bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
Characteristics of cromakalim‐induced relaxations in the smooth muscle cells of guinea‐pig mesenteric artery and vein
Authors: Nakao K. , Okabe K. , Kitamura K. , Kuriyama H. , Weston A.H. 
Published: July 2012

The effects of cromakalim (BRL 34915) on the smooth muscle cells of guinea‐pig mesenteric artery and vein were investigated with microelectrode and tension recording methods.
Cromakalim (> 10 μm) produced membrane hyperpolarization with an increase in ionic conductance. The hyperpolarization occurred to a greater extent and lasted longer in the vein than in the artery.
The hyperpolarization induced by cromakalim in mesenteric vein comprised two components, one of which was Mn sensitive. In mesenteric artery, the hyperpolarization was relatively insensitive to Mn.
From the current‐voltage relationship measured from arterial smooth muscle membranes, the reversal potential of cromakalim was estimated to be −80 mV. The cromakalim‐induced hyperpolarization was not modified in Na‐ or Cl‐deficient solution.
In both mesenteric artery and vein, cromakalim relaxed tissues precontracted with high K with (below 40 mm) or without (above 40 mm) hyperpolarization of the membrane.
In the mesenteric artery, action potentials evoked by electrical stimulation ceased before the generation of hyperpolarization.
Cromakalim produced a cross‐desensitization with nicorandil on the evoked membrane hyperpolarization in mesenteric artery.
It is concluded that the relaxing actions of cromakalim result from the hyperpolarization which follows the opening of Ca‐dependent K channels. The inhibition of a voltage‐dependent Ca current may also be involved in this inhibitory effect.
Control of interval‐force relation in canine ventricular myocardium studied with ryanodine
Authors: Bose D. , Hryshko L.V. , King B.W. , Chau T. 
Published: July 2012

The mechanism of post‐extrasystolic, rest and frequency potentiation was studied in canine isolated ventricular muscle.
Ryanodine, which impairs Ca availability from the sarcoplasmic reticulum (SR), reduced the amplitude of the extrasystole less than that of the steady state contraction. Ryanodine also inhibited post‐extrasystolic potentiation and converted rest‐potentiation into rest depression. Rest‐potentiation was blocked preferentially by ryanodine compared to post‐extrasystolic potentiation. An increase in the contribution of extracellular Ca to the extrasystolic contraction could not entirely account for the post‐extrasystolic potentiation.
Prolonged rest, by itself, also caused depression of the first post‐rest contraction. During rest‐potentiation, SR Ca seemed to play a greater role in contraction than transmembrane Ca influx. However, the ability of the ‘release pool’ of Ca in the SR to be reprimed after a contraction was reduced. This was seen as a decrease in post‐extrasystolic potentiation elicited immediately after rest.
A decrease in stimulus interval was associated with a transient decrease in contraction amplitude followed by an increase. An abrupt increase in stimulus interval had the opposite effect. Ryanodine blocked the initial transient changes and accelerated the delayed changes. These results suggest that the transient changes in contraction after sudden changes in drive interval are dependent on the SR.
Transmembrane Ca entry and the rate of recovery of the Ca release process (repriming) in the SR after a contraction seem to be interval‐dependent. The data also indicate that different mechanisms are involved in post‐extrasystolic and rest‐potentiation.
The results are consistent with a model which proposes ‘recirculation’ of activator Ca within the SR after a contraction or of the presence of an appreciable amount of inactivation of the SR Ca release process during normal stimulation. An increased pool of releasable Ca due to longer recirculation time or a time‐dependent decay in the level of inactivation of Ca release from the SR may give rise to rest‐potentiation.