bluuebunny/crossref_metadata_2025_split huggingface dataset:
Desensitization of the P2‐purinoceptors on the rat colon muscularis mucosae
Authors: Hourani S.M.O. , Johnson C.R. , Bailey S.J. 
Published: July 2012

Adenosine 5′‐triphosphate (ATP) and adenosine have been shown to contract the rat colon muscularis mucosae, and the receptors at which they act have been classified as P2Y and A1 respectively. Uridine 5′‐triphosphate (UTP) also contracts this tissue, and desensitization was used to investigate the receptors by which it acts, in the light of recent suggestions that specific pyrimidinoceptors may exist for UTP, or that nucleotide receptors may exist which are responsive to both ATP and UTP but not to some ATP analogues such as 2‐methylthioadenosine 5′‐triphosphate (2‐MeSATP).
ATP, UTP and adenosine each contracted the rat colon muscularis mucosae in a concentration‐dependent manner over the concentration range 0.3–300 μm, although maximal responses to ATP and UTP were not obtained. ATP was approximately 4 times as potent as UTP and approximately equipotent with adenosine although the maximal response to adenosine appeared to be less than that to ATP or UTP.
Desensitization of the tissue with ATP (200 μm) given immediately before each concentration of the agonists reduced subsequent contractions induced by ATP itself and also by UTP, but did not reduce contractions induced by adenosine. Desensitization of the tissues with UTP (200 μm) also reduced contractions induced by ATP and UTP but not by adenosine, whereas desensitization with adenosine (200 μm) reduced contractions induced by adenosine itself but not by ATP or UTP.
Desensitization of the tissue with 2‐MeSATP (200 μm), which is a more potent agonist than ATP at P2Y‐purinoceptors, greatly reduced the responses to ATP and to UTP, but had no effect on responses induced by adenosine. Attempts to desensitize the tissue with adenosine 5′‐(α,β‐methylene)triphosphonate (AMPCPP), which is a more potent agonist than ATP at P2X‐purinoceptors but is less potent at P2Y‐purinoceptors, were unsuccessful.
These results show that cross desensitization to ATP and UTP occurred and was specific for these agonists rather than being due to a general decrease in the ability of the muscle to contract. This implies that ATP and UTP act at the same receptor, which does not support the existence of specific pyrimidinoceptors but which could be taken as evidence for the existence of a nucleotide receptor on this tissue. However, the ability of 2‐MeSATP, which is inactive at the proposed nucleotide receptors, also selectively to desensitize this receptor indicates instead that ATP and UTP are both acting at a purinoceptor of the P2Y type in this tissue.
Effects of two β3‐adrenoceptor agonists, SR 58611A and BRL 37344, and of salbutamol on cholinergic and NANC neural contraction in guinea‐pig main bronchi in vitro
Authors: Martin Corinne A.E. , Naline Emmanuel , Manara Luciano , Advenier Charles 
Published: July 2012

The aim of the present study was to investigate the type of adrenoceptor which modulates constriction of the guinea‐pig isolated main bronchus in response to electrical field stimulation (EFS). Drugs used were salbutamol and two agonists reportedly selective for the putative β3‐adrenoceptor: BRL 37344 and SR 58611A.
At basal tone, all three drugs induced relaxation, however, SR 58611A and BRL 37344 (10−9 to 10−6 m) relaxed guinea‐pig isolated main bronchus more weakly than salbutamol (10−9 to 10−6 m). The effects observed at 10−6 m were 43% ± 9%, 63% ± 4% and 98% ± 1% of the maximal effect induced by theophylline (3 × 10−3 m) for SR 58611A, BRL 37344 and salbutamol, respectively.
SR 58611A and BRL 37344 (10−8 to 10−6 m) did not significantly modify the cholinergic component of the response to EFS, but caused a concentration‐dependent reduction of the nonadrenergic non‐cholinergic (NANC) excitatory component (41.8% ± 10.1% and 56.8% ± 7.4% respectively at 10−6 m, n = 6–7). Salbutamol (10−9 to 10−7 m) strongly inhibited both components, with 91.1% ± 4.2% of inhibition for the NANC contraction and 62.0% ± 5.2% of inhibition for the cholinergic contraction (10−7 m, n = 7).
Whereas the inhibitory effects of salbutamol were strongly inhibited by both propranolol (10−6 m) and ICI 118,551 (10−6 m), those of BRL 37344 were only slightly, albeit significantly reduced by both propranolol and ICI 118,551, and those of SR 58611A were unaffected by treatment with either β‐adrenoceptor antagonist. An α2‐adrenoceptor antagonist, yohimbine, did not influence the inhibitory effects of any of the β‐adrenoceptor agonists tested.
Concentration‐response curves to acetylcholine (10−8 to 10−3 m), [Nle10]NKA(4–10) (10−10 to 10−6 m) and substance P (10−10 to 3 × 10−6 m) were also significantly shifted to the right by salbutamol (10−6 m), whereas SR 58611A and BRL 37344 (10−6 m) had no effect.
These results suggest that the stimulation of putative β3‐adrenoceptors exerts a specific prejunctional inhibitory action on NANC excitatory response induced by EFS of the isolated main bronchus of the guinea‐pig. They also suggest that a β2‐adrenoceptor agonistic component may be involved in the effects of BRL 37344.
Cardiovascular effects of intrathecally administered bradykinin in the rat: characterization of receptors with antagonists
Authors: Lopes Paulo , Regoli Domenico , Couture Réjean 
Published: July 2012

The effects of intrathecal (i.t.) pretreatment with selective B1 or B2 kinin receptor antagonists were studied on the cardiovascular response to i.t. injection of bradykinin (BK) in conscious freely moving rats.
BK (81 pmol) produced an increase in mean arterial pressure (MAP: 9–13 mmHg) and decrease in heart rate (HR: 20–30 beats min−1) that reached a maximum 2 min after injection.
The BK‐induced cardiovascular responses were dose‐dependently and reversibly reduced by four antagonists with the following rank order of potency: Tyr, d‐Arg[Hyp3,d‐Phe7,Leu8]‐BK = d‐Arg[Tyr3,d‐Phe7,Leu8]‐BK = d‐Arg[Hyp3,d‐Phe7,Leu8]‐BK > d‐Arg[Hyp3,Thi5,d‐Tic7,Oic8]‐BK (Hoe 140). These compounds failed to alter the cardiovascular response to i.t. injection of 8.1 nmol of substance P.
Other compounds acting on the B2 receptor, namely d‐Arg[Hyp3,Gly6,Leu8]‐BK, d‐Arg[Hyp3,d‐Phe7]‐BK, d‐Arg[Hyp2,Thi5,8,d‐Phe7]‐BK and d‐Arg[Hyp3,Gly6,d‐Phe7,Leu8]‐BK or on the B1 receptor, [Leu8]‐desArg9‐BK, did not influence the cardiovascular responses to BK at doses devoid of intrinsic activity on MAP and HR.
None of the kinin receptor antagonists caused motor impairment, respiratory arrest or persisting cardiovascular changes.
These results confirm that the cardiovascular effects induced by i.t. BK are mediated by the activation of a B2 receptor in the rat spinal cord. However, the rank order of potency of antagonists does not conform to the classical B2 functional site characterized in peripheral tissues.
Cardiotonic actions of selective phosphodiesterase inhibitors in rat isolated ventricular cardiomyocytes
Authors: Kelso Elizabeth J. , McDermott Barbara J. , Silke Bernard 
Published: July 2012

The contractile effects of the novel cardiotonic agent HN‐10200 (2‐[3‐methoxy‐5‐methylsulphinyl‐2‐thienyl]‐1H‐imidazo‐[4,5‐c]‐pyridine hydrochloride), were examined and comparisons made with the responses obtained to a structurally similar compound, sulmazole, and to a number of other compounds which are known to inhibit phosphodiesterase (PDE) isoenzymes with differing selectivities; namely, enoximone (PDE III inhibitor), Ro 20–1724 (PDE IV inhibitor) and 3‐isobutyl‐1‐methylxanthine (non‐selective PDE inhibitor).
Contractile function, as measured by mechanical shortening, and biochemical systems involving cyclic AMP were investigated in ventricular cardiomyocytes isolated from adult Sprague‐Dawley rats (200–250 g).
HN‐10200 exerted a concentration‐dependent (10−8 m − 10−4 m) positive contractile effect, which was independent of α‐ or β‐adrenoceptor, or histamine receptor stimulation.
The efficacies of the contractile responses to the PDE inhibitors were of the order: HN‐10200 > IBMX > sulmazole > enoximone and maximum stimulations, which were obtained at concentrations of 10−4 m, were 54 ± 4%, 41 ± 7%, 38 ± 7% and 26 ± 5% (mean ± s.e.) greater than basal levels, respectively (n = 6); the basal value of contractile amplitude (dL), in the absence of PDE inhibitors was 7.39 ± 0.18% (mean ± s.e.). Ro 20–1724 did not have any effect on contractile activity.
Due to low basal levels of cyclic nucleotides in isolated cells, accumulation of cyclic AMP due to the presence of the PDE inhibitors was detected only when the levels of cyclic nucleotide were enhanced with forskolin (10 μm).
The PDE inhibitors increased levels of cyclic AMP only at concentrations > 10−4 m. HN‐10200 and sulmazole had similar concentration‐dependent profiles for the accumulation of cyclic AMP; their potencies were lower than that of IBMX (concentrations of forskolin required to increase cyclic AMP by 4 pmol mg−1 protein, in the presence of maximum concentrations of the PDE inhibitors, were 13 ± 3 μm, 14 ± 3 μm and 3 ± 0.6 μm [mean ± s.e.], respectively).
These results indicate that a similar mechanism, probably through a weak inhibition of the cyclic AMP‐specific PDE isoenzymes, is responsible for the increase in levels of cyclic AMP by HN‐10200 and sulmazole. However, cyclic AMP is only partially responsible for the positive contractile effect of HN‐10200 and, similarly, sulmazole and IBMX. The lack of apparent increase in levels of cyclic AMP by enoximone, highlights its degree of selectivity for the PDE III isoenzyme, such that the PDE IV isoform is still present in sufficient quantity to degrade cyclic AMP within the cell. On the other hand, the potent action of Ro 20–1724 on accumulation of cyclic AMP, in addition to the lack of effect on contractile function, is in agreement with the selectivity of this compound for the PDE IV isoenzyme and compartmentalization of cyclic AMP in rat isolated ventricular cardiomyocytes.
Selective inhibition by dexamethasone of induction of NO synthase, but not of induction of l‐arginine transport, in activated murine macrophage J774 cells
Authors: Baydoun Anwar R. , Bogle Richard G. , Pearson Jeremy D. , Mann Giovanni E. 
Published: July 2012

Effects of dexamethasone on induction of nitric oxide (NO) synathase and l‐arginine transport by lipopolysaccharide (LPS) were examined in a murine cultured macrophage cell line J774. Metabolism of l‐arginine to l‐citrulline and subsequent changes in intracellular amino acids pools were correlated with changes in nitrite production.
Despite a high intracellular concentration of arginine in activated J774 cells, LPS (1 μg ml−1, 8 h) induced a 2.4 fold increase in arginine transport. Treatment of cells with cycloheximide (1 μg ml−1) inhibited the time‐dependent (1–8 h) induction of NO synthase and arginine transport mediated by LPS.
Induction of NO synthase by LPS (1 μg ml−1, 24 h) alone was accompanied by a marked increase in arginine utilisation leading to decreased intracellular arginine levels and elevated intracellular and extracellular l‐citrulline levels. These changes were further enhanced in the presence of interferon‐γ (IFN‐γ, 100 units ml−1, 24 h).
Dexamethasone (1 μm) abolished the increases in both nitrite and citrulline production induced by LPS alone but only partially reversed the combined effects of LPS and IFN‐γ. In contrast, treatment of cells with dexamethasone (10 μm) had no effect on the LPS‐mediated induction of arginine transport or the decrease in intracellular arginine concentration.
We conclude that induction of arginine transporter activity in LPS‐stimulated J774 cells involves de novo synthesis of carrier proteins, which increases transport of exogenous arginine during enhanced NO production. Moreover, the intracellular signalling pathways mediating induction of arginine transport and of NO synthase by LPS in activated macrophages diverge, since only the latter is sensitive to dexamethasone.
Induction of bradykinin B1 receptors in vivo in a model of ultra‐violet irradiation‐induced thermal hyperalgesia in the rat
Authors: Perkins M.N. , Kelly D. 
Published: July 2012

The role of bradykinin B1 receptors in the thermal hyperalgesia following unilateral ultra‐violet (u.v.) irradiation of the hindpaw of rats has been investigated.
In non‐irradiated (naive) animals the B1 receptor agonist des‐Arg9‐bradykinin and bradykinin (BK) (up to 1 μmol kg−1 i.v.) had no effect on withdrawal latency to a noxious heat stimulus when administered 60 min before testing.
Following exposure of one hindpaw to strong u.v. irradiation the withdrawal latency of the u.v.‐treated paw to radiant noxious heat fell by a maximum of 50% after 48 h. There was no reduction in latency in the contralateral paw.
des‐Arg9‐BK (1–100 nmol kg−1 i.v.) administered 24 h after u.v. exposure caused a further dose‐dependent fall (50 ± 4% reduction from saline injected animals at 100 nmol kg−1 i.v.) in withdrawal latency in the u.v.‐treated paw when measured 60 min after injection. The withdrawal latency of the contralateral paw was also reduced but to a lesser extent following des‐Arg9‐BK (100 nmol kg−1 i.v.) with a maximum reduction of 19 ± 3%.
Bradykinin also induced a further reduction in withdrawal latency (33 ± 5% reduction at 1 μmol kg−1) although it was not as effective as des‐Arg9‐BK. Bradykinin did not reduce the withdrawal latency in the contralateral paw.
The hyperalgesic action of both des‐Arg9‐BK (10 nmol kg−1 i.v.) and bradykinin (100 nmol kg−1 i.v.) were antagonized by the B1 receptor antagonist, des‐Arg9,Leu8‐BK (200 nmol kg−1 i.v.) but not by the B2 receptor antagonist, HOE 140 (0.5 μmol kg−1 i.v.).
The results suggest that in conditions of inflammatory hyperalgesia bradykinin B1 receptors are induced both locally and distant to the inflamed area, activation of which leads to further thermal hyperalgesia. In addition, in these conditions bradykinin appears to act predominantly via B1 receptors, presumably after degradation to des‐Arg9‐BK.
Homologous and heterologous desensitization of histamine H1‐and ATP‐receptors in the smooth muscle cell line, DDT1MF‐2: the role of protein kinase C
Authors: Dickenson John M. , Hill Stephen J. 
Published: July 2012

The possible role of protein kinase C (PKC) in homologous and heterologous desensitization of histamine H1‐ and ATP‐receptors has been studied in monolayers of cultured vas deferens smooth muscle cells (DDT1MF‐2). Cells were loaded with the calcium‐sensitive fluorescent dye fura‐2 and increases in intracellular free Ca2+ concentration ([Ca2+]i) monitored in response to histamine H1‐ or ATP‐receptor activation.
Histamine and ATP stimulated the release of Ca2+ from intracellular Ca2+ stores and Ca2+ influx across the plasma membrane. Activation of PKC with the phorbol ester β‐phorbol‐12,13 dibutyrate (PDBu; 1 μm) attenuated histamine (100 μm) and ATP (10 μm)‐induced release of intracellular Ca2+ and Ca2+ influx.
The selective PKC inhibitor, Ro 31–8220 (10 μm), reversed the PDBu‐induced attenuation of histamine (100 μm)‐stimulated Ca2+ responses.
Histamine H1‐ and ATP‐receptors are readily susceptible to homologous desensitization since short‐term exposure to histamine or ATP (450 s) attenuated the Ca2+ responses elicited by a second application of the same agonist. Furthermore, H1‐receptor activation‐induced heterologous desensitization of ATP stimulated Ca2+ responses and vice versa.
Homologous and heterologous desensitization of histamine and ATP Ca2+ responses still occurred in the presence of the PKC inhibitor, Ro 31–8220 (10 μm).
These data suggest that PKC activation can attenuate histamine H1‐ and ATP‐receptor mediated Ca2+ responses. However, based on our experimental data, PKC‐independent mechanisms appear to be involved in the homologous and heterologous desensitization of histamine H1‐ and ATP‐receptor mediated Ca2+ responses in DDT1MF‐2 cells.
EDRF release from canine coronary artery by lectins
Authors: Kleha Joseph F. , Devesly Pierre , Johns Anthony 
Published: July 2012

The effect of wheat germ agglutinin (WGA), concanavalin A (Con A) and lentil lectin agglutinin (LCA) were investigated on pre‐contracted canine coronary artery rings in vitro.
In endothelium‐intact canine coronary artery, contracted with the thromboxane A2‐analogue, U46619, WGA relaxed the tissue in a concentration‐dependent manner, with an inhibitory concentration (IC50) of 112 ± 17 nm (n = 6). In the absence of an endothelium, WGA did not cause any relaxation of the tissue.
In endothelium‐intact canine coronary artery, contracted with the thromboxane A2‐analogue, U46619, LCA relaxed the tissue in a concentration‐dependent manner, with an inhibitory concentration (IC50) of 423.1 ± 41 nm (n = 6). In the absence of an endothelium, LCA produced a 20.1 ± 1.1% (n = 6) relaxation at the highest concentration tested (3 μm).
Concanavalin A (Con A) relaxed canine coronary artery in a partial endothelium‐dependent manner with an IC50 of 104 ± 19 nm on endothelium‐intact coronary artery and an IC50 of 1.3 ± 0.3 μm (n = 6) on endothelium‐denuded tissues.
The relaxation effects of WGA were attenuated by 1 mm NG‐monomethyl l‐arginine (l‐NMMA) and completely inhibited by haemoglobin (3 μm), methylene blue (10 μm) and LY 83583 (30 μm). Ibuprofen had no effect on WGA‐induced relaxation.
The relaxant effects of WGA were reversed by addition of 20 mm N‐acetyl‐d‐glucosamine (GlcNAc) and N‐acetyl‐d‐galactosamine (Ga1NAc) but not by α‐mannose, d‐(+)‐galactose, and β‐lactose, whereas the endothelin‐dependent relaxations to LCA and Con A were unaffected.
The endothelium‐dependent relaxation induced by the lectins was unaffected by pretreatment of the tissue with 1 μm atropine.
In the absence of extracellular calcium, WGA was also able to release EDRF suggesting that WGA acts through a second messenger system to release intracellular calcium.
We suggest that WGA acts as an agonist to release EDRF from endothelial cells possibly by binding to a sugar moiety, specific receptor or adhesion molecules on the endothelial cell surface.
ZD1542, a potent thromboxane A2 synthase inhibitor and receptor antagonist in vitro
Authors: Brownlie R.P. , Brownrigg N.J. , Butcher H.M. , Garcia R. , Jessup R. , Lee V.J. , Tunstall S. , Wayne M.G. 
Published: July 2012

The thromboxane A2 synthase (TXS) inhibitory activity and the thromboxane A2 (TP)‐receptor blocking action of ZD1542 (4(Z)‐6‐[2S,4S,5R)‐2‐[1‐methyl‐1‐(2‐nitro‐4‐tolyloxy)ethyl]‐4‐(3‐pyridyl)‐1,3‐dioxan‐5‐yl]hex‐4‐enoic acid) has been evaluated in vitro on platelets and whole blood from a range of species including man. Antagonist activity has also been investigated in vascular and pulmonary smooth muscle preparations in vitro.
ZD1542 caused concentration‐dependent inhibition of human platelet microsomal thromboxane B2 (TXB2) production in vitro (IC50 = 0.016 μm); this inhibition was associated with an increase in prostaglandin E2 (PGE2) and PGF2α formation.
ZD1542 also inhibited collagen‐stimulated TXS in human, rat and dog whole blood giving IC50 values of 0.018, 0.009 and 0.049 μm respectively. The drug did not modify platelet cyclo‐oxygenase activity as inhibition of TXB2 formation was associated with a concomitant increase in the levels of PGD2, PGE2 and PGF2α. ZD1542 had little if any effect against cultured human umbilical vein endothelial cell (HUVEC) cyclo‐oxygenase (IC50 > 100 μm) and prostacyclin (PGI2) synthase (IC50 = 18.0 ± 8.6 μm).
ZD1542 caused concentration‐dependent inhibition of U46619‐induced aggregation responses of human, rat and dog platelets yielding apparent pA2 values of 8.3, 8.5 and 9.1 respectively. The drug was selective as, at concentrations up to 100 μm, it did not modify 5‐hydroxytryptamine (5‐HT) or the primary phases of adenosine diphosphate (ADP) and adrenaline‐induced aggregation. Furthermore, ZD1542 (100 μm) modified only weakly the platelet inhibitory effects of PGD2, PGE1 and PGI2.
ZD1542 also caused concentration‐dependent inhibition of U46619‐mediated contractions of rat thoracic aorta, guinea‐pig trachea and lung parenchyma preparations giving apparent pA2 values of 8.6, 8.3 and 8.5 respectively. At concentrations approaching three orders of magnitude greater than those required to block U46619‐mediated contractions, the drug did not affect the actions of non‐prostanoid agonists or exhibit agonist activity in any of the smooth muscle preparations employed; neither did it interact at EP‐ or FP‐receptors.
In conclusion, the present study demonstrates that ZD1542 is a drug that exhibits both potent, selective TXS inhibition and TXA2 receptor antagonism.
Antinociceptive activity of NK1 receptor antagonists: non‐specific effects of racemic RP67580
Authors: Rupniak N.M.J. , Boyce S. , Williams A.R. , Cook G. , Longmore J. , Seabrook G.R. , Caeser M. , Iversen S.D. , Hill R.G. 
Published: July 2012

Release of substance P in the dorsal horn is considered a primary event in the perception of pain. The profile of racemic RP67580, a non‐peptide antagonist at the NK1 (substance P) receptor, was examined in a range of antinociception tests on rodents.
At doses up to 30 mg kg−1, s.c. racemic RP67580 exhibited antinociceptive activity in writhing and formalin paw tests in mice and gerbils. Acetic acid induced writhing and the licking response to formalin were reduced to 40–50% of the level observed in vehicle‐treated animals (P < 0.05). However, this agent was not active in mouse tail flick, rat paw pressure or rat and guinea‐pig formalin paw tests.
Like racemic RP67580, the calcium channel blockers nifedipine (30 mg kg−1, i.p.) and verapamil (10 or 20 mg kg−1, s.c.) inhibited the response to formalin by approximately 60% in gerbils (P < 0.05 compared with vehicle‐treated animals).
Evidence for calcium channel antagonist activity of RP67580 was obtained in vitro. Racemic RP67580 inhibited calcium entry into depolarized strips of guinea‐pig ileum longitudinal muscle myenteric plexus (apparent KB = 587 ± 115 nm), inhibited [3H]‐diltiazem binding to rabbit skeletal membranes (IC50 = 298 nm) and depressed high threshold calcium currents in neurones cultured from rat cortex (10% inhibition at 10 μm).
These findings indicate that the acute antinociceptive effects of RP67580 may not be attributable to a specific interaction with NK1 receptors and may be mediated via calcium channel blockade.