Autonomic and Autacoid Pharmacology最新文献

1 The magnitude of responses to prostaglandin F_2α (PGF_2α) and adenosine (ADO) in pressurized rabbit epicardial coronary arteries (367 ± 44 μm o.d.) with intact endothelium was assessed when they developed spontaneous tone.

2 The arteries were cannulated and changes in arterial diameter registered with an automated video perfusion system. The vessels, in the stabilization period at 60 mmHg, were divided into two groups, one exposed to a longitudinal stretch of +20% of unstretched initial length (Lo), and the other to +35% Lo, which developed spontaneous tone. In both cases, diameter–pressure curves were obtained by changing the intravascular pressure from 30 to 120 mmHg in aleatory steps of 30 mmHg (dp/dt = 15 mmHg s⁻¹).

3 Diameter reduction of the arteries with stretch of +35% Lo in response to 1 μm PGF_2α was greater than that with stretch of +20% Lo. Likewise, increase of the arteries that had +35% Lo in response to 1 μm ADO was greater than with +20% Lo.

4 Intravascular flow (40 μl min⁻¹) increased the tone level of arteries. The addition of PGF_2α enhanced this tone which was similar to that obtained with a stretch of +35% Lo and no flow, whereas the effect of ADO was increased.

5 These data indicate that the vasomotor responses of PGF_2α and ADO are modulated by the degree of longitudinal stretch in epicardial arteries.

1 The aim of the study was to test the hypothesis that the offset of action of β-adrenoceptor antagonists on the heart is related to their lipophilicity, with low and highly lipophilic drugs having a rapid and slow offset, respectively. The effects of β-blockers with low (atenolol), moderate (celiprolol), high (propranolol) and very high (bopindolol) lipophilicity on the contractile responses of the rat right ventricle to isoprenaline were determined.

2 Atenolol at 10⁻⁻⁶ and 10⁻⁻⁵ m, celiprolol at 10⁻⁻⁷, 10⁻⁻⁶ and 10⁻⁻⁵ m, propranolol at 10⁻⁻⁸, 10⁻⁻⁷ and 10⁻⁻⁶ m and bopindolol at 2 × 10⁻⁻⁹ and 10⁻⁻⁸ m caused parallel rightward shifts of the isoprenaline response curves with no effect on maximum responses. The Schild plots for atenolol, celiprolol and propranolol had slopes that were not significantly different from 1, which is indicative of competitive reversible antagonism. The pK_B values were 7.33, 7.78, and 8.79 for atenolol, celiprolol, and propranolol, respectively. The Schild plot for bopindolol had a slope that was significantly greater than 1.

3 Our hypothesis is supported as the effects of propranolol and bopindolol were more slowly offset than those of atenolol and celiprolol. Thus, the concentration-ratio of 141 in the presence of atenolol at 10⁻⁻⁵ m was reduced to 4 after the first wash, whereas the ratio of 100 in the presence of propranolol at 10⁻⁻⁷ m was only reduced to 45 after a similar wash. The ratio of 54 with celiprolol at 10⁻⁻⁶ m was reduced to 5, whereas the ratio of 70 with bopindolol at 10⁻⁻⁸ m was only reduced to 28 by the first wash.

4 The effects of bopindolol were very slowly or not reversible over two washes in the absence or presence of atenolol at 10⁻⁻⁶ m. It is suggested that bopindolol is a very slowly reversible β-blocker, and that this contributes to its slow offset of action.

1 Possible effects of new and conventional H₃-receptor antagonists towards various non-histaminergic receptors (α₂-adrenergic, 5-HT₃-serotonin, μ-opiate, A₁-adenosine, M₁-and M₃-muscarinic) involved in neurogenic and myogenic contractile responses of guinea-pig ileum are investigated.

2 When the isolated ileum was contracted by the 5-HT₃ receptor agonist, 2-methyl-5-HT (5 × 10⁻⁻⁷–8 × 10⁻⁻⁶ m), acetylcholine (1 × 10⁻⁻⁹–1 × 10⁻⁻⁷ m), KCl (3 × 10⁻⁻² m) or electrical stimulation some of the drugs, included thioperamide and clobenpropit, reduced the contractile response when tested at micromolar concentrations (1–3 × 10⁻⁻⁵ m) (only compound IV exhibited an M₃ competitive antagonism with a pK_B = 5.49 ± 0.18).

3 Ileal twitch responses to electrical stimulation were dose-dependently inhibited by the selective agonists clonidine (3 × 10⁻⁻¹⁰–1 × 10⁻⁻⁷ m), dermorphin (1 × 10⁻⁻¹¹–1 × 10⁻⁻⁸ m), R-N⁶-(2-phenylisopropyl)-adenosine (1 × 10⁻⁻⁹–3 × 10⁻⁻⁸ m) and McN-A-343 (1 × 10⁻⁻⁷–1 × 10⁻⁻⁵ m) with different potencies and comparable efficacy (spike amplitude reduction > 85%). All the H₃ antagonists under study (up to 1 × 10⁻⁻⁵ m) showed no or minor interactions at the neuronal sites except the compound V which behaved as a weak competitive antagonist at α₂-adrenoreceptors (pK_B = 5.96 ± 0.06).

4 In conclusion, both new and conventional H₃-blockers interacted at the enteric neuronal sites here studied with a 1000–30 000 fold lower antagonistic potency than that previously reported for the ileal H₃ histamine receptors. Their spasmolytic activity precludes firm conclusions about the non-competitive interaction with 5-HT₃ ileal receptor which requires further investigations.

1 The properties of β-adrenoceptors mediating vascular relaxation in rat isolated carotid artery were investigated. Ring segments of arteries were preconstricted with the thromboxane A₂ receptor agonist U-46619 and relaxation to β-adrenoceptor agonists determined.

2 Isoprenaline produced a concentration-dependent relaxation of U-44619-constricted arteries. The concentration-response curve (CRC) to isoprenaline was shifted to the right by propranolol (1 μm) although the shift was less (105 fold; pA₂, 8.02) than would be expected for an effect of isoprenaline at classical β-adrenoceptors (300–1000 fold; pA₂, 8.5–9). L-NAME (100 μm) significantly reduced responses to isoprenaline, lowering the slope of the CRC and reducing the maximum response.

3 The selective β₃-adrenoceptor agonists, BRL 37344 and ZD2079, also produced concentration-dependent relaxation of the arteries. L-NAME (100 μm) shifted the BRL 37344 CRC to the right 15 fold with no reduction in the slope or maximum response. L-NAME (100 μm) had no significant effect on the ZD2079 CRC.

4 In conclusion, relaxation to isoprenaline in rat carotid artery is inhibited by propranolol in a manner suggesting a mixed population of classical (β₁-/β₂-) and atypical (β₃-) adrenoceptors. The presence of β₃-adrenoceptors was confirmed by the relaxant effects of the selective β₃-adrenoceptor agonists BRL 37344 and ZD2079. L-NAME attenuated responses to both isoprenaline and the β₃-adrenoceptor agonist BRL 37344, suggesting a role for endothelial release of nitric oxide in β-adrenoceptor mediated relaxation. However, the relaxant effect of BRL 37344 was attenuated by L-NAME to a lesser extent than that of isoprenaline. In addition, L-NAME had no effect on relaxation induced by ZD2079. These results suggest that there may be a differential contribution of endothelium to classical β-and β₃-adrenoceptor-mediated effects, with endothelium contributing less to β₃-adrenoceptor-mediated relaxation.

1 The effects on ATP breakdown of some modulators of adenosine transport or metabolism were studied in the rat colon muscularis mucosae, a tissue which contracts to ATP and is thought to contain P2Y₁ receptors. The compounds tested were the xanthine oxidase inhibitor allopurinol, the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and the adenosine uptake blocker S-(4-nitrobenzyl)-6-thioinosine (NBTI).

2 The degradation of adenosine 5′-triphosphate (ATP) (100 μm) and the appearance of metabolites was followed by high pressure liquid chromatography during incubation of isolated tissue preparations alone or in the presence of the drugs, following preincubation with the drugs for 1 h.

3 In the absence of drugs ATP was rapidly degraded by the rat colon muscularis mucosae with a half-life of 6.1 ± 0.7 min, the major breakdown product being inosine rather than adenosine. Allopurinol (1 μm) and NBTI (10 μm) had no effect on the rate of breakdown of ATP or on the pattern of metabolites produced. EHNA (1 or 10 μm) also had no effect on the half-life of ATP, but in the presence of EHNA (1 μm) the rate of production of inosine was significantly reduced and some adenosine was detected, while in the presence of 10 μm EHNA the production of inosine was abolished and adenosine became the final breakdown product.

4 These results indicate that allopurinol (1 μm) and NBTI (10 μm) have no detectable effect on extracellular purine metabolism in this tissue, and that the build-up of adenosine produced by treatment with EHNA does not have a feedback effect on ATP breakdown.

1 The effects of adrenergic drugs on the formation and resolution of cerebral oedema in a rat model of cold-induced vasogenic brain oedema were studied. Evans blue dye extravasation, water content and ultrastructural alterations (pinocytotic vesicle formation in capillary endothelial cells and apparent water accumulation in the brain parenchyma) were evaluated in parietal cortex.

2 Previous administration of the α-adrenoceptor antagonist phenoxybenzamine produced a reduction of Evans blue extravasation and water content, diminished vesicle formation and reduced water accumulation. Previous administration of the β₂-adrenoceptor agonist clenbuterol reduced Evans blue extravasation and water content, but did not change vesicle frequency.

3 The effects of clenbuterol on Evans blue passage to the brain were blocked by timolol (β-adrenoceptor antagonist) but not by metoprolol (selective β₁-adrenoceptor antagonist). When given after the application of cold, clenbuterol was also able to reduce Evans blue and water content in the brain. Isoprenaline (β-adrenoceptor agonist that does not cross the blood–brain barrier) showed a reduction in Evans blue extravasation only when given intracerebroventricularly. Vinblastine (a drug that prevents vesicle formation) produced a reduction of the amount of pinocytotic vesicles.

4 We conclude that there is an influence of the central adrenergic nervous system on the formation and/or resolution of vasogenic brain oedema and that the alterations on water movement and Evans blue transport mediated by adrenergic drugs seem to be due, at least in part, to alterations of pinocytotic activity in capillary endothelial cells.

1 The present study was undertaken to investigate the influence of the airway epithelium on the release of acetylcholine (ACh) from parasympathetic nerves of the rat trachea. Epithelium-intact and epithelium-denuded preparations of rat trachea were incubated with [³H]-choline to incorporate [³H]-ACh into the cholinergic transmitter stores. Release of radiolabelled transmitter ACh was evoked by electrical field stimulation (60 s trains of 1 ms pulses, 5 Hz, 15 V).

2 Field stimulation both of epithelium-intact and epithelium-denuded radiolabelled tracheal preparations evoked an increase in the efflux of radioactivity; however, the mean stimulation-induced (S-I) efflux from epithelium-denuded preparations (2932 ± 190 d.p.m., n=9) was approximately 60% of that from epithelium-intact preparations (4802 ± 820 d.p.m., n=11). We have shown previously that, in epithelium-intact (but not epithelium-denuded) tracheal preparations, a substantial proportion of the S-I efflux is resistant to tetrodotoxin (1 μM) and to the removal of extracellular Ca²⁺, indicating that much of the S-I efflux is not caused by exocytotic release of neuronal [³H]-ACh. In epithelium-denuded tracheal preparations, superfused individually, phosphorylcholine (1 and 100 μM) did not alter S-I efflux. In epithelium-intact tracheal preparations, both in the absence and in the presence of atropine (1 μM), neither N^G-nitro- L-arginine (100 μM), superoxide dismutase (100 units ml⁻¹), indomethacin (10 μM), capsaicin (30 μM) nor α-chymotrypsin (1 unit ml⁻¹) altered S-I efflux.

3 Experiments were also performed using two tracheal preparations superfused in series. When unlabelled epithelium-intact preparations were present in the upper chamber (superfused first), the S-I efflux from radiolabelled epithelium-denuded preparations in the lower chamber (superfused second) did not differ significantly from radiolabelled epithelium-denuded preparations superfused individually. Moreover, there was no significant difference in the S-I efflux from radiolabelled epithelium-denuded preparations in the lower chamber between experiments in which the upper chamber contained epithelium-intact or epithelium-denuded preparations.

4 Field stimulation of epithelium-intact tracheal preparations in the upper chamber with 90, 120 and 300-s periods (trains of 1 ms pulses, 5 Hz, 15 V) did not significantly alter the S-I efflux from radiolabelled epithelium-denuded tracheal preparations in the lower chamber.

5 When introduced into the upper (unlabelled epithelium-intact) and subsequently allowed to superfuse the lower (radiolabelled epithelium-denuded) tracheal preparations, the stable cholinomimetic carbachol (3 μM) markedly reduced the S-I efflux w

1 Electromechanical coupling in smooth muscle serves to coordinate the contractile activity of the syncytium. Electrical activity of smooth muscle of the gut is generated by ionic conductances that regulate and in turn are regulated by the membrane potential of smooth muscle cells. This activity determines the extent of Ca²⁺ entry into smooth muscle cells, and thus, the timing and intensity of contractions. 2 Potassium channels play an important role in regulating the excitability of the syncytium. The different types of K⁺ channel are characterized by different sensitivities to membrane potential, to intracellular Ca²⁺ levels and to modulation by agonists. 3 This review highlights the different types of K⁺ channels found in gut smooth muscle and describes their possible roles in regulating the electrical activity of the muscle.

1 The present study was carried out to further investigate the nature of the β-adrenoceptor in rabbit jejunum using BRL 37344, a selective β₃-adrenoceptor agonist, cyanopindolol, a β-adrenoceptor antagonist with blocking activity at β₃-adrenoceptors and SR 59230A, a new selective β₃-adrenoceptor antagonist.

2 Isoprenaline produced a concentration-dependent inhibition of the spontaneous contractions of rabbit jejunum with a pD₂ of 7.14. Propranolol (1 μm) shifted the isoprenaline concentration-response curve (CRC) to the right with a concentration-ratio of 5.85, considerably less than would be expected for an action at classical β-adrenoceptors (estimated pA₂ 6.66).

3 BRL 37344 also produced a concentration-dependent inhibition of spontaneous contractions with a pD₂ of 7.41. The BRL 37344 CRC was unaffected by propranolol (1 μm).

4 In the presence of propranolol (1 μm), cyanopindolol (1 μm) shifted the isoprenaline CRC to the right (concentration-ratio of 21). Cyanopindolol also shifted the BRL 37344 CRC to the right (concentration-ratio of 38). These shifts are consistent with the affinity of cyanopindolol for β₃-adrenoceptors (estimated pA₂ values of 7.27 and 7.38 against isoprenaline and BRL 37344, respectively).

5 In the presence of propranolol (1 μm), SR 59230A produced a concentration-dependent rightward shift of the isoprenaline CRC. The Schild plot gave a pA₂ value of 7.16, although the slope of the regression line was significantly different from unity (0.65). SR 59230A also produced a concentration-dependent shift of the BRL 37344 CRC. The Schild plot gave a pA₂ of 7.58 with the slope of the regression line not significantly different from unity (0.81).

6 The presence of β₃-adrenoceptors mediating relaxation of spontaneous contractions in rabbit jejunum is supported by the relatively poor antagonism of isoprenaline by propranolol, the relaxant effect of BRL 37344 and the antagonism of isoprenaline and BRL 37344 by cyanopindolol and SR 59230A. The lack of simple competitive antagonism of isoprenaline, but not BRL 37344, by SR 59230A may suggest more than one population of atypical β-adrenoceptor.

1 The present study examined the role of muscarinic receptors in the modulation of noradrenaline (NA) release in the guinea-pig isolated distal colon. The spontaneous endogenous NA overflow assayed by HPLC-ED was taken as an index of NA release from enteric noradrenergic nerve terminals.

2 Physostigmine (10 μm) significantly enhanced spontaneous endogenous NA overflow. Hyoscine (muscarinic antagonist), (R)-(-)-trihexyphenidyl and telenzepine (M₁-selective antagonists), and 11[[2-[(diethylamino)methyl]-1-piperydil]acetyl]-5,11-dihydro-6H-pyrido[2,3-b][1,4]benzodiazepine-6-one (AF-DX 116, M₂-selective antagonist) inhibited NA overflow in a concentration dependent manner, with the following EC₅₀ values: 131.74 (18.19–953.96), 101.62 (58.83–175.60), 150 (60–330), 30 (5–170) nm, respectively. 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP, M₁- and M₃- selective antagonist) had no significant effect up to 100 μm.

3 The muscarinic agonist oxotremorine inhibited NA overflow in a concentration dependent manner, with an EC₅₀ value of 0.67 (0.30–1.51) μm. The response to oxotremorine was inhibited by muscarinic antagonists with the following order of potency: hyoscine = (R)-(-)-trihexyphenidyl = telenzepine > 4-DAMP >> AF-DX 116.

4 In the presence of 3 μm tetrodotoxin (TTX), the effect of oxotremorine and 4-DAMP was unchanged, while hyoscine, (R)-(-)-trihexyphenidyl, telenzepine and AF-DX 116, instead of inhibiting, significantly enhanced NA overflow.

5 The present results indicate that, in the guinea-pig colon, endogenous acetylcholine sustains spontaneous NA release by activating muscarinic receptors possibly located on interneurones. In addition, inhibitory muscarinic receptors may exist on adrenergic terminals.