RESUMO
BACKGROUND AND PURPOSE: Olcegepant (BIBN4096BS) is a selective non-peptide CGRP receptor antagonist with acute antimigraine properties. Since systemic vascular tone is modulated by perivascular (primary sensory CGRPergic and sympathetic) nerves, this randomized study investigated in pithed rats the effect of acute i.v. treatment with olcegepant on the neurogenic and non-neurogenic: (i) CGRPergic vasodepressor responses; and (ii) noradrenergic vasopressor responses. The pithed rat is an experimental model predictive of systemic (cardio) vascular side effects. EXPERIMENTAL APPROACH: Seventy-five male Wistar rats (divided into 15 groups, n = 5 each) were pithed, artificially ventilated and prepared for: (i) spinal stimulation (T9 -T12 ; 0.56-5.6 Hz) of the sensory CGRPergic vasodepressor outflow or i.v. bolus injections (0.1-1 µg·kg-1 ) of α-CGRP, substance P or acetylcholine, which induced frequency-dependent or dose-dependent vasodepressor responses; or (ii) spinal stimulation (T7 -T9 ; 0.03-3 Hz) of the sympathetic vasopressor outflow or i.v. bolus injections (0.03-3 µg·kg-1 ) of noradrenaline, which produced frequency-dependent or dose-dependent vasopressor responses. KEY RESULTS: Olcegepant (1000 and 3000 µg·kg-1 , i.v.) dose-dependently blocked the vasodepressor responses to sensory nerve stimulation or i.v. α-CGRP, without affecting those to substance P or acetylcholine. Whereas it potentiated the vasopressor responses to sympathetic nerve stimulation or i.v. noradrenaline. CONCLUSIONS AND IMPLICATIONS: Olcegepant (i.v.) selectively blocked the neurogenic and non-neurogenic CGRPergic vasodepressor responses. This blockade by olcegepant potentiated the neurogenic and non-neurogenic noradrenergic vasopressor responses in pithed rats, an effect that might result in an increased vascular resistance and, consequently, in a prohypertensive action.
Assuntos
Peptídeo Relacionado com Gene de Calcitonina/antagonistas & inibidores , Dipeptídeos/farmacologia , Quinazolinas/farmacologia , Vasoconstritores/farmacologia , Animais , Relação Dose-Resposta a Droga , Estimulação Elétrica , Masculino , Piperazinas , Ratos , Ratos Wistar , Relação Estrutura-AtividadeRESUMO
This study assessed the possible antinociceptive role of peripheral 5-HT(1) receptor subtypes in the rat formalin test. Rats were injected into the dorsum of the hind paw with 50 microl of diluted formalin (1%). Nociceptive behavior was quantified as the number of flinches of the injected paw. Reduction of flinching was considered as antinociception. Ipsilateral, but not contralateral, peripheral administration of the 5-HT(1) receptor agonists R(+)-UH-301 (5-HT(1A); 0.1-3 microg/paw), CGS-12066A (5-HT(1B); 0.01-0.3 microg/paw), GR46611 (5-HT(1B/1D); 0.3-10 microg/paw), BRL54443 (5-HT(1E/1F); 3-300 microg/paw) or LY344864 (5-HT(1F); 3-300 microg/paw) significantly reduced formalin-induced flinching. The corresponding vehicle was devoid of any effect by itself. The local antinociceptive effect of R(+)-UH-301 (0.3 microg/paw) was significantly reduced by WAY-100635 (30-100 microg/paw; a 5-HT(1A) receptor antagonist). Moreover, the antagonists GR55562 (30-100 microg/paw; 5-HT(1B/D)) or SB224289 (30-100 microg/paw; 5-HT(1B)) dose-dependently reduced the antinociceptive effect of CGS-12066A (0.3 microg/paw) whereas GR55562 (30-100 microg/paw) or BRL15572 (30-100 microg/paw, 5-HT(1D)) reduced the antinociceptive effect of GR46611 (0.3 microg/paw). Interestingly, the effects of BRL54443 and LY344864 (300 microg/paw each) were partially reduced by methiothepin, but not by the highest doses of WAY-100635, SB224289 or BRL15572. The above antagonists did not produce any effect by themselves. These results suggest that peripheral activation of the 5-HT(1A,) 5-HT(1B), 5-HT(1D), 5-HT(1F) and, probably, 5-HT(1E) receptor subtypes leads to antinociception in the rat formalin test. Thus, the use of selective 5-HT(1) receptor agonists could be a therapeutic strategy to reduce inflammatory pain.
Assuntos
Dor/tratamento farmacológico , Dor/metabolismo , Nervos Periféricos/efeitos dos fármacos , Nervos Periféricos/metabolismo , Receptores de Serotonina/metabolismo , Agonistas do Receptor de Serotonina/farmacologia , Animais , Relação Dose-Resposta a Droga , Feminino , Formaldeído , Lateralidade Funcional , Membro Posterior/efeitos dos fármacos , Membro Posterior/metabolismo , Dor/induzido quimicamente , Medição da Dor , Ratos , Ratos Wistar , Receptor 5-HT1A de Serotonina/metabolismo , Receptor 5-HT1B de Serotonina/metabolismo , Receptor 5-HT1D de Serotonina/metabolismo , Agonistas do Receptor 5-HT1 de Serotonina , Agonistas do Receptor de Serotonina/administração & dosagem , Receptor 5-HT1F de SerotoninaRESUMO
Imidazoline derivatives (e.g. clonidine and moxonidine) and alpha(2)-adrenoceptor agonists (e.g. B-HT 933) have been shown to inhibit sympathetically-induced [(3)H]noradrenaline release in several isolated blood vessels. The present study has compared the potential capability of agonists at imidazoline I(1/2) receptors and/or alpha(1/2)-adrenoceptors to inhibit the sympathetically-induced vasopressor responses in pithed rats. For this purpose, male Wistar rats were pithed and prepared for measurement of diastolic blood pressure and heart rate. Then, the vasopressor responses induced by either selective electrical stimulation (2 ms, 60 V; 0.03, 0.1, 0.3, 1 and 3 Hz) of the vascular sympathetic outflow (T(7)-T(9)) or i.v. bolus injections of exogenous noradrenaline (0.03, 0.1, 0.3, 1 and 3 microg/kg) were determined before and during i.v. continuous infusions of the agonists B-HT 933 (alpha(2)), clonidine (alpha(2), I(1)), moxonidine (alpha(2), I(1)), cirazoline (alpha(1), I(2)), agmatine (putative endogenous ligand of imidazoline receptors) and methoxamine (alpha(1)), or equivalent volumes of physiological saline. Electrical sympathetic stimulation elicited frequency-dependent vasopressor responses which were significantly inhibited during the continuous infusions of B-HT 933, clonidine, moxonidine, cirazoline and agmatine, but not of physiological saline. Interestingly, the vasopressor responses to exogenous noradrenaline, which remained unaffected during the infusions of physiological saline, B-HT 933, moxonidine, cirazoline and agmatine, were significantly blocked during the infusions of clonidine or methoxamine. These results suggest that B-HT 933, moxonidine, cirazoline and agmatine induced a prejunctional inhibition of the vasopressor sympathetic outflow in pithed rats, whilst clonidine inhibited the vasopressor sympathetic outflow by both prejunctional and postjunctional mechanisms.
Assuntos
Pressão Sanguínea/efeitos dos fármacos , Vasos Sanguíneos/inervação , Imidazolinas/farmacologia , Sistema Nervoso Simpático/efeitos dos fármacos , Agonistas alfa-Adrenérgicos/administração & dosagem , Agonistas alfa-Adrenérgicos/farmacologia , Agmatina/administração & dosagem , Agmatina/farmacologia , Animais , Anti-Hipertensivos/administração & dosagem , Anti-Hipertensivos/farmacologia , Azepinas/administração & dosagem , Azepinas/farmacologia , Pressão Sanguínea/fisiologia , Clonidina/administração & dosagem , Clonidina/farmacologia , Estado de Descerebração , Relação Dose-Resposta a Droga , Estimulação Elétrica/métodos , Frequência Cardíaca/efeitos dos fármacos , Frequência Cardíaca/fisiologia , Imidazóis/administração & dosagem , Imidazóis/farmacologia , Receptores de Imidazolinas/agonistas , Imidazolinas/administração & dosagem , Injeções Intravenosas , Masculino , Metoxamina/administração & dosagem , Metoxamina/farmacologia , Ratos , Ratos Wistar , Sistema Nervoso Simpático/fisiologia , Sistema Vasomotor/efeitos dos fármacos , Sistema Vasomotor/fisiologiaRESUMO
BACKGROUND AND PURPOSE: Resistance blood vessels are innervated by sympathetic and primary sensory nerves, which modulate vascular tone through the release of noradrenaline and calcitonin gene-related peptide (CGRP), respectively. Moreover, electrical stimulation of the perivascular sensory outflow in pithed rats results in vasodepressor responses which are mainly mediated by CGRP release. The present study has investigated the role of alpha(2)-adrenoceptors in the inhibition of these vasodepressor responses. EXPERIMENTAL APPROACH: 144 pithed male Wistar rats were pretreated with hexamethonium (2 mg kg(-1) min(-1)) followed by i.v. continuous infusions of either methoxamine (15 and 30 microg kg(-1) min(-1)) or clonidine (3, 10 and 30 microg kg(-1) min(-1)). Under these conditions, electrical stimulation (0.56-5.6 Hz; 50 V and 2 ms) of the spinal cord (T(9)-T(12)) resulted in frequency-dependent decreases in diastolic blood pressure. KEY RESULTS: The infusion of clonidine (10 microg kg(-1) min(-1)), as compared to those of methoxamine (15 or 30 microg kg(-1) min(-1)), inhibited the vasodepressor responses to electrical stimulation without affecting those to i.v. bolus injections of alpha-CGRP (0.1-1 microg kg(-1)). This inhibition by clonidine was: (i) antagonized by 300 microg kg(-1) rauwolscine (alpha(2A/2B/2C)), 300 and 1000 microg kg(-1) BRL44408 (alpha(2A)), or 10 and 30 microg kg(-1) MK912 (alpha(2C)); and (ii) unaffected by 1 ml kg(-1) saline, 100 microg kg(-1) BRL44408, 3000 and 10,000 microg kg(-1) imiloxan (alpha(2B)) or 3 microg kg(-1) MK912. CONCLUSIONS AND IMPLICATIONS: The inhibition produced by 10 microg kg(-1) min(-1) clonidine on the vasodepressor (perivascular) sensory outflow in rats may be mainly mediated by prejunctional alpha(2A)/alpha(2C)-adrenoceptors.
Assuntos
Agonistas alfa-Adrenérgicos/farmacologia , Vasos Sanguíneos/efeitos dos fármacos , Vasos Sanguíneos/inervação , Clonidina/farmacologia , Estado de Descerebração/fisiopatologia , Neurônios Aferentes/efeitos dos fármacos , Receptores Adrenérgicos alfa 2/fisiologia , Antagonistas Adrenérgicos alfa/farmacologia , Animais , Pressão Sanguínea/efeitos dos fármacos , Peptídeo Relacionado com Gene de Calcitonina/farmacologia , Estimulação Elétrica , Frequência Cardíaca/efeitos dos fármacos , Imidazóis/farmacologia , Técnicas In Vitro , Isoindóis/farmacologia , Masculino , Quinolizinas/farmacologia , Ratos , Ratos Wistar , Receptores Adrenérgicos alfa 2/efeitos dos fármacos , Ioimbina/farmacologiaRESUMO
It has previously been shown that the androgen, 5beta-dihydrotestosterone (17beta-hydroxy-5beta-androstan-3-one, 5beta-DHT), is able to produce an endothelium-independent vasodilating effect in rat aorta. The present study analyzed the mechanisms underlying the above vasodilator effect of 5beta-dihydrotestosterone, with particular emphasis on verifying a possible interaction with GABA(A) receptors, beta-adrenoceptors and Ca2+ channels. Rat aortic rings without endothelium were isometrically recorded. 5Beta-dihydrotestosterone produced a concentration-dependent relaxation on the contractions induced by noradrenaline (NA; 0.3 microM) or K+ (KCl; 60 mM), with the latter being more sensitive to 5beta-dihydrotestosterone-induced relaxation than the former; the concentration-response curves showed that 5beta-dihydrotestosterone is significantly more potent than 17beta-estradiol(1,3,5(10)-estratrien-3,17beta-diol) to induce vasodilatation. The vasodilating effect of 5beta-dihydrotestosterone on noradrenaline-induced contraction was resistant to blockade by the GABA(A) receptor antagonists, picrotoxin or bicuculline, and the beta-adrenoceptor antagonist, propranolol, a finding that excludes an interaction of the steroid with GABA(A) receptors and beta-adrenoceptors. Interestingly, the contractions evoked by calcium in depolarized tissues were substantially inhibited by 5beta-dihydrotestosterone, implying that this steroid could be an endogenous calcium channel blocker; consistent with this finding, 5beta-dihydrotestosterone was able to relax tissues precontracted with the calcium channel opener, Bay K 8644. Moreover, although the rings precontracted with noradrenaline and potassium were almost equipotently relaxed by 5beta-dihydrotestosterone. Nifedipine was more potent than 5beta-dihydrotestosterone to block the potassium-induced contraction, but the steroid was more effective than nifedipine to prevent noradrenaline-induced contraction. The above results suggest that 5beta-dihydrotestosterone causes relaxation of rat aorta by acting directly on the membrane of smooth muscle cells; this non-genomic action may be explained in terms of a blockade of voltage- and receptor-dependent calcium channels, a mechanism that restricts the availability of extracellular calcium in the contractile machinery.
Assuntos
Canais de Cálcio/fisiologia , Di-Hidrotestosterona/farmacologia , Receptores Adrenérgicos beta/fisiologia , Receptores de GABA-A/fisiologia , Vasodilatação/efeitos dos fármacos , Animais , Aorta Torácica/efeitos dos fármacos , Bloqueadores dos Canais de Cálcio/farmacologia , Relação Dose-Resposta a Droga , Interações Medicamentosas , Estradiol/farmacologia , Técnicas In Vitro , Contração Isométrica/efeitos dos fármacos , Masculino , Músculo Liso Vascular/efeitos dos fármacos , Norepinefrina/farmacologia , Ratos , Ratos Wistar , Vasodilatação/fisiologiaRESUMO
Serotonin (5-hydroxytryptamine; 5-HT) elicits external carotid vasoconstriction in vagosympathectomized dogs via 5-HT1B/1D receptors and a mechanism unrelated to the 5-HT1, 5-HT2, 5-HT3 and 5-HT4 types. In order to further explore the nature of this novel mechanism, the canine external carotid effects of 2-(2-aminoethyl)-quinoline (D-1997), a novel 5-HT1 receptor agonist, were analyzed and compared with those of 5-HT and sumatriptan. Intracarotid (i.c.) infusions of 5-HT, D-1997 and sumatriptan to vagosympathectomized dogs dose-dependently decreased external carotid conductance, the rank order of agonist potency being 5-HT > sumatriptan > D-1997. The effects to D-1997 were resistant to intravenous (i.v.) pretreatment with 5-HT2 and 5-HT3/5-HT4 receptor antagonists. Remarkably, the effects induced by lower (10-100 microg/min), but not higher (300-1000 microg/min), doses of D-1997 were blocked by high doses of methiothepin (1 and 3 mg/kg, i.v.), as previously shown with 5-HT. In addition, GR-127935 (1-10 microg/kg, i.v.), partially and dose-dependently antagonized D-1997-induced responses. However, the effects of D-1997 remained unaltered after blockade of alpha- and beta-adrenoceptors, muscarinic, nicotinic, histamine and dopamine receptors, or inhibition of 5-HT-uptake or cyclo-oxygenase, depletion of biogenic amines or blockade of Ca2+ channels. These results may support our previous contention that lower doses of 5-HT elicit external carotid vasoconstriction in vagosympathectomized dogs by activation of 5-HT1B/1D receptors, whilst higher doses of 5-HT stimulate a novel vasoconstrictor mechanism.
Assuntos
Artéria Carótida Externa/efeitos dos fármacos , Quinolinas/farmacologia , Agonistas do Receptor de Serotonina/farmacologia , Simpatectomia , Vagotomia , Animais , Artéria Carótida Externa/fisiologia , Cães , Relação Dose-Resposta a Droga , Feminino , Hemodinâmica/efeitos dos fármacos , Hemodinâmica/fisiologia , Masculino , Metiotepina/farmacologia , Quinolinas/administração & dosagem , Fluxo Sanguíneo Regional/efeitos dos fármacos , Serotonina/farmacologia , Antagonistas da Serotonina/farmacologia , Agonistas do Receptor de Serotonina/administração & dosagem , Cloreto de Sódio/farmacologia , Sumatriptana/farmacologia , Vasoconstrição/efeitos dos fármacosRESUMO
We assessed the possible inhibition of airway smooth muscle contraction by progesterone and pregnanolones (5 alpha and 5 beta-reduced). Progesterone and 5 beta-pregnanolone prevented histamine- or carbachol-induced contraction in isolated guinea-pig trachea and potency was related to their respective chemical structure; progesterone was the most potent inhibitor in a concentration-dependent manner. The steroids also exhibited calcium antagonist activities in this tissue as assessed by their action on calcium entry in depolarized preparations; this event involved the immediate blockade of the extracellular calcium influx in the muscle cell membrane, indicating a nongenomic action. Classical GABAA antagonists did not block the progesterone response, implying no involvement of the GABAA-receptor complex. Our results suggest a bronchodilating effect induced by sex steroids, and probably by other related compounds, before the genomic mechanisms take place. This nongenomic action of steroids could have potential therapeutic usefulness in the treatment of asthma.
Assuntos
Músculo Liso/efeitos dos fármacos , Pregnanolona/farmacologia , Progesterona/farmacologia , Animais , Bicuculina/farmacologia , Cálcio/fisiologia , Antagonistas GABAérgicos/farmacologia , Antagonistas de Receptores de GABA-A , Cobaias , Masculino , Potenciais da Membrana/efeitos dos fármacos , Contração Muscular/efeitos dos fármacos , Picrotoxina/farmacologia , Pregnanolona/análogos & derivados , Traqueia/efeitos dos fármacosRESUMO
The subtype(t) of alpha-adrenoceptor-mediating contractions to alpha-methynoradrenaline in the rat aorta has been investigated by using alpha-adrenoceptor-selective competitive antagonists and the alpha 1-adrenoceptor selective agonist, phenylephrine, for comparison. alpha-Methylnoradrenaline and phenylephrine elicited concentration-dependent contractions in the endothelium-denuded and endothelium-intact aortic rings with similar potencies and maximal effects. alpha-Methylnoradrenaline- and phenylephrine-induced contractions in endothelium-denuded aortic rings were competitively antagonized by prazosin (pA2 = 9.38 and 9.13; respectively) and rauwolscine (pA2 = 7.19 and 6.60, respectively). This confirms that there is an alpha 1- and a non alpha 2-adrenoceptor response to alpha-methylnoradrenaline in the rat aorta. The subtype selective alpha 1D-adrenoceptor antagonist, BMY 7378, was found to antagonize contractions to alpha-methylnoradrenaline and phenylephrine competitively in endothelium-denuded and endothelium-intact aortic rings. The pA2 values of BMY 7378 against alpha-methylnoradrenaline (8.39 and 8.41; endothelium-intact and endothelium-denuded, respectively) and phenylephrine (8.64 and 8.76; endothelium-intact and endothelium-denuded, respectively), are consistent with its published functional potency and clonal alpha 1D-adrenoceptor binding affinity. In addition, contractions to alpha-methylnoradrenaline and phenylephrine in endothelium-denuded aortic rings, were potently inhibited by WB 4101 with pA2 values of 9.75 and 9.25, respectively. The high pA2 values for WB 4101 indicate that the alpha 1B-adrenoceptor subtype does not seem to participate in alpha-methylnoradrenaline (and phenylephrine) induced contractions in this artery. These results suggest that the alpha 1D-subtype plays a determining role in rat aorta contractions induced by alpha-methylnoradrenaline.
Assuntos
Agonistas alfa-Adrenérgicos/farmacologia , Aorta/efeitos dos fármacos , Contração Muscular/efeitos dos fármacos , Nordefrin/farmacologia , Fenilefrina/farmacologia , Vasoconstritores/farmacologia , Antagonistas Adrenérgicos alfa/farmacologia , Animais , Aorta/química , Aorta/fisiologia , Interações Medicamentosas , Endotélio Vascular/química , Endotélio Vascular/efeitos dos fármacos , Endotélio Vascular/fisiologia , Masculino , Contração Muscular/fisiologia , Ratos , Ratos WistarRESUMO
The mechanism of action on the uterine-relaxant effect of sex steroids has been suggested to involve an interaction with gamma-amino butyric acid (GABA) receptors. However, other lines of evidence do not seem to support this suggestion. In view of this controversy, this study was designed to investigate the potential relaxant effect of GABA, muscimol (a GABA(A) receptor agonist), testosterone, progesterone and their 5-reduced metabolites in rat uterus at different endocrine stages (pregnant, nonpregnant and estrogenized), with particular emphasis on verifying if the relaxant effect of steroids involves an interaction with GABA(A) receptors. Contractions from uterine rings were recorded by isometric method, the sequential addition of either GABA (at different concentrations) on the spontaneous and KCl-induced contraction or muscimol (also at different concentrations) on the contraction induced by KCl was devoid of any significant effect. In contrast, the sequential addition of progesterone relaxed the tonic KCl-induced contraction in a concentration-dependent manner. This effect of progesterone was mimicked by its 5-reduced metabolites. The 5(beta)-configured isomers were more potent than progesterone and the 5(alpha)-configured ones. Interestingly, the relaxation produced by the above steroids was not blocked by the GABA(A) receptor antagonists, picrotoxin or bicuculline, but was reversed by calcium. Taken together, the above findings suggest that the relaxant action of the sex steroids analyzed in this study is not mediated by an interaction with GABA(A) receptors, instead a blockade of calcium influx appears to be responsible.