bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for the involvement of different receptor subtypes in the pre‐ and postjunctional actions of angiotensin II at rat sympathetic neuroeffector sites
Authors: Cox S.L. , Ben A. , Story D.F. , Ziogas J. 
Published: July 2012

The effects of the nonpeptide angiotensin II receptor (AT) antagonists losartan and PD 123319 on actions of angiotensin II in the rat caudal artery and rat vas deferens preparations were investigated.
Angiotensin II (1.0 μm) increased perfusion pressure in isolated segments of the rat caudal artery. This increase in perfusion pressure was prevented by the AT1‐antagonist, losartan (0.1 μm) but was not affected by the AT2‐antagonist, PD 123319 (0.1 μm).
Angiotensin II (0.1 – 3.0 μm) produced a concentration‐dependent enhancement of the stimulation‐induced (S‐I) efflux of [3H]‐noradrenaline from isolated segments of rat caudal artery in which the noradrenergic transmitter stores had been labelled with [3H]‐noradrenaline. The maximum enhancement of S‐I efflux was approximately 60% with 1.0 μm angiotensin II.
Losartan (0.01 and 0.1 μm) reduced the enhancement of S‐I efflux produced by 1.0 μm angiotensin II in the caudal artery.
PD 123319 (0.01 μm) did not affect the enhancement of S‐I efflux produced by angiotensin II (1.0 μm) in the caudal artery. However, in a higher concentration (0.1 μm), PD 123319 reduced the enhancement of S‐I efflux produced by 1.0 μm angiotensin II.
Angiotensin II produced concentration‐dependent enhancement of the purinergic twitch responses (1 pulse/60 s) in the rat vas deferens,
Losartan (0.03 μm) and PD 123319 (0.03 μm) each reduced the angiotensin II‐induced enhancement of the twitch responses in the rat vas deferens.
These findings indicate that the enhancement of sympathetic neuroeffector transmission in both the caudal artery and vas deferens of the rat involves angiotensin receptor subtype(s) sensitive to both losartan and PD 123319. In contrast, the direct vasoconstrictor effect of angiotensin II in the rat caudal artery involves activation of a receptor subtype sensitive only to losartan.
Antiproliferative effects of A02011‐1, an adenylyl cyclase activator, in cultured vascular smooth muscle cells of rat
Authors: Yu Sheu‐Meei , Cheng Zhi‐Jiao , Kuo Sheng‐Chu 
Published: July 2012

1 The effects of A02011‐1, a pyrazole derivative, on the proliferation of rat vascular smooth muscle cells (VSMCs) were examined.2 A02011‐1 (1–100 μm) concentration‐dependently inhibited [3H]‐thymidine incorporation into DNA in rat VSMCs that were synchronized by 48 h serum depletion and then re‐stimulated by addition of foetal calf serum (FCS, 10%), platelet‐derived growth factor (PDGF, 10 ng ml−1), 5‐hydroxytryptamine (10 μm) or ADP (10 μm). The inhibitory effect of A02011‐1 was fully reversible. However, FCS‐induced [3H]‐thymidine incorporation into rat endothelial cells was unaffected by A02011‐1.3 The concentration of A02011‐1 necessary for inhibition of the FCS‐induced proliferation was similar to that necessary for adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) formation. Adenylyl cyclase activity was increased in A02011‐1‐treated VSMCs, whereas cyclic AMP‐specific phosphodiesterase activity was unchanged.4 A02011‐1 was equipotent with forskolin but was more potent than 8‐bromo‐cyclic AMP against FCS (10%)‐induced proliferation.5 The antiproliferative action of A02011‐1 was mimicked by 8‐bromo‐cyclic AMP, a membrane‐permeable cyclic AMP analogue and was antagonized by 2′,5′‐dideoxyadenosine, an adenylyl cyclase inhibitor and by Rp‐cyclic AMPS, a competitive inhibitor of cyclic AMP‐dependent protein kinase (PKA) type I and II. 3‐Isobutyl‐1‐methylxanthine (IBMX) caused significant potentiation of the antiproliferative activity of A02011‐1. However, Rp‐8‐bromo‐cyclic GMPS and staurosporine did not affect the antiproliferative activity of A02011‐1.6 A02011‐1 still inhibited the FCS‐induced DNA synthesis even when added 10–18 h after re‐stimulation of the serum‐starved VSMCs with 10% FCS. Flow cytometry in synchronized cells revealed an acute blockade of FCS‐inducible cell cycle progression at a point in the G1/S phase in A02011‐1‐treated cells. The inhibition of proliferation by A02011‐1 was shown to be independent of cell damage, as documented by several criteria of cell viability.7 These results indicate that A02011‐1 inhibition of VSMC proliferation was mediated by cyclic AMP and was due to a delay in the progression from the G1 into S phase of the cell cycle. A02011‐1 did not cause cell toxicity and may thus hold promising potential for the prevention of atherosclerosis or vascular diseases.
Human muscarinic receptors expressed in A9L and CHO cells: activation by full and partial agonists
Authors: Richards Mary H. , van Giersbergen Paul L.M. 
Published: July 2012

1 A comparative study of receptor activation by ten full and partial muscarinic agonists was undertaken on the five subtypes of human muscarinic receptors expressed at similar receptor densities in Chinese hamster ovary (CHO‐K1) cells. In addition, m1, m2 and m3 receptors were expressed in mouse fibroblast A9L cells in order to compare the influences of cell type on agonist activation of these receptors.2 Receptor‐effector coupling efficiencies were greater in CHO than A9L cells and agonists displayed greater potencies and similar or greater intrinsic activities at CHOm1 and CHOm3 than A9Lm1 and A9Lm3 receptors. Although m2 receptor density was 6 fold higher in A9L than CHO cells, carbachol elicited significantly greater inhibition of adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) formation in CHOm2 cells. These data suggest that not only receptor density but receptor‐effector coupling and/or coupling efficiencies play significant roles in agonist‐induced responses.3 In CHO cells, receptor‐effector coupling efficiencies were m3 = m1 > m5. Although CHOm5 receptors were the least efficiently coupled, some partial agonists displayed higher intrinsic efficacies at m5 than m3 receptors suggesting that, in CHO cells, m5 and m3 receptors may activate different G proteins and/or effectors to stimulate inositol monophosphate (IP1) formation.4 McN‐A‐343 was a functionally selective m4 agonist. It had little or no agonist activity at m3 receptors expressed in either A9L or CHO cells. The slopes of McN‐A‐343 concentration‐response curves in CHOm2 cells were significantly lower than the slopes obtained with this compound in CHOm4 cells suggesting that the mode of activation by McN‐A‐343 differed between the two muscarinic receptors negatively coupled to adenylyl cyclase.5 Cloned receptors provide valuable tools for the study of agonist‐receptor interaction and agonist‐receptor activation but caution should be applied in assuming that the results are valid for all cell types or for tissue‐expressed receptors.
Release by ultraviolet B (u.v.B) radiation of nitric oxide (NO) from human keratinocytes: a potential role for nitric oxide in erythema production
Authors: Deliconstantinos George , Villiotou Vassiliki , Stravrides John C. 
Published: July 2012

1 The mechanism of human sunburn is poorly understood but its characteristic features include the development of erythema. In this study we attempted to determine whether human keratinocytes possess a nitric oxide (NO) synthase (NOS), if this enzyme could be activated to release NO following exposure to ultraviolet B (u.v.B) and to define whether this photo‐induced response could be involved in the pathogenesis of sunburn erythema.2 Treatment of human keratinocytes with various doses of u.v.B (290–320 nm) radiation (up to 100 mJ cm−2) resulted in a dose‐dependent release of NO and cyclic GMP production that was reduced by NG‐monomethyl‐l‐arginine (l‐NMMA).3 u.v.B irradiation of keratinocyte cytosol at varying doses (up to 50 mJ cm−2), resulted in a gradual rise in NO production, with a concomitant increase in soluble guanylate cyclase activity (sGC).4 NOS isolated from the keratinocyte cytosol was constitutively expressed and was dependent on NADPH, Ca2+/calmodulin, tetrahydrobiopterin and flavins.5 In reconstitution experiments, when purified NOS was added to purified sGC, both isolated from keratinocyte cytosol, a four fold increase in cyclic GMP was observed. The GMP was increased by NO synthesized following u.v.B radiation (up to 20 mJ cm−2) of NOS.6 In in vivo experiments, guinea‐pigs were subjected to u.v.B light. A Protection Factor (PF) of 8.71 ± 2.85 was calculated when an emulsified cream formulation containing l‐NMMA (2%) was applied to their skin.7 The present results indicate that u.v.B radiation acts as a potent stimulator of NOS in keratinocytes. NO is lipophilic and may diffuse out of the keratinocytes, activating sGC in endothelial cells and neighbouring smooth muscle cells. This may be a major part of the integrated response of the skin leading to vasodilatation and erythema.
Bronchodilator and pre‐protective effects of urodilatin in bovine bronchi in vitro: comparison with atrial natriuretic peptide
Authors: Nally Jane E. , Docherty Cheryl C. , Clayton Robin A. , Thomson Neil C. 
Published: July 2012

1 This study examined the activity and mechanisms of action of urodilatin in bovine bronchi. For comparison, the ability of urodilatin to evoke bronchodilatation or protect against subsequent challenge was compared to that of the closely related peptide α‐human atrial natriuretic peptide (ANP).2 Urodilatin reversed methacholine‐evoked contraction in a concentration‐dependent manner in bovine bronchi. In the absence of any attempt to prevent degradation by neutral endopeptidases, urodilatin was more potent than ANP in this tissue.3 The bronchodilator properties of urodilatin were significantly augmented by the neutral endopeptidase inhibitor, phsophoramidon (3.68 × 10−5 M). This provides evidence for at least partial degradation of urodilatin by neutral endopeptidases. With phosphoramidon present, urodilatin and ANP were equipotent.4 In the presence of phosphoramidon (3.68 × 10−5 m), pre‐incubation with urodilatin (10−6 M) had a protective effect against subsequent methacholine‐induced contraction. This action of urodilatin was quantitatively similar to that of ANP in the presence of this endopeptidase inhibitor.5 The actions of urodilatin appear to involve ATP‐sensitive K+ channels since tolbutamide (10−6‐10−5m) significantly attenuated the relaxations induced by this peptide.6 Small conductance Ca2+‐activated K+ channels seem likewise to be implicated in the actions of urodilatin since blockade of these channels with apamin (10−7‐10−6m) resulted in a marked attenuation of urodilatin‐evoked responses.7 The presence of charybdotoxin (10−9 m‐10−7 m) had no significant effect on subsequent responses to urodilatin suggesting that large conductance Ca2+‐activated K+ channels are not involved in the relaxations evoked by this peptide.8 In the presence of phosphoramidon (3.68 × 10−5 m), urodilatin (10−6 m) evoked elevation of cyclic GMP levels within bovine bronchial tissue. Levels of cyclic GMP increased significantly within 5–10 s in response to this peptide and preceded the initiation of relaxant responses. Maximum increases in cyclic GMP levels were reached within 5 min; the time required for maximal relaxation evoked by this peptide.9 In conclusion, urodilatin, like ANP reversed and protected against, subsequent methacholine‐induced bronchoconstriction; an action enhanced by the presence of phosphoramidon (3.68 × 10−5 M). Associated with these actions of urodilatin was a rise in cyclic GMP levels as well as the opening of ATP‐sensitive K+ and small conductance Ca2+‐activated K+ channels.
Increase by NG‐nitro‐L‐arginine methyl ester (L‐NAME) of resistance to venous return in rats
Authors: Wang Yong‐Xiang , Lim Su Lin , Pang Catherine C.Y. 
Published: July 2012

1 The effects of the nitric oxide (NO) synthase inhibitor, NG‐nitro‐L‐arginine methyl ester (L‐NAME), on mean circulatory filling pressure (MCFP), total peripheral resistance (TPR), cardiac output (CO) and resistance to venous return (Rv) were studied in rats.2 In conscious, unrestrained rats, L‐NAME (0.5–16 mg kg−1) dose‐dependently increased mean arterial pressure (MAP) but not MCFP, an inverse index of venous compliance, either in the absence or presence of the ganglionic blocker mecamylamine (l0 mgkg−1).3 In pentobarbitone‐anaesthetized rats, L‐NAME (2, 4, 8 mg kg−1) increased MAP and reduced CO in a dose‐related manner but did not change MCFP. TPR (+ 84, +140 and +192%) as well as Rv (+ 62, + 72, +110%) were dose‐dependently increased by L‐NAME.4 Our results show that L‐NAME reduces CO by increasing arterial as well as venous resistances. L‐NAME does not affect MCFP.
Blockade of mast cell histamine secretion in response to neurotensin by SR 48692, a nonpeptide antagonist of the neurotensin brain receptor
Authors: Miller Lisa A. , Cochrane David E. , Carraway Robert E. , Feldberg Ross S. 
Published: July 2012

1 Pretreatment of rat isolated mast cells with SR 48692, a nonpeptide antagonist of the neurotensin (NT) receptor, prevented histamine secretion in response to NT.2 This inhibition was rapid in onset (∽1 min) and dependent upon the concentration of SR 48692 (IC50 ∽1–10 nM).3 SR 48692 (l‐1000 nM) did not inhibit histamine secretion elicited by substance P, bradykinin or compound 48/80, or by anti‐IgE stimulation of sensitized mast cells.4 When SR 48692 was injected intradermally (5 pmol in 50 μl) into anaesthetized rats, 15 min before the intradermal injection of NT, it reduced the effect of NT on vascular permeability.5 When injected intravenously, SR 48692 attenuated the effects of NT on haematocrit and blood stasis.6 These results demonstrate that SR 48692 selectively antagonizes the actions of NT on rat isolated mast cells as well as mast cells in vivo. Given the demonstrated specific interaction of SR 48692 with receptors for NT in brain, our results suggest the presence of specific NT receptors on mast cells.
Different effects of salmeterol, formoterol and salbutamol on cholinergic responses in the ferret trachea
Authors: Bergendal A. , Linden A. , Skoogh B.‐E. , Löfdahl C.‐G. , Lötvall J. 
Published: July 2012

1 In the present study, the inhibitory effects of the selective β2‐adrenoceptor agonists, salmeterol, formoterol and salbutamol, have been investigated on contractions of ferret trachea induced both by endogenous and exogenous acetylcholine. The aim of the study was to evaluate quantitative and/or qualitative differences in response which may indicate both pre‐and post‐junctional sites of action. The non‐selective β‐antagonist, sotalol, was used to estimate β‐adrenoceptor involvement.2 Isometric tension was measured in ferret isolated tracheal strips. The inhibitory effects of the drugs were studied on tonic contractions induced by pre‐junctional activation with electrical field stimulation (EFS) (2 Hz, 700 mA) or postjunctional activation with exogenous acetylcholine (ACh) (0.5 μm, about EC80), giving a similar degree of smooth muscle response.3 Concentration‐response experiments were performed with formoterol (0.3 nM‐0.3 μm) and salmeterol and salbutamol (10 nM‐10 μm). The experiments ended with the addition of sotalol (10 μm).4 All three P‐agonists inhibited the contractions in a concentration‐dependent manner. Salbutamol, formoterol and salmeterol inhibited the EFS‐induced contractions by 66(8)%, 105(5)% and 103(8)% (mean(s.e.mean)) respectively. ACh‐induced contractions were inhibited by 37(6)%, 72(11)% and 33(8)%. Theophylline (10nM‐3mM) inhibited the contractions to the same degree.5 β‐Adrenoceptor blockade by sotalol significantly antagonized the inhibitory effects of salbutamol and formoterol on both EFS‐ and ACh‐induced contractions. The effect of salmeterol on ACh‐induced contraction was also significantly antagonized, whereas the inhibition of EFS‐induced contraction was virtually unaffected.6 In conclusion, salbutamol, salmeterol and formoterol produced greater inhibitory effects in preparations contracted by EFS than in preparations contracted by exogenously‐added ACh. In the case of formoterol and salbutamol, the effects on both levels are most probably due to β‐adrenoceptor stimulation, whereas for salmeterol the dominant pre‐junctional effect is probably not mediated via β‐adrenoceptors. This non‐β‐mediated effect could represent an additional relaxant mechanism for salmeterol.
Significance of nitric oxide in the stimulation of intestinal fluid absorption in the rat jejunum in vivo
Authors: Schirgi‐Degen Andrea , Beubler Eckhard 
Published: July 2012

The effects of inhibiting nitric oxide (NO)‐synthase on fluid transport, mucosal cyclic GMP and cyclic AMP levels and intraluminal prostaglandin E2 (PGE2)‐release were studied in a model of ligated jejunal loops of anaesthetized rats in vivo. Experiments were performed under basal conditions as well as under conditions, when net fluid secretion was induced by Escherichia coli heat stable enterotoxin a (E. coli STa) or PGE2.
Intravenous infusion of the NO‐synthase inhibitor Nω‐nitro‐l‐arginine methyl ester (l‐NAME, 0.25–50 mg kg−1, 45 min) dose‐dependently reversed net fluid absorption to net secretion, whereas infusion of d‐NAME, the inactive enantiomer of l‐NAME, in corresponding doses did not influence net fluid transport. Nω‐nitro‐l‐arginine (l‐NOARG, 25 mg kg−1), another NO‐synthase inhibitor, also elicited net secretion of fluid.
l‐NAME (25 mg kg−1)‐induced net fluid secretion was reversed to net absorption by infusion of l‐arginine (400 mg kg−1) or sodium nitroprusside (1 mg kg−1) and s.c. administration of indomethacin (10 mg kg−1). Hexamethonium (1 mg kg−1, s.c.), a ganglionic blocker and granisetron (100 μg kg−1, s.c.), a 5‐HT3‐receptor antagonist, did not influence l‐NAME‐induced net secretion.
Net fluid secretion induced by intraluminal instillation of E. coli STa (10 units ml−1) was enhanced by infusion of l‐NAME (25 mg kg−1) and was inhibited by infusion of l‐arginine (400 mg kg−1) and sodium nitroprusside (1 mg kg−1). d‐Arginine (400 mg kg−1) did not influence E. coli STa‐induced fluid secretion. Likewise, net fluid secretion induced by i.a. infusion of PGE2 (79 ng ml−1, 30 min) was enhanced by infusion of l‐NAME and was inhibited by l‐arginine and sodium nitroprusside. d‐Arginine (400 mg kg−1) did not influence PGE2‐induced fluid secretion.
PGE2 levels in intraluminal fluid were not elevated after infusion of l‐NAME (25 mg kg−1) compared to controls.
Mucosal cyclic GMP and cyclic AMP levels after l‐NAME‐treatment were not different from control values.
These results indicate that nitric oxide plays an important role in the regulation of intestinal fluid transport. The data suggest a nitric oxide‐dependent proabsorptive tone in the intestine, which possibly involves the enteric nervous system and suppression of prostaglandin formation. This proabsorptive tone also may downregulate fluid secretion induced by E. coli STa or PGE2.
Functional characterization of the adenosine receptor mediating inhibition of intestinal secretion
Authors: Hancock Debra L. , Coupar Ian M. 
Published: July 2012

Previous studies have shown that the mixed A1/A2 adenosine agonist 5′‐N‐ethylcarboxamido‐adenosine (NECA) inhibits intestinal fluid secretion which is thought to contribute to its antidiarrhoeal effect in the rat. The aim of this study was to characterize the adenosine receptor mediating this antisecretory effect via functional studies using a range of selective agonists and antagonists and by applying the pharmacological criteria of relative agonist and antagonist potencies.
Adenosine agonists and antagonists were administered i.v. to anaesthetized rats. Intestinal secretion was then stimulated by i.a. infusion of vasoactive intestinal peptide (VIP, 0.8 μg min−1) and the net fluid transport across the wall of the jejunum was measured by a recirculation technique.
The rank order of agonist potency to reduce the response to VIP was: NECA > N6‐cyclopentyladenosine (CPA) > R‐N6‐(2‐phenylisopropyladenosine) (R‐PIA) > S‐PIA > chloroadenosine (2‐CADO) > 2‐phenylaminoadenosine (CV‐1808). This order best complies with the rank order of agonist potency that represents activation of the recently described A2B receptor: NECA > 2‐CADO R‐PIA = CHA > S‐PIA > = CV‐1808 > = CGS‐21680. The most potent agonists (NECA, CPA and R‐PIA) had ED50 values in the low microgram range.
The anitsecretory action of NECA (submaximal dose of 40μg kg−1) was antagonized equally (approximately 50%) by the selective adenosine antagonists 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX, 0.1 mg kg−1) and 8‐phenyltheophylline (8‐PT, 0.1 mg kg−1). This equipotent activity indicates the presence of an A2 and not an A1 receptor.
It is suggested that adenosine A2B receptor agonists could be evaluated for potential use as antidiarrhoeal drugs.
Pharmacology of stretch‐activated K channels in Lymnaea neurones
Authors: Small Daniel L. , Morris Catherine E. 
Published: July 2012

Single‐channel recording was used to describe the pharmacology of stretch‐activated K channels in Lymnaea neurones using channel blockers amiloride, tetraethylammonium (TEA), quinidine, gadolinium (Gd) and diltiazem.
Amiloride, TEA and quinidine applied to the outside face of the membrane all produced a fast flickery block of stretch‐activated K channels. All of these agents were without effect when applied at the inside face at concentrations as high as 10, 200 and 10 mm respectively. Neither Gd nor diltiazem had any effect on stretch‐activated K channels extracellularly (100 μm).
Amiloride, TEA and quinidine block were voltage‐independent with IC50 values at positive (and negative membrane potentials of 2.3 (and 2.0) mm, 48 (and 54) mm and 0.8 (and 0.7) mm respectively. Woodhull plots for TEA and quinidine block confirmed the voltage independence of stretch‐activated K channel block by these agents.
Hill plots of the amilorde, TEA and quinidine block yield Hill coefficients at positive (and negative) membrane potentials of 1.7 (and 1.5), 1.4 (and 1.2) and 1.5 (and 1.6 mm) respectively.
Ethanol (3%) had no apparent effect on stretch‐activated K channel kinetics or conductance yet reduced the efficacy of quinidine block.
The above pharmacological fingerprint of the stretch‐activated K channel is discussed with reference to other K‐selective and stretch‐activated channels.