| 1. |
- Bergendal, A, et al.
(författare)
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Extent of salmeterol-mediated reassertion of relaxation in guinea-pig trachea pretreated with aliphatic side chain structural analogues
- 1996
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Ingår i: British Journal of Pharmacology. - 1476-5381. ; 117:6, s. 1009-1015
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Tidskriftsartikel (refereegranskat)abstract
- 1. Salmeterol is a potent, selective and long acting beta 2-adrenoceptor agonist. In vitro, salmeterol exerts 'reassertion' relaxation of airways smooth muscle. Reassertion relaxation refers to the capacity of salmeterol to cause repeated functional antagonism of induced contraction when airway smooth muscle is intermittently exposed to, then washed free from, beta-adrenoceptor antagonists such as sotalol. The mechanism(s) underlying reassertion relaxation are unknown but may relate to high affinity binding of the long aliphatic side chain of salmeterol to an accessory site, distinct from the agonist recognition site, in or near the beta 2-adrenoceptor (exosite binding hypothesis). 2. In order to test the exosite hypothesis, three pure analogues of salmeterol, each exactly preserving the molecular structure of the aliphatic side chain but with zero or low efficacy at the beta 2-adrenoceptor were synthesized. The effect of pre-incubating guinea-pig tracheal smooth muscle with these analogues on salmeterol-induced reassertion relaxation was determined. 3. Computer Assisted Molecular Modelling of these molecules revealed that each of them exactly preserved the low energy linear conformation of the aliphatic side chain of salmeterol. Measurement of lipophilicity (octanol:water partition coefficient; log P) and direct partition into synthetic membranes (membrane partition coefficient; Kpmem) showed that all compounds had high affinity for lipids and membranes. In particular the biophysical properties of CGP 59162 (log P 1.89, Kpmem 16500) were very similar to salmeterol (log P 1.73, Kpmem 16800). 4. Two of the analogues, CGP 54103 and D 2543 (1 microM), which are structural mimics of the side chain of salmeterol, differing slightly in their length, did not prevent either the initial relaxation induced by salmeterol (0.1 microM) or the reassertion relaxation; however, it was not possible to determine whether either of these molecules occupied the beta 2-adrenoceptor. 5. The third analogue, CGP 59162, which has the substituents on the active saligenin head group of salmeterol in transposed positions, itself exerted a weak beta 2-adrenoceptor-mediated relaxation antagonized by ICI 118551 (beta 2-selective antagonist) but not CGP 20712 (beta 1-selective antagonist) and, at higher concentrations CGP 59162 caused reassertion relaxation suggesting that it may occupy and activate the beta 2-adrenoceptor in a manner analogous to salmeterol. 6. CGP 59162, at concentrations up to ten fold molar excess, did not prevent or reduce salmeterol-induced reassertion relaxation. 7. In conclusion these data are not consistent with the existence of a distinct 'exosite' recognising the aliphatic side chain of salmeterol mediating reassertion.
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| 2. |
- Ekelund, Ulf, et al.
(författare)
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In vivo receptor characterization of neuropeptide Y-induced effects in consecutive vascular sections of cat skeletal muscle
- 1997
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Ingår i: British Journal of Pharmacology. - : Wiley. - 1476-5381 .- 0007-1188. ; 120:3, s. 387-392
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Tidskriftsartikel (refereegranskat)abstract
- 1. It has been suggested that the vasoconstrictor response to neuropeptide Y (NPY) is located in the microvessels and that it increases with reduced vessel diameter. The aim of the present study was to analyse quantitatively, on the cat gastrocnemius muscle preparation in vivo, the effects of NPY on total regional vascular resistance (RT) and its distribution to large-bore arterial resistance vessels (> 25 microns; Ra,prox), small arterioles (< 25 microns; Ra,micro) and the veins (Rv). Associated effects on capillary pressure (Pc,v) and fluid exchange were also studied. 2. Close-arterially infused NPY (1-32 micrograms kg-1 min-1) caused a dose-dependent, slowly developing vasoconstriction in all three vascular sections, yet with a preferential action in the small arterioles. At 32 micrograms kg-1 min-1, NPY raised RT by 133 +/- 22%, Ra,prox by 94 +/- 15%, Ra,micro by 277 +/- 104% and Rv by 81 +/- 11%. However, the veins (ED50 = 3.9 +/- 1.2 micrograms kg-1 min-1) were more sensitive to NPY than both large-bore arterial vessels (ED50 = 7.7 +/- 1.6) and small arterioles (ED50 = 7.0 +/- 1.4). NPY decreased Pc,v due to an increase in the pre-to post-capillary resistance ratio. 3. Close-arterial infusions of Pro34NPY and peptide YY evoked vasoconstrictor responses which did not differ from the response to NPY. In contrast, the Y2-preferring C-terminal fragments: Ac-[Leu28, Leu31]-NPY (24-36) and NPY(13-36) were without effect in the muscle vascular bed. The selective NPY Y1 receptor antagonist BIBP3226 (100 micrograms kg-1 min-1, i.a.) abolished the vascular response to NPY. 4. The present findings indicate that the vasoconstrictor response to NPY in skeletal muscle is preferentially located in the small arterioles and mediated via the Y1 receptor and, further, that Y2 and Y3 receptors do not play a significant role in the vasoconstrictor response to NPY in cat skeletal muscle. BIBP3226 was found to be an effective NPY antagonist in vivo and to lack agonist activity.
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| 3. |
- Erlinge, David, et al.
(författare)
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Tyrphostin inhibition of ATP-stimulated DNA synthesis, cell proliferation and fos-protein expression in vascular smooth muscle cells
- 1996
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Ingår i: British Journal of Pharmacology. - 1476-5381. ; 118:4, s. 1028-1034
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Tidskriftsartikel (refereegranskat)abstract
- 1. We and others have shown that extracellular ATP (adenosine triphosphate), released from sympathetic nerves and platelets, stimulates growth of vascular smooth muscle cells (SMC). To study the importance of tyrosine kinases for ATP-mediated proliferation in vascular smooth muscle cells we used tyrphostins, a recently developed group of highly specific inhibitors of tyrosine kinases. 2. ATP induced a powerful concentration-dependent increase in DNA synthesis measured by [3H]-thymidine incorporation in rat aorta SMC (RASMC) and an increase in total cell number after 72 h of incubation as measured by an enzymatic cell proliferation assay. Tyrphostin 25 (10(-5) M) had no effect per se on basal DNA synthesis but reduced ATP-stimulated DNA synthesis and increase in cell number in a dose-dependent manner. Higher concentrations of ATP could not reverse the inhibitory effect of tyrphostin 25. The potency of several (six) other tyrphostins was also examined and found to be slightly greater than tyrphostin 25 with equal efficacy. 3. When RASMC were incubated with 10(-5) M ATP for 2 h, nearly all of the cells (87 +/- 5%) were intensely stained with an antibody to the Fos protein while in the controls only 1 +/- 2% of the cells were weakly stained. Tyrphostin 25 greatly reduced the Fos-protein staining (14 +/- 2%). 4. ATP induced a concentration-dependent increase in 45Ca(2+)-influx and formation of inositol phosphates (IPtotal) in RASMC. These effects were not inhibited by tyrphostin 25. 5. Tyrphostin 25 did not alter ATP-induced contraction in ring segments of rat aorta. 6. In conclusion, tyrphostin 25 inhibited ATP-induced DNA synthesis, cell proliferation and Fos-protein expression, but not ATP-induced 45Ca(2+)-influx, inositolphosphate-production or vasoconstriction. This indicates that the mitogenic effect of ATP on vascular smooth muscle cells is dependent on tyrosine kinases in contrast to the contractile effect of ATP in blood vessels.
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| 4. |
- Hedlund, Petter, et al.
(författare)
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NO synthase in cholinergic nerves and NO-induced relaxation in the rat isolated corpus cavernosum
- 1999
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Ingår i: British Journal of Pharmacology. - : Wiley-Blackwell. - 0007-1188 .- 1476-5381. ; 127:2, s. 349-360
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Tidskriftsartikel (refereegranskat)abstract
- In the rat corpus cavernosum (CC), the distribution of immunoreactivity for neuronal and endothelial NO synthase (nNOS and eNOS), and the pattern of NOS-immunoreactive (-IR) nerves in relation to some other nerve populations, were investigated. Cholinergic nerves were specifically immunolabelled with antibodies to the vesicular acetylcholine transporter protein (VAChT).In the smooth muscle septa surrounding the cavernous spaces, and around the central and helicine arteries, the numbers of PGP- and tyrosine hydroxylase (TH)-IR terminals were large, whereas neuropeptide Y (NPY)-, VAChT-, nNOS-, and vasoactive intestinal polypeptide (VIP)-IR terminals were found in few to moderate numbers.Double immunolabelling revealed that VAChT- and nNOS-IR terminals, VAChT- and VIP-IR terminals, nNOS-IR and VIP-IR terminals, and TH- and NPY-IR terminals showed coinciding profiles, and co-existence was verified by confocal laser scanning microscopy. TH immunoreactivity was not found in VAChT-, nNOS-, or VIP-IR nerve fibres or terminals.An isolated strip preparation of the rat CC was developed, and characterized. In this preparation, cumulative addition of NO to noradrenaline (NA)-contracted strips, produced concentration-dependent, rapid, and almost complete relaxations. Electrical field stimulation of endothelin-1-contracted preparations produced frequency-dependent responses: a contractile twitch followed by a fast relaxant response. After cessation of stimulation, there was a slow relaxant phase. Inhibition of NO synthesis, or blockade of guanylate cyclase, abolished the first relaxant phase, whereas the second relaxation was unaffected.The results suggest that in the rat CC, nNOS, VAChT-, and VIP-immunoreactivities can be found in the same parasympathetic cholinergic neurons. Inhibitory neurotransmission involves activation of the NO-system, and the release of other, as yet unknown, transmitters.
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| 5. |
- Hedlund, Petter, et al.
(författare)
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Pituitary adenylate cyclase-activating polypeptide, helospectin, and vasoactive intestinal polypeptide in human corpus cavernosum
- 1995
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Ingår i: British Journal of Pharmacology. - 0007-1188 .- 1476-5381. ; 116:4, s. 2258-2266
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Tidskriftsartikel (refereegranskat)abstract
- 1. The distribution and effects of pituitary adenylate cyclase-activating polypeptide (PACAP-27 and -38), helospectin (Hel-1 and Hel-2), and vasoactive intestinal polypeptide (VIP), were investigated in isolated preparations of human corpus cavernosum (CC). 2. Immunohistochemistry revealed coinciding profiles of nerve structures that showed immunoreactivities for VIP and PACAP, and VIP and Hel. Confocal microscopy showed the co-existence of VIP- and PACAP-immunoreactivities, and VIP- and Hel-immunoreactivities in most (90%) varicose nerve structures. 3. As determined by radioimmunoassay, the amounts of VIP, PACAP-27, and PACAP-38 in the preparations were 61.7 +/- 11.6, 0.1 +/- 0.05, and 3.7 +/- 0.5 pmol g-1 wet weight of tissue (pmol g-1 wet wt.), respectively. In tissue from patients with diabetes, the content of VIP was lower (13.7 +/- 0.5 pmol g-1 wet wt.), whereas that of PACAP (-27 and -38) was unchanged. 4. Cyclic nucleotide levels were determined in preparations exposed to PACAP-27, PACAP-38, Hel-1, Hel-2, and VIP. All the peptides, but Hel-2, significantly increased the concentrations of cyclic AMP, whereas the levels of cyclic GMP were unchanged. 5. The peptides concentration-dependently relaxed noradrenaline-contracted preparations. The order of potency was VIP > PACAP 27 > Hel-1 > Hel-2 > PACAP-38. 6. Hel-1, VIP and PACAP-27 effectively counteracted electrically induced contractions. At 10(-6) M, the highest peptide concentration used, the inhibitory effects obtained reached 96 +/- 3%, 87 +/- 6%, and 80 +/- 3%, respectively. 7. The results suggest that PACAP and Hel-1 are co-localized with VIP in nerve structures within the human cavernous tissue, and that the peptides are effective relaxants of CC preparations in vitro. The role of the investigated peptides for penile erection remains to be established.
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| 6. |
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| 7. |
- Larsson, Susanne, et al.
(författare)
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IL-2 and IL-4 counteract budesonide inhibition of GM-CSF and IL-10, but not of IL-8, IL-12 or TNF-alpha production by human mononuclear blood cells
- 1999
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Ingår i: British Journal of Pharmacology. - : Wiley. - 1476-5381 .- 0007-1188. ; 127:4, s. 980-986
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Tidskriftsartikel (refereegranskat)abstract
- 1. The combination of interleukin-2 (IL-2) and IL-4 reduces the inhibitory effects of glucocorticoids on granulocyte-macrophage colony-stimulating factor (GM-CSF) production, in agreement with the hypothesis that this combination causes glucocorticoid resistance. Whether a general cytokine resistance to glucocorticoids is induced by IL-2 and IL-4 has not been reported. 2. Mononuclear blood cells from healthy individuals were pre-treated with IL-2, IL-4, or IL-2+ IL-4 (31.3-500 U ml(-1)) for 48 h, prior to lipopolysaccharide (LPS; 10 ng ml(-1); 20 h) and budesonide addition. Cytokine levels in the supernatants were analysed using specific immunoassays. DNA content was analysed to estimate cell numbers. 3. GM-CSF production was totally inhibited by budesonide at 10(-8) M in vehicle treated cultures, while IL-10 was inhibited to 33.4+/-4.3% of control. IL-2, IL-4, or IL-2 + IL-4 reduced the inhibitory effects of budesonide on GM-CSF to similar levels (23.7 6.7, 31.6+/-8.5 and 35.1+/-4.3% of control, respectively). IL-2, IL-4, or IL-2 + IL-4 also reduced the inhibitory effects of budesonide on IL-10 production (46.5+/-6.6, 55.9+/-7.3%, and 68.3+/-9.9% of control, respectively). In contrast, IL-8, IL-12 and TNF-alpha production did not become resistant to budesonide. 4. Thus, glucocorticoid resistance induced by IL-2 and IL-4 is not general at the cytokine production level. While the glucocorticoid sensitivity of GM-CSF and IL-10 production decreased, the sensitivity of IL-8, IL-12 or TNF-alpha production was unchanged. Also, the mixture of IL-2 and IL-4 is not crucial for induction of glucocorticoid resistance of GM-CSF production.
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| 8. |
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| 9. |
- Malmsjö, Malin, et al.
(författare)
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P2U-receptor mediated endothelium-dependent but nitric oxide-independent vascular relaxation
- 1998
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Ingår i: British Journal of Pharmacology. - : Wiley. - 1476-5381 .- 0007-1188. ; 123:4, s. 719-729
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Tidskriftsartikel (refereegranskat)abstract
- 1. The dilator effect of extracellular adenosine triphosphate (ATP) has mainly been characterized as a direct effect on smooth muscle or as an endothelium-dependent effect mediated by nitric oxide (NO) or prostaglandins. We tested the hypothesis that endothelium-derived hyperpolarizing factor (EDHF) may also be involved. Dilator effects were studied in vitro by continuous recording of isomeric tension in cylindrical segments of rat blood vessels precontracted by noradrenaline (NA), in the presence of indomethacin (10 microM). 2. By screening different blood vessels in the rat we found that both acetylcholine (ACh) and ATP dilate mesenteric arteries with a resting tone of 1 mN by an endothelium-dependent non-NO mechanism. With an increased resting tone (4 mN) the dilatation was mediated by NO. Thus by varying the resting tension the different dilator mechanisms could be examined. However, in the carotid artery the dilatation was solely mediated by an endothelium-dependent NO mechanism, even at different resting tones (1 and 4 mN). 3. The N-nitro-L-arginine methyl ester (L-NAME)-resistant dilatation to ACh and ATP was further inhibited by the NO-scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), indicating L-NAME insensitive NO-synthesis. 4. In carotid arteries and mesenteric arteries at high resting tones (4 mN) the ATP-dilatation was totally inhibited by endothelium removal or L-NAME (10(-3) M). In mesenteric arteries at low resting tone (1 mN) the ATP, UTP (uridine-triphosphate) and 2-MeSATP (2methylthioATP)-dilatation was totally inhibited by endothelium removal. However, L-NAME in combination with indomethacin attenuated only 5% of the UTP dilatation, 70% of the ATP dilatation but all of the 2-MeSATP-dilatation. The inhibitors of Ca2+-activated K+ channels charybdotoxin (0.5 x 10(-7) M) together with apamin (10(-6) M), and the cytochrome P450 inhibitor, SKF 525A (10(-4) M), each in combination with indomethacin. L-NAME and PTIO (0.5 x 10(-3) M) totally abolished the remaining ATP and UTP-dilatation. This indicates a dilatation mediated by an endothelium-dependent non-NO factor, probably EDHF. 5. Agonist potency (UTP>ATP>>2-MeSATP), indicates that the EDHF-mediated dilatation was stimulated by a P2U-receptor, possibly by a selective pyrimidine-receptor. In contrast, a P2Y-receptor stimulated NO-mediated dilatation (2-MeSATP=ATP>UTP). 6. In conclusion, the dilator effects of ATP and especially UTP can be mediated by an endothelium-dependent non-NO-mediated mechanism, probably EDHF, mediated by a P2U-receptor, possibly a selective pyrimidine-receptor, while NO-mediated dilatation is stimulated mainly by a P2Y1-receptor. Furthermore, the EDHF-dilatation is dependent on the resting tone of the blood vessel.
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| 10. |
- Wallerstedt, Susanna, et al.
(författare)
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Differential effect of propofol on sympathetic neurotransmission in isolated human omental arteries and veins
- 1998
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Ingår i: British Journal of Pharmacology. - : Wiley. - 1476-5381 .- 0007-1188. ; 125:1, s. 120-126
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Tidskriftsartikel (refereegranskat)abstract
- 1. The present study was undertaken to elucidate the effect of propofol on sympathetic neurotransmission in isolated human omental vessels. 2. Segments of both arteries and veins were exposed to 0, 10(-7), 10(-6), 10(-5) or 10(-4)M propofol, and studied in vitro to determine effects on: (i) isometric tension after electrical field stimulation (EFS) or after exogenous administration of noradrenaline (NA); (ii) EFS-stimulated release of [3H]-NA from vessel segments preincubated with [3H]-NA; (iii) uptake of [3H]-NA. 3. Propofol at 10(-6) M enhanced EFS-induced contraction in artery segments, 10(-7) and 10(-5) M had no effect, and 10(-4) M propofol depressed EFS-induced contraction in both artery and vein segments. 4. Propofol did not affect the response to exogenous NA in artery and vein segments. 5. EFS-stimulated release of [3H]-NA was depressed by 10(-5) and 10(-4) M propofol in artery segments, and by 10(-4) M in vein segments. 6. Uptake of [3H]-NA was depressed by 10(-6)-10(-4) M propofol in artery but not in vein segments. 7. The results suggest that sympathetic neurotransmission is enhanced at clinical concentrations (10(-6) M) of propofol in human omental arteries, but not veins. This may be due to an increased availability of NA in the neuromuscular junction resulting from a reduced presynaptic reuptake. Propofol at probably supraclinical concentrations (10(-5)-10(-4) M) impairs the sympathetic neurotransmission in both human omental arteries and veins, probably due to an inhibitory effect on the NA release from the sympathetic nerves.
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| 11. |
- Wallerstedt, Susanna M, et al.
(författare)
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Endothelium-dependent relaxation by substance P in human isolated omental arteries and veins: relative contribution of prostanoids, nitric oxide and hyperpolarization
- 1997
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Ingår i: British Journal of Pharmacology. - : Wiley. - 1476-5381 .- 0007-1188. ; 120:1, s. 25-30
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Tidskriftsartikel (refereegranskat)abstract
- 1. The objective of the present study was to investigate human omental arteries and veins with respect to: (i) the contractile effect of the thromboxane A2 analogue U46619, (ii) endothelium-dependency and mediators of the relaxing effect of substance P (SP) and acetylcholine (ACh). 2. Changes in isometric tension in response to administration of U46619, SP and ACh were measured in human isolated omental arteries and veins with and without endothelium. To investigate the mechanism of action of SP, the SP-induced relaxation was measured in the presence of indomethacin (cyclo-oxygenase inhibitor), NG-monomethyl-L-arginine (L-NMMA, nitric oxide-synthase inhibitor), KCl (inhibitor of endothelium-dependent hyperpolarization), tetraethylammonium (TEA; non-selective inhibitor of K(+)-channels, with some preference for the high conductance Ca(2+)-activated K(+)-channel, BKCa), glibenclamide (inhibitor of the ATP-sensitive K(+)-channel) and/or clotrimazole (inhibitor of the cytochrome P450-system and the intermediate conductance Ca(2+)-activated K(+)-channel, IKCa). 3. U46619 contracted both the artery and the vein segments. Endothelium removal did not alter the contraction. 4. ACh caused neither contraction nor relaxation in artery and vein segments precontracted with U46619. 5. In both artery and vein segments precontracted with U46619, SP produced endothelium-dependent relaxation. The relaxation was unaffected by indomethacin, but was incompletely reduced by L-NMMA and KCl respectively. The L-NMMA-resistent relaxation was abolished in the presence of KCl. 6. TEA inhibited the SP-induced relaxation in artery and vein segments both in the presence and absence of L-NMMA and indomethacin, while glibenclamide and clotrimazole had no effect. 7. In conclusion, the SP-induced relaxation in human omental arteries and veins seems to be mediated via NO and endothelium-dependent hyperpolarization. KATP and IKCa are probably not involved in the hyperpolarization, but activation of BKCa may contribute to the hyperpolarization. Prostanoid synthesis and the cytochrome P450-system are probably not involved in the SP-induced relaxation in this area.
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| 12. |
- Werkström, Viktoria, et al.
(författare)
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Carbon monoxide-induced relaxation and distribution of haem oxygenase isoenzymes in the pig urethra and lower oesophagogastric junction
- 1997
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Ingår i: British Journal of Pharmacology. - : Wiley. - 1476-5381 .- 0007-1188. ; 120:2, s. 312-318
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Tidskriftsartikel (refereegranskat)abstract
- 1. The distribution of the carbon monoxide (CO) producing enzymes haem oxygenase (HO)-1 and -2 was studied by immunohistochemistry in the pig's lower urinary tract, including bladder extramural arteries, and the oesophagogastric junction (OGJ). In isolated smooth muscle from the urethra and the OGJ, the mechanisms for CO-induced relaxations were characterized by measurement of cyclic nucleotide levels and by responses to the guanylate cyclase inhibitor methylene blue and some K+ channel inhibitors. 2. HO-2 immunoreactivity was observed in coarse nerve trunks within the smooth muscle of the urethra and OGJ, and in nerve cell bodies of the enteric plexuses of the OGJ. Furthermore, the vascular endothelium of the intramural vessels of the urethra, bladder and OGJ, and the extramural vessels of the bladder, displayed HO-2 immunoreactivity. Two different antisera against HO-1 were used, but only one displayed immunoreactivity in neuronal structures. HO-1 immunoreactivity, as displayed by this antiserum, was seen in nerve cells, coarse nerve trunks and varicose nerve fibres in the smooth muscle of the urethra and OGJ. Some HO-2 and/or HO-1 (as displayed by both HO-1 antisera) immunoreactive cells with a non-neuronal appearance were observed within the smooth muscle of the OGJ, bladder and urethra. 3. In the urethral preparations, exogenously applied CO (72 microM) evoked a relaxation amounting to 76 +/- 6%. The relaxation was associated with an increase in cyclic GMP, but not cyclic AMP, content. CO-evoked relaxations were not significantly reduced by treatment with methylene blue, or by inhibitors of voltage-dependent (4-aminopyridine), high (iberiotoxin, charybdotoxin) and low (apamin) conductance Ca(2+)-activated, and ATP-sensitive (glibenclamide) K+ channels. Bladder strips, and ring preparations from the extramural arteries of the bladder, did not respond to exogenously administered CO (12-72 microM). 4. In the OGJ, exogenously applied CO evoked a relaxation of 86 +/- 6%, which was associated with an increase in cyclic GMP, but not cyclic AMP, content. Treatment with 30 microM methylene blue raised the spontaneously developed muscle tone, and reduced the maximum relaxation evoked by CO to 33 +/- 9%. Addition of 4-aminopyridine, apamin, glibenclamide, iberiotoxin, charybdotoxin or glibenclamide had no effect on the relaxations. 4-aminopyridine (0.1-1 mM), iberiotoxin (0.1 microM) and charybdotoxin (0.1 microM) increased the spontaneously developed tone, and a combination of charybdotoxin and apamin reduced CO-induced (24 microM CO) relaxations. 5. The present findings demonstrate the presence of HO in both neuronal and non-neuronal cells in the pig OGJ and lower urinary tract. CO produces relaxation of the smooth muscle in the OGJ and urethra, associated with a small increase in cyclic GMP concentration in both regions. Relaxations evoked by CO in the urethra do not seem to involve voltage-dependent, low and high conductance, or ATP-dependent K+ channels. However, in the OGJ relaxations evoked by CO can be attenuated by methylene blue and a combination of charybdotoxin and apamin.
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| 13. |
- Werkström, Viktoria, et al.
(författare)
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Factors involved in the relaxation of female pig urethra evoked by electrical field stimulation
- 1995
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Ingår i: British Journal of Pharmacology. - 1476-5381. ; 116:1, s. 1599-1604
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Tidskriftsartikel (refereegranskat)abstract
- 1 Non-adrenergic, non-cholinergic (NANC) relaxations induced by electrical field stimulation (EFS)were studied in pig isolated urethra. The mechanism for relaxation was characterized by measurement of cyclic nucleotides and by study of involvement of different subsets of voltage-operated calcium channels (VOCCs). 2 EFS evoked frequency-dependent and tetrodotoxin-sensitive relaxations in the presence of propranolol (1 yM), phentolamine (1 pM) and scopolamine (1 pM). At low frequencies (< 12 Hz), relaxations were rapid, whereas at high (> 12 Hz) frequencies distinct biphasic relaxations were evoked. The latter consisted of a rapidly developing first phase followed by a more long-lasting second phase. 3 Treatment with the NO-synthesis inhibitor N0-nitro-L-arginine (L-NOARG; 0.3 mM) inhibited relaxations at low frequencies of stimulation. At high frequencies (> 12 Hz) only the first relaxation phase was affected. 4 Measurement of cyclic nucleotides in preparations subjected to continuous nerve-stimulation, revealed an increase in guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels from 1.3 ± 0.3 to 3.0±0.4 pmol mg'- protein (P<0.01). In the presence of L-NOARG, there was a significant decrease in cyclic GMP content to control. However, there was no increase in cyclic GMP content in response to EFS. Levels of cyclic AMP remained unchanged following EFS. 5 Treatment with the N-type VOCC-inhibitor, wo-conotoxin GVIA (0.1 FM) reduced NO-dependent relaxations, the effect being most pronounced at low frequencies (1-4 Hz) of stimulation. The NOindependent second phase of the relaxation, studied in the presence of L-NOARG (0.3 mM) at 16- 30 Hz, was however markedly reduced or abolished by w-conotoxin GVIA. w-Conotoxin MVIIC (1 pM)or w-agatoxin IVA (30 nM) had no effect on electrically evoked relaxations. 6 These results suggest that NANC-nerve derived urethral relaxation in the pig consists of two apparently independent components. One is mediated by NO and associated with an increase in cyclic GMP content. The other mediator is unknown and produces relaxations not associated with changes in levels of cyclic nucleotides. The release of this mediator seems to involve the N-type VOCC, since the relaxation was markedly reduced or abolished by w-conotoxin GVIA.
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| 14. |
- Werkström, Viktoria, et al.
(författare)
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NANC transmitters in the female pig urethra--localization and modulation of release via alpha 2-adrenoceptors and potassium channels
- 1997
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Ingår i: British Journal of Pharmacology. - : Wiley. - 1476-5381 .- 0007-1188. ; 121:8, s. 1605-1612
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Tidskriftsartikel (refereegranskat)abstract
- 1. To investigate further the release, localization and identity of a non-nitrergic mediator of smooth muscle relaxation in the female pig urethra, we studied the effects of drugs acting at alpha 2-adrenoceptors or K+ channels, the effects of capsaicin and chemical sympathectomy, and the actions of several transmitter candidates. 2. Electrical field stimulation (EFS; frequencies above 12 Hz) of spontaneously contracted smooth muscle strips from the female pig urethra evoked long-lasting, frequency-dependent relaxations in the presence of prazosin, scopolamine, and NG-nitro-L-arginine. Treatment with the selective alpha 2-adrenoceptor agonist UK-14 304 markedly reduced the relaxations evoked by EFS at all frequencies tested (16-30 Hz). The inhibitory effect of UK-14 304 was completely antagonized by the alpha 2-adrenoceptor antagonist rauwolscine. The muscarinic M1 receptor antagonist, pirenzepine, or exogenously administered carbachol, did not have any effects on the electrically evoked relaxations. 3. Inhibition of high conductance Ca2+ activated K+ channels by iberiotoxin or charybdotoxin significantly enhanced the relaxations evoked by EFS at all frequencies. However, inhibition of voltage-sensitive K+ channels with 4-aminopyridine or dendrotoxin-1, treatment with the ATP-sensitive K+ channel blocker, glibenclamide, or treatment with the high and low conductance Ca2+ activated K+ channel blockers, tetraethylammonium chloride and apamin, had no effect on the relaxations evoked by EFS. 4. Electrically evoked relaxations were not affected by adrenergic denervation with 6-hydroxydopamine (6-OHDA) at any frequency. However, treatment with 6-OHDA abolished prazosin-sensitive electrically induced contractions, and a long-lasting relaxation was revealed. Treatment with capsaicin, believed to damage selectively a subpopulation of primary afferent fibres, did not affect basal tone or relaxations evoked by EFS. 5. Exogenously applied vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP)-27, PACAP-38, adenosine, ATP and 5-hydroxy-tryptamine caused relaxations of the urethral preparations, whereas prostaglandin E2 and calcitonin gene-related peptide had no effects. VIP 10-28, alpha, beta-methylene-ATP, reactive blue-2, suramin or indomethacin did not reduce the electrically-evoked relaxations at any frequency. However, the relaxations were slightly reduced by trypsin or alpha-chymotrypsin. 6. The present results suggest that the release of the unknown mediator in the female pig urethra can be modulated via alpha 2-adrenoceptors and high conductance Ca2+ activated K+ channels. Furthermore, the mediator does not appear to be localized to or released from adrenergic or capsaicin-sensitive sensory nerve-endings. The identity of the transmitter remains to be established.
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| 15. |
- Åkesson, Björn, et al.
(författare)
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Interaction of the islet nitric oxide system with L-arginine-induced secretion of insulin and glucagon in mice
- 1996
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Ingår i: British Journal of Pharmacology. - 1476-5381. ; 119:4, s. 758-764
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Tidskriftsartikel (refereegranskat)abstract
- 1. Several recent in vitro studies have suggested that production of nitric oxide (NO) from the islet NO system may have an important regulatory influence on the secretion of insulin and glucagon. In the present paper we have investigated, mainly with an in vivo approach, the influence and specificity of the NO synthase (NOS) blocker NG-nitro-L-arginine methyl ester (L-NAME) on L-arginine-induced secretion of insulin and glucagon. 2. In freely fed mice, L-NAME pretreatment (1.2 mmol kg-1) influenced the dynamics of insulin and glucagon release following an equimolar dose of L-arginine, the specific substrate for NOS activity, in that the NOS inhibitor enhanced the insulin response but suppressed the glucagon responses. This was reflected in a large decrease in the plasma glucose levels of the L-NAME pretreated animals. 3. L-NAME pretreatment did not influence the insulin and glucagon secretory responses to the L-arginine-enantiomer D-arginine, which cannot serve as a substrate for NOS activity. 4. Replacing L-NAME pretreatment by pretreatment with D-arginine or L-arginine itself, which both carry the same cationic change and are devoid of NOS inhibitory properties, did not mimic the effects of L-NAME on L-arginine-induced hormone release. 5. Fasting the animals for 24 h totally abolished the L-NAME-induced potentiation of L-arginine stimulated insulin release suggesting that the sensitivity of the beta-cell secretory machinery to NO-production is greatly changed in the fasting state. However, the L-NAME-induced suppression of L-arginine stimulated glucagon release was unaffected by starvation. 6. In isolated islets from freely fed mice, L-arginine (5 mM) stimulated insulin release was greatly enhanced and glucagon release markedly suppressed by the presence of the NOS inhibitor L-NAME in the incubation medium. These effects were abolished in isolated islets taken from 24 h fasted mice. 7. Our present results, which showed that the NOS inhibitor L-NAME markedly enhances insulin release but suppresses glucagon release induced by L-arginine in the intact animal, give strong support to our previous hypothesis that the islet NO system is a negative modulator of insulin secretion and a positive modulator of glucagon secretion. Additionally, we observed that the importance of the beta-cell NO-production for secretory mechanisms, as evaluated by the effect of L-NAME on L-arginine-induced insulin release, was greatly changed after starvation, an effect less prominent with regard to glucagon release.
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