Antimuscarinic action of an alkane-bis-ammonium compound alone and in combination with (+)-benzetimide.

Heptane-1,7-bis-(dimethyl-3'-phthalimidopropylammonium bromide) ('C7/3-phthalimido-propyl') in concentrations of 10(-7) to 0.5 X 10(-3) inhibited negative inotropic responses to carbachol or acetylcholine to a similar extent in the electrically stimulated isolated guinea-pig left atrium. However, the degree of antagonism of responses to carbachol was less than expected for a competitive antagonist when the higher concentrations of 'C7/3-phthalimido-propyl' were employed. When 'C7/3-phthalimido-propyl' was combined with competitive antagonists such as (+)-benzetimide, atropine or homatropine the degree of antagonism was greater than expected for combination of 2 competitive antagonists. Qualitatively similar results were obtained in the presence of practolol (1.5 X 10(-5) M). The results obtained with 'C7/3-phthalimido-propyl' are shown to agree with theoretical predictions for a metaffinoid antagonist which influences the affinities of both agonists and competitive antagonists by combining with a regulatory site distinct from, but interdependent with the binding sites for agonists and competitive antagonists. Further, it is shown that the alkane-bis-ammonium compound produces a much greater reduction in the affinity of carbachol than that of the competitive antagonists and as a consequence causes 'supra-additive' effects when combined with a competitive antagonist. The reduction in the affinity of (+)-benzetimide produced by 'C7/3-phthalimido-propyl' did not differ significantly from the reduction in the affinities of atropine or homatropine.     

The interaction of hemicholinium-3 (HC-3) with cholinomimetics and atropine.

In either spontaneously beating or electrically driven atrial preparations of the guinea pig HC-3 (0.01-1 mM) inhibited negative inotropic responses to acetylcholine or carbachol. Although there was a parallel rightwards shift of the log concentration--response curves for acetylcholine or carbachol and no depression of the maximal response the type of antagonism was not competitive as the relationship between dose ratio -- 1) and concentration of HC-3 was not linear over the whole range investigated. A lesser degree of antagonism than expected for a competitive antagonist was observed with higher concentrations of HC-3. HC-3 was a more effective antagonist of responses to carbachol than to acetylcholine and pretreatment of animals with dyflos did not modify this difference. In addition, HC-3 was found to antagonize the inhibitory action of atropine on responses to acetylcholine and to a lesser extent carbachol. The results can be explained in terms of the interaction of HC-3 at a regulatory site distinct from the binding sites for cholinomimetics and atropinics. Interaction of HC-3 at the postulated site produces a noncompetitive antagonism of both agonists and competitive antagonists by modifying the affinities of the compounds for their respective binding sites.     

Effect of antimuscarinic agents on the contractile responses to cholinomimetics in the rat anococcygeus muscle

1 The effects of antimuscarinic agents alone and in the presence of neostigmine on the contractile responses to exogenously applied cholinomimetics or (-)-noradrenaline were studied in the rat anococcygeus muscle.

2 Atropine (1 × 10^-9 -1 × 10^-6M) alone, in the presence of hexamethonium (1 × 10^-4M), or phentolamine (1 × 10^-6M), inhibited responses to acetylcholine but not to (-)-noradrenaline. The inhibitory effect with the higher concentrations of atropine (1 × 10^-8 - × 10^-6M), was seen as an increase in the slopes of the concentration-response curves. Atropine (1 × 10^-8M) alone inhibited the responses to methacholine and carbachol without altering the slopes of the concentration-response curves.

3 Homatropine (1 × 10^-6M) alone had no effect on responses to (-)-noradrenaline and inhibited responses to acetylcholine and methacholine. The inhibitory effect on responses to acetylcholine but not to methacholine, included an increase in the slopes of the concentration-response curves.

4 Neostigmine (1 × 10^-6M) alone had no effect on responses to (-)-noradrenaline and potentiated responses to acetylcholine and methacholine. The potentiating effect included an increase in the slopes of the concentration-response curves.

5 In the presence of neostigmine (1 × 10^-6M), atropine (1 × 10^-9M - 1 × 10^-6M) caused a parallel concentration-dependent shift of the concentration-response curves to acetylcholine. The pA₂ values, in the presence of neostigmine, were independent of the concentration of atropine and of the agonist (acetylcholine, methacholine, or carbachol) used. In the presence of neostigmine (1 × 10^-6M), homatropine (1 × 10^-6M) also failed to alter the slopes of the concentration-response curves to acetylcholine and was approximately 100 times less potent than atropine as an antimuscarinic agent.

6 These results illustrate that, in the rat anococcygeus muscle, it is necessary to inhibit acetylcholinesterase before determining the relative potencies of antagonists at muscarinic receptors.

     

Prejunctional Muscarinic Receptor Modulation of Noradrenaline Release from Sympathetic Neurones in Rabbit Aorta *

The prejunctional muscarinic modulation of stimulation‐evoked release of ³H‐noradrenaline from sympathetic neurones in rabbit aorta was examined. The role of transmitter uptake, α‐adrenoceptor blockade, stimulation frequency and endothelium on the modulation was investigated. Rings of aorta were incubated with (‐)‐³H‐noradrenaline and subsequently subjected to electrical‐field stimulation. Fractional ³H‐overflow was determined by liquid scintillation counting. Acetylcholine (10^?8–3×10^?6 M) added cumulatively, reduced the stimulation‐evoked ³H‐overflow up to 80%. The effect of acetylcholine was the same in intact and endothelium‐free aorta. The inhibitory effect of acetylcholine was inversely related to the frequency of stimulation (1–10 Hz). The maximal inhibition (%) was 80 (1 Hz), 53 (3 Hz) and 14 (10 Hz). The inhibitory effect of acetylcholine (10^?6 M) and carbachol (10^?5 M) reached a maximum 15 min. after addition and then remained almost constant. Cocaine (3×10^?5 M) did not alter the effect of acetylcholine. Desipramine (10^?6 M) and corticosterone (4×10^?5 M) attenuated the inhibition seen with low concentrations (10^?8–10^?7 M) of acetylcholine. The acetylcholine‐induced inhibition was antagonized by desipramine. Cocaine plus corticosterone attenuated the inhibition seen with high concentrations (10^?6–3×10^?6 M) of acetylcholine. Rauwolscine (10^?6 M) enhanced the maximal inhibitory effect of acetylcholine. We conclude that the inhibitory effect of acetylcholine on ³H‐overflow from rabbit aorta preloaded with ³H‐noradrenaline is (1) inversely related to stimulation frequency; (2) independent of endothelium; (3) unaffected by neuronal and extraneuronal transmitter uptake; (4) that cocaine is not a prejunctional muscarinic antagonist; (5) that cocaine, but not desipramine, is suited as a neuronal uptake inhibitor in studies of prejunctional muscarinic receptor subtypes; and (6) and that there is an inverse interaction between prejunctional α₂‐adrenoceptors and muscarinic receptors.     

Interactions of D600 (methoxyverapamil) and local anesthetics with rat brain α-adrenergic and muscarinic receptors

D600 (methoxyverapamil) was found to inhibit the specific binding assayed in rat brain homogenates of the antagonist agents [³H]WB 4101 and [³H]QNB to the α-adrenergic and muscarinic receptors respectively. The IC₅₀ concentrations of D600 in standard binding experiments were 1.7 × 10_?6 M and 1.4 × 10 _?5M, with calculated k₁ values of 0.98 × 10_?6 M and 8.83 × 10_?6M.Scatchard analyses showed these inhibitions to be competitive. Lidocaine and tetracaine also inhibited radioligand binding to these receptors, with K₁ values of 5.25 × 10^?4M and 4.85 × 10^?5 M for the α-receptor and 8.2 × 10^t-5 M and 6.94 × 10^?6 M for the muscarinic receptor; these inhibitions also appeared to be competitive. Increasing the Ca²⁺ concentration in the assays to 10 mM did not influence the effects of D600 or the anesthetics. Analyses of inhibitions of muscarinic receptor binding produced by D600 and lidocaine over a range of pH indicated that the inhibitory species of D600 is the uncharged form, whereas the charged form of lidocaine is inhibitory. Interactions of D600 and lidocaine with the agonist site on the muscarinic receptor were studied by measuring the effects of these agents on the displacement of [³H]QNB by the muscarinic agonist carbachol. Comparison of these results with a theoretical model indicates that carbachol, [³H]QNB, and D600 or lidocaine competitively displace one another at the same agonist site. The binding of labeled naloxone to the opiate receptor was also inhibited by D600, the IC₅₀g being 4 × 10^t?6 M. These inhibitory effects of D600 and the local anesthetics on different receptors suggest that these agents may act by a common mechanism, namely by perturbing membrane structures. These results suggest caution in interpreting experiments in which D600 and verapamil are used analytically as Ca antagonists to assess the involvement of Ca in a biological system.     

Antihistaminic effect of terfenadine: A new piperidine-type antihistamine

The antihistaminic effect of terfenadine was studied in the isolated guinea pig ileum, histamine skin wheals in guinea pigs and monkeys, and i.v. histamine-induced death in guinea pigs. In the guinea pig ileum, terfenadine, 1 × 10^?7 M, shifted the histamine dose-response curve to the right in a parallel fashion without affecting the dose-response curve of acetylcholine and barium chloride. However, as the dose of terfenadine was increased (3.16 × 10^?7 and 1 × 10^?6 M) the histamine dose-response curves were displaced to the right with a depression of the maximum response and a reduction of the slope. Thus an unsurmountable type of antagonism was observed. Acetylcholine was also antagonized in a similar fashion by these two concentrations. In contrast, terfenadine appeared to displace the barium chloride dose-response curve to the right in a parallel fashion. At 0.4 and 0.8 mg/kg p.o., terfenadine shifted the histamine skin wheal dose-response curves to the right in a parallel fashion, but at 1.6 to 6.4 mg/kg, terfenadine antagonized the histamine wheal dose-response curves with a depression of the maximum and the slope of the curve. These results were also similar to those of cyproheptadine but were different from those of chlorpheniramine, which produced parallel shifts. In monkeys, terfenadine produced a substantially greater effect on the histamine wheal than did chlorpheniramine (both administered at 30 mg/kg p.o.). Terfenadine also completely protected against i.v. histamine-induced death in guinea pigs. Terfenadine produced no atropine-like effect against pilocarpine-induced salivation in rabbits, no demonstrable histamine H₂ antagonism, no antiserotonin activity, no α or β antagonism, and no untoward cardiovascular effects. Most significantly, terfenadine had no overt central nervous system (CNS) effects in mice, rats, guinea pigs, or monkeys; whereas chlorpheniramine produced tremors and convulsions in mice and monkeys when tested at much lower doses than those used for terfenadine. It is concluded that terfenadine is an effective and specific antihistaminic compound with the potential advantage of a lack of CNS sedative effects.     

Effect of Dopexamine Hydrochloride on Contractions of Rabbit Isolated Aorta Evoked by Various Agonists

The inhibitory affinity of dopexamine hydrochloride to postsynaptic adrenoceptors, cholinoceptors, 5-hydroxytryptamine and histamine receptors was studied in rabbit isolated aorta. Dopexamine (10^?7–10^?5M) antagonized competitively the contractions of rabbit aorta evoked by noradrenaline (pA₂: 6.60). Neither cocaine plus corticosterone nor cocaine, corticosterone plus propranolol altered the inhibition (pA₂: 6.77 and 6.63, respectively). The antagonism of dopexamine against noradrenaline-evoked contractions was the same after 1 and 4 hr of pretreatment with dopexamine. In the presence of cocaine plus corticosterone, dopexamine antagonized the contractions evoked by phenylephrine (pA₂: 6.94). Removal of endothelium did not influence this antagonism (pA₂: 7.06). Dopexamine (10^?7–10^?5M) did not antagonize the contractions of aorta evoked by histamine (3×10^?7–6 × 10^?5M) and by 5-hydroxytryptamine (3 × 10^?7 –3 × 10^?4M). Dopexamine (10^?8 and 10^?7M) did not alter the contractions of endothelium-free aorta evoked by carbachol. Dopexamine (10^?7–10^?5M) slightly enhanced the contractions of aorta evoked by potassium (10^?2–5.5 × 10^?2M). These results suggest that dopexamine is an α₁-adrenoceptor antagonist. Furthermore, dopexamine has no affinity to cholinoceptors, histamine and 5-hydroxytryptamine (5-HT₂) receptors and is apparently not a calcium antagonist.     

Separate receptors mediating the positive inotropic and chronotropic effect of histamine in guinea-pig atria

The direct positive inotropic effect of histamine was studied on paced left atrial preparations from guinea pigs. Histamine (10^?8 to 10^?4 M) increased the maximum tension developed in left atria incubated at 35°C and driven at 2 Hz. The maximum increase in tension was 60% of that observed with norepinephrine. Metiamide (3 × 10^?5 M; a specific H₂-receptor antagonist) did not alter the inotropic response of left atria to histamine. However, tripelennamine (a typical H₁-receptor antagonist) competitively shifted the histamine inotropic dose—response curve to the right at concentrations from 10^?8 to 10^?7 M. Higher concentrations (3 × 10^?7 and 10^?6 M) caused little further additional shift to the right. The positive chronotropic effect of histamine on spontaneously beating atria was competitively antagonized by metiamide (10^?6 and 3 × 10^?6 M). These results demonstrate that in guinea-pig atria histamine increases myocardial contractility by an interaction with receptors closely related to classical H₁-receptors while its chronotropic effects is mediated by interaction with H₂-receptors.     

Carbachol-methohexitone interactions at the chick neuromuscular junction: Experiments with the moving fluid electrode technique

The moving fluid electrode was used to record simultaneously the depolarization and contracture responses produced by drug action. Carbachol (CCh) (5.5 × 10^?6 ?5.5 × 10^?4M) and acetylcholine (ACh) (5.5 × 10^?6 ? 1.1 × 10^?2M) produced large depolarization and contracture responses in the isolated chick biventer cervicis (BVC) muscle. These responses were greatly reduced by methohexitone (8.8 × 10^?5 M). The concentration-response curves for ACh and carbachol in the control Krebs solution were shifted in the presence of methohexitone to the right in a non-competitive manner. The present results indicate that both ACh and carbachol act postjunctionally by depolarizing the membrane and producing contractures in the chick biventer cervicis muscle.     

Effects of S 9977-2 on the guinea pig isolated trachea and the human isolated bronchus

The effects of S 9977-2, a new compound which belongs to the trimethylxanthine family and has shown in vivo promnesic activity and in vitro acetylcholinesterase activities inhibition, were studied on the guinea pig isolated trachea and on human isolated bronchi. On the guinea pig isolated trachea, S 9977-2 in concentrations of 10^?7–10^?4 M potentiated the contractile effect of acetylcholine. The potency of acetylcholine was increased 3.39, 4.26, 9.54, and 13.18 fold with concentrations of 10^?7, 10^?6, 10^?5, and 10^?4M, respectively. The maximum effect of acetylcholine was not modified. S 9977-2 did not potentiate the effects of carbachol or pilocarpine. Under similar conditions, eserine (10^?8 and 10^?6M) and tacrine (10^?8–10^?6M) also potentiated the effects of acetylcholine. The potentiating effect of these two substances was stronger than that of S 9977-2, with a 44.7 fold increase for eserine (10^?7M) and a 64.6 fold increase for tacrine (10^?6M). However, both eserine and tacrine had a contractile effect of their own on the guinea pig isolated trachea, whereas S 9977-2 had no such effect. On the human isolated bronchus, S 9977-2 at a concentration of 10^?5M produced a 19.1 fold increase of acetylcholine effects. On the guinea pig isolated trachea, the effects of S 9977-2 vs. acetylcholine were not modified by epithelium removal. They were increased by pretreatment with indomethacin 10^?6M. In very high concentrations (10^?4 and/or 10^?3M), S 9977-2 reduced the effects of histamine and those of serotonin on the guinea pig isolated trachea. S 9977-2 had no effect on the contractile action of potassium chloride or on the relaxant action of adenosine. The results suggest that in the airway smooth muscle S 9977-2 partially inhibits acetylcholinesterase and/or pseudocholinesterase activity. © 1992 Wiley-Liss, Inc.     

The interaction of bis-pyridinium oximes with mouse brain muscarinic receptor

The bispyridinium oximes toxogonin [N, N′-oxydimethylene bis (pyridinium 4-aldoxim) dichloride] and its structural analogs HS-3, HS-6, HI-6 and MMB-4, and the bispyridinium salt SAD-128, which serve as antidotes to certain types of organophosphorus poisoning, bind competitively to mouse brain muscarinic receptors. This was determined in vitro employing the potent and specific muscarinic antagonist ³H-4NMPB (³H-4-N-methyl piperidyl benzilate). All the bispyridinium compounds also exerted a mild anti-acetylcholine activity (K_d = 10^?4?10^?5M) measured physiologically in the guinea pig ileum, which correlated well with the dissociation constants obtained from binding studies with mouse brain homogenate. The most potent muscarinic blocker was SAD-128 (K′_d = (7.1 ± 1.2) × 10^?6M for whole mouse brain), whose remarkable therapeutic action against soman intoxication may be partly attributed to this antimuscarinic activity.The binding data are best fitted by a competitive model, and the deviation from the law of mass action observed here may be related either to the heterogeneity of muscarinic receptors in the mouse brain or to nonequivalency of the number of binding sites for bisquaternary pyridines and 4-NMPB.     

Fourth international symposium on quantitative mass spectrometry in life sciences

The compound 4(5)-[2-(4-azido-2-nitroanilino)ethyl]imidazole (AAH), a photoaffinity label analog of histamine, has been observed previously to produce a photolysis-dependent, specific and irreversible antagonism of histamine-induced contractile responses of the guinea-pig vas deferens. The pharmacological effects of AAH in isolated guinea-pig aorta (GPA) and dog trachealis (DT) were evaluated in the present study. Photolysis of 3 × 10^?5 M AAH for 5 min with visible light in organ baths containing the GPA resulted, after washout of AAH, in a nonequilibrium competitive antagonism of contractile responses to histamine; responses to norepinephrine and KCl were not affected. In contrast, photolyzed AAH (3 × 10^?5 M, one or two photoalysis treatments; 10^?4 M AAH, two treatments) did not antagonize contractile responses of the DT to histamine, nor were responses to acetylcholine or KCl affected. To test the possibility that AAH lacks affinity for histamine receptors in the DT, molar K_B values were obtained for nonphotolyzed AAH used as a conventional equilibrium competitive antagonist; K_B values for GPA and DT were not different (?log K_B were 5.48±0.18 and 5.04±0.23 for GPA and DT, respectively; P>0.05). pA₂ values for diphenhydramine, an H₁-histamine receptor antagonist, indicated a moderately greater potency in GPA compared to DT (pA₂ were 7.58±0.10 and 6.89±0.13 for GPA and DT, respectively; P<0.05); however the diphenhydramine: AAH potency ratio did not explain the resistance of the DT to photolyzed AAH. Cimetidine (10^?6?10^?4 M), an H₂-receptor antagonist, potentiated contractile responses of the GPA to histamine but was without an effect in the DT. No evidence for relaxation by histamine in preparations with induced tone was obtained; the resistance of the DT to photolyzed AAH therefore does not involve an inhibition of H₂-inhibitory receptors. Photolyzed AAH thus demonstrates tissue-selective antihistamine activity, perhaps as a result of differences in the characteristics of H₁-receptors in the GPA and DT.     

Relation between Cyclic GMP Generation and Cerebrovascular Reactivity: Modulation by NPY and α-Trinositol

Abstract It is considered that cyclic guanosine monophosphate (cGMP) plays a pivotal role in mediating the relaxation of vascular and nonvascular smooth muscles. cGMP steady state levels are regulated by guanylyl cyclase, cGMP phosphodiesterases and its flux from cells. The present study examines the possible relation between cerebrovascular vasodilator agents and generation of cGMP in guinea pig cerebral vessels. Acetylcholine, substance P, nitroglycerine and sodium nitroprusside significantly increased the generation of cGMP. The application of acetylcholine, substance P, nitroglycerine and sodium nitroprusside elicited concentration-dependent relaxation of basilar artery segments. Neuropeptide Y increased the generation of cGMP by 2%–46% of control levels (at 10^?7-10^?6 M of neuropeptide Y; *P<0.05). In addition, neuropeptide Y (10^?6 M) induced a transient relaxation of the precontracted guinea pig basilar arteries with endothelium. This transient relaxation was blocked by nitro-L-arginine (10^?4 M). α-Trinositol does not alter the formation of cGMP nor the neuropeptide Y-induced relaxation. In the presence of α-trinositol neuropeptide Y (10^?7-10^?6 M) did not significantly elevate the production of cGMP as compared with controls. The rise in cGMP induced by acetylcholine, substance P and nitroglycerine was slightly increased by the addition of neuropeptide Y (3×10^?7 M). Acetylcholine and substance P induced an endothelium-dependent relaxation of the precontracted guinea pig basilar arteries, while sodium nitroprusside and nitroglycerine induced an endothelium-independent relaxation. Acetylcholine, substance P and nitroglycerine induced concentration-dependent relaxations of basilar artery, respectively. The relaxation elicited by acetylcholine or substance P, but not nitroglycerine, was markedly attenuated by neuropeptide Y (3×10^?7 M). This inhibitory effect of NPY on vasomotor responses was completely reversed by α-trinositol (10^?6 M).     

The effect of 5-hydroxytryptamine on the chick biventer cervics muscle

The actions of 5-hydroxytryptamine have been studied in the chick biventer cervics nerve—muscle preparation. At concentrations between 2.5 × 10^?3 and 3.7 × 10^?3 M, 5HT produced a transient increase in responses to indirect stimulation, but not to direct stimulation. At higher concentrations, 5HT produced a reversible depression of twitches, which was much more marked in indirectly than in directly stimulated preparations. In a concentration range of 2.5–3.7 × 10^?3 M, 5HT increased the response to exogenous acetylcholine but reduced the response to carbachol. After pretreatment with neostigmine, 5HT inhibited responses to both acetylcholine and carbachol. It is suggested that the facilitatory effects of 5HT are due to its anticholinesterase activity. The blocking actions of 5HT are thought to be curare-like. In addition, irreversible toxic effects on the muscle preparations were found after repeated exposures to high concentrations of 5HT.     

Antimuscarinic action of methoctramine, a new cardioselective M-2 muscarinic receptor antagonist, alone and in combination with atropine and gallamine

The antimuscarinic effects of methoctramine (N,N'-bis[6- [(2-methoxybenzyl)amino]hexyl]-1,8-octanediamine tetrahydrochloride) were investigated in vitro in isolated paced left (force) and spontaneously beating right (force and rate) atria of guinea pigs as well as ileum of guinea pig and rat. Methoctramine was a potent competitive antagonist of M-2 muscarinic receptors in myocardium and pacemaker cells over a wide range of concentrations. The pA2 values ranged from 7.74 to 7.93. They were not significantly different in the two cardiac preparations and were independent of the agonist used (muscarine and carbachol). A combination of methoctramine with atropine resulted in addition of the dose ratios for left atria, which is expected for two antagonists interacting competitively with the same receptor site. In contrast, a combination of methoctramine with gallamine produced a less than additive shift of the dose-response curve for carbachol, confirming that gallamine acts as an allosteric antagonist at cardiac muscarinic receptors. Methoctramine was 54 to 132-fold less potent in ileal than in atrial preparations (pA2 values ranging from 5.81 to 6.20) which makes it the most cardioselective antimuscarinic agent now available. A combination of methoctramine with atropine gave a slight supra-additive antagonism on guinea pig ileum, which suggests that methoctramine interacts to some extent with a second independent site. These results strongly reinforce the view that M-2 muscarinic receptors are not a homogeneous population.     

Mechanism of action of histamine in the estrogen-primed rat uterus

Histamine produced a dose-dependent relaxation of uterine strips obtained from the estrogen-primed rat uterus. The responses to histamine were blocked competitively by metiamide (10^?8 ?10^?8M), a specific H₂-receptor antagonist. Propranolol, a selective β-receptor blocker also produced competitive antagonism of the responses to histamine in the same dose range (10^?8?10^?6 M). The pA₂ value obtained for metiamide (8.9) was not significantly different from that obtained for propranolol (8.6). Nialamide (2.2 × 10^?6 M), the monoamine oxidase inhibitor, and cocaine (4.3 × 10^?6 M), the selective noradrenaline uptake blocker, potentiated the responses to histamine. However bretylium (2.4 × 10^?5 M), an adrenergic neuron blocker inhibited the responses to histamine. The combined effect of tyramine and histamine was found to be additive. Our data suggest that the histamine-induced relaxation of rat uterus may be produced through the stimulation of presynaptic H₂-receptors which causes the release of noradrenaline. The released noradrenaline acts on the postsynaptic β-receptors and produces relaxation of the rat uterus.     

Studies on beta-adrenoceptors mediating changes in mechanical events and adenosine 3',5'-monophosphate levels. Guinea-pig trachea.

In quinea-pig tracheal smooth muscle, (?)-isoproterenol and (?)-soterenol increase cyclic AMP levels, the latter being classified as a partial agonist. The ED₅₀ values were 1.74 × 10^?7 M and 2.48 × 10^?7M for isoproteronol and soteronol, respectively. Isoproterenol and soterenol were also examined as competitive antagonists of isoproterenol-induced increase in cyclic AMP levels. The apparent dissociation constants calculated from dose ratios for antogonism were 2.19 × 10^?8 M for isoproterenol and 08.38 × 10^?8 M for soterenol. These values are the same as apparent dissociation constants obtained in previous studies on relaxation produced by these agonsits. Carbachol, the functional antagonist use to estimate agonist dissociation constants for production of relaxation, antagonized isoproterenol- and soterenol-induced increases in cyclic AMP only in the central region of their dose-response curves without blocking effects of small or large doses of either agonist. This antagonism was demonstrated to be calcium-dependent. The results are consistent with the view that β-receptors mediating relaxation and diseases in cyclic AMP levels in guinea-pig trahea are of the same type and that differences in concentrations required to elicit the two responses is a result of the receptor reserve. A larger receptor reserves for β-agonist in tracheal smooth muscle vs. heart is considered to be a major determinant in quantitative responses produced in the two tissues.     

Inhibition by (−)-Deprenyl of Agonist-Evoked Contractions in Rabbit Aorta

Abstract: The effect of (?)-deprenyl, a relatively selective MAO-B inhibitor, was examined for its ability to inhibit the contractions of rabbit isolated aorta evoked by various agonists and potassium. (?)-Deprenyl (10^?5?3 × 10^?4 M) antagonized the contractions evoked by noradrenaline (10^?8?3 × 10^?4 M); pA₂: 5.10. The antagonism was reversible. It was attenuated by cocaine (3x M); pA₂: 4.38, unchanged by corticosterone (4 × 10^?5 M); pA₂ 4.79 and enhanced by cocaine (3 × 10^?5 M) plus corticosterone (4 × 10^?5 M); pA₂: 5.48. (+)-Deprenyl (10^?6?10^?4 M) did not alter the contractions evoked by noradrenaline (3 × 10^?9?10^?4 M). Clorgyline (10^?5 and 10^?4 M) antagonized the noradrenaline-evoked contractions. Pargyline (10^?4 and 3 × 10^?4 M) had no effect. (?)-Deprenyl (10^?5?3 × 10^?4 M) antagonized the contractions evoked by phenylephrine (10^?8?10^?4 M); pA₂: 5.10. Removal of the endothelium did not alter the antagonism; pA₂: 5.35. (?)-Deprenyl (10^?5?3 × 10^?4 M) antagonized the contractions evoked by either 5-hydroxytryptamine (3 × 10^?8?3 × 10^?4 M); pA₂: 4.61 or by histamine (10^?6?3 × 10^?2 M); pA₂: 4.84. (?)-Deprenyl (3 × 10^?4 M) caused a non-competitive antagonism of the contractions evoked by potassium (1.5-5.5 × 10^?2 M). It is concluded that (?)-deprenyl is a weak inhibitor of postjunctional α-adrenoceptors, 5-hydroxytryptamine (5-HT₂) receptors, and histamine (H₁) receptors.     

Neurotransmitter modulation of prostaglandin E1-stimulated increases in cyclic AMP. I. Characterization of a cultured neuronal cell line in exponential growth phase.

Two sympathetic ganglion cell X neuroblastoma somatic cell hybrids (TC × 11 and TC × 17) were found to have a PGE₁-sensitive adenylyl cyclase which was inhibited in whole cells by carbachol, norepinephrine and dopamine. Serotonin and morphine were without effect, the latter despite the presence of opiate receptors. In the TC × 17 clone, carbachol produced a greater degree of inhibition (30 per cent of control levels) than norepinephrine or dopamine (55–65 per cent of control). The ed₅₀ for inhibition was of the order norepinephine > dopamine > carbachol (10^?7, 3 × 10^?7 and 10^?6 M respectively). The inhibition by carbachol could be reversed by the muscarinic antagonists scopolamine and atropine, while the nicotinic antagonists α-bungarotoxin and d-tubocurarine were without effect. The inhibition by norepinephrine and dopamine possessed the following properties: (1) the inhibition was mimicked by phenylephrine but not by isoproterenol, nor by dopaminergic agonists apomorphine and ET495; (2) the α-antagonists phenoxybenzamine and phentolamine reversed the inhibition by norepinephrine and dopamine; and (3) chlorpromazine reversed the inhibition of cyclic AMPformation by dopamine. Other phenothiazines tested, trifluoperazine, and fluphenazine, had no effect. It is concluded that the TC × 17 clone expresses two classes of receptors capable of modulating PGE₁. The cholinergic receptor is muscarinic and the catecholamine receptor has α-adrenergic properties.     

Anticholinergic action of disopyramide in intestinal smooth muscle of the guinea pig: inhibition of muscarinic receptors (M1 and M2).

Antimuscarinic actions of disopyramide were investigated by measuring the contractile responses of intestinal smooth muscles and ligand binding in cardiac and intestinal membrane preparations. Disopyramide caused a parallel shift of the dose-response curves for acetylcholine, McN-A-343, and carbachol to the right in the guinea pig taenia caeci; pA2 values were 5.4 for acetylcholine, 5.5 for McN-A-343 and 5.9 for carbachol. In the guinea pig ileum, disopyramide competitively antagonized acetylcholine in the contractile responses, having the pA2 value of 6.1. In microsomal fractions of the guinea pig taenia caecum and heart, disopyramide was capable of replacing 3H-QNB; K1 values were 7 x 10(-6) M for the taenia and 2 x 10(-6) M for the heart. These results suggest that disopyramide exerts antimuscarinic action through M1 and M2 receptors with a potency approximately 3 times greater for M2 than M1.