation and production of extracellular matrix by cabergoline are mediated by 5-HT(2A)Rs. However, the moderate potency of cabergoline at native 5-HT(2A)Rs suggests that these are not the preferential target in VHD in vivo.

Effects of ginger constituents on the gastrointestinal tract: role of cholinergic M3 and serotonergic 5-HT3 and 5-HT4 receptors.

The herbal drug ginger (Zingiber officinale Roscoe) may be effective for treating nausea, vomiting, and gastric hypomotility. In these conditions, cholinergic M (3) receptors and serotonergic 5-HT (3) and 5-HT (4) receptors are involved. The major chemical constituents of ginger are [6]-gingerol, [8]-gingerol, [10]-gingerol, and [6]-shogaol. We studied the interaction of [6]-gingerol, [8]-gingerol, [10]-gingerol (racemates), and [6]-shogaol with guinea pig M (3) receptors, guinea pig 5-HT (3) receptors, and rat 5-HT (4) receptors. In whole segments of guinea pig ileum (bioassay for contractile M (3) receptors), [6]-gingerol, [8]-gingerol, [10]-gingerol, and [6]-shogaol slightly but significantly depressed the maximal carbachol response at an antagonist concentration of 10 µM. In the guinea pig myenteric plexus preparation (bioassay for contractile 5-HT (3) receptors), 5-HT maximal responses were depressed by [10]-gingerol from 93 ± 3 % to 65 ± 6 % at an antagonist concentration of 3 µM and to 48 ± 3 % at an antagonist concentration of 5 µM following desensitization of 5-HT (4) receptors and blockade of 5-HT (1) and 5-HT (2) receptors. [6]-Shogaol (3 µM) induced depression to 61 ± 3 %. In rat esophageal tunica muscularis mucosae (bioassay for relaxant 5-HT (4) receptors), [6]-gingerol, [8]-gingerol, [10]-gingerol, and [6]-shogaol (2-6.3 µM) showed no agonist effects. The maximal 5-HT response remained unaffected in the presence of the compounds. It is concluded that the efficiency of ginger in reducing nausea and vomiting may be based on a weak inhibitory effect of gingerols and shogaols at M (3) and 5-HT (3) receptors. 5-HT (4) receptors, which play a role in gastroduodenal motility, appear not to be involved in the action of these compounds.

Postjunctional α2C-adrenoceptors mediate vasoconstriction in rat tail artery: influence of precontraction and temperature on vasoreactivity.

The isolated rat tail artery (RTA) represents an in vitro model of the cutaneous circulation. We have characterised the postjunctional α(2)-adrenoceptor subtype mediating vasoconstriction to the α(2)-adrenoceptor (α(2)-AR) agonist UK14304 in RTA. In non-precontracted arterial rings at 32°C, a physiological temperature for the RTA, UK14304 elicited only slight contractions which were markedly enhanced after precontraction with serotonin (5-HT; 10-50 nM). Under the condition of elevated vascular tone, the contractile UK14304 response was competitively antagonised by MK912 (pA(2) = 10.05 ± 0.07), rauwolscine (pA(2) = 8.82 ± 0.06), yohimbine (pA(2) = 8.45 ± 0.04), WB4101 (pA(2) = 8.05 ± 0.05), BRL44408 (pA(2) = 7.20 ± 0.04), ARC239 (pA(2) = 6.90 ± 0.05) and prazosin (pA(2) = 6.80 ± 0.05). Schild regressions were linear and had slopes of unity. Affinities (pA(2)) for MK912, rauwolscine, yohimbine and WB41104 were in the same range as binding data (pK(D)) for these drugs at α(2C)-ARs of rat cerebral cortex. In addition, the presence of α(2C)-ARs was confirmed by Western blotting. In experiments to study the influence of temperature on vasoreactivity, UK14304-induced contractions did not differ at 37°C, 32°C or 27°C and were similarly blocked by rauwolscine (apparent pA(2) = 8.73-8.90). After rapid cooling (from 37°C to 27°C), the maximal UK14304 response was enhanced only in precontracted arteries; antagonism by rauwolscine was the same before and after cooling (apparent pA(2) = 8.80-8.90). The enhancement of the maximal UK14304 response was abolished by rewarming to 37°C. It is concluded that α(2C)-ARs predominantly mediated vasoconstriction in RTAs at any temperature tested. Since α(2C)-ARs may be involved in Raynaud's phenomenon, the isolated RTA represents a convenient in vitro bioassay to test novel compounds for the treatment of this syndrome.

Search for influence of spatial properties on affinity at α1-adrenoceptor subtypes for phenylpiperazine derivatives of phenytoin.

A series of phenylpiperazine derivatives of phenytoin was evaluated for their affinity at α(1)-adrenoceptor subtypes in functional bioassays (rat tail artery: α(1A) and/or α(1B); guinea pig spleen: α(1B); rat aorta: α(1D)). The most potent compounds at α(1A)-, α(1B)- and α(1D)-adrenoceptors, 11, 18 and 8, showed affinities in the submicromolar range. The role of a hydrogen bond donor group for affinity and selectivity at α(1B)-adrenoceptors, postulated by Bremner's pharmacophore model, was confirmed by functional and molecular modelling studies.

Phenylephrine contracts porcine pulmonary veins via alpha(1B)-, alpha(1D)-, and alpha(2)-adrenoceptors.

We have recently shown that the postjunctional alpha(2)-adrenoceptor mediating contraction of porcine pulmonary veins is of the alpha(2C)-subtype. We could also demonstrate that alpha(1)-adrenoceptors might contribute to the contraction in that blood vessel. In the present study, we aimed at characterising the alpha(1)-adrenoceptor subtype(s) involved using pharmacological and molecular biological methods. In isolated rings of porcine pulmonary veins the typical alpha(1)-adrenoceptor agonist phenylephrine caused a concentration-dependent contraction that was inhibited by the alpha(1B)-adrenoceptor selective antagonists 1-[4-(4-amino-6,7-dimethoxyquinazolin-2-yl)piperazin-1-yl]-2-[2-(isopropyl)-6-methoxyphenoxy]ethan-1-one (Rec15/2615; pA(2) 8.96+/-0.13) and 4-amino-2-[4-[1-(benzyloxycarbonyl)-2(S)-[[(1,1-dimethylethyl)amino]carbonyl]-piperazinyl]-6,7-dimethoxyquinazoline (L-765,314; pA(2) 7.22+/-0.05), as well as the alpha(1D)-adrenoceptor selective antagonist 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione (BMY7378; pA(2) 8.29+/-0.15, slope of the Schild plot 0.75+/-0.09, significantly different from unity, P<0.05), but not by the alpha(1A)-adrenoceptor selective antagonists (+/-)-1,3,5-trimethyl-6-[[3-[4-((2,3-dihydro-2-hydroxymethyl)-1,4-benzodioxin-5-yl)-1-piperazinyl]propyl]amino]-2,4(1H,3H)-pyrimidinedione (B8805-033) and N-[2-(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro-alpha,alpha-dimethyl-1H-indole-3-ethanamine (RS-17053). These findings suggest that phenylephrine activates both alpha(1B)- and alpha(1D)-adrenoceptors. The observation was confirmed by reverse-transcriptase polymerase chain reaction (RT-PCR) in porcine pulmonary veins, where mRNA signals for alpha(1B)- and alpha(1D)-adrenoceptors could be detected. However, the antagonist properties of rauwolscine and yohimbine (non-subtype selective alpha(2)-adrenoceptor antagonists) against phenylephrine showed that this agonist also activates alpha(2)-adrenoceptors in pulmonary veins. This was strengthened in experiments using tissues that were stimulated with forskolin (cell permeable activator of adenylyl cyclase). Phenylephrine mimicked the effect of the selective alpha(2)-adrenoceptor agonist UK14304 by causing an inhibition of forskolin-stimulated cAMP accumulation that was blocked by rauwolscine. It is concluded that, in addition to alpha(1B)- and alpha(1D)-adrenoceptors, phenylephrine can stimulate alpha(2)-adrenoceptors in porcine pulmonary veins.

Pharmacological profile of the inhibition by dihydroergotamine and methysergide on the cardioaccelerator sympathetic outflow in pithed rats.

The present study set out to analyse the pharmacological profile of the inhibitory responses induced by the antimigraine agents dihydroergotamine (DHE) and methysergide on the tachycardic responses to preganglionic sympathetic stimulation in pithed rats. For this purpose, 132 male Wistar normotensive rats were pithed and prepared to: (i) selectively stimulate the preganglionic (C(7)-T(1)) cardiac sympathetic outflow; or (ii) receive intravenous (i.v.) bolus injections of exogenous noradrenaline. Electrical sympathetic stimulation or exogenous noradrenaline produced, respectively, frequency-dependent and dose-dependent tachycardic responses. Moreover, i.v. continuous infusions of DHE (1.8, 3.1 and 5.6 microg/kg x min) or methysergide (100, 300 and 1000 microg/kg x min) dose-dependently inhibited the tachycardic responses to sympathetic stimulation, but not those to exogenous noradrenaline. Using physiological saline or antagonists (given as i.v. bolus injections), the cardiac sympatho-inhibition induced by either DHE (3.1 microg/kg x min) or methysergide (300 microg/kg x min) was: (1) unaffected by saline (1 ml/kg); (2) partially blocked by the antagonists rauwolscine (300 microg/kg; alpha(2)) or N-[4-methoxy-3-(4-methyl-1-piperazinyl) phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl) [1,1,-biphenyl]-4-carboxamide hydrochloride monohydrate (GR127935, 300 microg/kg; 5-HT(1B/1D)); and (3) completely antagonised by the combination rauwolscine plus GR127935. These antagonists, at doses high enough to completely block their respective receptors, failed to modify the sympathetically-induced tachycardic responses per se. The above results, taken together, suggest that the cardiac sympatho-inhibition induced by DHE (3.1 microg/kg x min) and methysergide (300 microg/kg x min) may be mainly mediated by stimulation of both alpha(2)-adrenoceptors and 5-HT(1B/1D) receptors.

Pharmacological characterization of ergotamine-induced inhibition of the cardioaccelerator sympathetic outflow in pithed rats.

Ergotamine inhibits the sympathetically-induced tachycardia in pithed rats. The present study identified the pharmacological profile of this response. Male Wistar rats were pithed and prepared to stimulate the preganglionic (C(7)-T(1)) cardiac sympathetic outflow. Intravenous continuous infusions of ergotamine dose-dependently inhibited the tachycardic responses to sympathetic stimulation, but not those to exogenous noradrenaline. Using several antagonists, the sympatho-inhibition to ergotamine was: (1) partially blocked by rauwolscine (alpha(2)), haloperidol (D(1/2)-like) or rauwolscine plus GR127935 (5-HT(1B/1D)); (2) abolished by rauwolscine plus haloperidol; and (3) unaffected by either saline or GR127935. In animals systematically pretreated with haloperidol, this sympatho-inhibition was: (1) unaffected by BRL44408 (alpha(2A)), partially antagonized by MK912 (alpha(2C)); and (3) abolished by BRL44408 plus MK912. These antagonists failed to modify the sympathetically induced tachycardic responses per se. Thus, the cardiac sympatho-inhibition by ergotamine may be mainly mediated by alpha(2A)/alpha(2C)-adrenoceptors, D(2)-like receptors and, to a lesser extent, by 5-HT(1B/1D) receptors.

17-Beta-estradiol inhibits transforming growth factor-beta signaling and function in breast cancer cells via activation of extracellular signal-regulated kinase through the G protein-coupled receptor 30.

Breast cancer development and breast cancer progression involves the deregulation of growth factors leading to uncontrolled cellular proliferation, invasion and metastasis. Transforming growth factor (TGF)-beta plays a crucial role in breast cancer because it has the potential to act as either a tumor suppressor or a pro-oncogenic chemokine. A cross-communication between the TGF-beta signaling network and estrogens has been postulated, which is important for breast tumorigenesis. Here, we provide evidence that inhibition of TGF-beta signaling is associated with a rapid estrogen-dependent nongenomic action. Moreover, we were able to demonstrate that estrogens disrupt the TGF-beta signaling network as well as TGF-beta functions in breast cancer cells via the G protein-coupled receptor 30 (GPR30). Silencing of GPR30 in MCF-7 cells completely reduced the ability of 17-beta-estradiol (E2) to inhibit the TGF-beta pathway. Likewise, in GPR30-deficient MDA-MB-231 breast cancer cells, E2 achieved the ability to suppress TGF-beta signaling only after transfection with GPR30-encoding plasmids. It is most interesting that the antiestrogen fulvestrant (ICI 182,780), which possesses agonistic activity at the GPR30, also diminished TGF-beta signaling. Further experiments attempted to characterize the molecular mechanism by which activated GPR30 inhibits the TGF-beta pathway. Our results indicate that GPR30 induces the stimulation of the mitogen-activated protein kinases (MAPKs), which interferes with the activation of Smad proteins. Inhibition of MAPK activity prevented the ability of E2 from suppressing TGF-beta signaling. These findings are of great clinical relevance, because down-regulation of TGF-beta signaling is associated with the development of breast cancer resistance in response to antiestrogens.

Dopamine/serotonin receptor ligands. Part 17: a cross-target SAR approach: affinities of azecine-styled ligands for 5-HT(2A) versus D1 and D2 receptors.

Dibenzo- and benzindolo-azecines represent a novel class of high-affinity dopamine receptor antagonists. To further characterize these drugs as potential neuroleptics, we selected a set of azecine derivatives and ring expanded homologues and we measured their antagonist activity at the 5-HT(2A) receptor in the porcine coronary artery. SARs found for the 5-HT(2A) receptor resemble those for the D1 but not the D2 receptor. The protein-ligand interactions were discussed with respect to the different binding pockets.

Characterization of the molecular fragment that is responsible for agonism of pergolide at serotonin 5-Hydroxytryptamine2B and 5-Hydroxytryptamine2A receptors.

Cardiac-valve regurgitation observed in Parkinson patients treated with the ergoline dopamine receptor agonist 8beta-methylthiomethyl-6-propylergoline (pergolide) has been associated with the agonist efficacy of the drug at 5-hydroxytryptamine(2B) (5-HT(2B)) receptors. 5-HT(2A) receptors may also play a role in pergolide-induced cardiac-valve regurgitation. We studied the pharmacological profile of pergolide and eight derivatives in porcine vascular rings endowed with 5-HT(2B) and 5-HT(2A) receptors to detect the molecular fragment of the pergolide molecule that may be responsible for agonism at these receptors. Pergolide derivatives showed a different substitution pattern at N(6), and the side chain at C(8) was modified by replacement of the sulfur against an oxygen atom. We demonstrate that the potent agonism of pergolide both at 5-HT(2B) and 5-HT(2A) receptors is retained when the N(6) propyl substituent is replaced by ethyl. However, agonism can be converted into antagonism if N(6) propyl is replaced by methyl. The N(6)-unsubstituted derivative was a low efficacy 5-HT(2B) receptor partial agonist and a 5-HT(2A) receptor antagonist. This pharmacological pattern was also applicable for pergolide congeners with an oxygen in the side chain at C(8). 6-Methylpergolide retained agonist efficacy and potency compared with pergolide at human (h) D(2LONG(L)) and hD(2SHORT(S)) receptors as determined by guanosine 5'-O-(3-[(35)S]thio)triphosphate binding. Based on the ability of pergolide to produce potent agonism at 5-HT(2B) receptors and the failure of 6-methylpergolide to act as an agonist but as a potent antagonist, we conclude that the N(6) propyl substituent of pergolide is crucial for 5-HT(2B) receptor agonism and thus a determinant of valvular regurgitation.

Pharmacological properties of a wide array of ergolines at functional alpha(1)-adrenoceptor subtypes.

Ergot alkaloids act as (partial) agonists or antagonists at serotonergic, dopaminergic and alpha-adrenergic receptors. In contrast to their affinity at serotonergic (5-HT) and dopaminergic receptor subtypes, only limited information is available concerning their interaction with alpha-adrenoceptor subtypes. This especially holds true for native alpha-adrenoceptors. Therefore, we studied the pharmacological profile of 25 ergolines at alpha(1A)-, alpha(1B)- and alpha(1D)-adrenoceptors in vascular rings or strips of rat and guinea pig endowed with these receptors. Contractile responses were studied by measurement of isometric tension changes in rat tail artery (alpha(1A), alpha(1B)), guinea pig spleen (alpha(1B)) and rat thoracic aorta (alpha(1D)). The anti-migraine drugs ergotamine and dihydroergotamine, the anti-parkinsonian drug lisuride and the anti-hyperprolactinemic drug terguride behaved as antagonists or low-efficacy partial agonists at all three alpha(1)-adrenoceptor subtypes with nanomolar receptor affinity. Derivatives of these drugs showed lower affinity at alpha(1)-adrenoceptors than the parent compounds. Each individual ergoline derivative tested showed low discriminatory capability at the subtypes, alpha(1A), alpha(1B), alpha(1D). A low discriminatory power between the subtypes (alpha(1A), alpha(1B), alpha(1D)) seems to be a class effect of the ergolines. The nanomolar affinities of ergotamine, dihydroergotamine and lisuride for alpha(1)-adrenoceptors may affect their effectiveness as anti-migraine and anti-parkinsonian drugs, respectively.

Characterization of the relaxant response to N,N'-dipropyl-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine in porcine coronary arteries.

N,N'-Dialkyl-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamines show structural analogy with estrogens and selective estrogen receptor modulators. Because the vasodilator properties of these compounds are unknown, we investigated their potential to relax porcine coronary arteries and determined the mechanism(s) of relaxation. Isolated porcine coronary arterial rings were suspended in organ chambers, precontracted with KCl (30 mM), and the relaxant response was determined by measurement of changes in isometric force. Dependent on the chemical structure, the drugs induced concentration-dependent relaxation in rings with and without endothelium. N,N'-Dipropyl-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine (8) was most potent and showed a 12- to 15-fold higher vasodilatory effect than 17beta-estradiol (E2). The vasorelaxation was independent of endothelium. Calcium concentration-dependent contractions in high-potassium depolarizing medium were insurmountably inhibited by 8. The effect of the L-type Ca2+ channel activator (S)-(-)-Bay K 8644 [(S)-(-)-1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-3-pyridine-carboxylic acid methyl ester], which induced a leftward shift of Ca2+ contraction, was blocked by 8. The relaxant response to 8 was unaffected by the estrogen receptor antagonist ICI 182,780 (7alpha-[9-[(4,4,5,5,5-pentafluoropentyl]-sulfinyl]nonyl]-estra-1,3,5(10)-triene-3,17beta-diol) and K+ channel blockers, i.e., TEA, glibenclamide, and 4-aminopyridine. Furthermore, the vasodilatory effect of 8 was unaffected by the adenylyl cyclase inhibitor SQ 22536 [9-(tetrahydro-2-furanyl)-9H-purin-6-amine], the guanylyl cyclase inhibitor ODQ [1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one], the protein kinase A inhibitor KT 5720 [(9S,10S,12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg: 3',2',1'-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid hexyl ester], the protein kinase G inhibitor KT 5823 [(9S,10R,12R)-2,3,9,10,11,12-hexahydro-10-methoxy-2,9-dimethyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid methyl ester], and the p38 mitogen-activated protein kinase (MAPK) inhibitor SB 203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole]. Western blot analysis demonstrated that 8, unlike E2, raloxifene, and tamoxifen, failed to stimulate p38 MAPK. It is concluded that N,N'-dipropyl-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine induces endothelium-independent relaxation of coronary arteries; the mechanism apparently involves inhibition of L-type Ca2+ channels. The drug may be protective against cardiovascular diseases.