bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of potassium channel blockade and α2‐adrenoceptor activation on the release of nitric oxide from non‐adrenergic non‐cholinergic nerves
Authors: De Man Joris G. , Boeckxstaens Guy E. , Herman Arnold G. , Pelckmans Paul A. 
Published: July 2012

Using a superfusion bioassay cascade, we studied the effect of K+ channel blockers and α2‐adrenoceptor agents on the release of a transferable factor, previously characterized as nitric oxide (NO) or a nitric oxide‐related substance (NO‐R), in response to non‐adrenergic non‐cholinergic (NANC) nerve stimulation in the canine ileocolonic junction (ICJ).
The non‐selective K+ channel blockers, 4‐aminopyridine (4‐AP, 50 μm) and tetraethylammonium (TEA, 1 mm) and the more selective blocker of Ca2+‐activated K+ channels, charybdotoxin (Leiurus quinquestriatus venom (LQV), 0.4 μg ml−1), significantly enhanced the release of NO‐R induced by low frequency stimulation (2–4 Hz). In the presence of 4‐AP and TEA, the release of NO‐R was nearly abolished by tetrodotoxin (2 μm), and by l‐NG‐nitroarginine (l‐NOARG, 0.1 mm). Relaxations induced by direct injection of exogenous NO (5–50 pmol) or nitroglycerin (GTN, 10–30 pmol) onto the rabbit aortic detector ring were not affected.
The α2‐adrenoceptor agonist, UK‐14,304 (0.3 μm) inhibited the release of NO‐R induced by low (2–4 Hz), but not that induced by high (16 Hz), frequency stimulation. This inhibitory effect was completely reversed by the α2‐adrenoceptor antagonist, yohimbine (0.3 μm). Neither UK‐14,304 nor yohimbine affected the relaxations induced by exogenous NO (5 pmol) or GTN (10 pmol) on the aortic detector ring.
On the other hand, in the presence of the K+ channel blockers 4‐AP (50 μm) or charybdotoxin (LQV, 0.4 μg ml−1), UK‐14,304 (0.3 μm) failed to inhibit the electrically‐induced release of NO‐R.
From these results, we conclude that the electrically‐induced release of NO‐R from NANC nerves of the canine ICJ is enhanced by K+ channel blockers but inhibited by α2‐adrenoceptor activation. In addition, these results suggest that the prejunctional modulation of NO‐R release by α2‐adrenoceptors may involve neuronal K+ channels.
Interdependence of contractile responses of rat small mesenteric arteries on nitric oxide and cyclo‐oxygenase and lipoxygenase products of arachidonic acid
Authors: Wu X.C. , Johns E. , Michael J. , Richards N.T. 
Published: July 2012

We have examined the effects of nitric oxide inhibition, indomethacin and the dual lipoxygenase/cyclo‐oxygenase inhibitor, 3‐amino‐1‐[m‐(trifluoromethyl)‐phenyl]‐2‐pyrazoline (BW755C), on the responses of small mesenteric arteries of Wistar rats, with and without endothelium, to noradrenaline, potassium chloride, endothelin‐1, acetylcholine and sodium nitroprusside.
Noradrenaline, potassium chloride and endothelin‐1 caused concentration‐dependent contraction of small mesenteric arteries. Indomethacin (14 μm) attenuated the contractile response to both noradrenaline and potassium chloride. The inhibitory action of indomethacin persisted in vessels treated with CHAPS.
Acetylcholine produced concentration‐dependent relaxation in these vessels. Indomethacin (14 μm) had no significant effect on the acetylcholine concentration‐response relationship.
NG‐nitro‐l‐arginine methyl ester (l‐NAME, 100 μm) potentiated the contractile response to both noradrenaline and potassium chloride and inhibited acetylcholine‐induced relaxation. Indomethacin attenuated the effects of l‐NAME.
BW755C inhibited the contractile response to noradrenaline and potassium chloride but not to endothelin‐1. The inhibitory effects of BW755C persisted in the presence of indomethacin and in vessels treated with CHAPS.
BW755C enhanced endothelium‐dependent relaxation, as assessed by the response to acetylcholine. In the presence of indomethacin, BW755C produced a shift to the right of the concentration‐response curve to acetylcholine.
Inhibition of nitric oxide synthase with l‐NAME, reversed the inhibitory effect of BW755C on noradrenaline‐ and potassium‐induced contraction. l‐NAME and BW755C in combination resulted in a shift to the right of the concentration‐response curve to acetylcholine.
Sodium nitroprusside produced concentration‐dependent relaxation of the vessels. Endothelium removal reduced the maximum relaxation to nitroprusside. BW755C did not alter the response to sodium nitroprusside in vessels with or without endothelium.
These data support the existence of two vasoconstrictor products of arachidonic acid released during contraction of small mesenteric arteries with noradrenaline and potassium chloride: a cyclo‐oxygenase product and a lipoxygenase product both of which appear to be largely endothelium‐independent.
Molecular cloning and expression of human EP3 receptors: evidence of three variants with differing carboxyl termini
Authors: Regan J.W. , Bailey T.J. , Donello J.E. , Pierce K.L. , Pepperl D.J. , Zhang D. , Kedzie K.M. , Fairbairn C.E. , Bogardus A.M. , Woodward D.F. , Gil D.W. 
Published: July 2012

The polymerase chain reaction (PCR) was used in combination with plaque hybridization analysis to clone four variants of the EP3 prostaglandin receptor from a human small intestine cDNA library.
Three of these variants, i.e. the EP3A, EP3E and EP3D, share the same primary amino acid sequence except for their carboxyl termini, which diverge from one another at the same point, approximately 10 amino acids away from the end of the seventh membrane spanning domain of the receptor. The fourth variant (EP3A1) has a nucleotide coding sequence identical to EP3A but has a completely different 3′;untranslated sequence.
The carboxyl termini of the three isoforms differ most obviously in length with the EP3A being the longest (41 amino acids) and the EP3E being the shortest (16 amino acids). They also differ in content with the EP3A containing 9 serine and threonines in its carboxyl terminus and the EP3E none.
Transient expression in eukaryotic cells showed that the human EP3 receptor variants had similar but not identical radioligand binding properties and differed in their functional coupling to second messenger pathways. Up to 3 pmol mg−1 protein of [3H]‐prostaglandin E2 binding could be obtained with more than 95% specific binding. Using a reporter gene assay, as a measure of intracellular cyclic AMP levels, the EP3A coupled more efficiently to the inhibition of adenylyl cyclase than did the EP3E.
PCR was used to confirm the presence of mRNAs encoding the four human EP3 receptor variants in tissues of the human small intestine, heart and pancreas. These findings indicate that the EP3 receptor variants identified here are likely to be expressed in tissues. The differences in the carboxyl termini at the protein level, and in the 3′ untranslated regions at the mRNA level, could be profound in terms of the regulation and functional coupling of these receptor isoforms.
The effect of the ETA receptor antagonist, FR 139317, on [125I]‐ET‐1 binding to the atherosclerotic human coronary artery
Authors: Dashwood Michael R. , Allen Sean P. , Luu Thin N. , Muddle John R. 
Published: July 2012

The distribution of [125I]‐endothelin (ET‐1) binding sites on atherosclerotic human epicardial coronary arteries has been studied by in vitro receptor autoradiography.
[125I]‐ET‐1 binding was to the tunica media and regions of neovascularization.
Competition studies were carried out in the presence of ET‐1 and the ETA receptor antagonist, FR 139317. The IC50 values for ET‐1 at the tunica media and regions of neovascularization were similar (mean ± s.e.mean of n = 4 patients, 2.5 ± 0.9 nm and 2.9 ± 0.9 nm, respectively) whereas IC50 values for FR 139317 at regions of neovascularization (607 ± 34 nm) were significantly higher than those of the tunica media (12.6 ± 2.4 nm) (P < 0.0001).
These results indicate that ETA receptors are present on the tunica media of the diseased human coronary artery whereas a different ET receptor subtype exists at regions of neovascularization.
Increase of extracellular brain calcium involved in interleukin‐1β‐induced pyresis in the rabbit: antagonism by dexamethasone
Authors: Palmi M. , Frosini M. , Becherucci C. , Sgaragli G.P. , Parente L. 
Published: July 2012

This study investigates the role of extracellular brain calcium in the hyperthermia induced by interleukin‐1β (IL‐1β).
Intracerebroventricular (i.c.v.) injection of IL‐1β (12.5 ng kg−1) in rabbits caused a prompt and sustained rise in cerebrospinal fluid (CSF) Ca2+ concentration ([Ca2+]) followed by enhanced prostaglandin E2 (PGE2) release and hyperthermia.
A linear and significant correlation was observed between the increase in [Ca2+] induced by IL‐1β and the rise in body temperature.
Ventriculo‐cisternal perfusion with artificial CSF containing the calcium chelator EGTA (1.3 mm) blocked the IL‐1‐induced PGE2 release and countered the febrile response.
I.c.v. administration of dexamethasone (Dex) (2.4 and 24 μg kg−1) 100 min prior to IL‐1β, dose‐dependently antagonized the cytokine‐induced Ca2+ increase, the PGE2 release and the febrile response.
These results suggest that changes in extracellular brain calcium are involved in the regulation of body temperature. In this light, the antipyretic action of Dex may be related to its effect on Ca2+ uptake.
Triflocin, a novel inhibitor for the Na‐HCO3 symport in the proximal tubule
Authors: Belachgar Fouzia , Hulin Philippe , Anagnostopoulos Takis , Planelles Gabrielle 
Published: July 2012

Triflocin, applied at millimolar concentration hyperpolarizes the basolateral membrane of Necturus proximal convoluted tubular cells, in vivo.
Barium, 2.5 × 10−3 m, ouabain, 10−3 m, or amiloride 10−4 m, fail to prevent this hyperpolarization.
Triflocin has no effect on the intracellular chloride activity.
In physiological acid base conditions, Triflocin increases intracellular pH.
Upon an acute isohydric hypercapnia, Triflocin depolarizes the basolateral membrane potential.
It is concluded that, Triflocin inhibits the basolateral electrogenic Na‐(HCO3)n > 1 cotransport in proximal tubules.
Vasoconstrictor responses after neo‐intima formation and endothelial removal in the rabbit carotid artery
Authors: De Meyer Guido R.Y. , Bult Hidde , Üstünes Levent , Kockx Mark , Jordaens François H. , Zonnekeyn Ludo L. , Herman Arnold G. 
Published: July 2012

The present study examined the responses of the rabbit carotid artery to five vasoconstrictors after neo‐intima formation induced by perivascular collar treatment and evaluated the role of constitutive and inducible nitric oxide (NO) synthase and endothelial cells (ECs).
Ring segments of the rabbit carotid artery were mounted in organ chambers for isometric tension recording. Neo‐intima‐bearing vessels developed less force (Emax) in response to KCl, the thromboxanemimetic U‐46619 and 5‐hydroxytryptamine (5‐HT), but not to angiotensin I and II.
The collar‐treatment increased the sensitivity to 5‐HT, and decreased the sensitivity to angiotensin II. The sensitivity to U‐46619 and angiotensin I remained unchanged.
Mechanical removal of ECs and inhibition of NO biosynthesis by NG‐monomethyl‐l‐arginine (l‐NMMA) and NG‐nitro‐l‐arginine (l‐NOARG) increased the sensitivity to 5‐HT in sham and collar‐treated segments to the same extent. The effects of collar‐treatment and endothelial removal or treatment with inhibitors of NO biosynthesis were additive. Inhibition of NO biosynthesis failed to augment sensitivity to 5‐HT after endothelial denudation. l‐NOARG increased the force development to KCl in sham and collar‐treated segments to the same extent. However, l‐NMMA and l‐NOARG failed to augment the contractile responses of neo‐intima‐bearing vessels to 5‐HT and KCl after endothelial removal.
The responses to angiotensin I were not altered, either by the neo‐intima or by endothelial removal. In arteries with a neo‐intima the sensitivity to angiotensin II was decreased. Removal of the endothelium or incubation with l‐NOARG counteracted this rightward shift and increased Emax.
Our results demonstrate that contractions to 5‐HT, angiotensin II and KCl are modulated by NO in both sham and neo‐intima‐bearing vessels. Inhibition of NO biosynthesis and collar treatment resulted in additive effects on the EC50 values, suggesting that the 5‐HT and angiotensin (AT) receptors on the smooth muscle cells are also modified by the formation of a neo‐intima. Furthermore, the reduced contractile responses of segments with a neo‐intima are not due to NO formed by an inducible NO synthase in those vessels.
Rapid desensitization of adrenaline‐ and neuropeptide Y‐stimulated Ca2+ mobilization in HEL‐cells
Authors: Michel Martin C. 
Published: July 2012

Desensitization of Gs‐coupled receptors, the β2‐adrenoceptor for example, involves rapid and slower components but little is known regarding the existence of rapid desensitization of Gi‐coupled receptors and its possible mechanisms. In HEL‐cells stimulation of α2A‐adrenoceptors by adrenaline or Y1‐like neuropeptide Y receptors by neuropeptide Y, transiently mobilizes Ca2+ from intracellular stores via a Gi‐protein. We have used this model to study the existence and possible mechanisms of rapid desensitization of a Gi‐mediated cellular response.
Following stimulation by adrenaline or neuropeptide Y Ca2+ levels returned towards baseline a few minutes after agonist addition and were refractory to a second agonist exposure demonstrating rapid desensitization. Cross‐desensitization experiments with neuropeptide Y, adrenaline and moxonidine demonstrated the presence of homologous (both receptors) and heterologous desensitization (neuropeptide Y receptors only), and that the α2A‐adrenoceptor desensitization was not specific for phenylethylamine (adrenaline) or imidazoline agonists (moxonidine).
The protein kinase C activator, phorbol ester, rapidly desensitized the hormonal Ca2+ responses and inhibitors of protein kinase C enhanced the hormonal responses inconsistently. The tyrosine kinase inhibitor, herbimycin, enhanced Ca2+ mobilization by adrenaline and neuropeptide Y, whereas the protein phosphatase inhibitor, okdadaic acid, did not affect Ca2+ mobilization or its desensitization.
In the absence of extracellular Ca2+ the endoplasmic reticulum Ca2+‐ATPase inhibitor, thapsigargin, reduced hormone‐stimulated Ca2+ elevations, demonstrating that mobilization occurs from a thapsigargin‐sensitive pool in the endoplasmic reticulum. The inositol phosphate‐independent Ca2+ release modulator, ryanodine, significantly enhanced adrenaline‐ and neuropeptide Y‐stimulated Ca2+ elevations. Blockade of the endoplasmic reticulum Ca2+‐ATPase by thapsigargin in the presence of extracellular Ca2+ enhanced hormone‐stimulated Ca2+ increases, demonstrating the importance of this enzyme for the termination of the Ca2+ signal.
It is concluded that adrenaline and neuropeptide Y‐stimulated Ca2+ mobilization in HEL‐cells occurs from a thapsigargin‐ and ryanodine‐sensitive store in the endoplasmic reticulum and desensitizes rapidly; this appears to involve multiple mechanisms including protein kinases, possibly acting on receptors, and Ca2+ release and sequestration mechanisms.
Nitrovasodilator‐induced relaxation and tolerance development in porcine vena cordis magna: dependence on intact endothelium
Authors: Kojda Georg , Beck Jan Klaus , Meyer Wilfried , Noack Eike 
Published: July 2012

Isolated segments of porcine vena cordis magna exhibited a reproducible contractile activity upon application of prostaglandin F2α (PGF2α) or KCl, that was independent of the presence of intact endothelium. Substance P (3 nm) elicited strictly endothelium‐dependent relaxations amounting to 46.1 ± 1.4% (n = 206) of contractions induced by 10 μm PGF2α.
S‐nitroso‐N‐acetyl‐d,l‐penicillamine (SNAP), a compound that spontaneously liberates nitric oxide, concentration‐dependently relaxed PGF2α‐precontracted (50 μm) venous segments. Tolerance induction (incubation with 100 μm SNAP for 30 min) within the same segments resulted in a 3 fold attenuation of this effect, which was not further reduced after additional preincubation with glyceryl trinitrate (GTN). Removal of endothelium or the presence of Nω‐nitro‐l‐arginine methylester (l‐NAME) significantly improved the potency of SNAP before and after tolerance induction.
Concentration‐dependent relaxations induced by GTN in non‐tolerant veins were similar in the presence and absence of endothelium but much more reduced in tolerant endothelium‐denuded (75 fold) compared to intact (20 fold) segments. In contrast, the presence of l‐NAME significantly improved GTN‐activity solely in non‐tolerant veins, which, therefore, also resulted in a more pronounced attenuation of activity due to tolerance induction (100 fold). Preincubation of intact veins with SNAP also reduced GTN‐activity but to a lesser extent (10 fold).
The more delayed but much longer, and compared to GTN somewhat weaker, acting new nitrovasodilator N‐(3‐nitrato‐pivaloyl)‐1‐cysteineethylester (SPM 3672) was more potent in denuded than intact non‐tolerant venous segments. Induction of tolerance by GTN resulted in a 2 fold‐attenuation of potency. This effect was increased to 15 fold in denuded veins but solely due to enhanced potency of SPM 3672 caused by removal of endothelium.
These data demonstrate that intact endothelium of porcine vena cordis magna attenuates the relaxant potency of nitrovasodilators but also probably participates in vascular bioactivation of GTN. We suggest that the reduced potency of nitrovasodilators is due to endogenous production of nitric oxide, which may affect the soluble guanylate cyclase/cyclic GMP‐system or inhibit nitrate bioactivation pathways.
The effect of leukocyte depletion on pulmonary M2 muscarinic receptor function in parainfluenza virus‐infected guinea‐pigs
Authors: Fryer Allison D. , Yarkony Kathryn A. , Jacoby David B. 
Published: July 2012

Parainfluenza infections of the airways cause dysfunction of inhibitory M2 muscarinic receptors on the pulmonary parasympathetic nerves. To distinguish the direct effects of virus from the effects of virus‐induced airway inflammation on M2 muscarinic receptor function, guinea‐pigs were depleted of leukocytes by pretreating with cyclophosphamide (30 mg kg−1, i.p. daily for 7 days) after which they were infected with parainfluenza virus type 1 (Sendai virus).
Guinea‐pigs were anaesthetized, tracheotomized, and ventilated. The vagus nerves were isolated and cut, and the distal ends were electrically stimulated causing bronchoconstriction. In control animals, pilocarpine (1–100 μg kg−1, i.v.) inhibited and gallamine (0.1–10 mg kg−1, i.v.) potentiated vagally‐induced bronchoconstriction by stimulating or blocking M2 muscarinic receptors on the vagus. These effects of pilocarpine and gallamine were almost completely lost in virus‐infected animals, demonstrating loss of M2 receptor function.
Cyclophosphamide depleted peripheral blood leukocytes and inhibited the virus‐induced influx of inflammatory cells into the lung. Depletion of leukocytes protected M2 receptor function from viral infection in some, but not all, guinea‐pigs tested.
Among infected animals that had been depleted of leukocytes, the viral content (expressed as the log of the number of tissue culture infectious doses per g lung tissue) of those that retained normal M2 receptor function was 4.29 ± 0.05 (mean ± s.e.mean), while the viral content of those that lost M2 receptor function despite leukocyte depletion was 5.45 ± 0.20 (P = 0.011). Thus the viral content of the lungs in which M2 receptor function was lost was 16 times greater than that of the lungs in which M2 receptor function was preserved. Viral content correlated with the inhibition of vagally‐mediated bronchoconstriction after the maximum dose of pilocarpine (100 μg kg−1; r2 = 0.81, P = 0.0004).
In antigen‐challenged animals, inhibitory M2 muscarinic receptor function is restored when positively charged inflammatory cell proteins are bound and neutralized by heparin. However, heparin (2000 u kg−1, i.v.) did not reverse virus‐induced loss of M2 muscarinic receptor function, even in those guinea‐pigs with a lower viral titer.
Because leukocyte depletion protected M2 muscarinic receptor function only in animals with mild viral infections, it appears that viruses have both an indirect, leukocyte‐dependent effect on M2 receptors and, in animals with more severe infections, a leukocyte‐independent effect on M2 receptors. The failure of heparin to restore M2 receptor function demonstrates that the leukocyte‐dependent loss of M2 receptor function is not mediated by positively charged inflammatory cell proteins.
Metabolic disposition of leukotriene B4 (LTB4) and oxidation‐resistant analogues of LTB4 in conscious rabbits
Authors: Marleau Sylvie , Dallaire Nancy , Poubelle Patrice E. , Borgeat Pierre 
Published: July 2012

The kinetics of leukotriene B4 (LTB4), after single i.v. injections of doses of 0.1 to 1 μg kg−1, were investigated in conscious rabbits and compared with those of the Ω‐ and β‐oxidation resistant bioactive analogues, 20, 20, 20‐trifluoro‐LTB4 (20‐F3‐LTB4) and 3‐thio‐LTB4, respectively.
Immunoreactive LTB4 (IR‐LTB4) elimination was first‐order, as shown by a constant systemic clearance (ClLTB4) and a proportional increase in the area under the curve (AUC) of the plasma concentration versus time curve over the dose‐range studied. Our results showed a good correlation between observed steady‐state plasma concentrations (Css) of IR‐LTB4 after continuous infusion of LTB4 and those predicted by using the mean estimated ClLTB4 of 93 ± 4 ml min−1 kg−1, further confirming the linearity of IR‐LTB4 elimination.
The half‐life (t½) or IR‐LTB4 increased from 0.47 ± 0.02 to 0.63 ± 0.04 min as a consequence of a change in the apparent volume of distribution (Vd) from 72 ± 5 to 109 ± 13 ml kg−1, for the 0.1 and 1 μg kg−1 doses injected, respectively.
Single i.v. injections of [3H]‐LTB4 (4.7 ng kg−1) were administered, and the decay of plasma [3H]‐LTB4 following h.p.l.c. purification was used to estimate the kinetic parameters. The kinetic parameters of [3H]‐LTB4 were characterized by a mean systemic clearance (Cl) of 96 ± 11 ml min−1 kg−1, a t½ of 0.53 ± 0.03 min, and an apparent Vd of 85 ± 9 ml kg−1, similar to the parameters obtained after LTB4 boluses.
The disposition of LTB4 analogues, whether resistant to β‐ or to β‐oxidation in vitro, did not differ significantly from the disposition of the LTB4 molecule. The half‐lives of 20‐F3‐LTB4 and 3‐thio‐LTB4 in the circulation were 0.52 ± 0.07 min and 0.70 ± 0.11 min, respectively.
In summary, our results showed that LTB4, as well as Ω‐oxidation‐ and β‐oxidation‐resistant analogues were cleared very rapidly from the rabbit circulation and indicate that in situ, metabolism in blood is not a rate‐limiting factor for the elimination of LTB4.