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K Beaumont

Publications and source records attributed to K Beaumont.

54 records · Page 3Linked to original sources
PubMed1987

Adrenocorticoid receptors in C6 glioma cells: effects on cell growth.

Rat C6 glioma cells contain two receptors for adrenocorticoids--the predominant glucocorticoid receptor and low densities of the Type I corticosteroid (mineralocorticoid) receptor. Nanomolar concentrations of deoxycorticosterone, corticosterone and aldosterone, which fully occupy Type I receptors, produced a slight stimulatory effect on C6 cell growth in serum-free media. However, spironolactone, a Type I receptor antagonist, and pregnenolone, which does not bind to Type I receptors, had similar effects. Therefore, the slight growth stimulation produced by low steroid concentrations is not mediated by Type I or glucocorticoid receptors, but may be due to an effect on cell membrane properties or other receptor-independent action. Occupation of glucocorticoid receptors by higher concentrations of corticosteroids inhibited C6 cell growth.

Aldosterone↗
PubMed1987

Effect of adrenocorticoid receptors on potassium and sodium flux in rat C6 glioma cells.

C6 glioma cells contain two types of receptors for adrenocorticoids. Glucocorticoid (Type II) receptors are present at higher density and mediate increases in glycerol phosphate dehydrogenase and glutamine synthetase activity. The function of mineralocorticoid (Type I) receptors present at low density in C6 cells is unknown. Since mineralocorticoid (Type I) receptors in renal epithelial cells regulate cation transport, we sought to determine whether adrenocorticoid receptors located in glioma cells are similarly linked to electrolyte transporting activity. Occupation of mineralocorticoid receptors in C6 glioma by adrenocorticoids did not alter Na+ or K+ transport, in contrast to their effects on renal epithelial and vascular smooth muscle cells. Occupation of glucocorticoid receptors produced a 20-25% decrease in K+ uptake into C6 cells, but did not alter Na+ influx. Stimulation of Na+ influx with the ionophore monensin produced a large ouabain-sensitive increase in glucose utilization, as measured by 2-deoxyglucose uptake. However, mineralocorticoid receptor occupation did not alter glucose utilization, providing further evidence that these receptors do not influence Na+ transport in C6 cells. These studies provide evidence that mineralocorticoid receptors in glioma cells do not regulate Na+ or K+ transport. Glial glucocorticoid receptors have an inhibitory effect on glial K+ influx, which may contribute to glucocorticoid hormone effects on brain excitability.

Animals↗
PubMed1986

Physicochemical properties of type I corticosteroid receptors from rat brain.

[3H]Aldosterone binds with high affinity to Type I corticosteroid receptors in cytosols from adrenalectomized rat forebrains. Physicochemical parameters of these receptors were determined in the presence of molybdate, which stabilized receptors and maintained them in a presumably untransformed state. The Stokes' radius of the molybdate-stabilized receptor was 8.1 nm, as determined by gel filtration on Sephacryl S-300. Its sedimentation coefficient was 9.1S in linear sucrose density gradients. The receptor is asymmetric, with an axial ratio of 8-10 and an apparent mol. wt of 303,000 dalton. The [3H]aldosterone-receptor complex is anionic and elutes from DEAE-Trisacryl in a single peak with a maximum at 160 mM KCl. Exposure to heat or salt in the absence of molybdate, conditions which transform other steroid receptors to smaller DNA-binding forms, causes marked instability of the [3H]aldosterone-receptor complex. The [3H]aldosterone-binding protein of rat forebrain, which displays the binding characteristics of a renal Type I (mineralocorticoid) receptor, is similar in size, shape and charge to the molybdate-stabilized oligomeric forms of other steroid hormone receptors.

Aldosterone↗
PubMed1985

Rat C6 glioma cells contain type I as well as type II corticosteroid receptors.

Rat brain cytosol contains Type I corticosteroid receptors. Unlike Type II (glucocorticoid) receptors, Type I receptors have high affinity for the endogenous corticosteroids - aldosterone, deoxycorticosterone, and corticosterone - and much lower affinities for synthetic glucocorticoids. In the present study, we report that Type I corticosteroid receptors are present in C6 glioma cells. Type I receptors were identified in C6 cell cytosol and whole cells by the binding of [3H]aldosterone. The specific glucocorticoid RU 26988 was used to block Type II receptors. Measured in whole C6 cells, Type I receptors had a density of 2.1 +/- 1.1 fmol/10(6) cells and a dissociation constant (Kd) for [3H]aldosterone of 0.41 +/- 0.06 nM. The density of Type I receptors was only 2% of the density of Type II corticosteroid receptors (96 +/- 7 fmol/10(6) cells), measured in whole C6 cells by [3H]triamcinolone binding. The steroid specificity of glial cytosolic Type I receptors (deoxycorticosterone greater than corticosterone greater than aldosterone greater than dexamethasone greater than triamcinolone much greater than RU 26988) was identical to the steroid specificity of Type I receptors in rat brain cytosol. The potency of deoxycorticosterone was somewhat reduced when measured in whole cells. The steroid specificity of the Type I receptor differed markedly from that of the Type II (glucocorticoid) receptor (triamcinolone greater than dexamethasone greater than RU 26988 corticosterone greater than deoxycorticosterone greater than aldosterone). Since Type I receptors in the kidney mediate effects of aldosterone upon renal transport of sodium and potassium, it is proposed that glial Type I corticosteroid receptors may be involved in the regulation of glial ion transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex Hormones↗
PubMed1984

Peripheral-type benzodiazepine binding sites in a renal epithelial cell line (MDCK).

Madin-Darby canine kidney (MDCK) cells express a high density of binding sites (Bmax = 0.67 pmol/10(6) cells) for [3H]RO 5-4864, a peripheral-type benzodiazepine (BZD) receptor ligand. Receptor affinity (Kd = 45 nM) in MDCK cells is 30-50 fold lower than in rat kidney, but its pharmacological specificity is identical to that of peripheral-type BZD receptors in the rat kidney (PK 11195 greater than RO 5-4864 greater than diazepam = flunitrazepam greater than clonazepam). The MDCK cell line should provide a useful model system for studying the role of peripheral type BZD receptors in renal function.

Animals↗
PubMed1984

Autoradiographic localization of benzodiazepine receptors in the rat kidney.

The localization of benzodiazepine (BZD) receptors in the rat kidney was studied by autoradiography after in vitro labeling of kidney slices with flunitrazepam. The affinity, density, and rank order of displacement of [3H]-flunitrazepam by several BZDs (RO 5-4864 greater than diazepam greater than clonazepam) demonstrated that binding was to BZD receptors of the peripheral type. In autoradiograms obtained with tritium-sensitive film, a high density of silver grains was obtained in the outer medulla, with lower densities in the cortex. Binding was absent from the inner medulla (papilla). In higher resolution autoradiograms obtained with an emulsion-coated cover slip procedure, silver grains were seen to be concentrated over a tubular element in both outer medulla and cortex, identifiable by morphology and distribution as the thick ascending limb of the loop of Henle and the distal convoluted tubule. The identity of the labeled tubules was confirmed by immunofluorescent localization in adjacent slices of Tamm-Horsfall protein, a specific marker for these segments of tubules. Investigation of the effects of peripherally specific BZDs such as RO 5-4864 on distal tubule function is indicated.

Animals↗
PubMed1983

Inhibitors of peripheral-type benzodiazepine receptors present in human urine and plasma ultrafiltrates.

Several endogenous substances that inhibit central-type benzodiazepine (BZD) receptor binding have recently been identified. We have found that ultrafiltrates of human uremic plasma, normal plasma, and urine contain competitive inhibitors of peripheral-type benzodiazepine receptors. Using urine as source, we have partially purified a peripheral-type BZD receptor inhibitor(s) by adsorption to and selective elution from small octadecyl-silane (Sep-pak) columns and thin layer chromatography. The inhibitor has a 125-fold greater affinity for peripheral-type than central-type BZD receptors and has been purified 8000-fold from urine.

Adsorption↗
PubMed1983

Characterization of rat brain aldosterone receptors reveals high affinity for corticosterone.

The two [3H]aldosterone-binding proteins of rat brain cytosol were characterized by a dextran-coated charcoal method. With molybdate present to stabilize receptors, the affinities of the two sites for [3H]aldosterone in adrenalectomized perfused rat brain cytosols were 0.28 and 18.0 nM at 4 C. High affinity sites comprised 15% of the total receptor number. A small contamination of perfused brain cytosol preparations with corticosteroid-binding globulin (CBG) was found. However, due to the very high affinity of CBG for corticosterone at 4 C, this slight contamination resulted in significant alterations in the apparent affinity of steroids competing for aldosterone-binding sites. Selective precipitation of cytosol receptors with 36% (NH4)2SO4 reduced CBG concentrations to negligible levels. After blockade of low affinity sites with a highly selective glucocorticoid (RU 26988), the order of steroids in competing for the high affinity receptor was desoxycorticosterone greater than fludrocortisone greater than corticosterone greater than aldosterone greater than progesterone greater than dexamethasone. Readdition of a small quantity of dialyzed serum to cytosol preparations yielded a profile of steroid binding similar to that of the kidney mineralocorticoid receptor (aldosterone greater than desoxycorticosterone greater than corticosterone). The distribution of both receptors in brain regions of adrenalectomized rats was determined. Both receptors were at greatest density in the hippocampus and lowest density in the hypothalamus. The high affinity site was at greatest density in limbic regions, whereas the low affinity receptor, apparently identical to the glucocorticoid type II receptor, was at greatest density in cortex and cerebellum. It is concluded that the high affinity aldosterone receptor of rat brain, which had been identified in preliminary studies as a mineralocorticoid receptor, may bind either corticosterone or aldosterone in vivo.

Adrenalectomy↗
PubMed1983

Interactions of neurotensin with brain dopamine systems: biochemical and behavioral studies.

Intracisternal (i.c.) injection of neurotensin (NT) to rats or mice attenuated the locomotor hyperactivity induced by d-amphetamine, methylphenidate or cocaine, but not the increased activity induced by apomorphine or lergotrile. The reduction of methylphenidate-induced locomotor activity by i.c. NT was not due to an increased drug metabolism because i.c. NT did not change plasma methylphenidate concentrations. These actions of NT are distinct from those of the dopamine receptor antagonist haloperidol, which blocked the locomotor hyperactivity induced by all five stimulant drugs in rats. A further difference between NT and neuroleptics was demonstrated by the observation that i.c. NT did not block apomorphine-induced stereotypic behavior. In vitro, NT did not displace [3H]spiperone from its binding sites in homogenates of either the striatum or nucleus accumbens from rat brain. Moreover, i.c. injection of NT did not alter the subsequent in vitro binding of [3H]spiperone to membranes of the nucleus accumbens or striatum. In addition, NT did not alter basal or dopamine-stimulated adenylate cyclase activity in homogenates of the nucleus accumbens or striatum. However, i.c. injection of NT produced a significant increase in the concentrations of homovanillic acid, a major dopamine metabolite, in the nucleus accumbens, olfactory tubercles and striatum. In addition, the concentration of dihydroxyphenylacetic acid was increased in the nucleus accumbens and olfactory tubercles after i.c. NT. Peripheral injection of haloperidol produced qualitatively similar effects on dopamine metabolism, but the effects of haloperidol, unlike those of i.c. NT, were attenuated by apomorphine injection. Taken together, these data indicate that centrally administered NT affects certain brain dopamine systems without interacting directly with those dopamine receptors labeled by [3H]spiperone, coupled to adenylate cyclase or mediating the pharmacological effects of apomorphine.

Adenylyl Cyclases↗
PubMed1982

Glycine receptors in the human substantia nigra as defined by [3H]strychnine binding.

Specific [3H]strychnine binding was used to identify the glycine receptor macromolecular complex in human spinal cord, substantia nigra, inferior olivary nucleus, and cerebral cortex. In material from control patients a high-affinity KD (3--8 nM) was observed in the spinal cord and the substantia nigra, both the pars compacta and the pars reticulata. This is very similar to the values observed in the rat and bovine spinal cord (8 and 3 nM, respectively) and rat substantia nigra (12 nM). In the human brain the distribution of [3H]strychnine binding (at 10 nM) was: spinal cord = substantia nigra, pars compacta greater than substantia nigra, pars reticulata = inferior olivary nucleus greater than cerebral cortex. The binding capacity (Bmax) of the rat brain (substantia nigra or spinal cord) was approximately 10-fold that of the human brain. [3H]Strychnine binding was significantly decreased in the substantia nigra from Parkinson's disease patients, both in the pars compacta (67% of control) and the pars reticulata (50% of control), but not in the inferior olivary nucleus. The results were reproduced in preliminary experiment in rats with unilateral 6-hydroxydopamine lesions of the medial forebrain bundle. In the substantia nigra from patients who died with Huntington's disease, [3H]strychnine binding tended to be high (150% of control, NS) in both the pars compacta and the reticulata. [3H]Strychnine binding was unaltered in the substantia nigra of patients with senile dementia. Together with previous neurophysiological and neuropharmacological findings, those results support the hypothesis of glycine receptors occurring on dopamine cell bodies and/or dendrites in the substantia nigra.

Adult↗
PubMed1982

gamma-Aminobutyric acid (GABA) receptor stimulation. II. Specificity of progabide (SL 76002) and SL 75102 for the GABA receptor.

Progabide and its immediate metabolite SL 75102 displace [3H]gamma-aminobutyric acid (GABA), [3H]muscimol and [3H]isoguvacine from their binding sites to membranes prepared from rat brain or human cerebellum and increase (SL 75102) [3H]flunitrazepam binding to rat cerebral cortex membranes. In contrast, these compounds have very weak or no effects on alpha or beta noradrenergic, histamine, muscarinic cholinergic or glycine receptors or on the [3H]imipramine or [3H]kainate binding sites. Neither progabide nor SL 75102 inhibit GABA synthesis, metabolism or uptake. Also, the uptake of norepinephrine, serotonin and dopamine into synaptosomes of cerebral regions is not affected by progabide. [3H]GABA release from substantia nigra slices is decreased by SL 75102 and progabide, in agreement with the hypothesis of a GABAergic autoreceptor controlling GABA release from its nerve terminals. These data suggest a specific agonist action of progabide and SL 75102 on GABA receptors.

Animals↗
PubMed1979

The localization of receptor binding sites in the substantia nigra and striatum of the rat.

Neurotransmitter receptor binding of 5 ligands was examined in the striatum, substantia nigra (SN) and frontal cortex of rats which had received either unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal pathway (NSP) or unilateral kainic acid lesions of the striatum. 6-OHDA lesions of the NSP significantly reduced [3H]dihydroalprenolol ([3H]DHA) and [3H]naloxone ([3H]Nal) binding by 31% and 28% respectively, in the denervated striatum compared to the contralateral side. Scatchard analysis revealed that the alteration in [3H]DHA binding was not due to a change in the affinity of the beta-adrenergic receptor for [3H]DHA. In marked contrast to these changes in the striatum, destruction of the NSP resulted in a significant increase in [3H]DHA and [3H]Nal binding by 44% and 26%, respectively, in the frontal cortex of the lesioned compared to the control side. 6-OHDA lesions in the NSP did not alter striatal receptor binding for [3H]quinuclidinyl benzilate ([3H]QNB), [3H]muscimol ([3H]Mus) or [3H]flunitrazepam ([3H]Flu). Similarily, intrastriatal kainic acid injections did not alter striatal receptor binding for [3H]Nal, [3H]Flu or [3H]Mus. Of the various receptor densities measured in the SN after the above lesions the only alteration observed was a 43% increase in [3H]Flu binding following 6-OHDA lesions of the NSP. Scatchard analysis indicated no change in the affinity of the benzodiazepine receptor for [3H]Flu. 6-OHDA lesions of the NSP did not alter [13H]QNB or [3H]Nal binding in the SN. Striatal kainic acid lesions did not alter nigral [3H]QNB or [3H]Flu binding. The results are discussed in terms of neurotransmitter localization and plasticity within the striatum, SN and frontal cortex.

Animals↗
PubMed1978

Muscimol binding in rat brain: association with synaptic GABA receptors.

[3H]Muscimol binding to crude synaptic membrane fractions of the rat central nervous is saturable with a high affinity dissociation constant of 2.2 nM. The regional distribution of this binding in rat brain and the effects of freezing, sodium and Triton X-100 are similar to those previously reported for [3H]GABA binding to the the synaptic GABA receptor site. Also, the substrate specificity of [3H]muscimol binding is identifical to that observed for the GABA receptor. Thus, [3H]muscimol is displaced, stereospecifically, only by those drugs and amino acids which are known to neurophysiologically interact with the synaptic GABA receptor but is unaffected by agents which activate or inhibit other neurotransmitter receptors. This suggests that the behavioral effects observed after the systemic administration of muscimol are probably the result of GABA receptor activation.

Aminobutyrates↗
PubMed1978

Videoendoscopic feedback in training velopharyngeal closure.

Each of two adolescents with velopharyngeal closure deficits was taught to position him or herself on an endoscope attached to a television camera and to observe the velopharyngeal port during the production of syllables and other units. The videoendoscope was then used as a training apparatus, and each subject was given practice attempting to increase velopharyngeal closure while producing vowels and syllables. Videorecordings of each subject made without feedback before, during, and after the training period were played to panels of observers who were to rate closure during each utterance, and the data obtained indicated that the subjects more frequently approximated complete closure as the study progressed but improved performance was not established on an automatic level. Suggestions are made for the refinement and further investigation of videoendoscopic closure training.

Adolescent↗
PubMedDate not supplied

Bioanalytical data in decision making: discovery and development.

1. Bioanalysis is traditionally associated with the development phase of drugs; its use in discovery programmes is often ignored but can have a major impact. 2. Pharmacokinetic studies conducted in conjunction with pharmacology screening can provide additional information to that considered in conventional structure activity relationships. Such factors as half-life and bioavailability can be critical in designing improved drugs. 3. Analytical methods in discovery programmes may differ from those used in later development work: for instance bioassay allows a common assay system for a large number of project compounds. Moreover its use, when combined with conventional methods, such as h.p.l.c., allows active metabolites to be readily detected. 4. Bioanalytical data generated in discovery and pre-clinical programmes are a valuable guide to early clinical programmes. Plasma concentration-response data from these programmes can be compared with those obtained in man. Such comparisons are particularly valuable during the phase one-initial dose escalation study. To maximize this it is our practice to generate pharmacokinetic data between each dose increase.

Animals↗