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R J Summers

Publications and source records attributed to R J Summers.

At least 73 records · Page 4Linked to original sources
PubMed1991

Characterization of beta 1- and beta 2-adrenoceptors in rat skeletal muscles.

Binding studies with (-)-[125I]cyanopindolol (ICYP) were conducted to characterize beta-adrenoceptors in plantaris and soleus muscles of rats (male, 250-300 g). The distribution of beta 1- and beta 2-adrenoceptors in different muscle fiber types, identified in serial sections by succinic dehydrogenase (SDH) staining, was studied by autoradiography. The densities of binding sites (Bmax, fmol/mg protein) were 5.4 +/- 0.9 (mean +/- SEM) in plantaris and 11.5 +/- 2.0 in soleus muscle. In plantaris muscle, monophasic competition curves were observed when binding experiments were performed using CGP20712A (50 pM to 0.5 mM), a beta 1-adrenoceptor selective antagonist, or ICI 118,551 (50 pM to 20 microM), a beta 2-adrenoceptor selective antagonist, to compete for ICYP binding. Analysis with LIGAND revealed a single binding site with a KD value of 2.41 +/- 0.56 nM (mean +/- SEM) for ICI 118,551 and 8.93 +/- 3.00 microM for CGP 20712A, indicating the presence of a homogeneous population of beta 2-adrenoceptors. In soleus muscle, competition curves were biphasic with 16-21% beta 1-adrenoceptors. Autoradiographic studies supported the findings from binding studies with membrane homogenates. The ICYP binding pattern was associated closely with the muscle fiber types identified by SDH staining. Propranolol-resistant binding sites were observed, and these sites were associated with muscle fibers positive to SDH staining.

Adrenergic beta-Antagonists↗
PubMed1990

The autoradiographic localization of adenylate cyclase in rat kidney using [3H]forskolin.

The localization of [3H]forskolin binding to microscope slide mounted sections of rat kidney has been examined using autoradiography. Saturation studies showed [3H]forskolin binding to two sites, a high affinity site (KD = 8.7 nM, Bmax = 0.14 pmol/mg protein) and a low affinity site (KD = 6.7 microM, Bmax = 11.0 pmol/mg protein). Autoradiographs showed high affinity binding (thought to identify stimulatory guanine nucleotide binding protein (Gs)-linked adenylate cyclase) to all renal structures known to possess hormone sensitive adenylate cyclase, including all tubular segments, glomeruli and blood vessels. High concentrations of binding were associated with a portion of the proximal tubule and with papillary collecting tubules and ducts.

Adenylyl Cyclases↗
PubMed1990

Densitometric analysis of beta 1- and beta 2-adrenoceptors in guinea-pig atrioventricular conducting system.

Quantitative autoradiography was used to determine the densities of beta 1- and beta 2-adrenoceptors in the atrioventricular conducting system in guinea-pig. (-)[125I]Cyanopindolol (CYP) was used to label beta 1- and beta 2-adrenoceptors in the absence or presence of the beta 1-adrenoceptor selective antagonist CGP 20712A (100 nM) or the beta 2-adrenoceptor selective antagonist ICI 118,551 (70 nM) or the non-selective beta-adrenoceptor antagonist (-)-propranolol (1 microM). Protein in discrete anatomical regions was determined using a densitometric method based on the dye Coomassie brilliant blue G. In the atrioventricular conducting system the proportion of beta 2-adrenoceptors determined by inhibition of total (-)[125I]-CYP binding by CGP 20712A (100 nM) ranged from 32.5% (atrioventricular node) to 48.7% (left bundle branch). In the atrioventricular node (16.8 fmol/mg protein), bundle of His (12.1 fmol/mg protein), right (17.4 fmol/mg protein) and left (21.1 fmol/mg protein) bundle branches and Purkinje cells there was a higher density of beta 2-adrenoceptors than in the interventricular septum (8.4 fmol/mg protein) and right atria (8.3 fmol/mg protein). The medial smooth muscle of the aorta, aortic valve, adventitia of the aorta, nerve tissue, tricuspid and mitral valves contained only beta 2-adrenoceptors. It is speculated that the use of beta-adrenoceptor antagonists to control cardiac arrhythmias involving a defect in conduction in the atrioventricular node should take into consideration both beta 1- and beta 2-adrenoceptors.

Adrenergic beta-Antagonists↗
PubMed1990

SIMUL: an accurate method for the determination of receptor subtype proportions using a personal computer.

Many tissues possess two classes of binding sites for a drug. To estimate the proportions of each it is necessary either to use selective ligands or to perform competition experiments in which the binding of a radioligand is inhibited by a selective unlabeled ligand. However, this method will only be accurate provided the radioligand is non-selective. A selectivity of 2- to 3-fold for one receptor may produce errors of 50% or more in the estimates, depending on the concentration of radioligand chosen. Since most ligands are selective to some extent simple estimates will often provide inaccurate information. The computer program described here (SIMUL) determines the proportions of receptor subtypes by considering the relative affinities of the competing agent for the receptor subtypes, the selectivity of the radioligand and their associated concentrations.

Animals↗
PubMed1990

Excitatory amino acid projections to the periaqueductal gray in the rat: a retrograde transport study utilizing D[3H]aspartate and [3H]GABA.

The afferents to the periaqueductal gray utilizing excitatory amino acid transmitters have been described in rat brain by autoradiography following microinfusion and retrograde transport of D[3H]aspartate. Parallel experiments employing injections of [3H]GABA established that the retrograde labelling found with D[3H]aspartate was transmitter-selective. Following infusion of D[3H]aspartate, perikaryal labelling was found in nine subcortical areas, particularly infralimbic and cingulate cortices, with a predominance of ipsilateral labelled perikarya. Heaviest cortical labelling was localized in perirhinal cortex, in an extensive band of cells adjoining the rhinal sulcus. The hypothalamus contained the heaviest perikaryal labelling within brain: D[3H]aspartate labelled cells in 11 hypothalamic and mammillary nuclei. Intense bilateral labelling was obtained in ventromedial hypothalamus, although the number of perikarya was lower contralaterally. D[3H]Aspartate also produced heavy ipsilateral labelling of perikarya in posterior hypothalamus. Labelling patterns in cortex and hypothalamus were precise and topographic, and [3H]GABA never labelled cells in these regions. Other telencephalic and diencephalic areas containing prominent, retrogradely labelled cells were the lateral septum, amygdala, zona incerta and lateral habenula. The relative density of labelled cells in mesencephalic areas was much lower than that found in cortex and hypothalamus, although D[3H]aspartate labelled a moderate number of perikarya in the inferior colliculus and cuneiform nucleus. A smaller number of heavily labelled cells was found in the parabrachial nuclei, Kolliker-Fuse nucleus and laterodorsal tegmental nucleus. Only occasional labelled perikarya were observed in the myencephalon. Low densities of labelled cells were found after the injection of [3H]GABA into the periaqueductal gray, and the only regions in which a small number of perikarya were labelled by both [3H]GABA and D[3H]aspartate were the dorsal raphe and parabrachial nuclei. Overall, the retrograde transport of D[3H]aspartate revealed a complex topographic and convergent network of afferent pathways to the periaqueductal gray likely to utilize an excitatory amino acid transmitter. Our findings confirm the selectivity of this neurochemical mapping technique and provide evidence that hypothalamic, habenular, subthalamic and cuneiform afferents to the periaqueductal gray utilize an acidic amino acid as their transmitter. They also confirm that corticofugal afferents to periaqueductal gray utilize an excitatory amino acid.

Afferent Pathways↗
PubMed1990

Effects of prolonged infusion of dopexamine on beta 1- and beta 2-adrenoceptors in guinea-pig myocardium.

1. The effects of 7-day infusion of dopexamine (50 and 200 micrograms kg-1h-1) were examined on beta 1- and beta 2-adrenoceptors in guinea-pig left ventricular membranes. 2. Receptor binding performed using the high affinity radioligand (-)-[125I]-cyanopindolol (CYP) and the beta 1-adrenoceptor antagonist CGP 20712A showed that treatment with dopexamine 200 micrograms kg-1h-1 caused a 45% reduction in beta 2-adrenoceptors and a small but not significant increase in beta 1-adrenoceptors. 3. Functional effects of dopexamine were examined in the guinea-pig isolated electrically driven left atria and K(+)-depolarized uterus. Dopexamine was an antagonist at beta 1-adrenoceptors in left atria (pKB = 4.49), and a partial agonist at beta 2-adrenoceptors in the uterus (alpha = 0.78, pD2 = 6.59). 4. The effects of dopexamine on beta 1- and beta 2-adrenoceptor density in guinea-pig ventricular myocardial membranes may be related to agonist activity at beta 2-adrenoceptors and antagonist activity at beta 1-adrenoceptors.

Adrenergic beta-Agonists↗
PubMed1990

Antidepressant binding sites in brain: autoradiographic comparison of [3H]paroxetine and [3H]imipramine localization and relationship to serotonin transporter.

Binding of two different antidepressant drugs, [3H]paroxetine and [3H]imipramine in 30 rat brain regions was visualized, compared and quantified by means of autoradiography and densitometry. Specific binding of [3H]paroxetine to coronal sections of diencephalon represented 85% of total binding and was saturable and of high affinity (KD, 0.36 +/- 0.07 nM) with a maximum number of binding sites of 276 +/- 41 fmol/mg protein. The autoradiograms showed a heterogenous distribution of [3H]paroxetine in brain with selective accumulation of label in brain regions known to contain serotonergic terminals, axons and cell bodies (amygdaloid and raphe nuclei, superior colliculus, substantia nigra and medial forebrain bundle). Binding was displaced selectively with other serotonin uptake inhibitors (clomipramine and fluoxetine) and almost abolished by lesioning the serotonergic neurons with p-chloroamphetamine. The desipramine-sensitive [3H]imipramine binding was more diffuse with relatively high density in cerebral cortex and hippocampus and was only decreased partially in animals treated with p-chloroamphetamine. The results indicate that [3H]paroxetine, but not [3H]imipramine, is a ligand of choice to selectively label serotonergic structures in brain.

Animals↗
PubMed1990

Differential regulation of beta-1 and beta-2 adrenoceptors in guinea pig atrioventricular conducting system after chronic (-)-isoproterenol infusion.

Quantitative autoradiography was used to determine the effects of chronic administration of (-)-isoproterenol (400 micrograms/kg/hr, 7 days) on the distribution and density of beta-1 and beta-2 adrenoceptors in guinea pig atrioventricular conducting system and surrounding regions. X-ray film was exposed to sections of heart labeled with (-)-[125I]-cyanopindolol in the absence or presence of ICI 118,551 (70 nM) to block beta-2 adrenoceptors, CGP 20712A (100 nM) to block beta-1 adrenoceptors or (-)-propranolol (1 microM) to define nonspecific binding. Quantitative autoradiography was performed using computer-assisted image processing and the AVID system. The proportions of beta-1 and beta-2 adrenoceptors were determined by the extent of inhibition of (-)-[125I]cyanopindolol binding by CGP 20712A (100 nM) together with equations which take into account the differing affinities of ligands for beta-1 and beta-2 adrenoceptors. In vehicle (1 mM HCl)-treated animals there was a higher density and proportion of beta-2 adrenoceptors in the atrioventricular node, bundle of His and right and left bundle branches than in myocardium. Chronic administration of (-)-isoproterenol produced marked loss of beta-2 adrenoceptor binding in all regions of the atrioventricular conducting system, surrounding myocardium, cardiac valves and the smooth muscle of the aorta accompanied by less pronounced effects on beta-1 adrenoceptors. Beta-1 adrenoceptors were significantly reduced only in the left bundle branch whereas there were trends toward a reduction in the right bundle branch, bundle of His and an increase in the atrioventricular node. There was no alteration in beta-1 adrenoceptor density in myocardium. Loss of beta adrenoceptor binding produced by (-)-isoproterenol was mainly confined to beta-2 adrenoceptors.

Animals↗
PubMed1989

Biochemical characterization of an autoradiographic method for studying excitatory amino acid receptors using L-[3H]glutamate.

A method was developed for radiolabeling excitatory amino acid receptors of rat brain with L-[3H]glutamate. Effective labeling of glutamate receptors in slide-mounted 10-microns sections was obtained using a low incubation volume (0.15 ml) and rapid washing: a procedure where high ligand concentrations were achieved with minimal waste. Saturation experiments using [3H]glutamate revealed a single binding site of micromolar affinity. The Bmax was trebled in the presence of Ca2+ (2.5 mM) and Cl- (20 mM) with no change in the Kd. Binding was rapid, saturable, stereospecific, and sensitive to glutamate receptor agonists. The proportions of [3H]glutamate binding sensitive to N-methyl-D-aspartate (NMDA), kainate, and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were 34, 54, and 51%, respectively. NMDA inhibited binding at a distinct subset of L-[3H]glutamate sites, whereas AMPA and kainate competed for some common sites. Labeling of sections with L-[3H]glutamate in the presence of the selective agonists allowed autoradiographic visualization of glutamate receptor subtypes in brain tissue.

Animals↗
PubMed1989

Bidirectional transport of NMDA receptor and ionophore in the vagus nerve.

Accumulations of binding sites for [3H]3-[+-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic ([3H]CPP) and [3H]-N-(1-[2-thienyl]cyclohexyl)-3,4-piperidine ([3H]TCP) were demonstrated both proximal and distal to 24-h ligatures of the central and peripheral vagus nerve in the rat using radioligand binding and autoradiography. Peaks of label occurred at the proximal and distal extremities of double ligations but not between the ligatures, or in sham-operated or colchicine-treated nerves. Together these results suggest that both the primary acceptor site and the ionophore of the N-methyl-D-aspartate receptor undergo bidirectional axonal transport in central and peripheral branches of the vagus nerve.

Animals↗
PubMed1989

Coexistence and localization of beta 1- and beta 2-adrenoceptors in the human heart.

Quantitative autoradiography was used to determine the location and density of beta 1- and beta 2-adrenoceptors in the right atrium (RA), left ventricular free wall (LVFW), right ventricular free wall (RVFW), interventricular septum (IVS), right atrium from an area near the atrioventricular node (RAAV) and cardiac nerves (N) taken from a patient with end-stage cardiac failure. The densities of beta-adrenoceptors detected by the non-selective beta-adrenoceptor antagonist radioligand (-)-[125I] cyanopindolol (50pM) were 4.93 (N), 10.6 (RVFW), 12.2 (RA), 12.4 (IVS), 15.8 (LVFW) and 18.7 fmol (mg protein)-1 (RAAV). The proportion of beta 2-adrenoceptors ranged from 19.5% (RAAV) to 95% (N). RA taken from patients with ischaemic heart disease had a higher density of beta-adrenoceptors (29.3 fmol (mg protein)-1). The results suggest that both beta 1- and beta 2-adrenoceptors are down-regulated in patients with end-stage cardiac failure. Positive inotropic responses were established to (-)-isoprenaline, RO363 (beta 1-selective), procaterol (beta 2-selective) and dopexamine in the absence or presence of the antagonist CGP 20712A (beta 1-selective) or ICI 118,551 (beta 2-selective) in electrically driven human right atrial appendage strips. RO363 and procaterol were nearly full agonists in this preparation and produced their responses through activation of beta 1- or beta 2-adrenoceptors, while dopexamine was a partial agonist which produced its inotropic responses through activation of both receptor subtypes. These studies demonstrate the presence and location of beta 1- and beta 2-adrenoceptors in the human heart.

Animals↗
PubMed1989

Function, characterization and autoradiographic localization and quantitation of beta-adrenoceptors in cardiac tissues.

1. This paper demonstrates the use of organ bath, radioligand binding and autoradiography to detect beta 1- and beta 2-adrenoceptors in human and guinea-pig cardiac tissues. 2. In organ bath experiments, non-selective and beta 1- and beta 2-adrenoceptor selective agonists produced concentration-dependent inotropic responses in human right atrial appendage. Both subtypes mediate inotropic responses. In guinea-pig right atria chronotropic responses were mediated predominantly through beta 1-adrenoceptors. 3. Receptor binding studies using (-)[125I]-cyanopindolol (CYP) and beta 1- and beta 2-adrenoceptor selective antagonists showed that beta 2-adrenoceptors comprised 25% of the total population of beta-adrenoceptors in guinea-pig right atria. In human right atria the proportion is higher (40%). 4. Quantitative autoradiography was used to determine the location and densities of beta 1- and beta 2-adrenoceptors in guinea-pig heart. Both beta 1- and beta 2-adrenoceptors were distributed on myocardium. The atrioventricular conducting system had a higher density of beta 2-adrenoceptors compared with myocardium.

Adrenergic beta-Agonists↗
PubMed1989

New tools for the localization of second messenger systems.

1. Probes available for the localization of components of second messenger systems include G-protein oligonucleotides which have been used to produce cDNA probes to label G-protein mRNA by in situ hybridization histochemistry. 2. Enzymes involved in second messenger responses have been labelled with [3H]-forskolin (Gs-linked adenylate cyclase), [3H]-cAMP (cAMP-dependent protein kinase) and [3H]-PDBu2 (protein kinase C). 3. [3H]-Inositol 1,4,5 trisphosphate labels a site on sarcoplasmic reticulum believed to trigger Ca2+ release. 4. These probes allow the comparison of location of receptors and second messengers and the examination of changes in second messenger systems with drug treatment and disease.

Animals↗
PubMed1988

An autoradiographic study of muscarinic cholinoceptors in blood vessels: no localization on vascular endothelium.

In vitro labelling and autoradiographic techniques were used to examine the localization of [3H]quinuclidinyl benzilate ([3H]QNB) and [125I]4-iodo-QNB ([125I]4IQNB) to slide-mounted sections of rabbit aorta and pulmonary artery, cat aorta, pulmonary and superior mesenteric arteries. These vessels all respond to acetylcholine (ACh) with endothelium-dependent relaxation, yet there was no evidence for endothelium-related binding of either [3H]QNB or [125I]4IQNB. Muscarinic receptors were localized over the medial smooth muscle and, in the rabbit pulmonary artery, the density of binding increased towards the adventitia. Binding of either radioligand to sections of rabbit pulmonary artery was not affected by the muscarinic M1 receptor antagonist pirenzepine (20 nM) but was markedly reduced by the muscarinic M2 antagonist 4DAMP (4-diphenylacetoxy-N-methyl-piperidine methobromide) (1 nM). This study provides evidence for muscarinic receptors located directly on smooth muscle cells, indicating that endothelium-dependent relaxation to ACh results from an indirect mechanism involving smooth muscle muscarinic receptors.

Acetylcholine↗
PubMed1988

Inhibition by cAMP of the phosphoinositide response to alpha 1-adrenoceptor stimulation in rat kidney.

The effect of increasing intracellular levels of cAMP has been investigated on the PI response to stimulation of alpha 1-adrenoceptors in rat kidney. Stimulation of adenylate cyclase with forskolin or incubation with dibutyryl cAMP (dcAMP) inhibited noradrenaline (NA)-stimulated [3H]inositol phosphate (IP) accumulation. Forskolin did not alter the EC50 to NA. No effect on NA-stimulated [3H]IP accumulation was seen with dibutyryl cGMP (dcGMP). The results suggest that hormones which produce alterations in cAMP levels influence alpha 1-adrenoceptor-mediated responses.

Animals↗
PubMed1988

Late systemic-allergic reactions to inhalant allergen immunotherapy.

Late systemic-allergic reactions (defined as occurring between 30 minutes and 6 hours after injection) to inhalant allergen immunotherapy were prospectively studied in four allergy treatment centers; 35,674 injections were administered to 712 patients. Twenty-nine patients (4% of all patients) experienced 33 late reactions. Fifty-six injections (0.16% of all injections) were associated with the 33 late reactions. The most common clinical manifestation of a late reaction was urticaria. However, objective respiratory airway involvement, as manifested by wheezing and/or stridor, occurred in 10 (27%) of the late reactions. Delayed reactions involving wheezing and/or stridor were only related to injections from maintenance vials, and all these more severe reactions occurred no later than 60 minutes after injection. We conclude that late systemic-allergic reactions account for a significant percent of the total number of systemic-allergic reactions to inhalant allergen immunotherapy. It is our belief that a 60-minute postinjection waiting period for injections administered from maintenance vials of extract would enhance the safety of inhalant allergen immunotherapy.

Female↗