bluuebunny/crossref_metadata_2025_split huggingface dataset:
The physiological relevance of low agonist affinity binding at opioid μ‐receptors
Authors: Carroll Jacqueline A. , Shaw John S. , Wickenden Alan D. 
Published: July 2012

Inhibition constants (Ki) were determined for a range of opioid standards using two binding assays; [3H]‐[d‐Ala2, MePhe4, Gly‐ol5]enkephalin ([3H]‐GLYOL) binding to guinea‐pig brain membranes in HEPES buffer and [3H]‐naloxone binding to rat whole brain membranes in Krebs/HEPES buffer.
These values were compared with affinity measurements determined by antagonism of GLYOL on the rat isolated vas deferens preparation and by the receptor occlusion technique of Furchgott on the guinea‐pig ileum longitudinal muscle, myenteric plexus preparation.
Agonists demonstrated markedly reduced binding affinity in the [3H]‐naloxone binding assay where binding was conducted in the presence of sodium.
A strong correlation was obtained between values from the [3H]‐naloxone binding assay and affinity values determined in both isolated tissue preparations. Ki values obtained from [3H]‐GLYOL binding did not correlate well with affinity data determined by isolated tissue techniques.
These findings suggest that functionally relevant receptors exhibit low agonist affinity.
β‐Adrenoceptor stimulation enhances transmitter output from the rat phrenic nerve
Authors: Wessler Ignaz , Anschütz Stephanie 
Published: July 2012

Neurally‐evoked output of newly synthesized [3H]‐acetylcholine from the rat phrenic nerve was measured in the absence of cholinesterase inhibitors.
Noradrenaline and isoprenaline enhanced neurally‐evoked transmitter output markedly. Moreover, immediately after the application of noradrenaline the basal tritium efflux increased significantly.
Pretreatment with propranolol (0.1 μmol l−1) or atenolol (0.3 μmol l−1) completely prevented the stimulatory effect of noradrenaline and isoprenaline on evoked transmitter output.
The facilitatory effect of isoprenaline declined, when the exposure time was increased. This observation supports the assumption that β‐adrenoceptors can be desensitized or inactivated during continued exposure to agonists.
It was shown for the first time that stimulation of β‐adrenoceptors enhances transmitter output from the motor nerve. It is proposed that these β‐adrenoceptors are of the β1‐subtype and are localized on the endings of motor nerves. Circulating catecholamines may facilitate neuromuscular transmission by stimulation of presynaptic β‐adrenoceptors.
Comparison of the effects of epithelium removal and of an enkephalinase inhibitor on the neurokinin‐induced contractions of guinea‐pig isolated trachea
Authors: Devillier Philippe , Advenier Charles , Drapeau Guy , Marsac Jean , Regoli Domenico 
Published: July 2012

The influence of epithelium removal and/or thiorphan on the effects of neurokinins (substance P (SP), neurokinin A (NKA), neurokinin B (NKB)) and related peptides on airway contractility was investigated on the guinea‐pig isolated trachea.
Removing the tracheal epithelium significantly enhanced the sensitivity but not the maximum contractile responses to the peptides.
After removal of the epithelial layer, the shifts to the left of the log concentration response curves were greater for SP and SP‐OMe (1.62 and 1.94 log units, respectively) than for two SP analogues substituted in position 9 namely [Pro9]SP sulfone and [β‐Ala,4 Sar9]SP(4–11)sulfone (0.66 and 0.68 log units, respectively). The leftward shifts for compounds related to NKA or NKB lay between 0.58 and 0.73 log units.
The leftward shifts of the log concentration‐response curves for SP, SP‐OMe, [Pro9]SP sulfone, [β‐Ala4, Sar9]SP(4–11) sulfone and NKA were of similar magnitude after removal of the epithelium or after pretreatment with thiorphan (10−5 m), an enkephalinase inhibitor, in the presence of epithelium. No significant additional shift of the curves to the left was observed with thiorphan plus epithelium removal.
The results obtained with the selective agonists for each of the three classes of neurokinin receptor (i.e NK1, NK2, NK3) suggest that the guinea‐pig trachea contains receptors for SP and NKA but few if any for NKB.
It was concluded that neurokinins and related peptides (especially SP and analogues not substituted in position 9) are degraded by enkephalinase mainly located in the tracheal epithelium and that the addition of thiorphan or epithelium removal results in an inhibition or loss of enkephalinase activity, thereby increasing similarly the potencies of these peptides. It was, therefore, suggested that the supersensitivity to neurokinins produced by epithelium removal was due neither to the elimination of a permeability barrier nor to reduced production of a relaxant factor, but mainly to reduced peptide degradation.
An examination of experimental design in relation to receptor binding assays
Authors: Dunn Graham , Koshikawa Noriaki , Durcan Michael J. , Campbell Iain C. 
Published: July 2012

Real and computer‐simulated data were used to examine the efficiency of designs for receptor binding assays.
Initially, several different concentrations of [3H]‐ketanserin were used in receptor binding studies, using membrane preparations from rat cerebral cortex to establish the form of the binding curves and to investigate the relationship between the variance of the binding measurements and their means.
The data showed that the specific binding could be modelled by a simple rectangular hyperbola, and were consistent with the assumption that the binding measurements have a constant coefficient of variation (0.1).
Computer‐simulated data, with a coefficient of variation of 0.1, were then used to look at the precision of estimates of KD and Bmax obtained through the use of assay designs based on replicate incubations at two radioligand concentrations, or through the use of a geometric sequence of 5–7 radioligand concentrations. In each case, the influence of varying amounts (3.8–50%) of non‐specific binding at KD on the precision of these estimates was monitored.
The results (a) illustrate the problems which arise in the analysis of receptor binding data when there are relatively high amounts of non‐specific binding in combination with a constant coefficient of variation, (b) calculate the errors involved and (c) quantitate the relative merits of 2, 5, 6 and 7 point saturation curves in the estimation of Bmax and KD.
Comparative study of the actions of AP5 A and α,β‐methylene ATP on nonadrenergic, noncholinergic neurogenic excitation in the guinea‐pig vas deferens
Authors: MacKenzie Ian , Kirkpatrick Karen A. , Burnstock Geoffrey 
Published: July 2012

The agonistic and antagonistic effects of two nucleotide analogues, P1,P5‐di‐(adenosine‐5′) pentaphosphate (AP5A) and α,β‐methylene ATP (α,β‐Me ATP), have been compared in the guinea‐pig isolated vas deferens.
In organ bath studies, both AP5A and α,β‐Me ATP were approximately 100 times more potent than ATP in producing phasic contractions of the vas deferens smooth muscle. Repeated additions of either agonist (1–10 μm) produced desensitization to a subsequent addition of the test substance. AP5A and α,β‐Me ATP were approximately equipotent in the production of desensitization.
After desensitization had been produced in the vas deferens by AP5A or α,β‐Me ATP, excitatory responses elicited by ATP (100–150 μm) and nonadrenergic field stimulation (2–20 Hz) were blocked, whereas those elicited by carbachol (1–10μm) were augmented.
Intracellular electrical recordings demonstrated that AP5A and α,β‐Me ATP produced similar effects on membrane activity of the vas deferens. Concentration‐dependent depolarizations alone were produced by both substances until the voltage threshold for action potential discharge was attained; thereafter, action potential discharges were superimposed on the depolarization and an accompanying phasic contraction was recorded. Upon restoration of the membrane potential to its control value (5–10 min after addition of either AP5A or α,β‐Me ATP), excitatory junction potentials (e.j.ps) elicited by field stimulation (up to 3 Hz) and spontaneous e.j.ps were reduced by AP5A (> 0.1 μm) in a concentration‐dependent manner (as previously described for α,β‐Me ATP).
The antagonistic effects of AP5A on mechanical responses elicited by field stimulation were more quickly reversed on washout of AP5A than were the effects of α,β‐Me ATP, suggesting some dissimilarity in their mechanism of action at the receptor level.
The antagonistic effects of AP5A on the nonadrenergic contractile responses of the vas deferens were not produced by the structurally related P1,P4‐di‐(adenosine‐5′) tetraphosphate (AP4A) even with cumulative concentrations up to 200 μm
Desensitization of P2‐purinoceptors can be produced by some nucleotide analogues such as AP5A and α,β‐Me ATP, whose activity may arise partly because of their structural conformation and stability.
Tachykinin involvement in parasympathetic nerve‐evoked salivation of the ferret
Authors: Ekström Jörgen , Håkanson Rolf , Månsson Bengt , Tobin Gunnar 
Published: July 2012

The tachykinin antagonist (D‐Arg1, D‐Cl2Phe5, Asn6, D‐Trp7.9, Nle11)‐substance P, injected intravenously, blocked salivary secretion from the ferret parotid and submandibular glands in response to subsequent i.v. injections of the tachykinins, substance P and neurokinin A.
The tachykinin antagonist reduced the parasympathetic nerve‐evoked secretion of parotid and submandibular saliva by 15–20% and 35–40%, respectively. Atropine abolished the remaining secretory response.
The ‘atropine‐resistant’ parasympathetic nerve‐evoked secretion of saliva from the parotid and submandibular glands (about 5 and 30%, respectively, of that before administration of atropine) was abolished by the tachykinin antagonist.
The tachykinin antagonist was without effect on the protein concentration of parotid and submandibular saliva secreted in response to parasympathetic nerve stimulation. Parotid and submandibular saliva lacked amylase.
Atropine reduced the protein concentration of the submandibular saliva secreted in response to parasympathetic nerve stimulation by 50%; this was the protein concentration of substance P‐evoked saliva.
The secretory response to methacholine and to stimulation of preganglionic sympathetic nerve fibres, tested in rats, was unaffected by the tachykinin antagonist, contra‐indicating an unspecific action of the antagonist.
The results suggest that the neuronal release of tachykinins is probably important in the nerve‐evoked secretory response of the parotid and submandibular glands.
Release of [3H]‐noradrenaline from the sympathetic nerves to bovine mesenteric lymphatic vessels and its modification by α‐agonists and antagonists
Authors: Allen J.M. , McCarron J.G. , McHale N.G. , Thornbury K.D. 
Published: July 2012

Isolated segments of bovine mesenteric lymphatic vessels were loaded with [3H]‐noradrenaline and its efflux in response to field stimulation examined. Vessels were attached to an isometric force transducer for the simultaneous recording of mechanical activity.
Field stimulation at 1, 4 and 8 Hz (0.3 ms pulses, 1 min train) increased spontaneous contraction rate and evoked 3H release up to a maximum of 4.5% of total tissue 3H at 8 Hz. Output per pulse was maximal at 4 Hz.
Tetrodotoxin (3 × 10−6 m) blocked the release of 3H in response to field stimulation although the drug did not attenuate release evoked by high K+ (65 mm) solution. Field‐evoked release of 3H was also absent in Ca2+‐free solution containing EGTA (1 mm).
When vessels were preincubated with labelled transmitter plus cocaine (5 × 10−5 m) evoked release of 3H was absent. After preloading with [3H]‐noradrenaline, cocaine (10−6 m) potentiated both the mechanical response to field stimulation and evoked 3H release.
The relatively non selective α‐adrenoceptor antagonist phentolamine (3 × 10−6 m) and the α2‐antagonists yohimbine (10−8 m) and rauwolscine (10−6 m) significantly increased evoked 3H release at both of the frequencies examined (1 and 4 Hz). In contrast, the selective α1‐antagonist prazosin (10−6 m) failed to alter 3H release to 4 Hz stimulation although release at 1 Hz was potentiated in the presence of the drug.
The postsynaptic excitatory response to field stimulation remained in the presence of prazosin (10−6 m), but was converted to an inhibitory effect in the presence of phentolamine (3 × 10−6 m), yohimbine (10−6 m) or rauwolscine (10−6 m).
Evoked 3H efflux was significantly reduced by clonidine (10−6 m), xylazine (10−6 m) and exogenous noradrenaline (5 × 10−7 m), although phenylephrine (10−6 m) reduced release only at the lower of the two frequencies tested (1 Hz).
These findings suggest that release of 3H by field stimulation reflects endogenous transmitter release and that this is subject to autoinhibition via feedback onto inhibitory prejunctional α2‐adrenoceptors. The postjunctional excitatory response is mediated via postjunctional α2‐adrenoceptors.
Actions of dopamine antagonists on stimulated striatal and limbic dopamine release: an in vivo voltammetric study
Authors: Stamford Jonathan A. , Kruk Zygmunt L. , Millar Julian 
Published: July 2012

Fast cyclic voltammetry at carbon fibre microelectrodes was used to study the effects of several dopamine antagonists upon stimulated dopamine release in the rat striatum and nucleus accumbens.
In both nuclei, stimulated dopamine release was increased by D2‐receptor‐selective and mixed D1/D2‐receptor antagonists. The D1‐selective antagonist SCH 23390 had no effect.
Striatal and limbic dopamine release were elevated by cis‐ but not trans‐flupenthixol.
The ‘atypical’ neuroleptics (clozapine and thioridazine) did not cause a selective elevation of dopamine release in the limbic terminal region, whereas the non‐antipsychotic drug metoclopramide increased dopamine release more in striatum than nucleus accumbens.
We conclude from this study that striatal and limbic dopamine release are under the control of a stereoselective dopamine D2‐autoreceptor on the nerve terminal and that atypical neuroleptics do not show a limbic‐selective effect at this receptor after acute administration.
The affinity of some acetylenic analogues of 4‐DAMP methobromide for muscarinic receptors in guinea‐pig ileum and atria
Authors: Barlow R.B. , Shepherd M.K. , Tydeman Hilary , Veale M.A. 
Published: July 2012

The replacement of 4‐hydroxy‐N‐methyl piperidine (HO‐NMe) in 4‐diphenylacetoxy‐N‐methyl piperidine (4‐DAMP) metho‐bromide by 4‐hydroxy‐but‐2‐ynylamines (HOCH2CĈH2NR2) reduces the affinity for muscarine‐sensitive acetylcholine receptors in guinea‐pig ileum and atria. It does not abolish selectivity. The tertiary amines are more active and more selective than the corresponding quaternary salts.
Analogous derivatives of 4‐hydroxy‐but‐2‐ynylamines which lack the ester group (i.e. substituted 4‐hydroxymethyl‐propynyl amines) are less active and less selective. The quaternary compounds are more active than the tertiary bases.
The diphenylcarbamyl ester of 4‐hydroxy‐N‐methylpiperidine methobromide has less than one‐thousandth of the activity of the diphenylacetyl ester (4‐DAMP methobromide) and is not selective.
Although 4‐diphenylacetoxy‐butynyl dimethylamine is only about one‐hundredth as active as 4‐DAMP methobromide it appears to have comparable selectivity. It is an interesting compound because it is a tertiary amine and should cross membranes.
The mechanism of action of AMP‐induced inhibition of sympathetic neurotransmission in the isolated vas deferens of the rat and guinea‐pig
Authors: Dalziel H.H. , Sneddon P. 
Published: July 2012

The proposal that adenosine 5′‐monophosphate (AMP) can be used as a selective antagonist of ATP at P2‐purinoceptors on smooth muscle was investigated by examining the electrical and mechanical responses of guinea‐pig and rat vasa deferentia to stimulation of sympathetic nerves and to exposure to exogenous agonists.
The magnitude of the contractile response of the rat vas deferens to field stimulation of the sympathetic nerves was reduced by addition of AMP. This effect was rapid in onset and readily reversed by washout.
The action of AMP on these contractile responses was reversed by the subsequent addition of the specific P1‐purinoceptor antagonist 8‐phenyltheophylline (8‐PT). 8‐PT on its own had no significant effect on contractile responses to nerve stimulation.
The magnitude of excitatory junction potentials (e.j.ps) in the guinea‐pig vas deferens evoked by a train of stimuli at 0.5 Hz was reduced in a dose‐dependent manner by introduction of AMP (10−6‐10−3 m). The inhibitory effect of 10−5 m AMP on e.j.p. magnitude was completely and rapidly reversed by introduction of 10−5 m 8‐PT. The effect of 10−4 m AMP was partially reversed by 10−5 8‐PT.
The contractile responses of the guinea‐pig vas deferens to exogenously applied adenosine 5′‐triphosphate (ATP) were not reduced by AMP, even at a concentration of 2.5 × 10−4 m. Similarly in the rat vas deferens, contractile responses to exogenously applied α,β‐methylene ATP (a more potent P2‐purinoceptor agonist) were reduced by only 27.2%. The same concentration of AMP did not affect the contractile responses of the rat vas deferens to noradrenaline.
We conclude that the primary mechanism of action of AMP is to inhibit sympathetic neurotransmission by an agonist action at P1‐purinoceptors on the sympathetic nerve terminal reducing the release of neurotransmitter, and therefore AMP cannot be used as a selective P2‐purinoceptor antagonist.
Effects of naloxone and opioid agonists on gastric excitatory responses to stimulation of the vagus nerve in cats
Authors: Okamoto Toshihiro , Kurahashi Kazuyoshi , Fujiwara Motohatsu 
Published: July 2012

An investigation was made into the contribution of endogenous opioids to the initial and delayed excitatory response of the stomach induced by stimulation of the vagal trunk in cats.
Naloxone (100 to 1000 μg kg−1) had no effect on the initial excitatory response to stimulation of the vagal efferent fibres. However, the same treatment dose‐dependently enhanced the delayed excitatory response to stimulation of the vagal afferent fibres.
In comparison with the μ‐opioid‐receptor agonist, [d‐Ala2, MePhe4, Gly‐ol5]enkephalin and the κ‐opioid‐receptor agonist dynorphin A (1–13), lower doses of methionine enkephalin ([Met]enkephalin) markedly inhibited the excitation caused by stimulation of the vagal efferent and afferent fibres. The inhibitory effect of [Met]enkephalin was antagonized by naloxone.
The δ‐opioid‐receptor selective agonist [d‐Pen2, d‐Pen5]enkephalin mimicked the inhibitory effects of [Met]enkephalin and inhibition by [d‐Pen2, d‐Pen5]enkephalin was antagonized by the δ‐opioid‐receptor antagonist, ICI 174,864.
It is concluded that the inhibitory effects of exogenous opioids on the excitatory response of the stomach to stimulation of the vagal efferent and afferent fibres are mediated, at least in part, by δ‐opioid‐receptors. Naturally occurring opioids may participate in the inhibition of the delayed gastric excitation to stimulation of the vagal afferent fibres.
The negative inotropic effect of nicorandil is independent of cyclic GMP changes: a comparison with pinacidil and cromakalim in canine atrial muscle
Authors: Yanagisawa Teruyuki , Hashimoto Hiroo , Taira Norio 
Published: July 2012

The negative inotropic effects of nicorandil, a nitrate with K‐channel opening properties, have been compared with those of pinacidil, cromakalim and nifedipine, in canine right atrial muscle.
Cromakalim, pinacidil and nicorandil all produced a negative inotropic effect. However, even at their maximally effective concentrations, the force of contraction remained at about 10% of control levels, whereas contraction was abolished by nifedipine.
The pD2 values for the negative inotropic effects of cromakalim, pinacidil and nicorandil were 5.93, 5.37 and 4.35, respectively.
The negative inotropic effects of cromakalim (3 × 10−5 m), pinacidil (3 × 10−5 m and 3 × 10−4 m) and nicorandil (3 × 10−5 m) were not accompanied by changes in cyclic AMP and cyclic GMP levels, whereas that of 3 × 10−4 m nicorandil was accompanied by an increase in cyclic GMP but not cyclic AMP concentrations.
The negative inotropic effect produced by 3 × 10−4 m nicorandil was greatly reduced by 10−2 m tetraethylammonium, whereas the increase in cyclic GMP produced by this concentration of nicorandil was not significantly changed. Sodium nitroprusside (10−3 m) produced a large increase in cyclic GMP concentrations but had no significant negative inotropic effect.
It is concluded that the negative inotropic effects of nicorandil like those of cromakalim and pinacidil do not result from an increase in cyclic GMP concentrations. Instead these effects may be due to their action as K‐channel openers.
Diffusion characteristics dissociate ouabain binding from inotropic effect in guinea‐pig myocardium
Authors: Ebner F. , Siegl H. 
Published: July 2012

[3H]‐ouabain uptake in resting guinea‐pig papillary muscles depended directly on incubation time and inversely with muscle radius. The equivalence of both parameters support the relevance of diffusion. A particular mechanism of receptor‐controlled diffusion was implicated by the saturation of initial rates of uptake with increasing ouabain concentrations. Saturation of initial uptake indicates an inhomogeneity of receptor occupancy with ouabain‐equilibrated receptors in the superficial areas of the preparation and free receptors in the muscle core.
For comparison [3H]‐ouabain diffusion was evaluated in a non‐cellular preparation i.e. glass fibre filters soaked with modified Krebs‐Henseleit solution. Diffusion was approximately 3 orders of magnitude faster when compared with the papillary muscles.
The time course of the inotropic effect of ouabain on rested‐state contractions dissociated from the tissue content of ouabain with an increased steroid concentration. This dissociation appears to be associated with the inhomogeneity of receptor occupancy, since equal amounts of the steroid correspond to different concentration profiles in the tissue when the bath concentration is changed. Functional coupling between different muscle areas may have modulated the influence of inhomogeneous receptor occupancy.
Modulation of the actions of tyrosine by α2‐adrenoceptor blockade
Authors: Al‐Damluji S. , Ross G. , Touzel R. , Perrett D. , White A. , Besser G.M. 
Published: July 2012

Eight normal subjects were given, in double‐blind, random order l‐tyrosine 50, 250 and 500 mg kg−1 and placebo orally. Plasma tyrosine concentrations rose in a dose‐dependent manner, without affecting the concentrations of the other large neutral amino acids. Tyrosine stimulated the secretion of prolactin and thyrotrophin (TSH) but had no effect on the plasma concentrations of adrenocorticotrophic hormone (ACTH), cortisol, growth hormone or the gonadotrophins.
The lack of a stimulant effect of tyrosine on ACTH secretion was presumed to be due to activation of one of the negative feedback mechanisms that control the rate of synthesis and release of the catecholamines, and this hypothesis was tested by examining the effects of the α2‐adrenoceptor antagonist idazoxan on the actions of tyrosine.
Seven normal males were given on 6 separate occasions tyrosine 250 and 500 mg kg−1 and placebo orally following pretreatment with saline and idazoxan (0.1 mg kg−1 i.v.). Following pretreatment with idazoxan, tyrosine stimulated the secretion of ACTH and noradrenaline in a dose‐dependent manner, although neither tyrosine nor idazoxan on their own had any effect on the secretion of either substance.
The lack of effect of tyrosine when given on its own appears to be due, partly, to activation of α2‐adrenoceptors, which inhibit the release of noradrenaline. Idazoxan caused a small increase in systolic blood pressure, both when given on its own and in combination with tyrosine. Neither tyrosine nor idazoxan had any significant effect on the state of behavioural arousal, as measured by visual analogue scales, or on the secretion of growth hormone or the gonadotrophins.