bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibitory effect of sodium cromoglycate on pulmonary responses to histamine administered after indomethacin in anaesthetized guinea‐pigs
Authors: Mitchell H.W.
Published: July 2012

Histamine (2–4 μg kg−1 i.v.) increased airways resistance (Raw) and decreased dynamic lung compliance (Cdyn) in urethane‐anaesthetized guinea‐pigs. The effects on Raw were almost abolished by atropine (0.1 mg kg−1 i.v.) and reduced by vagal cooling (11–16°C).

Histamine‐induced changes in Raw and Cdyn were significantly (P < 0.05) enhanced by indomethacin (1 mg kg−1 i.v.).

In animals not treated with indomethacin, exposure to an aerosol containing sodium cromoglycate (0.01–2% for 30 s) failed to affect subsequent (3 min) histamine‐induced bronchoconstriction.

Administration of an aerosol containing low (0.01–0.2%) concentrations of sodium cromoglycate had no effect on the enhanced responses (i.e. hyperreactivity) seen after indomethacin. However, more concentrated sodium cromoglycate aerosols (>0.2%) reduced or abolished the hyperreactivity to histamine seen after indomethacin.

It was concluded that sodium cromoglycate can prevent the development of hyperreactivity to histamine, possibly by interacting with some mechanism utilized by both histamine and indomethacin in this model.
Blockade of the inotropic effect of Bay K 8644 by cytochalasin‐B and phloretin
Authors: Dresel Peter E. , Ogbaghebriel Azieb
Published: July 2012

The positive inotropic effect in rabbit atria and papillary muscles of Bay K 8644 is blocked by cytochalasin‐B (Cyto‐B) and phloretin, two compounds known to block the facilitated diffusion of glucose. These compounds do not change the concentration‐response curve of calcium.

Cyto‐B is more potent in atria than in papillary muscles, 10−7 m having a maximal effect in atria whereas 2 × 10−5m was required for a maximal effect in papillary muscles. Phloretin was fully effective at 10−4m, the only concentration tested.

The inotropic effect of Bay K 8644 was virtually abolished in atria bathed in a glucose‐free medium or one containing 5 mM pyruvate. The contractile response to Bay K 8644 of papillary muscles was not changed significantly in glucose‐free or in pyruvate‐containing medium.

Cyto‐B (2 × 10−5 m) caused a slight but significant increase in the KD for the binding of nitrendipine to a crude sarcolemnal preparation from rabbit ventricles. The Bmax was unchanged.

These results may best be explained by the hypothesis that there is a metabolic requirement for the inotropic effect of Bay K 8644.
Involvement of central α‐ and β‐adrenoceptors in the pressor response to electrical stimulation of the rostral ventrolateral medulla in rats
Authors: Ward‐Routledge C. , Marshall P. , Marsden C.A.
Published: July 2012

Electrical stimulation of the C1 area of the rostral ventrolateral medulla in rats elicits an increase in mean arterial pressure (MAP).

This increase in MAP is attenuated by intra‐hypothalamic and intradsternal administration of the non‐selective β‐adrenoceptor antagonist (±)‐propranolol and the β2‐selective antagonist ICI 118551.

The selective β1‐antagonist atenolol and (+)‐propranolol, which is inactive on β‐adrenoceptors, did not alter the increase in MAP produced by stimulation of the C1 area.

The α2‐adrenoceptor antagonist idazoxan enhanced the effects of C1 stimulation on MAP when administered either into the posterior hypothalamus or intradsternally.

The results indicate that β2‐ and α2‐receptors both have a role in the mediation of the rise in MAP during stimulation of the C1 area and that the receptors involved are located both within the hypothalamus and the spinal cord.
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.
An in vitro model of 1‐methyl‐4‐phenyl‐pyridinium (MPP+) toxicity: incubation of rabbit caudate nucleus slices with MPP+ followed by biochemical and functional analysis
Authors: Feuerstein T.J. , Hedler L. , Jackisch R. , Hertting G.
Published: July 2012

Slices of rabbit caudate nucleus were preincubated for up to 24 h in vitro in the presence of the neurotoxic compound 1‐methyl‐4‐phenyl‐pyridinium (MPP+). Subsequently the levels of endogenous monoamines in the slices were determined by h.p.l.c. with electrochemical detection. MPP+, in concentrations higher than 32 nm significantly diminished the dopamine levels within the slices in a concentration‐ and time‐dependent manner; at 32 μm the depletion was more than 95%. The concentration of the major metabolite of dopamine, dihydroxyphenyl acetic acid (DOPAC) was decreased at concentrations of MPP+ that did not alter dopamine levels. Thus, MPP+ increased the dopamine/DOPAC ratio.

In contrast, both 5‐hydroxytryptamine (5‐HT) levels and 5‐HT/5‐hydroxyindolacetic acid (5‐HIAA) ratios were increased at nanomolar concentrations of MPP +. 5‐HT was significantly reduced only at 32 μm.

The dopamine uptake inhibitor nomifensine reduced the depletory effect of MPP + on dopamine and DOPAC content.

Following 24 h pretreatment with MPP+, the uptake of [3H]‐dopamine into rabbit caudate nucleus slices was either enhanced (at 0.32 μm, 1 μm and 3.2 μm MPP+) or reduced (at 32 μm MPP+).

Preincubation of slices with 10 μm MPP + for only 1 h increased their 3H‐labelling (in contrast to 24 h pretreatment) whereas after 9 h no net increase was detectable. After 1 and 9 h MPP + pretreatment, much less deaminated metabolites of [3H]‐dopamine were found in the incubation medium of MPP + treated slices than in the medium of control slices. These findings suggest that MPP + strongly inhibits the enzyme monoamine oxidase (MAO) within dopaminergic (and 5‐hydroxytryptaminergic) terminals before destroying them.

To validate the proposed in vitro model functionally, the electrically evoked release of [3H]‐acetylcholine ([3H]‐ACh) was investigated in MPP+ treated slices and controls. MPP+ reduced both the facilitatory effect of the D2‐receptor antagonist domperidone and the inhibitory effect of the catecholamine uptake inhibitor nomifensine on [3H]‐ACh release; effects compatible with a diminished inhibitory dopaminergic input on cholinergic neurones.

These findings also show that the terminal region of dopaminergic neurones, the caudate nucleus, is a site for MPP + toxicity. The present in vitro model may be useful for investigating the effects of MPP + and its interaction with other drugs under defined conditions.
Mechanism of action of nicotine in isolated iris sphincter preparations of rabbit
Authors: Hisayama Tetsuhiro , Shinkai Michiko , Takayanagi Issei , Morimoto Shin‐Ichi , Ishida Katsuko
Published: July 2012

Nicotine produced a transient contraction of rabbit isolated iris sphincter muscle, a parasympathetic ganglion‐free tissue. The response to nicotine was antagonized by hexamethonium, but was insensitive to tetrodotoxin (TTX). While single treatments with atropine, capsaicin or [d‐Arg1, d‐Pro2, d‐Trp7,9, Leu11]‐substance P (rpwwL‐SP) partially blocked the response, combined treatment abolished it.

Chronic treatment of animals with nicotine added to the drinking water (about 12 mg kg−1 per day) had no effect on the responsiveness to nicotine or the pharmacological properties of nicotine‐induced contraction.

These results suggest that acetylcholine and tachykinin(s) released via sodium channel‐independent mechanisms from nerve terminals of parasympathetic and primary sensory nerves, respectively, are involved in the nicotine‐induced contractile response.
Differences in agonist dissociation constant estimates for 5‐HT at 5‐HT2‐receptors: a problem of acute desensitization?
Authors: Leff P. , Martin G.R.
Published: July 2012

The agonist dissociation constant for 5‐hydroxytryptamine (5‐HT) was estimated in the guinea‐pig isolated trachea by the method of receptor inactivation. The value obtained (pKA = 6.45) was significantly lower than estimates previously obtained in the rabbit aorta and rat jugular vein, although all three tissues are supposed to contain the same 5‐HT2 class of receptor.

The antagonist dissociation constant for α,α‐dimethyltryptamine was also estimated in the guinea‐pig trachea. The pKB value (5.43) was not significantly different from previous estimates in the rabbit aorta and rat jugular vein, consistent with receptor homogeneity between the three tissues.

The effect‐time profiles corresponding to individual 5‐HT applications were more transient in the guinea‐pig trachea than in the rabbit aorta. This difference could be accounted for using a simple model of acute receptor desensitization (Leff, 1986), assuming that the conversion of active agonist‐receptor complexes into inactive ones was faster in the guinea‐pig trachea than in the rabbit aorta.

Computer simulation of the desensitization model showed that the discrepancy of pKA estimates for 5‐HT between the rabbit aorta and guinea‐pig trachea could also be explained using the same rate constant difference that accounted for the difference in effect‐time profiles. This analysis indicated that the estimate made in the trachea was erroneously low, whereas that made in the aorta was concluded to be correct.

The apparent association between transience of response and pKA estimates is discussed with particular attention to the reliability of agonist affinity estimates in receptor classification.
Differential sensitivity of antinociceptive tests to opioid agonists and partial agonists
Authors: Shaw John S. , Rourke Janet D. , Burns Karen M.
Published: July 2012

The antinociceptive activity of a range of opioid agonists and agonist‐antagonist analgesics was determined in mice by use of the 55°C hot plate and abdominal constriction assays.

Opioid agonists were approximately 10 times more effective in the abdominal constriction assay.

The agonist‐antagonists produced analgesia only in the abdominal constriction assay, and antagonized the antinociceptive action of opioid agonists in the 55°C hot plate test.

These differences were shown to be attributable to the different levels of stimulus employed in the two tests.

By comparing the antagonist potencies of the agonist‐antagonists in the 55°C hot plate test with their antinociceptive ED50 values in the abdominal constriction assay, an index of intrinsic activity was calculated.
Vitamin K 2,3‐epoxide reductase: the basis for stereoselectivity of 4‐hydroxycoumarin anticoagulant activity
Authors: Thijssen H.H.W. , Baars L.G.M. , Vervoort‐Peters H.T.M.
Published: July 2012

The administration of S‐warfarin (1 mg kg−1 i.v.) to rats that were pre‐loaded 48 h before with tracer doses (6 μg) of 14C‐labelled R‐ or S‐warfarin caused the plasma levels of these compounds to increase. This is due to the substitution of the microsomal (vitamin K 2,3‐epoxide (K0) reductase) bound R‐ or S‐[14C]‐warfarin by the unlabelled 4‐hydroxycoumarin administered. The rate of reappearance was 3–4 fold higher for R‐ than for S‐warfarin; t1/2 of release: 1.2 ± 0.04 and 3.7 ± 0.6 h, respectively.

Liver microsomes prepared from rats pretreated with R‐ or S‐[14C]‐warfarin, released these compounds only in the presence of dithiothreitol (DTT; 10 mm). The rate of release was higher for R‐ than for S‐warfarin‐treated microsomes.

Liver microsomes treated in vitro with R‐ or S‐acenocoumarol could be reactivated by DTT (10 mm). Reactivation was higher for the R‐ than for the S‐acenocoumarol‐treated microsomes.

The microsomal vitamin K0 reductase activity under ‘normal’ assay conditions ([DTT] = 2 mm) was as sensitive for R‐ as for S‐4‐hydroxycoumarins. At elevated DTT concentrations (=42mm) the rate of vitamin K0 conversion was about 1.5 fold higher in the presence of the R‐isomers than in the presence of the S‐isomers. For instance, at 2mM DDT the reductase activities in the presence of 2.6 μm R‐ and S‐warfarin were about 15% of control. At 42 mM DTT the activities were 90 and 65% of control, respectively.

In the in vitro experiments acenocoumarol appeared to be more potent than warfarin and phenprocoumon.

The following mechanism is proposed: vitamin K0 reductase becomes oxidized during substrate reduction. The oxidized (i.e. inactive) form binds equally to the R‐ and S‐enantiomers of 4‐hydroxycoumarins. The attached (covalently bound?) coumarin is released by the reactivation (i.e. reduction) of the enzyme. However, the rate of reactivation is strongly attenuated by the attached coumarin. This effect is more pronounced for the S‐configuration of the 4‐hydroxycoumarin anticoagulants.
Secretory effects of kinins on colonic epithelium in relation to prostaglandins released from cells of the lamina propria
Authors: Phillips Judith A. , Hoult J.R.S.
Published: July 2012

Sheets of muscle‐stripped rat and rabbit colon with epithelium intact or removed were mounted in Ussing‐type chambers for recording of transepithelial p.d., resistance and short circuit current (Isc), and measurement by radioimmunoassay (RIA) of the release of prostaglandins into serosal and mucosal bathing solutions.

In epithelial‐intact preparations prostaglandin E2 (PGE2), PGE1, PGF2α, U46619 and prostacyclin (10−7‐10−6m) caused increases in Isc and transepithelial p.d., in (approximate) descending order of potency. Epithelial‐removed preparations did not exhibit any transepithelial p.d.

In epithelial‐intact preparations, lysyl‐bradykinin (LBk) applied serosally but not mucosally caused increased p.d. and release of PGE2 (and to a lesser extent other prostaglandins) into serosal but not mucosal bathing solutions. In epithelial‐removed tissues, responsiveness to LBk was maintained, but it did not exhibit ‘sidedness’, i.e. LBk was effective when applied on either side and PGE2 release occurred into both compartments.

Indomethacin and other non steroidal anti‐inflammatory drugs (NSAIDs) abolished the LBk‐induced p.d. and reduced PGE2 release if applied serosally but not mucosally in epithelial‐intact preparations. In epithelial‐removed tissues, indomethacin added to either side abolished prostaglandin release into both compartments.

Calcium removal from serosal but not mucosal bathing solution (Ca2+‐free EGTA Krebs) abolished p.d. generation by LBk in epithelial‐intact preparations, and reduced PGE2 release in rabbit but not rat colon. Similarly, in epithelial‐removed preparations, calcium removal did not affect kinin‐induced PGE2 generation in rat but strongly attenuated it in rabbit colon.

We conclude that (i) kinins activate the arachidonate cascade principally by interactions with cells in the subepithelial (lamina propria) layer, rather than with the epithelial cells themselves, (ii) PGE2 contributes substantially to the kinin‐induced increase of transepithelial p.d. as a messenger released from kinin‐responsive subepithelial cells and acting on the basolateral pole of the epithelial cells, (iii) the apparent sidedness of colonic epithelium in terms of responses to kinins, NSAIDs and calcium removal is due to the barrier properties of the epithelial cell layer, and (iv) there are differences in calcium sequestration and apparent calcium dependence of prostaglandin biosynthesis between rat and rabbit colonic subepithelial cells.
Agonist and antagonist characterization of a putative adrenoceptor with distinct pharmacological properties from the α‐ and β‐subtypes
Authors: Bond Richard A. , Clarke David E.
Published: July 2012

Experiments were done to characterize a putative adrenoceptor which functions to inhibit longitudinal muscle tension development in the guinea‐pig ileum. Several phenylethylamine based agonists were investigated: BRL 37344, (−)‐isoprenaline, (+)‐isoprenaline, noradrenaline, adrenaline, and fenoterol. Propranolol and nadolol were tested as antagonists. Agonist‐induced inhibition of the contractile response to histamine was measured under equilibrium conditions with α‐adrenoceptors and muscarinic cholinoceptors inhibited.

Inhibitory responses were obtained to (−)‐isoprenaline and BRL 37344 that were resistant to β‐adrenoceptor blockade with propranolol (5 μm) and nadolol (10μm). These resistant responses were antagonized by much higher concentrations of nadolol (30 to 1000 μm) yielding apparent pA2 values for nadolol of 4.31 with (−)‐isoprenaline as the agonist, and 4.68 with BRL 37344 as the agonist. Similar apparent pA2 values for nadolol at the putative adrenoceptor were obtained with noradrenaline (4.79), adrenaline (4.68), and fenoterol (4.38).

The order and relative potency of agonists at the putative adrenoceptor was: BRL 37344 (20) > (−)‐isoprenaline (8) > noradrenaline (1) > adrenaline (0.5) > fenoterol (0.35) > (H‐)‐isoprenaline (0.27).

The resistance to blockade by propranolol (5 μm), the low affinity of nadolol, and the order and relative potency of agonists, suggest the presence of an adrenoceptor with distinct pharmacological characteristics from currently defined α‐ and β‐adrenoceptors.
Cardioprotective actions of human superoxide dismutase in two reperfusion models of myocardial ischaemia in the rat
Authors: Aoki Nobuo , Bitterman Haim , Brezinski Mark. E. , Lefer Allan M.
Published: July 2012

In rats under ether anaesthesia, the left coronary artery was ligated and reperfused after 10 min of ischaemia. Forty‐eight hours later the myocardium was analyzed for creatine kinase (CK) activity.

Human superoxide dismutase (h‐SOD) given 1 min after occlusion and again 6h later significantly improved survival and retarded the loss of myocardial CK.

In rat isolated hearts perfused at 15% of normal flow for 30 min followed by re‐establishment of normal flow for 20 min, perfusion pressure increased by 72% and myocardial CK decreased by 44%. No significant changes occurred in wet‐to‐dry heart weight ratio.

Administration of h‐SOD at 2.5 or 5.0 mg, significantly attenuated the elevated post‐ischaemic perfusion pressure and the loss of myocardial CK activity in rat perfused hearts.

h‐SOD appears to be an effective anti‐ischaemic agent in the intact animal as well as the isolated perfused heart of the rat subjected to low flow followed by reperfusion at normal flow. The mechanism of this cardioprotective effect is not totally dependent upon the formed elements of the blood, but may be partially due to a direct cytoprotective effect.
Evaluation of the potassium channel activator cromakalim (BRL 34915) as a bronchodilator in the guinea‐pig: comparison with nifedipine
Authors: Arch J.R.S. , Buckle D.R. , Bumstead J. , Clarke G.D. , Taylor J.F. , Taylor S.G.
Published: July 2012

The potential of the potassium channel activator, cromakalim (BRL 34915), as a bronchodilator has been evaluated in guinea‐pig models in comparison with nifedipine. Some effects of the compounds on guinea‐pig tracheal spirals have been studied in an attempt to elucidate their different efficacies in vivo.

When given by the intraduodenal route to anaesthetized guinea‐pigs, cromakalim (3 and 10 mg kg−1) inhibited 5‐hydroxytryptamine (5‐HT)‐induced bronchospasm for at least 60 min. When given by the i.v. route, the dose of cromakalim producing 50% inhibition of the 5‐HT response was 84 μg kg−1. Nifedipine failed to show any protective effect up to 100 μg kg−1, i.v. and was lethal at higher dose levels.

Cromakalim protected conscious guinea‐pigs from asphyxic collapse in response to histamine aerosol. The maximal effect occurred 60 min following oral dosing, with 2.5 mg kg−1 providing complete protection for almost half of the animals. Nifedipine had only a weak protective effect even at a high dose level of 50 mg kg−1, p.o.

Cromakalim prolonged the time before convulsive cough in response to an antigen challenge in actively sensitized guinea‐pigs. Its minimum protective dose was 1 mg kg−1, p.o. Nifedipine (50 mg kg−1, p.o.) was ineffective.

Cromakalim inhibited both spontaneous and prostaglandin E2‐induced tone in guinea‐pig isolated tracheal spirals with IC50 values, relative to the maximum inhibition achieved by isoprenaline (10−3m), of 1.1 × 10−6m and 8.9 × 10−7m, respectively. Its maximal effect was 89% of that produced by isoprenaline. Removal of the epithelium did not influence its activity. Studies using the two enantiomers showed that the activity of cromakalim resided almost entirely in the (−)‐enantiomer.

Nifedipine (2 × 10−5 m) achieved only 49% of the relaxant effect of 10−3 m isoprenaline in isolated tracheal spirals. Addition of cromakalim (10−5 m) at the end of the nifedipine concentration‐response experiment caused further relaxation to 94% of the effect of isoprenaline.

It is concluded that cromakalim has greater potential than nifedipine as a bronchodilator. It appears that opening of potassium channels, with consequent hyperpolarization and stabilization of the membrane potential, prevents calcium entering the cytosol through routes that are unaffected by calcium entry blockers.
Studies of the effects of subacute treatment with N‐(cyclopropylmethyl)−19‐isopentylnororvinol (M320) on timing of parturition in the rat
Authors: Evans R.G. , Rice G.E. , Olley J.E.
Published: July 2012

Administration of 10 μg kg−1 of the long lasting potent κ‐ and weaker μ‐opioid agonist N‐(cyclopropylmethyl)‐l 9‐isopentylnororvinol (M320) twice daily from day 20 of gestation prolonged the internal gestation period of the rat and retarded the development of the offspring in the perinatal period.

The capacities of myometrial, placental and cervical tissues to produce prostaglandin E2 (PGE2) were not affected by M320 treatment.

During the period in which parturition normally occurred in saline‐treated rats, foetal pituitary levels of immunoreactive oxytocin (ir‐OXY) but not immunoreactive arginine‐vasopressin (ir‐AVP) were greater in M320‐ compared to saline‐treated animals. Following the completion of parturition, foetal pituitary ir‐OXY and ir‐AVP levels continued to rise in saline‐treated rats, but fell dramatically in rats treated subacutely with M320.

These data indicate that subacute treatment with M320 may inhibit foetal oxytocin release at term. This foetal OXY release may be a stimulus for the initiation of labour.
Effect of Captopril on the bradykinin‐induced release of prostacyclin from guinea‐pig lungs and bovine aortic endothelial cells
Authors: de Nucci G. , Warner T. , Vane J.R.
Published: July 2012

In guinea‐pig isolated lungs perfused with Krebs solution, Captopril (10 μm) inhibited the metabolism of bradykinin (Bk) and the conversion of angiotensin I to angiotensin II, as measured by bioassay. Captopril significantly enhanced Bk‐stimulated output of prostacyclin.

In bovine aortic endothelial cells grown on microcarrier beads, Captopril (10 μm) did not affect the release of prostacyclin or of endothelium‐derived relaxing factor (EDRF) induced by Bk.

Angiotensin I or angiotensin II did not release prostacyclin from guinea‐pig isolated lungs or bovine aortic endothelial cells. They were also ineffective as releasers of EDRF from bovine aortic endothelial cells.

Thus, activation of angiotensin converting enzyme is not involved in the release of prostacyclin from guinea‐pig isolated lungs or bovine aortic endothelial cells, or in release of EDRF from bovine aortic endothelial cells.