benzofurans and cirazoline

Presynaptic imidazoline receptors (R(i-pre)) are found in the sympathetic axon terminals of animal and human cardiovascular systems, and they regulate blood pressure by modulating the release of peripheral noradrenaline (NA). The cellular mechanism of R(i-pre)-induced inhibition of NA release is unknown. We, therefore, investigated the effect of R(i-pre) activation on voltage-dependent Ca(2+) channels in rat superior cervical ganglion (SCG) neurons, using the conventional whole-cell patch-clamp method. Cirazoline (30 μM), an R(i-pre) agonist as well as an α-adrenoceptor (R(α)) agonist, decreased Ca(2+) currents (I(Ca)) by about 50% in a voltage-dependent manner with prepulse facilitation. In the presence of low-dose rauwolscine (3 μM), which blocks the α(2)-adrenoceptor (R(α2)), cirazoline still inhibited I(Ca) by about 30%, but prepulse facilitation was significantly attenuated. This inhibitory action of cirazoline was almost completely prevented by high-dose rauwolscine (30 μM), which blocks R(i-pre) as well as R(α2). In addition, pretreatment with LY320135 (10 μM), another R(i-pre) antagonist, in combination with low-dose rauwolscine (3 μM), also blocked the R(α2)-resistant effect of cirazoline. Addition of guanosine-5-O-(2-thiodiphosphate) (2 mm) to the internal solutions significantly attenuated the action of cirazoline. However, pertussis toxin (500 ng ml(1)) did not significantly influence the inhibitory effect of cirazoline. Moreover, cirazoline (30 μM) suppressed M current in SCG neurons cultured overnight. Finally, omega-conotoxin (omega-CgTx) GVIA (1 μM) obstructed cirazoline-induced current inhibition, and cirazoline (30 μM) significantly decreased the frequency of action potential firing in a partly reversible manner. This cirazoline-induced inhibition of action potential firing was almost completely occluded in the presence of omega-CgTx. Taken together, our results suggest that activation of R(i-pre) in SCG neurons reduced N-type I(Ca) in a pertussis toxin- and voltage-insensitive pathway, and this inhibition attenuated repetitive action potential firing in SCG neurons.

Topics: Action Potentials; Adrenergic alpha-2 Receptor Antagonists; Animals; Benzofurans; Calcium Channel Blockers; Calcium Channels, N-Type; Calcium Signaling; Cells, Cultured; Dose-Response Relationship, Drug; Guanosine Diphosphate; Imidazoles; Imidazoline Receptors; Kinetics; Male; Neurons; Norepinephrine; omega-Conotoxin GVIA; Patch-Clamp Techniques; Pertussis Toxin; Potassium Channels; Presynaptic Terminals; Rats; Rats, Sprague-Dawley; Receptors, Presynaptic; Superior Cervical Ganglion; Thionucleotides; Yohimbine

This study was designed to assess the potential neuroprotective effect of several imidazol(ine) drugs and agmatine on glutamate-induced necrosis and on apoptosis induced by low extracellular K+ in cultured cerebellar granule cells. Exposure (30 min) of energy deprived cells to L-glutamate (1-100 microM) caused a concentration-dependent neurotoxicity, as determined 24 h later by a decrease in the ability of the cells to metabolize 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) into a reduced formazan product. L-glutamate-induced neurotoxicity (EC50=5 microM) was blocked by the specific NMDA receptor antagonist MK-801 (dizocilpine). Imidazol(ine) drugs and agmatine fully prevented neurotoxicity induced by 20 microM (EC100) L-glutamate with the rank order (EC50 in microM): antazoline (13)>cirazoline (44)>LSL 61122 [2-styryl-2-imidazoline] (54)>LSL 60101 [2-(2-benzofuranyl) imidazole] (75)>idazoxan (90)>LSL 60129 [2-(1,4-benzodioxan-6-yl)-4,5-dihydroimidazole](101)>RX82 1002 (2-methoxy idazoxan) (106)>agmatine (196). No neuroprotective effect of these drugs was observed in a model of apoptotic neuronal cell death (reduction of extracellular K+) which does not involve stimulation of NMDA receptors. Imidazol(ine) drugs and agmatine fully inhibited [3H]-(+)-MK-801 binding to the phencyclidine site of NMDA receptors in rat brain. The profile of drug potency protecting against L-glutamate neurotoxicity correlated well (r=0.90) with the potency of the same compounds competing against [3H]-(+)-MK-801 binding. In HEK-293 cells transfected to express the NR1-1a and NR2C subunits of the NMDA receptor, antazoline and agmatine produced a voltage- and concentration-dependent block of glutamate-induced currents. Analysis of the voltage dependence of the block was consistent with the presence of a binding site for antazoline located within the NMDA channel pore with an IC50 of 10-12 microM at 0 mV. It is concluded that imidazol(ine) drugs and agmatine are neuroprotective against glutamate-induced necrotic neuronal cell death in vitro and that this effect is mediated through NMDA receptor blockade by interacting with a site located within the NMDA channel pore.

Topics: Agmatine; Animals; Antazoline; Benzofurans; Cell Line; Cells, Cultured; Cerebellum; Dioxanes; Dizocilpine Maleate; Dose-Response Relationship, Drug; Electrophysiology; Glutamic Acid; Humans; Idazoxan; Imidazoles; Neuroprotective Agents; Patch-Clamp Techniques; Potassium; Radioligand Assay; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Styrenes

Although many of the behavioral effects of cocaine are widely believed to be mediated by blockade of dopamine transporters, recent studies suggest that norepinephrine (NE) may play a modulatory role. In this study, selective and nonselective beta-adrenergic receptor antagonists were administered alone or in combination with cocaine (2.5 mg/kg, i.p.) to rats trained to discriminate a low dose (2.5 mg/kg) from a high dose of cocaine (10 mg/kg) in a two-lever, FR10 drug discrimination procedure. The central beta 2/beta 1-adrenergic antagonists (-)-propranolol and tertatolol, and the beta 2-adrenergic antagonist, ICI 118,551, produced high-dose appropriate responding in a dose-related manner when administered (i.p.) in combination with the low training dose of cocaine. In contrast, neither the peripheral beta 2/beta 1-adrenergic antagonist, nadolol, nor the central beta 1-adrenergic antagonist, beta-xolol enhanced the behavioral effects of the low dose of cocaine in a manner comparable with that produced by compounds with central beta 2-adrenergic antagonist properties. Also in contrast to findings obtained using beta-adrenergic antagonists, neither the alpha 1-adrenergic agonist cirazoline, nor the alpha 2-adrenergic ligands (+/-)-efaroxan and UK-14304 enhanced the behavioral effects of the low dose of cocaine. Overall, these results suggest that central beta 2-adrenergic receptors may play a modulatory role in the discriminative stimulus effects of cocaine.

Topics: Adrenergic beta-Antagonists; Animals; Benzofurans; Betaxolol; Brimonidine Tartrate; Cocaine; Discrimination Learning; Discrimination, Psychological; Drug Synergism; Imidazoles; Male; Nadolol; Narcotics; Propanolamines; Propranolol; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Adrenergic, alpha; Receptors, Adrenergic, beta-1; Receptors, Adrenergic, beta-2; Thiophenes

The novel selective imidazoline radioligand [3H]2-(2-benzofuranyl)-2-imidazoline (2-BFI) was used to characterize and assess further the nature of I2-imidazoline receptors in rat brain and liver. In the cerebral cortex, 2-BFI displayed high affinity (Ki = 9.8 nM) for a single class of [3H]2-BFI binding sites. Other imidazoline/guanidine compounds (e.g. aganodine, cirazoline and idazoxan) displayed biphasic competition curves, indicating the existence of high (KiH = 2.9-78 nM; R(H) = 61-83%) and low (KiL = 4.7-158 microM) affinity sites. The pharmacological profile for [3H]2-BFI binding (aganodine > cirazoline > 2-BFI >> clonidine > amiloride >> efaroxan) was typical of that for I2-sites. This profile was almost identical to that obtained against [3H]idazoxan (correlation between pKi values, r = 0.97) which indicated that the sites characterized with [3H]2-BFI in brain corresponded to I2-imidazoline receptors. The low affinity of amiloride against [3H]2-BFI (Ki = 900 nM) further indicated that these brain I2-sites belong to the I2B-subtype. [3H]2-BFI binding sites (Bmax = 72 fmol/mg protein) in brain were differentially modulated by treatment (7 days) with cirazoline (up-regulation: 25%) and the MAO inhibitor phenelzine (down-regulation: 31%), indicating that these I2-sites are regulated in vivo, as is the case for those labelled by [3H]idazoxan. Chronic treatment with 2-phenylethylamine, a phenelzine metabolite and endogenous amine, did not alter the density of brain of I2-imidazoline receptors labelled by [3H]idazoxan. Preincubation of liver membranes with the MAO inhibitor clorgyline (10(-7) M) abolished the binding of [3H]Ro 41-1049 (N-(2-aminoethyl)-5-(m-fluorophenyl)-4-thiazole carboxamide) to MAO-A, but it did not alter the binding of [3H]Ro 19-6327 (N-(2-aminoethyl)-5-chloro-2-pyridine carboxamide) to MAO-B or that of [3H]2-BFI to I2-sites. At 10(-4) M it also abolished MAO-B sites, but a substantial proportion of I2-sites (40%) remained intact. Preincubation of liver membranes at 60 degrees C also abolished MAO-A/B sites, whereas still 22% of I2-sites remained. The results indicate that [3H]2-BFI is a good tool for the identification of I2-imidazoline receptors and suggest further that certain I2-sites and MAO are different proteins.

Topics: Adrenergic beta-Antagonists; Affinity Labels; Animals; Benzofurans; Binding, Competitive; Brain; Cerebral Cortex; Idazoxan; Imidazoles; Imidazoline Receptors; In Vitro Techniques; Isoenzymes; Ligands; Liver; Male; Monoamine Oxidase; Monoamine Oxidase Inhibitors; Phenelzine; Protein Binding; Rats; Rats, Sprague-Dawley; Receptors, Drug

The concentration of the astrocytic marker, glial fibrillary acidic protein (GFAP) was quantitated by immunoblotting (Western blotting) in the rat brain after treatment with the novel ligand for imidazoline I2 receptors LSL 60101 [2-(2-benzofuranyl)imidazole] and its 6-methoxy derivative LSL 60125. Chronic (7-21 days), but not acute (1 day) or short-term (3 days), treatment with LSL 60101 (10 mg/kg i.p.) markedly increased (44-49%) GFAP immunoreactivity in the rat cerebral cortex. In contrast, chronic (7 days) treatment with LSL 60125 (10 mg/kg i.p.) did not significantly modify GFAP concentrations. In vitro, both drugs displayed moderate high affinity and high selectivity for imidazoline I2 receptors versus alpha 2-adrenoceptors; however, only chronic treatment with LSL 60101 (10 mg/kg i.p.) but not with LSL 60125 (10 mg/kg i.p.) was associated with an up-regulation of imidazoline I2 receptors. These data indicate that glial imidazoline I2 receptors may have a direct physiological function related to GFAP expression and that LSL 60101 could be a good tool for the study of the implication of these receptors on astrocyte activation and neuronal regeneration.

Topics: Adrenergic alpha-Agonists; Adrenergic alpha-Antagonists; Animals; Astrocytes; Benzofurans; Brain Chemistry; Cerebral Cortex; Dioxanes; Glial Fibrillary Acidic Protein; Idazoxan; Imidazoles; Imidazoline Receptors; Immunoblotting; Male; Rats; Rats, Sprague-Dawley; Receptors, Drug; Up-Regulation

The effect on insulin release of efaroxan, an alpha 2-adrenoceptor antagonist and a highly potent drug at imidazoline I1 receptors, and the effects of seven other imidazoline compounds selective for the imidazoline I1 or I2 receptors, were studied in the rat insulinoma cell line RIN-5AH. The cells released insulin in response to glucose (0.3-10 mM), and efaroxan (100 microM) potentiated glucose-induced insulin release. (-)-Adrenaline completely displaced the binding of [125I]p-iodoclonidine to membranes of RIN-5AH cells, indicating that these cells do not express imidazoline I1 receptors. Cirazoline and idazoxan (100 microM), both highly potent drugs at imidazoline I2 receptors, and the guanidines guanoxan and amiloride (200 microM), also promoted insulin release from RIN-5AH cells. Irreversible blockade of imidazoline I2 receptors with 10 microM clorgyline did not prevent the stimulatory effects of cirazoline or idazoxan; however, these compounds completely reversed the inhibition by diazoxide (250 microM), an opener of ATP-dependent K+ channels (K+ATP channels), of glucose-induced insulin release. These data indicate that the imidazoline/guanidine compounds promote insulin release from RIN-5AH cells, by interacting with a novel binding site related to K+ATP channels that does not represent any of the known imidazoline I1 or I2 receptors.

Topics: Adrenergic alpha-Agonists; Adrenergic alpha-Antagonists; Adrenergic beta-Agonists; Affinity Labels; Animals; Benzofurans; Binding, Competitive; Clonidine; Clorgyline; Diazoxide; Dioxanes; Guanidines; Idazoxan; Imidazoles; Imidazoline Receptors; Insulin; Insulinoma; Ligands; Pancreatic Neoplasms; Potassium Channels; Rats; Receptors, Drug; Regression Analysis; Software; Tumor Cells, Cultured

In the present investigation, the alpha-adrenoceptor blocking effect of (imidazolinyl-2)-2-dihydro 2,3 benzofurane or S 9871 and its stereoisomers was studied. In the pithed rat (+/-) and (+) S 9871 competitively antagonized the pressor effects of azepexole and clonidine more effectively than those of cirazoline and phenylephrine. (-) S 9871 only blocked the pressor response of the alpha 1-agonists used: phenylephrine and cirazoline. (+/-) and (+) S 9871 antagonized the inhibitory effects of clonidine on the increase in heart rate produced by stimulation of the sympathetic efferent fibres of the thoracic spinal cord. (-) S 9871 was twenty times less potent on the decrease in heart rate induced by clonidine. On the vas deferens of the rat, (+/-) and (+) S 9871 appeared to be more potent than (-) S 9871 in antagonizing the inhibitory effects of clonidine on the twitch response produced by electrical stimulation. Therefore, (+/-) and (+) S 9871 appear to be more preferential for alpha 2-adrenoceptors than for alpha 1-adrenoceptors; in contrast (-) S 9871 appears to be selective for alpha 1-adrenoceptors. (+/-) and (+) S 9871 appears to be one of the most selective agents for blocking alpha 2-adrenoceptors.

Topics: Adrenergic alpha-Antagonists; Animals; Azepines; Benzofurans; Blood Pressure; Clonidine; Drug Interactions; Electric Stimulation; Imidazoles; In Vitro Techniques; Male; Muscle Contraction; Muscle, Smooth; Phenylephrine; Rats; Rats, Inbred Strains; Stereoisomerism; Vas Deferens

Peripheral postsynaptic alpha-adrenoceptor blocking properties of six new dihydrobenzofurane and imidazoline derivatives have been investigated in pithed rat against the pressor effects of phenylephrine and cirazoline (alpha 1-agonists) and clonidine and azepexole (alpha 2-agonists). Except for (N-methylimidazolinyl-2)-2 dihydro-2,3 benzofurane (II) that acted neither on alpha 1- nor alpha 2-adrenoceptors, all the compounds revealed blocking effects - plus or minor - on both alpha 1- and alpha 2-adrenoceptors. (Imidazolinyl-2)-2-chloro-7 dihydro-2,3-benzofurane (IV) is equipotent in blocking both alpha 1- and alpha 2-adrenoceptors. 7-Methoxy-(imidazolinyl-2)-2 dihydro-2,3-benzofurane (III) and (imidazolinyl-2)-2-fluoro-7-dihydro-2,3-benzofurane (V) block more effectively alpha 1- than alpha 2-adrenoceptors whereas (imidazolinyl-2)-2-benzocyclobutane (VI) is more potent in blocking alpha 2- than alpha 1-adrenoceptors. (Imidazolinyl-2)-2-dihydro-2,3-benzofurane (I) is a preferential alpha 2-adrenoceptor blocking agent. The most effective agents on alpha 2-adrenoceptors are under further pharmacological investigations.

Topics: Adrenergic alpha-Agonists; Adrenergic alpha-Antagonists; Animals; Azepines; Benzofurans; Blood Pressure; Clonidine; Drug Interactions; Imidazoles; Male; Phenethylamines; Phenylephrine; Rats; Rats, Inbred Strains; Receptors, Neurotransmitter