Report of a unique meeting between the alpha-blocker subcommittee and the pharmaceutical industry.
Explore the source record for details and available documents.
Adrenergic alpha-1 Receptor Antagonists↗
Biomedical subjects
M G Wyllie
Publications and source records attributed to M G Wyllie.
A comparison of the effects of doxazosin and terazosin on the spontaneous sympathetic drive to the bladder and related organs in anaesthetized cats.
The effects of i.v. infusion of the alpha1-adrenoceptor antagonists doxazosin and terazosin (2 mg kg-1 h-1) on spontaneous hypogastric, renal and inferior cardiac nerve activity, spontaneous bladder contractions, blood pressure, heart rate and femoral arterial flow were investigated separately in alpha-chloralose-anaesthetized cats. Both drugs caused a reduction in hypogastric nerve activity associated with no overt changes in spontaneous bladder contractions. Doxazosin was more potent than terazosin, in that there was a significant reduction in hypogastric nerve activity after 20 min (0.67 mg kg-1) of infusion, while for terazosin this occurred after 40 min (1.33 mg kg-1). Both drugs also caused significant falls in blood pressure of 34 +/- 3 mm Hg and 33 +/- 4 mm Hg after 60 min. This was associated with no change in heart rate for doxazosin while terazosin caused an initial and significant increase in heart rate of 20 +/- 3 beats min-1 by 5 min, declining by 30 min to 1 +/- 5 beats min-1. This terazosin-induced tachycardia was associated with a significant increase in cardiac nerve activity of 128 +/- 22%. Both drugs caused increases in renal nerve activity however only for doxazosin was this increase significant. Femoral arterial conductance was also increased by both drugs, however, for doxazosin this increase was immediate and larger over the infusion period. These results demonstrate that alpha1-adrenoceptor antagonists can reduce sympathetic drive to the bladder and related organs.
Adrenergic alpha-1 Receptor Antagonists↗
Comparison of testosterone metabolism in benign prostatic hyperplasia and human prostate cancer cell lines in vitro.
Pathways of testosterone metabolism in tissue slices and cell suspensions of human benign hyperplastic prostate (BPH) tissue and human prostate cancer cell lines (DU145, HPC-36M, PC-3/MA2 and LNCaP) were investigated. Thin layer chromatography analysis was used to identify the following tritiated metabolites: testosterone, 5 alpha-dihydrostestosterone (DHT), 5 alpha-androstane-3 alpha/3 beta-17 beta-diol (androstanediols), 4-androstene-3,17-dione (androstenedione) and 5 alpha-androstanedione. The predominant pathway for testosterone metabolism in BPH was via 5 alpha-reductase producing 5 alpha-dihydrotestosterone (71% and 75% total metabolites in slices and suspensions incubated for 24 h, respectively). The cancer cell lines DU145 and HPC-36M resembled BPH by metabolizing testosterone predominantly to DHT (68% and 82% total metabolites, respectively), although the rate of metabolism was much lower in the cell lines (0.099 and 0.05 pmol testosterone/mg protein/h in DU145 and HPC-36M) compared to the BPH cell suspensions (6.4 pmol testosterone/mg protein/h). In contrast, PC-3/MA2 contained high 17 beta-HSD activity forming large amounts of 4-androstene-3,17-dione (84% total metabolites), converting testosterone at a rate faster (12.8 pmol testosterone/mg protein/h) than the BPH cell suspensions. LNCaP rapidly converted testosterone exclusively to a glucuronide conjugate (7.4 pmol testosterone/mg protein/h), although after incubation with [3H]-4-androstene-3,17-dione, 5 alpha-reductase activity was demonstrated. LNCaP was the only cell line whose growth and colony-forming ability was stimulated by testosterone and DHT. BPH and all the cell lines tested had 5 alpha-reductase activity, but only the prostate tissue and the cell lines DU145 and HPC-36M converted testosterone predominantly to DHT.
3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
Effect of alpha 1 adrenoceptor antagonists on prostatic pressure and blood pressure in the anesthetized dog.
OBJECTIVES: In the current study we have profiled a range of compounds at alpha 1 adrenoceptor subtypes in vitro and have assessed their effects in vivo using the anesthetized dog in an attempt to elucidate the predominant alpha 1 adrenoceptor subtype mediating contractile responses of the canine prostate. METHODS: The affinity of compounds for alpha 1 adrenoceptor subtypes was determined by displacement of [3H] prazosin binding from stably transfected rat 1 fibroblasts expressing alpha 1A, alpha 1B, and alpha 1C, adrenoceptor subtypes. The potency of these agents was then assessed in vivo using an anesthetized dog model allowing simultaneous measurement of prostatic pressure and blood pressure following intravenous (i.v.) administration of phenylephrine (1 to 128 micrograms/kg). RESULTS: All compounds examined in this study showed high and similar affinity for alpha 1 adrenoceptor subtypes, with the exception of 5-Methyl-urapidil, which was selective for alpha 1C (pKi = 9.3) over alpha 1B (pKi = 7.2) and alpha 1A (pKi = 8.1). Doxazosin, terazosin, alfuzosin, and tamsulosin were potent antagonists of phenylephrine responses and in vivo derived "pseudo pA2" determinations showed that the drugs did not discriminate between prostatic and vascular receptors. 5-Methyl-urapidil was also a potent antagonist of phenylephrine-induced responses but was selective for prostatic pressure ("pseudo pA2" = 8.7) over blood pressure ("pseudo pA2" = 7.2). CONCLUSIONS: Data in the present study suggest a predominant role of the alpha 1C adrenoceptor subtype in the contractile response of the canine prostate to phenylephrine in vivo. This model therefore provides a suitable means of assessing putative prostate-selective antagonists for the treatment of benign prostatic hyperplasia.
Adrenergic alpha-Antagonists↗
Pharmacological properties of the cloned alpha 1A/D-adrenoceptor subtype are consistent with the alpha 1A-adrenoceptor characterized in rat cerebral cortex and vas deferens.
1. The pharmacological characteristics of cloned mammalian alpha 1A/D-, alpha 1B- and alpha 1C-adrenoceptor subtypes expressed in rat 1 fibroblasts were determined in comparison to the binding and functional properties of these subtypes in rat tissues. 2. Analysis of [3H]-prazosin binding to membrane homogenates from rat 1 fibroblast cells expressing each of the alpha 1-subtypes indicated high affinity binding to a single population of binding sites. Binding affinities were similar for alpha 1A/D-, alpha 1B- and alpha 1C-subtypes (Kds: 0.13, 0.10 and 0.15 nM respectively) although a higher density of alpha 1B- and alpha 1C-receptors (Bmax: 4068 and 10,323 fmol mg-1 protein respectively) were expressed in comparison to alpha 1A/D (838 fmol mg-1). 3. Displacement of [3H]-prazosin from membranes expressing cloned alpha 1-adrenoceptor subtypes revealed that 5-methyl-urapidil, WB 4101, benoxathian and phentolamine displayed high affinity and selectivity for alpha 1A/D- over alpha 1B-subtypes. These compounds also had high affinity and selectivity for alpha 1C- over alpha 1B-subtypes. 5-Methyl-urapidil showed selectivity for alpha 1C (Ki 0.60 +/- 0.16 nM) over both alpha 1A/D (Ki, 9.8 +/- 2.8 nM) and alpha 1B (Ki 57.2 +/- 12 nM) subtypes. Prazosin and doxazosin were not subtype selective. 4. In comparison to [3H]-prazosin a similar pharmacological profile was obtained with [125I]-HEAT using cloned alpha 1A/D-, alpha 1B- and alpha 1C-adrenoceptors expressed in rat 1 fibroblasts. 5. The affinities of prazosin, WB 4101, 5-methyl-urapidil, phentolamine and benoxathian at cloned alpha 1A/D-receptors were consistent with alpha 1A affinities determined with chlorethylclonidine-treated rat cortical membranes. Affinities at cloned XIB-receptors were consistent with alpha 1B affinities determined with rat liver membranes.6. Using the epididymal rat vas deferens as a functional measure of alpha 1A affinity, prazosin (pA29.23 +/- 0.28), WB 4101 (pA2 9.58 +/- 0.12), phentolamine (pKB 7.90 +/- 0.16), benoxathian (pKB 9.21 +/- 0.21)and 5-methyl-urapadil (pKB 8.51 +/-0.16) were potent antagonists of noradrenaline-induced contractions.7. At present, evidence from cloning studies suggests the existence of at least three alpha 1-adrenoceptor subtypes. In contrast to the recent proposal for alpha l-adrenoceptor classification, the pharmacology of the cloned alpha 1A/D (or alpha lD)-adrenoceptor is more consistent with that of an alpha 1A-adrenoceptor characterized in rat cerebral cortex and vas deferens.
Adrenergic alpha-Antagonists↗
The involvement of potassium channels in the action of ciclazindol in rat portal vein.
1. In whole portal veins, ciclazindol (0.3-10 microM) increased the amplitude and duration, but decreased the frequency of spontaneous contractions. Glibenclamide (0.3-10 microM) produced a small increase in contraction amplitude and duration with a small reduction in contraction frequency. 2. In whole portal veins, ciclazindol (1-10 microM) antagonized the relaxant effects of BRL 38227 in a non-competitive manner. Under identical conditions, the effects of glibenclamide (0.3-10 microM) appeared to be competitive. 3. In whole portal veins loaded with 42K, ciclazindol itself (up to 3 microM) had no detectable effect on basal 42K exchange. However, the increase in 42K efflux produced by BRL 38227 (5 microM) was antagonized by ciclazindol (3 microM). Similar effects were produced by glibenclamide (up to 3 microM). 4. In freshly-isolated portal vein cells examined by the whole-cell voltage-clamp technique, ciclazindol (1-100 microM) inhibited the slowly-activating and inactivating transient outward current (ITO) which could be generated at potentials more positive than -30 mV. In addition ciclazindol (1-10 microM) inhibited the non-inactivating K-current (IKCO) induced by BRL 38227 (10 microM). 5. In freshly-isolated portal vein cells under current-clamp conditions, the hyperpolarization produced by BRL 38227 (10 microM) was reversed by ciclazindol (1-10 microM). 6. In porcine brain membrane fragments, glibenclamide (0.65 nM) displaced 50% of the binding of [3H]-glibenclamide whereas ciclazindol (up to 10 microM) had no effect. 7. It is concluded that ciclazindol is a K-channel blocker. Its action is not selective for the channel(s) which carry IKCO but also extends to those which carry ITO.Its inability to displace [3H]-glibenclamide from porcine brain fragments may indicate that antagonism of BRL 38227 by ciclazindol in smooth muscle is exerted at a site different from that of glibenclamide.
Animals↗
Disposition and pharmacokinetics of meptazinol in the CSF. Studies after intrathecal administration in the non-human primate Erythrocebus patas.
A preliminary study is reported on the kinetics of meptazinol following intrathecal and i.m. administration in the Patas monkey. Following intrathecal administration (single dose of 0.5 mg) at T12/L1, meptazinol rapidly disappeared from the CSF with a T1/2 of 35 min. At 240 min after intrathecal injection, most of the meptazinol had been distributed within the spinal tissue near the region of the injection, with minimal amounts reaching the brain (less than 5% of the concentrations present in the lumbar and thoracic tissue). Following i.m. administration (16 mg kg-1) peak concentrations were present in the CSF and plasma within 60 min. Appreciable concentrations persisted in the CSF up to 180 min after i.m. administration. The results would suggest that meptazinol should give rapid but short acting pain relief following intrathecal injection with minimal CNS-related side effects.
Animals↗
Examination of the relationship between the uptake system for 5-hydroxytryptamine and the high-affinity [3H]imipramine binding site--I. Inhibition by drugs.
The relationship between the binding site for imipramine and the uptake system for 5-hydroxytryptamine was examined. This was determined from the interaction between various drugs (including tricyclic antidepressants) and the high affinity accumulation of [3H]5-hydroxytryptamine in cortical synaptosomes from the rat, and with the high affinity binding of [3H]imipramine to cortical membranes of the rat. Imipramine and clomipramine, but not desipramine, were potent inhibitors of both binding of [3H]imipramine and the uptake of [3H]5-hydroxytryptamine. However, ouabain, panuramine and 5-hydroxytryptamine itself, all inhibited the binding of [3H]imipramine only at concentrations greater than those required to inhibit the uptake of [3H]5-hydroxytryptamine. Kinetic analysis revealed that inhibitors of the uptake system for 5-hydroxytryptamine produced inhibition by different mechanisms, but this did not account for their differential potency against uptake and binding. It is concluded that the binding site for [3H]imipramine and the uptake site for 5-HT are not directly linked and that drugs may inhibit the uptake of 5-HT at sites other than the binding site for [3H]imipramine.
Animals↗
A reassessment of the binding of [3H]rauwolscine to membranes from the rat cortex.
In order to fully resolve the binding profile of [3H]rauwolscine to membranes from the cortex of the rat, saturation, competition and association-dissociation data were analysed by means of computerised curve-fitting techniques. The binding isotherm for [3H]rauwolscine was best fitted to a two-component model consisting of a high-affinity, saturable site (approx. Kd 1.8 nM) and a low-affinity, apparently non-saturable, component. Displacement experiments revealed shallow inhibition curves for both antagonist and agonist ligands with a rank order of potency indicative of an interaction at the alpha 2-adrenoceptor. Inclusion of spiroperidol, but not prazosin, markedly steepened the antagonist, but not the agonist inhibition curves. In addition, spiroperidol attenuated, but did not eliminate, the low-affinity component in saturation experiments. Dissociation and association data revealed a biphasic paradigm, the more slowly-associating/dissociating component of which was sensitive to spiroperidol. It was concluded that [3H]rauwolscine binds to two sites on membranes of the rat cortex; a high-affinity site corresponding to alpha 2-adrenoceptors and a low-affinity, spiroperidol-sensitive component. The possible identity of the low-affinity site is discussed with particular emphasis on displacement data for [3H]rauwolscine and the interaction with rauwolscine in isolated organs.
Animals↗
Subcellular site of action of imipramine in rodent brain.
To determine the site of action of imipramine, the subcellular distribution of [3H]imipramine in rodents was followed after both in vivo administration and in vitro incubation with tissue slices under "physiological" conditions. Total [3H]imipramine (10-1,000 nM) binding was associated with all primary fractions, but in particular with the nuclear (P1) and mitochondrial (P2) pellets and the synaptosomal (P2B) and myelin (P2A) fractions. Using an excess of imipramine to define any nonspecific interactions, a specific association was observed mainly in those fractions containing isolated nerve terminals and to a lesser extent with the purified myelin fraction. Preparation of subsynaptosomal fractions by osmotic lysis indicated that [3H]imipramine was associated with the synaptic vesicle and microsomal fractions and also with synaptosomal membranes. The degree of binding to the vesicular and microsomal fractions was increased with the length of preparation time, whereas there was an inverse relationship between the length of preparation and the amount bound to the synaptosomal membrane fraction. There was no evidence of an intrasynaptosomal accumulation of [3H]imipramine at concentrations up to 1,000 nM. [3H]2-Nitroimipramine, a slowly dissociating imipramine derivative, was exclusively located in synaptic membrane fractions. Prior treatment of rats with a combination of 5,7-dihydroxytryptamine and desipramine reduced 5-hydroxytryptamine levels and the levels of [3H]imipramine associated with the synaptosomal fractions to the same extent. It is concluded that imipramine is associated with a binding site localised on 5-hydroxytryptaminergic nerve terminals and that there is a redistribution to other sites (vesicular and microsomal) during the isolation procedure.
Animals↗
Is there a common, high-affinity opioid binding site in rat brain?
At low concentrations, 3H-naloxone apparently bound to two sites, of high (KD 0.50 nM) and low (KD 2.0 nM) affinity. Binding to the high affinity site was preferentially blocked by naloxonazine. This is consistent with the high and low affinity sites representing the mu 1 and mu 2 sites respectively. Binding of 3H-naloxone to the mu 1 and mu 2 sites was differentially inhibited by opioids. Compared to mu 2 binding, DADLE and DAGO preferentially inhibited mu 1 binding. DADLE inhibited the binding of 3H-DAGO potently and in a competitive manner. DAGO inhibited the binding of 3H-DADLE from two sites for which DAGO had high and low affinities. Scatchard analysis indicated that both 3H-DAGO and 3H-DADLE bound to one class of sites, with 3H-DADLE having a 2-3 fold greater Bmax. It is concluded that 3H-opioids bind to at least three sites--mu 1, mu 2 and delta. The mu 1 site represents a high affinity binding site for both opioid peptides and opioid alkaloids. DAGO is a selective ligand for the mu 1 site, whilst DADLE interacts with mu 1 and delta sites with similar affinities.
Animals↗
Assessment of noradrenaline and 5-hydroxytryptamine uptake in intact rat brain.
A method for the measurement of 3H-monoamine [noradrenaline (NA) and 5-hydroxytryptamine (5-HT)] uptake into intact brain following intracerebroventricular injection is described. Most of the accumulated monoamine was associated with nerve terminals (synaptosomes). Radioactivity in the synaptosomal fraction was retained by 0.45-micron filters and was osmotically sensitive, features indicative of accumulation within particles rather than binding to membranes. [3H]5-HT associated with synaptosomes was reduced in animals pretreated with the neurotoxin 5,7-dihydroxytryptamine, in parallel with a reduction in endogenous 5-HT levels. Oral administration of tricyclic antidepressants including clomipramine, desipramine, and imipramine inhibited the synaptosomal accumulation of 3H-monoamines. Overall, the features of the accumulation of 3H-monoamines, after intracerebroventricular administration, displayed many of the characteristics expected of a physiological monoamine reuptake system.
5,7-Dihydroxytryptamine↗
Effects of histamine antagonists on noradrenaline-stimulated blood flow and oxygen consumption of brown adipose tissue in the rat.
The effects of histamine antagonists on noradrenaline-stimulated metabolic rate, tissue blood flow (estimated from the distribution of radiolabelled microspheres) and brown adipose tissue (BAT) oxygen extraction were studied in male anaesthetised rats. Injection of cimetidine (H2-receptor antagonist), reduced the noradrenaline-stimulation of metabolic rate and the increase in blood flow to BAT, but did not affect blood flow to white adipose tissue, skin, leg muscle, kidney, brain, or testes. Following noradrenaline, in vivo oxygen consumption of BAT, estimated from blood flow and oxygen extraction was depressed to 31% of control values by treatment with cimetidine, blood pressure was unaffected. Injection of the histamine (H1-receptor) antagonist, mepyramine, did not affect tissue blood flow or metabolic rate. In conscious animals, cimetidine did not affect resting oxygen consumption, but depressed the thermogenic responses to noradrenaline. These data suggest that the stimulation of BAT blood flow and thermogenesis by noradrenaline may be mediated in part by histamine acting on an H2-type receptor.
Adipose Tissue, Brown↗
Panuramine, a selective inhibitor of uptake of 5-hydroxytryptamine in the brain of the rat.
The neurochemical profile of the novel inhibitor of uptake of 5-hydroxytryptamine (5-HT) panuramine (Wy 26002) has been investigated in the rat. In vitro, panuramine was found to be a potent and selective inhibitor of uptake of 5-HT with an IC50 of 22 +/- 4 nM. The IC50 for inhibition of uptake of noradrenaline was 848 nM and that for uptake of dopamine greater than 10 micron. Panuramine, in concentrations up to 10 micron did not displace the specific binding of either [3H]spiroperidol or [3H]5-HT and had no effect on the spontaneous or potassium-evoked release of 5-HT, suggesting that the compound had little effect on serotonergic transmission other than the inhibition of uptake of 5-HT. Panuramine also produced a dose-related antagonism of the depletion of 5-HT in brain induced by p-chloroamphetamine, confirming the ability of the drug to inhibit uptake of 5-HT in vivo.
Animals↗
Evidence for functionally distinct mu receptors modulating acetylcholine release.
Explore the source record for details and available documents.
Acetylcholine↗
Thermogenic properties of ciclazindol and mazindol in rodents.
Ciclazindol, a noradrenaline (NA) uptake inhibitor originally introduced as an antidepressant, has recently been shown to produce weight loss in experimental animals and patients. Unlike CNS-stimulant anti-obesity drugs, such as amphetamine, ciclazindol may induce weight loss in animals by stimulating thermogenesis in brown adipose tissue (BAT), and it is known to stimulate resting metabolic rate (RMR) of rats and depress energetic efficiency. These effects can be achieved in the absence of overt CNS stimulation and with certain analogues of ciclazindol may be due to an exclusive peripheral action. Mazindol, a structural analogue of ciclazindol also produces an increase in RMR. However the increment is qualitatively and quantitatively different from that observed with ciclazindol and cannot be dissociated from central stimulant actions. In this report we examine some of the physiological and behavioural effects of ciclazindol and mazindol analogues in rats.
Amphetamine↗
Parasympathethic effects on diet-induced thermogenesis.
Injection of atropine methyl nitrate or atropine sulphate enhanced the acute thermogenic response to food in rats. The main effector of diet-induced thermogenesis is brown adipose tissue (BAT), but acetylcholine (determined by bioassay) and acetylcholinesterase activity (determined histochemically) were not detected in BAT. This suggests that BAT has no parasympathetic innervation, and atropine must therefore act elsewhere to affect thermogenesis.
Acetylcholinesterase↗
Restoration of mean arterial pressure in endotoxic shock by meptazinol. Contributions from lysosomal membrane stabilisation, opiate antagonism and noradrenaline release.
Meptazinol elevated mean arterial pressure in rats which had been treated with endotoxin. The drug also reduced the titer of circulating lysosomal enzymes. This effect was secondary to the restoration of mean arterial pressure (MAP). In vitro, meptazinol stabilised lysosomal membranes, increased noradrenaline release and interacted with the opiate receptor (naloxone-binding site) as an antagonist. The relevant contributions of these phenomena to the restoration of MAP are discussed.
Animals↗