Effects of oxyfedrine on isolated portal vein and other smooth muscles

1. Oxyfedrine (0.01-1.0 mug/ml), inhibited spontaneous myogenic activity in rat isolated portal vein and carbachol-induced contractions of rat isolated uterus, and relaxed the rabbit duodenum and the guinea-pig tracheal chain preparation. These actions were prevented by the beta-adrenoceptor blocking drug alprenolol. Oxyfedrine was a relatively weak beta-adrenoceptor stimulant (10-100 times less active than isoprenaline) but its actions were more prolonged.2. In the same concentrations, oxyfedrine reduced or prevented the inhibition of myogenic activity of the rat portal vein induced by isoprenaline and by repeated doses of oxyfedrine itself, acting as a partial agonist at beta-adrenoceptor sites.3. Oxyfedrine, 1-12 mug/ml increased myogenic activity in the rat portal vein. This effect was not due to direct or indirect stimulation of alpha-adrenoceptors (because it was unaffected by phentolamine) or to potentiation of acetylcholine or 5-hydroxytryptamine.4. Oxyfedrine (>20 mug/ml) inhibited spontaneous myogenic activity in the portal vein and relaxed the saphenous vein contracted with noradrenaline. This spasmolytic effect of the drug was not due to beta-adrenoceptor stimulation or to inhibition of phosphodiesterase since it was unaffected by alprenolol and by concentrations of imidazole which antagonized the effects of the active phosphodiesterase inhibitor, papaverine. In the portal vein this effect of oxyfedrine was similar to that of the calcium inhibitor iproveratril; some of the effects of oxyfedrine on venous smooth muscle may be mediated through effects on calcium transport.     

Studies on the action and mechanism of action of oxyfedrine on isolated tracheal chains

Oxyfedrine, a β-sympathomimetic drug, did not affect isolated rat and rabbit trachea in concentration from 2.86 × 10^?8 to 2.86 × 10^?4 M, but on the guinea-pig trachea, it caused a dose dependent relaxation of natural tone in lower concentrations (1.79 × 10^?7 to 2.86 × 10^?6 M. In higher concentrations (1.14 × 10^?5 to 2.86 × 10^?4 M), however, a contraction was observed, which was also dose dependent. This contraction was not affected by atropine, lysergic acid diethylamide or by pretreatment with reserpine but was blocked by antihistaminics (isothipendyl and clemastine). Adrenaline, noradrenaline, phenylephrine and isoprenaline did not contract the guinea-pig trachea, whereas contractions were observed after high concentrations of norephedrine, amphetamine, ephedrine and tyramine. These contractions were also unaffected by reserpine pretreatment.It is concluded that the contraction of the guinea-pig trachea by oxyfedrine is related to its structural relationship to the phenylethylamines and might be due to histamine release, an action on histamine receptors or a histamine-like action.     

Adrenergic receptors in the guinea-pig trachea

The effects of adrenaline, noradrenaline and isoprenaline have been investigated on the guinea-pig isolated trachea in the presence of propranolol hydrochloride 10^?5 and 10^?6 g/ml. Adrenaline and noradrenaline were both shown to produce contractions of the tissue. The relative order of potency of the catecholamines (adrenaline > noradrenaline > isoprenaline), together with the antagonism exhibited by phenoxybenzamine, suggests that the contractions were due to α-adrenergic receptor involvement.     

Effect of Molsidomine and Linsidomine on the Human Isolated Bronchus and the Guinea-pig Isolated Trachea

Abstract— The effects of molsidomine and its metabolite linsidomine were studied on the guinea-pig isolated trachea and on the human isolated bronchus. These effects were compared with those of nitrate derivatives (sodium nitroprusside, isosorbide dinitrate), theophylline, zardaverine and isoprenaline. Linsidomine exerted a relaxant effect similar to that of sodium nitroprusside on the two types of preparations precontracted with acetylcholine, histamine or potassium chloride. Molsidomine was about one-hundredth as potent as linsidomine, and less efficacious. The effects of the two substances were not modified by removal of the human bronchial epithelium. The concentration-response curves of linsidomine and sodium nitroprusside were significantly shifted to the right by methylene blue (3 × 10^?5 m ) but the effects of isoprenaline were unmodified. The effects of linsidomine and sodium nitroprusside were potentiated specifically by zaprinast (10^?6-10^?5 m ), an inhibitor of type Ia or V phosphodiesterases, whereas the effects of isoprenaline were potentiated by zardaverine (10^?9-10^?8 m ), an inhibitor of class III and IV phosphodiesterases. The effects of all three substances (linsidomine, isoprenaline and sodium nitroprusside) were potentiated equally by theophylline (10^?5-10^?4 m ), a nonspecific inhibitor of phosphodiesterases. It is concluded that linsidomine is a potent relaxant of the smooth muscle of the guinea-pig isolated trachea and human isolated bronchus. In terms of potency and efficacy, its effect is much superior to that of the parent compound molsidomine. It is suggested that linsidomine acts, like nitrate derivatives, through the guanylate cyclase-cGMP system.     

Effects of Cholinoceptor Blocking Drugs,Adrenoceptor Stimulants,and Calcium Antagonists on the Transmurally Stimulated Guinea-pig Urinary Bladder in Vitro and in Vivo

Abstract The effects of different drugs on the response to transmural electrical stimulation of the guinea-pig urinary bladder were studied in vitro and in vivo. In vitro, atropine (3.0 × 10^-8-5.9 × 10^-4M) did not influence the contractions. When used in high concentrations (>5.2 × 10^-5M), PR 197, another anticholinergic compound, reduced the responses by 25-40%, probably by a non-specific action. Noradrenaline (2.0×10^-6-2.0 × 10^-4M) and isoprenaline (2.0 × 10^-8-2.0 × 10^-4M) had concentration-related inhibitory effects that could be blocked by propranolol (5.2 × 10^-6M). Adenosine (2.0 × 10^-2M) inhibited the response by 27±3% (mean±S.E.M., n = 9). Theophylline (2.0 × 10^-3-6.0 × 10^-4M) had no consistent effects. The calcium antagonist nifedipine (1.2 × 10^-6-1.7 × 10^-5M) reduced the contractions by 25-50%; verapamil (2.2 × 10^-5-4.4 × 10^-4M) was little effective. In vivo, atropine (10 mg/kg) reduced the contractions by 55±5 % (n= 10), whereas PR 197 (5 mg/kg) almost completely suppressed the responses. Noradrenaline (20-100 μg/kg) and isoprenaline (20-300 μg/kg) also caused a marked inhibition that could be blocked by propranolol (0.25-2.0 mg/kg). Theophylline (5 and 10 mg/kg) had a weak (10-20%) inhibitory effect. Adenosine (3.0 mg/kg) reduced the contractions by 47±4% (n= 14); in guinea-pigs pretreated with atropine (10 mg/kg), adenosine produced a further 10 to 20% decrease of the responses. Verapamil (0.5-2.0 mg/kg) had no consistent effect, whereas nifedipine (0.1-0.2 mg/kg) caused an inhibition of 20-50%. The results suggest that β-adrenoceptor stimulants, and drugs with a combined anticholinergic and non-specific action, can effectively suppress the electrically evoked contractions in the guinea-pig urinary bladder.     

Relaxation of the guinea-pig tracheal chain preparation by N6,2'-O-dibutyryl 3',5'-cyclic adenosine monophosphate

N⁶,2′-O-Dibutyryl 3′,5′-cyclic adenosine monophosphate (dibutyryl 3′,5′-amp ), isoprenaline and theophylline relax the guinea-pig tracheal chain preparation; whereas 3′,5′-cyclic adenosine monophosphate (3′,5′-amp ) does not. The relaxant effect of isoprenaline, but not that of dibutyryl 3′,5′-amp , was blocked by propranolol. 3′,5′-amp is hydrolyzed rapidly by beef heart phosphodiesterase whereas dibutyryl 3′,5′-amp is not. The presence of equimolar concentrations of dibutyryl 3′,5′-amp does not alter the rate of phosphodiesterase mediated hydrolysis of 3′,5′-amp . These data are consistent with the theories that relaxation of the guinea-pig trachea may be mediated by 3′,5′-amp and that dibutyryl 3′,5′-amp acts by mimicking 3′,5′-amp at its site of action.     

THE CONTRACTILE RESPONSE OF SMOOTH MUSCLE TO IMMERSION IN HYPERTONIC SOLUTIONS

1. Strips of bovine tracheal muscle and rabbit aorta produced sustained contractions on perfusion with Krebs solution made twice normal strength by addition of sucrose. The contractures were relaxed on return to normal Krebs solution. 2. Similar contractures were produced by tracheal muscle strips in Krebs solutions made twice normal strength by addition of galactose, glucose or NaCl whereas urea caused only a transient contraction. 3. In twice normal strength Krebs solution (sucrose added) the basal tension of rat portal vein and guinea-pig taenia coli was increased. Spontaneous mechanical activity was maintained, but the frequency of contractions was reduced. 4. The hypertonic contracture of bovine trachea in twice normal strength Krebs solution (sucrose added) was reduced by 15% by omission of Ca from the bathing fluid (01 mmol/1 EGTA added). Severe Ca depeletion, by prolonged washing in Ca-free Krebs with 12.5 mmol/1 EGTA and Carbachol added, resulted in a 77% reduction in the hypertonic contracture. 5. In twice normal Krebs solution (sucrose added), the hypertonic contracture was partially relaxed by isoprenaline (4 × 10^?6 mol/1); the contractile response to carbachol was reduced; the contractile response to high-K Krebs solution was maintained. 6. Atropine (5 × 10^?7 mol/1) abolished the contractile response to carbachol, but had no effect on the hypertonic contracture. 7. It is suggested that the contraction of bovine tracheal strips in hypertonic solutions is mainly due to activation of the contractile myofilaments rather than simple cell shrinkage. Hypertonic solutions may also interfere with some steps in the excitation-contraction coupling sequence.     

Mechanism of action of relaxant effect of Agastache mexicana ssp.mexicana essential oil in guinea-pig trachea smooth muscle

Context: Agastache mexicana ssp. mexicana (Kunth) Lint &; Epling (Lamiaceae), popularly known as ‘toronjil morado’, is used in Mexican traditional medicine for the treatment of several diseases such as hypertension, anxiety and respiratory disorders.

Objective: This study investigates the relaxant action mechanism of A. mexicana ssp. mexicana essential oil (AMEO) in guinea-pig isolated trachea model.

Materials and method: AMEO was analyzed by GC/MS. The relaxant effect of AMEO (5–50?μg/mL) was tested in guinea-pig trachea pre-contracted with carbachol (3?×?10?^??⁶?M) or histamine (3?×?10?^??⁵?M) in the presence or absence of glibenclamide (10?^??⁵?M), propranolol (3?×?10?^??⁶?M) or 2′,5′-dideoxyadenosine (10?^??⁵?M). The antagonist effect of AMEO (10–300?μg/mL) against contractions elicited by carbachol (10?^??¹⁵–10?^??³?M), histamine (10?^??¹⁵–10?^??³?M) or calcium (10–300?μg/mL) was evaluated.

Results: Essential oil composition was estragole, d-limonene and linalyl anthranilate. AMEO relaxed the carbachol (EC_50?=_?18.25?±?1.03?μg/mL) and histamine (EC_50?=_?13.3?±?1.02?μg/mL)-induced contractions. The relaxant effect of AMEO was not modified by the presence of propranolol, glibenclamide or 2′,5′-dideoxyadenosine, suggesting that effect of AMEO is not related to β₂-adrenergic receptors, ATP-sensitive potassium channels or adenylate cyclase activation. AMEO was more potent to antagonize histamine (pA₂′?=??1.507?±?0.122) than carbachol (pA₂′?=??2.180?±?0.357). Also, AMEO antagonized the calcium chloride-induced contractions.

Conclusion: The results suggest that relaxant effect of AMEO might be due to blockade of calcium influx in guinea-pig trachea smooth muscle. It is possible that estragole and d-limonene could contribute majority in the relaxant effect of AMEO.     

Inhibition of ATP-Induced Contraction in the Guinea-pig Urinary Bladder in Vitro and in Vivo

Abstract Contractions were elicited by adenosine 5′-triphosphate (ATP) in the guinea-pig urinary bladder in vitro and in vivo. In isolated detrusor strips, tetrodotoxin (3.1 × 10^-6-4.4 × 10^-5M) did not affect contractions induced by a submaximum concentration (10^-3M) of ATP, nor did atropine (1.7 × 10^-6 - 2.1 × 10^-4M), or the anticholinergic agent PR 197 within the concentration range 2.6 × 10^-8 - 2.6 × 10^-5M. In higher concentrations (5.2 × 10^-5-2.6 × 10^-4M), PR 197 inhibited the ATP-response by 60-70% in a way that was not clearly concentration-related. Isoprenaline (10^-7-2.0 × 10^-5M) and noradrenaline (2.5 × 10^-6-10^-4M) reduced the ATP-induced contractions by up to 79%. The effects of the amines were abolished by propranolol (5.2 × 10^-6-3.8 × 10^-5M). Adenosine, 1.0-2.0 × 10^-2M, reduced the ATP-response by about 50%; in lower concentrations, it had no effect. Nifedipine, 7.8 × 10^-7-1.2 × 10^-5M, reduced the responses by 15-795%. Indomethacin (≤2.0 × 10^-4M), and theophylline (2.0 × 10^-4M) had no consistent effects on ATP-induced contractions. Exposure of the preparations to a calcium-free medium reduced and abolished the ATP-response within 60 min. Intravenous injection of ATP (1 -20 mg/kg) caused a rapid and transient increase in intravesical pressure in the anaesthetized guinea-pig. The effect of ATP (3mg/kg) was reduced by atropine(5-10 mg/kg) by approximately 35%. PR 197 (2.5-5 mg/kg) abolished the ATP-response. Isoprenaline (5-100 pg/kg) caused a 53-95% inhibition that could be blocked by propranolol (1 mg/kg). The inhibiting effect of noradrenaline (10-100,μg/kg) could not be blocked by propranolol (1 mg/kg). Adenosine (1.5-3.0 mg/kg) given immediately before ATP completely inhibited the ATP-response. Nifedipine, 0.1-0.2 mg/kg, reduced the ATP-induced contraction by 34 to 100%. It is concluded that the ATP-induced contraction is elicited by a direct effect on the smooth muscle cell. It can be inhibited non-specifically by drugs with different modes of action.     

Action of a novel potassium channel opener,SR 47063, on human bronchi and on guinea-pig trachea in vitro: comparison with cromakalim

Potassium channels are present on airway smooth muscle cells and their activation results in hyperpolarization and relaxation. Because these effects may have therapeutic relevance to asthma, the aim of our study was to examine the activity of SR 47063, a potassium channel opener (KCO), against a variety of spasmogens or against electrical field stimulation in guinea-pig isolated trachea and in human isolated bronchi in vitro; the effects of SR 47063 were compared with those of cromakalim, isoprenaline, and theophylline. Like cromakalim, SR 47063 reduced the contractility of guinea-pig isolated trachea and the human isolated bronchus in basal tone with pD₂ of 7.79 ± 0.01 and 7.83 ± 0.09, respectively, or during precontractions induced by acetylcholine 10^?4 M, histamine 10^?5 M, or low concentrations of KCl (<30 mM), but not by high KCl concentrations (≥30 mM); these effects were antagonized by glibenclamide 10^?5 M. This spectrum of action is typical of the compounds known as potassium channel openers. Electrical field stimulation (EFS: 16 Hz, 1 ms, 320 mA for 10 sec in the presence of indomethacin 10^?6 M and propranolol 10^?6 M) of guinea-pig isolated main bronchi induced 2 successive contractile responses. Both contractions were reduced significantly by SR 47063 and cromakalim. Although we have not studied the effects of KCOs on exogenous neurokinin A- or substance P-induced contractions, it might be suggested as a hypothesis that this inhibition seems to take place presynaptically and to affect the release of neuromediators produced by electrical field stimulation. In conclusion, SR 47063 exerts in vitro on the bronchial smooth muscle an inhibitory effect which seems to be due to the opening of glibenclamide-sensitive potassium channels. SR 47063 is 3- to 10-fold more potent than cromakalim. © 1993 Wiley-Liss, Inc.     

An investigation of the long duration of action of oxyfedrine

The long-lasting sympathomimetic effects of oxyfedrine on the rat perfused heart, rat uterus and guinea-pig trachealis can be prevented or terminated by propranolol. Reserpine pretreatment did not affect the early peak cardiac responses or the responses of the other two tissues but abolished the late phase of its cardiac action. Oxyfedrine caused partial depletion of cardiac noradrenaline. A high concentration was needed to affect the uptake of ³H-noradrenaline by the rat uterus. ¹⁴C-oxyfedrine was taken up by tissues — this uptake was unaffected by cocaine, desipramine, metanephrine or phenoxybenzamine; it was reduced by cooling and increased by reserpine pretreatment. The chloroform-aqueous phase partition of oxyfedrine indicated high lipid solubility and its tissue uptake was attributed to this property. In the rat uterus the slow efflux of active drug molecules could account for its long duration of action.     

β3-Adrenoceptors mediate smooth muscle relaxation in the rat lower oesophageal sphincter

1 The role of β₃-adrenoceptors in isoprenaline-induced relaxation of carbachol-precontracted ring segments of the rat lower oesophageal sphincter (LOS) was examined. 2 Isoprenaline (10^?8m – 10^?5m ) relaxed ring segments of the LOS in a concentration-dependent manner. Propranolol (10^?7m ) had very little antagonist effect on isoprenaline-induced relaxation. 3 Dobutamine (10^?7m – 10^?4m ), salbutamol (10^?7m – 10^?4m ) and BRL 37344 (10^?8– 10^?5m ) also all relaxed carbachol-contracted ring segments of the LOS in a concentration-dependent manner. The relaxant responses to these agonists were similarly not antagonized by propranolol (10^?7m ). 4 Cyanopindolol (10^?6m ), produced a parallel rightward displacement of isoprenaline, dobutamine, salbutamol and BRL 37344 concentration–response curves with similar potencies. The pK_B values range from 7.3 ± 0.1 to 7.7 ± 0.2. 5 The relaxant effect of isoprenaline in the rat LOS was not inhibited by N^G-nitro-l -arginine (l -NOARG; 3 × 10^?5m ), glibenclamide (10^?5m ) or tetraethylammonium (1 mm ). 6 It was concluded that β₃-adrenoceptors mediate isoprenaline-induced relaxation in rat lower oesophageal sphincter and that activation of these receptors was not linked to either ATPase-, Ca²⁺-dependent K⁺ channels or to NO release.     

Effect of venoms from Conidae on skeletal,cardiac and smooth muscles

J. Kobayashi, H. Nakamura, Y. Hirata and Y. Ohizumi. Effect of venoms from Conidae on skeletal, cardiac and smooth muscles. Toxicon20, 823–830, 1982.—The effects of the venoms of 29 species of Conidae were studied on the mouse isolated diaphragm, the guinea-pig isolated left atria and ileum, and the rabbit isolated aorta. When the directly stimulated mouse diaphragm was exposed to the venom (10^?4 g/ml) of C. geographus, there occurred a marked decline in twitch tension. The venoms of C. magus (3 × 10^?6 g/ml) and C. striatus (10^?3 g/ml) also caused complete loss of contractile response to electrical stimulation. This was followed by a gradual rise in the baseline.The venoms (10^?6?3 × 10^?5 g/ml) of C. magus and C. striatus caused dose-dependent increases in the contractile force of the electrically driven guinea-pig left atria. The venoms (10^?5?10^?4 g/ml) of C. eburneus and C. tessulatus also elicited long-lasting positive inotropic actions on the atria. The inotropic actions induced by the venoms of C. magus and C. striatus were abolished by tetrodotoxin (TTX, 10^?6 M), but were not affected by verapamil (3 × 10^?7 M), whereas those induced by the venoms of C. eburneus and C. tessulatus were completely inhibited by verapamil (3 × 10^?7 M), but were not modified by TTX (10^?6 M). These results suggest that the inotropic actions of the venoms of C. magus and C. striatus may be due to an increase in Na⁺ permeability of the cardiac cell membrane, while those of venoms of C. eburneus and C. tessulatus may be due to an increase in Ca²⁺ permeability.The venoms (10^?6 g/ml) of C. magus and C. striatus elicited rhythmic, transient contractions of the guinea-pig ileum followed by relaxations, which were blocked by TTX (10^?6 M). This suggests that these biphasic responses were caused by increasing Na⁺ permeability of the nerve cell membrane. On the other hand, the venoms (10^?4 g/ml) of C. eburneus and C. tessulatus caused transient contractions of the ileum followed by relaxations.The venoms (10^?4 g/ml) of C. tessulatus and C. eburneus caused marked, long-lasting contractions of the rabbit aorta which were abolished by verapamil (10^?6 M), but were not affected by TTX (5 × 10^?7 M) or phentolamine (10^?6 M). It is suggested that these venoms increase the verapamil-sensitive Ca²⁺ influx across the smooth muscle membrane of the aorta, resulting in contractions.The active principles in the venoms of C. geographus, C. textile and C. imperialis were stable at 100°C for 15 min and passed through PM 10 filters, suggesting molecular weights lower than 10,000. On the other hand, the active principles in the venoms of C. magus, C. striatus, C. tessulatus and C. eburneus were partially destroyed with heating and were kept in the retentate of the PM 10 filters.     

The effect of stercuronium on cardiac muscarinic receptors

In the electrically stimulated guinea-pig left atrium preparation stercuronium (10^?6?3 × 10^?4 M) a short-acting neuromuscular blocking drug, was found to produce parallel displacement of concentration-response curves for negative inotropic responses to acetylcholine, carbachol, methacholine and pilocarpine but not those to ATP or K⁺. The effect of stercuronium was not modified in the presence of mecamylamine (2 × 10^?5 M) or propranolol (3 × 10^?6 M). It was concluded that stercuronium possesess antimuscarinic activity but in contrast to the competitive antagonist homatropine (2 × 10^?6?3 × 10^?4 M) the degree of antagonism of cholinomimetics tended towards a limiting value at high concentrations of antagonist being more marked with acetylcholine than with carbachol and the other cholinomimetics. Pretreatment of guinea pigs with dyflos (1.2 mg/kg s.c. daily for 3 days) reduced but did not abolish the difference between acetylcholine and carbachol. Using acetylcholine as the agonist in atria obtained from dyflos-pretreated guinea pigs combination of stercuronium and homatropine produced dose ratios which were significantly less than expected for combination of 2 competitive antagonists. It is suggested that the antimuscarinic activity of stercuronium is due to a non-competitive antagonism of the metaffinoid type whereby interaction at an allosteric site may modify the bining of agonists and of competitive antagonists for the receptor.     

Hemoglobin formation in the explanted chick blastodisc; a model system for evaluation of embryotoxic agents as illustrated by effects of vinblastine, 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane (DDT) and sodium diethylbarbiturate

Concentrations of 4 × 10^?6m vinblastine and 5 μg/ml (1.77 × 10^?4m) DDT markedly inhibited formation of hemoglobin in the blood islands of explanted blastodiscs exposed to the agent before attaining the 6-somite stage of development. More advanced blastodiscs were less sensitive to inhibition by either vinblastine or DDT. Low concentrations of sodium diethylbarbiturate (10^?6m) markedly stimulated hemoglobin formation at all developmental stages examined.     

Sympathomimetic Effects of Scoparia dulcis L. and Catecholamines Isolated from Plant Extracts

The herb Scoparia dulcis L. is used in Brazilian folk medicine to treat bronchitis, gastric disorders, haemorrhoids, insect bites and skin wounds, and in oriental medicine to treat hypertension. A previous study has shown that extracts of S. dulcis have analgesic and anti-inflammatory properties; in this work the sympathomimetic activity of an ethanolic extract of Scoparia dulcis L. has been investigated in rodent preparations in-vivo and in-vitro. Administration of the extract (0.5-2 mg kg^?1, i.v.) to anaesthetized rats produced dose-related hypertension blocked by the α-adrenoceptor antagonist prazosin (1 mg kg^?1). Partition of the extract in chloroform-water yielded an aqueous phase 20 times more potent than the extract; this produced hypertension in either reserpine-treated or pithed rats. In untreated and reserpine-treated rats the same fraction (1–3 × 10³ μg mL^?1) produced concentration-dependent contractions of the vas deferens musculature parallel to those obtained with noradrenaline (10^?8-10^?4 m ). Prazosin (10^?7 m ) reduced the maximum contractile effect of the aqueous fraction, and shifted the concentration-response curves for noradrenaline to the right. The aqueous fraction (25 and 50 μg mL^?1) increased the inotropism of electrically driven left atria of rats, the effect being blocked by propranolol (0.4 μg mL^?1). In preparations of guinea-pig tracheal rings the aqueous fraction (1–3 × 10³ μg mL^?1) relaxed the muscle contraction induced by histamine (10^?4 m ) in proportion to the concentration. The effect was antagonized competitively by propranolol (1.5 μm ). High-performance liquid-chromatographic analysis of the aqueous fraction revealed the presence of both noradrenaline and adrenaline in the plant extract. The results indicated that both catecholamines may account for the hypertensive and inotropic effects obtained after parenteral administration of S. dulcis extracts. This sympathomimetic activity is, however, unrelated to the previously reported analgesic and anti-inflammatory properties of the plant extract, but may explain its effectiveness upon topical application in the healing of mucosal and skin wounds.     

Purine antagonists in the identification of adenosine-receptors in guinea-pig trachea and the role of purines in non-adrenergic inhibitory neurotransmission

1 To test the possibility that adenosine receptors exist within the trachea of the guinea-pig, an attempt has been made to identify a compound with adenosine antagonist activity in this tissue.

2 Quinidine, phentolamine, phenoxybenzamine, 2-2′-pyridylisatogen tosylate (PIT) and caffeine were tested for antagonism of spasmolytic responses to adenosine, adenosine 5′-triphosphate (ATP) and adenine on the guinea-pig isolated trachea.

3 Quinidine (10 and 25 μg/ml), phentolamine (10 and 30 μg/ml) and phenoxybenzamine (10 μg/ml) had little or no effect on response to adenosine, ATP and adenine. PIT (21 μg/ml) potentiated responses to adenosine, ATP and adenine by an unexplained mechanism.

4 Caffeine (25 μg/ml) partially relaxed the trachea and inhibited spasmolytic responses to both adenosine and ATP, but not to adenine, isoprenaline, aminophylline or prostaglandin E₂ (PGE₂).

5 A number of compounds related to caffeine (xanthine, hypoxanthine, theophylline and theobromine) were tested for adenosine antagonist activity. Xanthine (300 μg/ml) and hypoxanthine (300 μg/ml) did not relax the trachea or antagonize spasmolytic responses to adenosine. Both theophylline (10 μg/ml) and theobromine (30 μg/ml) partially relaxed the trachea; theophylline, but not theobromine, antagonized spasmolytic responses to adenosine.

6 pA₂ values for caffeine and theophylline as antagonists of adenosine were 4.3 and 4.7 respectively. However, the slopes of the Schild plot regressions were significantly less than 1.0 for both compounds.

7 Four compounds, adenine, AH 8883, M30966 and ICI 63197, which like caffeine and theophylline, have phosphodiesterase inhibitory activity were tested for adenosine antagonist activity in the trachea. Adenine and AH 8883 had no effect and M30966 and ICI 63197 caused significant potentiation.

8 The effects of caffeine and theophylline were also investigated on the non-adrenergic inhibitory response to nerve stimulation (NAIR). Both caffeine (100 μg/ml, n = 4) and theophylline (30 μg/ml, n = 4) enhanced the NAIR (20 Hz) while virtually abolishing matched responses to exogenous adenosine.

9 The results support the existence of adenosine receptors in the guinea-pig trachea.

     

The effects of phorbol 12,13-diacetate on responses of guinea-pig isolated trachea to methylxanthines, isoprenaline and ryanodine.

1. Using guinea-pig isolated trachea, we have studied how phorbol 12,13-diacetate (PDA) modulates mechanical responses of the tissue to methylxanthines, isoprenaline and ryanodine. 2. Caffeine (10 microM-5 mM), theophylline (10 microM-5 mM) and isoprenaline (1 nM-1 microM), each inhibited the spontaneous tone of the trachea. Pretreatment with PDA (0.1-10 microM) converted relaxant responses to high concentrations of the methylxanthines into contractions. PDA produced no equivalent effect against isoprenaline. Pretreatment with verapamil (1 or 10 microM), nifedipine (0.1 microM) or incubation with Ca(2+)-free, EGTA (0.1 mM)-containing physiological salt solution (PSS) suppressed the contraction produced by caffeine or theophylline in PDA (5 microM)-treated tissues. 3. The ability of PDA (5 microM) to convert caffeine-induced relaxation into caffeine-induced contraction was retained in tissues pretreated with a combination of atropine (1 microM) and mepyramine (1 microM) and in tissues denuded of the airway epithelium. 4. Caffeine (10 microM-5 mM), theophylline (10 microM-5 mM) and isoprenaline (1 nM-1 microM), each relaxed trachea contracted with histamine (0.1 mM). The relaxation induced by caffeine, theophylline and isoprenaline was markedly reduced in the presence of PDA (5 microM) and the responses to high concentrations of caffeine and theophylline, but not those to isoprenaline, were reversed to contractions. Verapamil (10 microM) prevented the effects of PDA against caffeine- or theophylline-induced relaxation. 5. PDA (1 microM) enhanced the tracheal spasm produced by caffeine (10 mM) and theophylline (10 mM) in indomethacin (2.8 microM)-treated trachea maintained at 20 degrees C. This enhancement was reduced in the presence of verapamil (10 microM).(ABSTRACT TRUNCATED AT 250 WORDS)     

A comparison between ATP and bradykinin as possible mediators of the responses of smooth muscle to non-adrenergic non-cholinergic nerves

The effects of ATP, bradykinin (BK) and electrical stimulation of intramural non-adrenergic non-cholinergic nerves (NS) were compared in four smooth muscle preparations. In the guinea-pig taenia caeci and rat duodenum, ATP (10^?7-5 × 10^?5 M) and BK (5 × 10^?10-10^?7 M) closely mimicked the response to NS. The relaxations to BK, but not to ATP or NS, were inhibited by carboxypeptidase B (3–15 U/ml) and apamin (10^?8-5 × 10^?8 M) prevented the relaxations to all three stimuli. BK contracted the guinea-pig distal colon whereas ATP and NS caused inhibition. In the guinea-pig bladder, ATP and NS induced rapid phasic contractions whereas BK caused tonic contractions. In the latter two preparations, incubation with indomethacin failed to reveal any BK relaxationic In view of its failure to mimic the nerve-mediated response in two of the tissues, and of its selective inhibition by carboxypeptidase B in the other two, BK is less likely than ATP to be the transmitter in non-adrenergic non-cholinergic nerves supplying smooth muscle.     

THE EFFECTS OF SOME BRONCHODILATOR AND ANTI-INFLAMMATORY DRUGS ON PROSTAGLANDIN F2a-INDUCED CONTRACTION OF GUINEA-PIG ISOLATED TRACHEA

1. The bronchodilator drugs isoprenaline, salbutamol, theophylline and prostaglandin E₁ (PGE₁) relaxed the guinea-pig isolated tracheal chain preparation dose-dependently and their potencies were compared by EC₅₀ values. 2. The non-steroid anti-inflammatory drugs flufenamate, mefenamate and phenylbutazone also relaxed the preparation dose-dependently, but were less potent than the sympathomimetic drugs and PGE₁. 3. The contractile response to a submaximal concentration of prostaglandin F_2a (PGF_2a) was antagonized by flufenamate, mefenamate, phenylbutazone, aspirin, theophylline, isoprenaline, salbutamol and PGE₁, at concentrations similar to or less than the clinical peak plasma levels in man. A relatively higher concentration of indomethacin was required. 4. The antagonism was relatively specific for PGF_2a in the case of the fenamates, which did not cause comparable reductions in responses to equi-effective concentrations of histamine and carbachol. The other anti-inflammatory drugs, theophylline and the sympathomimetic drugs were less or non-specific. 5. The nature of the shifts in the log dose-response curve for PGF_2a caused by increasing concentration levels of flufenamate indicates a dual competitive/non-competitive type of antagonism.