Suc-Tyr(SE)-Met-Gly-Trp-Met-Asp-beta-phenethylamide(410): a competitive antagonist of cholecystokinin-induced contractions in smooth muscles in vitro

Suc-Tyr(SE)-Met-Gly-Trp-Met-Asp-beta-phenethylamide(410) has been studied for its ability to antagonize contractile responses of guinea pig gall bladder, ileum and stomach muscle strips to desamino-cholecystokinin-octapeptide (CCK-7) and cholecystokinin octapeptide (CCK-8). Both CCK-7 and CCK-8 at concentrations of 10(-11)M to 10(-7)M produced dose-dependent tonic contractions in all muscle strips. Suc-Tyr(SE)-Met-Gly-Trp-Met-Asp-beta-phenethylamide (10(-8)M-10(-5)M) inhibited reversibly in a dose-dependent manner the contractile responses to CCK-7 and CCK-8. At the same concentrations the antagonist shifted to the right in parallel to the dose-response curves for CCK-7 and CCK-8 without decreasing their maximum response. Analysis of the data after Schild gave pA2 values (410 potency as antagonist) of CCK-7 in gall bladder, ileum and stomach of 8.36; 8.0 and 7.56, respectively, and pA2 values of CCK-8 of 7.64; 8.94 and 8.52, respectively. The slope of the Schild plots for both CCKs did not differ significantly from the unity, which suggests that 410 is a competitive antagonist. The antagonistic action of 410 is reversible and appeared to be specific since at concentrations of 5 X 10(-6), it had no effect on contractile responses of the gall bladder, ileum and gastric muscle strips to acetylcholine or histamine.     

Responses of guinea-pig gastric, ileal and gall bladder smooth muscle to desamino-cholecystokinin-octapeptide (CCK 7)

Cholecystokinin 7 (CCK 7), a synthetic analogue of cholecystokinin/pancreozymin (CCK 33), increased in a dose-dependent manner the tone of the guinea-pig ileal, gastric and gall bladder smooth muscle preparations. In all these preparations CCK 7 was more potent than CCK 8 and CCK 33 and all three cholecystokinins were more potent than acetylcholine (ACH). Atropine and tetrodotoxin (TTX) did not influence the CCK 7 action in fundus and gall bladder muscle strips but reduced non-competitively its effect in ileal muscle strips. Neither GE 410 nor dbcGMP affected the ACH and histamine (His) response of the muscle strips but both antagonists shifted the dose-response curve of CCK 7 to the right, GE 410 (cholecystokinin antagonist) being a much more potent antagonist of CCK 7 as compared to dbcGMP. In all muscle strips a competitive action on the CCK 7 responses was found for GE 410. In gastric muscle strips a competitive influence on the CCK 7 responses was found for dbcGMP at low concentration (1 x 10(-5)M) and a non-competitive influence at high concentration (5 x 10(-4)M). The results suggest that the contractile effects of CCK 7 in the isolated ileal smooth muscle are realized by cholinergic and direct myogenic mechanisms, whereas in the isolated gall bladder and gastric smooth muscles, by a direct myogenic mechanism only.     

Differences between muscular receptors and neural receptors for cholecystokinin-octapeptide in the guinea-pig gallbladder

To investigate the differences between muscular and neural receptors for cholecystokinin-octapeptide (CCK-OP) in the guinea-pig gallbladder, we studied the effects of dibutyryl cyclic GMP (dbc GMP) on CCK-OP-evoked contraction and [3H]acetylcholine (ACh) release. 10(-3) M dbc GMP significantly reduced CCK-OP (10(-8) M)-evoked contractions without affecting the peptide-induced [3H]ACh release. It is suggested that there are two types of CCK-OP receptors in the guinea-pig gallbladder (dbc GMP-sensitive muscular receptors and dbc GMP-insensitive neural receptors).     

The effects of time and indomethacin on contractile responses of the guinea-pig gall bladder in vitro.

1. The effects of time and of indomethacin on contractile responses of the guinea-pig gall bladder were studied in vitro. 2. The tissues contracted to field stimulation at 5 Hz (in the absence and presence of atropine 10(-6) M). (-)-noradrenaline (10(-5) M), acetylcholine (10(-5) M), and adenosine 5'-triphosphate (ATP, 10(-4) M); the magnitude of the contractile responses increased with time. 3. (-)-Isoprenaline 10(-5) M either relaxed (17 of 23 preparations tested) or had no effect on gall bladder strips. 4. The responses of strips of guinea-pig gall bladder to field stimulation at 5 Hz (in the absence or presence of atropine 10(-6) M), (-)-noradrenaline (10(-5) M), and acetylcholine (10(-5) M) obtained 4 h 45 min after setting up the tissue were reduced following incubation with indomethacin (7.9 x 10(-6) M for 1 h). The responses to (-)-isoprenaline (10(-5) M) and to ATP (10(-4) M) were abolished by incubation with indomethacin. 5. These results suggest that, in the guinea-pig gall bladder in vitro, the magnitude of the contractile responses to field stimulation at 5 Hz, (-)-noradrenaline (10(-5) M), and acetylcholine (10(-5) M) and the ability of the tissue to respond to (-)-isoprenaline (10(-5) M) and ATP (10(-4) M), may be dependent on the synthesis of a prostaglandin-like substance.     

Nitric oxide, an enteric nonadrenergic-noncholinergic relaxant transmitter: evidence using phosphodiesterase V and nitric oxide synthase inhibition.

1. The effects of NG-nitro-L-arginine (L-NOARG), a nitric oxide synthase inhibitor, and SK&F 96231, a phosphodiesterase type V inhibitor, on electrical field stimulated (EFS) nonadrenergic noncholinergic (NANC) relaxations of rat fundal strips, guinea-pig isolated ileum longitudinal muscle with intact myenteric plexus, and guinea-pig taenia caeci were investigated. 2. Reproducible repeated control random EFS frequency-response curves were obtained for all three tissues. 3. Depending on the frequency of stimulation, L-NOARG (10(-4)-5 x 10(-3) M) caused either a complete or partial inhibition of the NANC-induced relaxations of the rat fundal strips and the guinea-pig isolated ileum longitudinal muscle with intact myenteric plexus, but not of the guinea-pig taenia caeci. The inhibitory action of L-NOARG was partially or totally reversed, depending on the tissue, by L-arginine (5 x 10(-3) M). 4. SK&F 96231 (10(-6)-10(-4) M) caused a concentration- and frequency-dependent potentiation of both the size and duration of the EFS-induced NANC relaxant response of rat fundal strips and guinea-pig isolated ileum longitudinal muscle with intact myenteric plexus, but not of the guinea-pig taenia caeci. 5. Zaprinast, another phosphodiesterase type V inhibitor (10(-6)-10(-4) M) caused a concentration- and frequency-dependent potentiation of the NANC relaxant responses to EFS of rat fundal strips. 6. SK&F 96231 and zaprinast alone (10(-6)-10(-4) M) caused a concentration-dependent relaxation of the agonist-induced tone of all three tissues with the maximum degree of relaxation found to be in the order stomach < ileum < caecum. This is the reverse order for ability of SK&F 96231 to potentiate relaxant responses to EFS.(ABSTRACT TRUNCATED AT 250 WORDS)     

The occurrence of postsynaptic alpha- and beta-adrenoceptors in the guinea-pig gall bladder.

1 Guinea-pig gall bladder strips were contracted by (-)-noradrenaline, 10(-5) M, and by field stimulation at 5 Hz (in the absence or presence of 10(-6) M atropine) and relaxed to 10(-5) M (-)-isoprenaline. (-)-Adrenaline, 10(-5) M, predominantly contracted, but sometimes relaxed, this preparation. 2 In the presence of 10(-6) M phentolamine, contractions to (-)-noradrenaline and to (-)-adrenaline were reversed to relaxations. The relaxations produced by (-)-isoprenaline were unaltered. In the presence of 10(-6) M propranolol, contractions to (-)-noradrenaline increased in magnitude, relaxations to (-)-adrenaline were reversed to contractions, and relaxations to (-)-isoprenaline were abolished. These results demonstrate the presence of postsynaptic alpha-adrenoceptors which mediate contractions, and postsynaptic beta-adrenoceptors which initiate relaxations, in the guinea-pig gall bladder. 3 The contractile responses to continuous field stimulation for 5 min at 5 Hz in Krebs solution alone were reduced in magnitude by propranolol, 10(-6) M. In the presence of 10(-6) M atropine (added to eliminate the cholinergic component of the response), propranolol, 10(-6) M, had no effect on responses to stimulation at 5 Hz. Thus propranolol reduced the response to cholinergic stimulation in this tissue; the basis of this effect is unclear. In the absence or presence of atropine (10(-6) M), the responses to 5 Hz were smaller in magnitude in the presence than absence of phentolamine, 10(-6) M. This suggests that the responses to field stimulation of the guinea-pig gall bladder may, in part, be due to the release of endogenous noradrenaline which acts at postsynaptic alpha-adrenoceptors.     

The role of prostaglandins in the spontaneous and cholinergic nerve-mediated motility of guinea-pig gastric muscle

The role of PGE1, PGE2 and PGF2 alpha in the spontaneous and cholinergic nerve-mediated motility of guinea-pig gastric muscle strips was investigated. The prostaglandins (PGs) studied induce dose-dependent tonic activation in the longitudinal strips from fundus, corpus and antrum and inhibition of the phasic activity of circular strips from antrum and pyloric sphincter. These effects are not significantly changed in the presence of adrenergic and cholinergic blocking agents nor with tetrodotoxin, and are, therefore, direct effects on the smooth muscle. Indomethacin exerts effects opposite to those of PGs. The contractile responses of the longitudinal and circular smooth muscles to field stimulation (frequency of 10-20 Hz, duration of 0.5 ms and supramaximal voltage) are inhibited by atropine (1 X 10(-6) M), indicating that cholinergic transmission is involved. PGs potentiate the response of the longitudinal muscles but inhibit the response of the circular muscles to field stimulation. On the contrary, indomethacin (1 X 10(-6) to 1 X 10(-5) M) inhibits the response of the longitudinal and potentiates the response of the circular muscles to field stimulation. The data suggest that PGs may exert a negative feedback control over the excitatory transmission in the circular muscle of the guinea-pig stomach.     

The effect of an inhibitory factor from the bovine retractor penis on the gastro-intestinal tract and gall bladder of the guinea-pig.

1 The effect of a smooth muscle inhibitory factor extracted from the bovine retractor penis has been examined on a variety of in vitro smooth muscle preparations from the guinea-pig alimentary canal and on the guinea-pig gall bladder. 2 The inhibitory factor caused relaxation of spontaneous and carbachol-induced tone in the taenia coli, the stomach fundal strip and the duodenum and colon. There was little effect on the ileum. Sensitivity was highest in the taenia coli where the response to the inhibitory factor mimicked the response to stimulation of the non-adrenergic, non-cholinergic (NANC) inhibitory nerves. 3 In the taenia coli the inhibitory response to stimulation of the NANC nerves and to ATP was abolished by apamin 5 x 10(-8) M, whereas this or higher concentrations had no effect on the response to the inhibitory factor. This makes it unlikely that the latter is the neurotransmitter in these NANC nerves. 4 The inhibitory factor had no effect on the gall bladder. Inhibitory responses to field stimulation were obtained in this tissue but these were insensitive to tetrodotoxin in concentrations greater than those needed to block the motor cholinergic nerves.     

Pharmacological Properties of Pteleprenine,a Quinoline Alkaloid Extracted from Orixa japonica,on Guinea-pig Ileum and Canine Left Atrium

We have investigated the pharmacological properties of pteleprenine, a quinoline alkaloid, on contractile responses of the guinea-pig ileum and on inotropic responses of the canine left atrium. Although pteleprenine (0·1–1 μM) had no effect on the contraction of the ileum induced by acetylcholine at 10 μM it significantly inhibited acetylcholine-induced contraction of the ileum. Pteleprenine (0·1–10 μM) reduced nicotine induced-contraction of the ileum in a concentration-dependent manner yet had no maximum relaxant effect even at a concentration of 10 μM From Schild analysis the pA₂ of pteleprenine on the guinea-pig ileum was found to be 6-6. The contraction of the ileum induced by 10 μM 1,1-dimethyl-4-phenylpiperazinium, a specific agonist of nicotinic acetylcholine. receptors, was concentration-dependently suppressed by 10 nM-10 μM pteleprenine. In contrast, 0.1–10 μM pteleprenine did not antagonize the acetylcholine- and nicotine-induced negative inotropic contractile responses of the canine left atrium. These results show that pteleprenine has inhibitory action against nicotinic acetylcholine receptors in the guinea-pig ileum but not in the canine left atrium. Our findings also suggest that pteleprenine might be a novel lead compound as a nicotinic receptor antagonist.     

Cholinergic mechanism in cholecystokinin action on gall bladder motility

The participation of cholinergic mechanisms in cholecystokinin octapeptide (CCKOP) action on canine gall bladder was studied in vivo and in vitro, using three different experimental conditions. In vitro the responses of canine gall bladder smooth muscle to CCKOP (0.01 to 10 nm) were insensitive to atropine (1 to 10 microM) and tetrodotoxin (3 microM). When gall bladder muscle preparations were contracted by field electrical stimulation (0.7 ms, 40 Hz) CCKOP (0.001 to 0.1 nM) enhanced these contractions while atropine (1 microM) abolished them. This suggests that CCKOP is able to influence acetylcholine (ACH)-release from intrinsic cholinergic nerve terminals. In vivo the responses of canine gall bladder smooth muscle to CCKOP (1 to 10 ng/kg i.v.) were reduced and even abolished by atropine (10 to 50 micrograms/kg i.v.) and hexamethonium (0.5 to 3 mg/kg i.v.). The results suggest the participation of at least two mechanisms in CCKOP action on canine gall bladder motility: a direct action on smooth muscle cells, insensitive to atropine or tetrodotoxin, and an indirect action, which is dependent on pre- and post ganglionic cholinergic pathways.     

5-Hydroxytryptamine is a possible neurotransmitter of the non-cholinergic excitatory nerves in the longitudinal muscle of rainbow trout stomach (Salmo gairdneri).

1. The neurotransmitter of the non-cholinergic excitatory nerves in the rainbow trout stomach was identified on the basis of the pharmacological properties of the contractile responses to transmural stimulation (TMS) and nicotine. 2. TMS caused tetrodotoxin-sensitive contractions of rainbow trout stomach strips in a frequency-dependent manner (0.5-50 Hz). Atropine (1 microM) significantly decreased the contractile response to low-frequency stimulation (0.5-2 Hz), but did not affect that to high-frequency stimulation (3-20 Hz). 3. The atropine-resistant contractile response to TMS (20 Hz) was unaffected by hexamethonium (100 microM), phentolamine (5.4 microM), pyrilamine (1 microM), naloxone (1 microM) or substance P-induced desensitization. 4. 5-Hydroxytryptamine (5-HT, 3 nM-3 microM) caused atropine-resistant contractions in a concentration-dependent manner. In the presence of atropine, methysergide (1 microM) decreased the contractile responses to TMS and 5-HT. 5. Nicotine (3 microM-500 microM) induced atropine-resistant contractions that were completely abolished by tetrodotoxin or hexamethonium. Also methysergide inhibited the contractile responses to nicotine. 6. An acid extract of rainbow trout stomach exhibited atropine-resistant contractions that were decreased by methysergide, in both rainbow trout stomach and guinea-pig ileum longitudinal smooth muscle preparations. 7. The present results indicate that, in longitudinal muscle strips of the rainbow trout stomach, 5-HT is one of the mediators (neurotransmitters) of the non-cholinergic excitatory contractions induced by TMS and nicotine.     

Spasmolytic action of adenosine on the guinea-pig ileum

Adenosine (10^?5M) reduces the contractile response of the guinea-pig isolated ileum to 5-hydroxytryptamine or barium more than the responses to acetylcholine or histamine. Adenosine also inhibits the contractile response of the guinea-pig ileum to a calcium-free medium. These results suggest that adenosine effects a blockade of the indirect responses to barium or 5-hydroxytryptamine mediated through intrinsic nerves and has a weak direct inhibitory effect on the smooth muscle cells of this tissue.     

Evidence that 5-hydroxytryptamine may exert both facilitatory and inhibitory control of electrical field stimulation-evoked contractions in longitudinal muscle taken from the body of guinea-pig stomach

Electrical field stimulation (FS) of guinea-pig stomach body longitudinal muscle strips caused frequency-related contractions mediated via cholinergic mechanisms. Metoclopramide (10(-8)-10(-5) M), MDL 72222 (10(-9)-10(-7) M) and 5-hydroxytryptophan (5-HTP) (3 X 10(-7)-2.4 X 10(-4) M) enhanced these contractions in all tissues, whereas 5-hydroxytryptamine (5-HT) (3 X 10(-8)-3 X 10(-5) M) enhanced the contractions, but only in approximately 15% of the tissues tested. FS-induced contractions were also enhanced in tissues treated in-vitro with p-chlorophenylalanine (2.5 X 10(-7)-2.5 X 10(-5) M) or monofluoromethyldopa (6 X 10(-7)-10(-4) M) or in tissues taken from animals having received p-chlorophenylalanine or monofluoromethyldopa. It is concluded that cholinergic-mediated contractions of stomach strips are subject to 5-HT modulation in two ways. The predominant action of endogenous 5-HT is to exert an inhibitory tone mediated via a metoclopramide and MDL 72222-sensitive 5-HT neuronal receptor. Exogenously applied 5-HT has little overt action to increase the essentially maximal inhibitory action of endogenous 5-HT, but acts on a 5-HT facilitatory receptor system to enhance contractions. Therefore, the actions of 5-HT agonists and antagonists to modify contractions in stomach strips will reflect the balance between 5-HT inhibitory and facilitatory influences, and the specificity of action of the compounds for the two 5-HT receptor systems.     

5-Hydroxytryptamine can antagonize the ability of metoclopramide and SCH 23390 to enhance electrical field stimulation-evoked contractions of guinea-pig isolated stomach muscle

Electrical field stimulation of guinea-pig stomach strips caused frequency related contractions that were enhanced by metoclopramide and SCH 23390 (10(-7)-10(-5) M) and antagonized by atropine (5 X 10(-8) M. 5-HT (3 X 10(-8)-3 X 10(-5) M) antagonized the ability of metoclopramide and SCH 23390 to enhance the contractions. It is concluded that metoclopramide and SCH 23390 can enhance electrical field stimulation-induced contractions in the stomach strips by a 5-HT receptor blockade which can facilitate cholinergic mediated contractions.     

Inhibition of 5-carboxamidotryptamine-induced relaxation of guinea-pig ileum correlates with [125I]LSD binding

5-Hydroxytryptamine (5-HT), 5-carboxamidotryptamine (5-CT), 8-OH-DPAT and RU 24969 relax the guinea-pig ileum precontracted with histamine. This relaxation was characterized using 5-CT as agonist with a series of 8 competitive antagonists. [125I]LSD binding was measured in a membrane preparation of the longitudinal muscle of the guinea-pig ileum in the presence of 3 X 10(-7) M cinanserin in order to suppress binding to 5-HT2 receptors. There was a significant correlation (P less than 0.01) between the antagonism of 5-CT-induced relaxation (pA2 values) and the affinity values of the antagonists for [125I]LSD binding (pKD values). It was also shown that 5-CT relaxed histamine-precontracted longitudinal muscle strips of the guinea-pig ileum. The results suggest that the 5-HT receptor-mediating relaxation in the guinea-pig ileum can be labelled with [125I]LSD and that this receptor does not belong to the 5-HT2, 5-HT1A, 5-HT1B or 5-HT1C receptor subtypes.     

The effect of prostaglandin E2 on histamine-stimulated calcium mobilization as a possible explanation for histamine tachyphylaxis in canine tracheal smooth muscle

Isolated strips of canine tracheal smooth muscle rapidly lost their responsiveness to histamine when placed in a zero calcium Krebs buffer. Responsiveness to acetylcholine, however, was not rapidly lost, and following 120 min of incubation in zero calcium buffer with frequent washes, 10% of the contractile response still remained. The kinetics of each loss of response suggest that primarily a loosely bound source of calcium is mobilized by histamine and a more tightly bound source is mobilized by acetylcholine. Consistent with these data were the effects of the calcium antagonist verapamil. In normal calcium Krebs solution, dose-response curves to histamine were markedly reduced by verapamil while acetylcholine responses were relatively unaffected. In calcium depleted tracheal strips, indomethacin potentiated the calcium dose-response curve, determined by incremental readdition of calcium in the presence of histamine (10(-4) M), with comparatively little effect on the calcium dose-response curve in the presence of acetylcholine (10(-6) M). Also, in indomethacin pretreated tracheal strips, a reduction in the histamine-calcium dose-response curve could be produced by exogenous addition of 2.8 X 10(-9) M and 2.8 X 10(-8) M PGE2. In the acetylcholine-calcium responses there was a significant reduction only at 2.8 X 10(-8) M PGE2. These data suggest that histamine mobilizes primarily a loosely bound, possibly extracellular source of calcium necessary for contraction, and this histamine-stimulated calcium mobilization is sensitive to the effects of PGE2.     

Action of ouabain on rat heart: comparison with its effect on guinea-pig heart.

The inotropic dose-response curve of ouabain in rat cardiac ventricular strips exceeded a concentration range of two decades (1 X 10(-7) M to 3 X 10(-5) M) displaying an intermediate plateau phase. In guinea-pig ventricular strips the inotropic ouabain concentrations spanned only one decade (1 X 10(-7) M-1 X 10(-6) M). Ouabain-intoxication in guinea-pig ventricular strips occurring at 3 X 10(-6) M consisted of arrhythmia and contracture, while in rat ventricular strips at the toxic concentration of 1 X 10(-4) M only a progressive increase in diastolic tension was observed. By means of atomic absorption spectroscopy the ouabain-induced loss of cellular potassium and gain of sodium in rat ventricular strips was detected only at concentrations of ouabain higher than 10(-4) M. Ouabain reduced the activity of Na/K-ATPase prepared from rat and guinea-pig cardiac ventricles to half of its maximum at 6.5 X 10(-5) M in rat and 1.0 X 10(-6) M in guinea-pig, rat heart Na/K-ATPase thus being about 60 fold less sensitive towards ouabain. Specific [3H]-ouabain binding to membrane suspensions prepared from rat and guinea-pig ventricles was characterized by a similar affinity in rat (KD = 4 X 10(-8) M) and guinea-pig (KD = 13 X 10(-8) M). The number of ouabain binding sites in rat membranes was only about 10% of the number found in guinea-pig membranes. In rat the presence of additional ouabain-binding with low affinity and high capacity seemed possible, but could not be verified for methodological reasons. In the light of the biochemical results and binding data, the wider range of ouabain concentration exerting a positive inotropic effect in the rat may be attributed to the existence in the latter of two populations of receptors with different affinities for ouabain and different capacities. In contrast, in the guinea-pig, there is a single population. Nevertheless it is probable that all the receptors in both species are part of the Na/K-ATPase complex and mediate a positive inotropic effect after ouabain-binding in an identical manner.     

Cholecystokinin-octapeptide constricts guinea-pig and human airways.

1. Cholecystokinin-octapeptide (CCK-OP, 10(-10)-3 x 10(-6) M) produced a concentration-dependent contractile response in guinea-pig trachea which was enhanced by both the mechanical removal of the epithelium and by indomethacin (10(-5) M), with an EC50 of 6.18 +/- 0.10 x 10(-8) M. 2. Sub-threshold concentrations of CCK-OP, which did not alter the resting tone of the smooth muscle, did not alter responses produced to electrical field stimulation (EFS) or to vagal nerve stimulation in an intact tracheal tube preparation. Atropine (2 x 10(-6) M) did not alter the concentration-response curve to CCK-OP, indicating that CCK-OP contraction is not mediated by cholinergic mechanisms. 3. The inhibition of neutral endopeptidase (endopeptidase-24.11) by phosphoramidon (10(-5) M) gave a leftward shift in the CCK-OP concentration-response curve in tissues with intact epithelium obtained from normal animals, but had no effect in tissues denuded of epithelium or in tissues obtained from animals which had been actively sensitized and challenged with ovalbumin (OA). 4. CCK-OP-induced contractile responses were antagonized by the CCK-receptor antagonists dibutyryl cyclic guanosine monophosphate (pA2 = 4.3) and L-364,718 (pA2 = 9.6). 5. CCK-OP induced bronchoconstriction in large, but not small, human airways and was antagonized by the CCK-receptor antagonist L-364,718. CCK-OP had no effect on cholinergic neural responses elicited by EFS in human airways.     

Accumulation and overflow of 3H following incubation of the guinea-pig gall bladder with [3H]-noradrenaline

1 Strips of guinea-pig gall bladder readily accumulate ³H following incubation in the presence of 5 × 10^-8 M (-)-[³H]-noradrenaline. This accumulation was reduced by lowering the incubation temperature (from 37° to 23°C), by cocaine (10^-6 M), by nortriptyline (10^-8, 10^-6 and 10^-4 M) and following incubation of the tissues with 6-hydroxydopamine (10^-3 M for 3 h). At 10^-6 M, (-)-noradrenaline and (-)-adrenaline, but not (-)-isoprenaline, inhibited the accumulation of ³H.

2 Following preloading of strips of guinea-pig gall bladder with 3.6 × 10^-7 M (-)-[³H]-noradrenaline for 1 h, the spontaneous overflow of ³H was observed. Cocaine (10^-4 M), nortriptyline (10^-6 M), (-)-isoprenaline (10^-5 M), acetylcholine (10^-5 M) and adenosine 5′-triphosphate (ATP, 10^-4 M) had no effect on the spontaneous overflow of ³H. KCl (10^-1 M), (-)-noradrenaline (10^-5 M), (-)-adrenaline (10^-5 M), and tyramine (10^-5 M) increased the overflow of ³H. These results illustrate similar characteristics of the guinea-pig gall bladder to other noradrenergically-innervated tissues in accumulating and releasing ³H following incubation in the presence of [³H]-noradrenaline.

3 Following incubation in the presence of 3.6 × 10^-7 M (-)-[³H]-noradrenaline, field stimulation, at 5 Hz, of strips of gall bladder, in the absence or presence of 10^-6 M atropine, increased the overflow of ³H and, simultaneously, induced contractions. The contractile responses to 5 Hz were smaller in the presence than in the absence of 10^-4 M lignocaine. Lignocaine (10^-4 M) reduced the overflow of ³H evoked by field stimulation at 5 Hz. It is suggested that the contractile responses to 5 Hz are due to nerve stimulation and that the increased overflow of ³H is due to the stimulation of noradrenergic nerves.

4 The overflow of ³H evoked by field stimulation at 5 Hz was unaltered and increased by propranolol (10^-6 M) and phentolamine (10^-6 M), respectively. Clonidine (5 × 10^-5 M) had no effect in the absence but reduced the amount of ³H which overflowed in response to field stimulation at 5 Hz in the presence of 10^-6 M atropine. The contractile responses to field stimulation at 5 Hz were reduced by phentolamine (10^-6 M) or clonidine (5 × 10^-6, 10^-5 and 5 × 10^-5 M) whether or not atropine (10^-6 M) was present. These results illustrate the presence of postsynaptic α-adrenoceptors and suggest the presence of presynaptic α-adrenoceptors in the gall bladder of the guinea-pig.

     

Pharmacological alteration of antigen-induced contraction of lung parenchymal strips isolated from the actively sensitized guinea pig

Several drugs, known to influence the action or formation of histamine and SRS-A, were examined for their abilities to alter antigen (ovalbumin)-induced contractions of guinea-pig isolated lung parenchymal strips. Cumulative dose-response effects of ovalbumin were obtained on paired parenchymal strips, one used as control and the other drug treated. When used alone, mepyramine, 10(-6) M, phenoxybenzamine, 3 x 10(-5) M and FPL55712, 10(-5) M, did not alter ovalbumin-induced contractions, 5,8,11,14-eicosatetraynoic acid (ETYA), 10(-4) M, produced a small (2.5-fold) rightward shift of the dose-response curves to ovalbumin and histamine. Indomethacin, 5 x 10(-6) M, produced a small increase in the maximum response to ovalbumin and a small (2-fold) rightward shift of the histamine dose-response curve. The effect of indomethacin on ovalbumin-induced contraction was not seen in the presence of phenoxybenzamine and may therefore be due to an increase in histamine release. Combination of indomethacin with FPL55712 or ETYA did not alter antigen-induced contractions. The effect of ETYA on the histamine dose-response curve was not seen in the presence of indomethacin. Combination of phenoxybenzamine with FPL55712 or ETYA caused a marked reduction of the maximum contractile response to ovalbumin. The effect of phenoxybenzamine and ETYA was not observed in the presence of indomethacin. The results suggest that the ability of ETYA to reduce antigen responses in the absence or presence of phenoxybenzamine as well as histamine-induced contraction is related to inhibition of contractile product(s) of cyclooxygenase metabolism of arachidonic acid.(ABSTRACT TRUNCATED AT 250 WORDS)