Effects of moguisteine on the cough reflex induced by afferent electrical stimulation of the superior laryngeal nerve in guinea pigs.

The study aimed to further demonstrate the peripheral antitussive properties of moguisteine. Firstly, the antitussive effect of moguisteine on the cough reflex induced by inhalation of citric acid aerosol was evaluated in conscious guinea pigs. Secondly, the effects of both moguisteine and codeine on the centrally mediated cough reflex induced by afferent electrical stimulation of the superior laryngeal nerve were investigated in anesthetized guinea pigs. Moguisteine (2.5-10 mg/kg, intravenously, i.v.) reduced the cough reflex induced by 7.5% citric acid aerosol in a dose-dependent manner, with an ED50 value of 0.55 mg/kg. Both i.v. (0.5-4 mg/kg) and intracerebroventricular (i.c.v., 5-20 microg) injection of codeine dose dependently inhibited the cough reflex induced by afferent electrical stimulation of the superior laryngeal nerve; the ED50 values were 0.91 mg/kg and 7.90 microg, respectively. The inhibitory effect of codeine (4 mg/kg i.v.) was abolished by pretreatment with naloxone (2 mg/kg intraperitoneally). In contrast to codeine, neither i.v. (4 and 20 mg/kg) nor i.c.v. (20 microg) injection of moguisteine affected the cough reflex. These results suggest that the antitussive effect of codeine is mediated by central opioid mechanisms, whereas the antitussive effect of moguisteine is mediated by peripheral mechanisms.

Actions of moguisteine on cough and pulmonary rapidly adapting receptor activity in the guinea pig.

With anaesthetized guinea pigs, the actions of moguisteine were tested on the cough reflex, the resting discharge of lung rapidly adapting receptors (RARs), RAR activity induced by aerosols of capsaicin, stimulation of RARs due to i.v. injection of capsaicin, and on the reflex responses to i.v. capsaicin. I.v. moguisteine (20 microg kg(-1)), compared with vehicle, decreased the spontaneous firing of RARs. Intragastric (i.g.) moguisteine (200 mg kg(-1)) had no effect on resting discharge. I.g. moguisteine depressed the cough response due to capsaicin aerosol (0.01(-1) mg ml(-1)) and significantly reduced the increased discharge of the RARs due to the aerosol. I.v. and i.g. moguisteine reduced the proportionate increase in RAR discharge due to i.v. capsaicin (50 microg kg(-1)). It did not appreciably affect the cardiovascular and respiratory responses to i.v. capsaicin, which presumably activated lung C-fibre receptors. We conclude that the antitussive action of moguisteine is mediated at least in part by a decrease in the excitatory response of RARs to tussive stimuli.

Effects of moguisteine, a peripheral nonnarcotic antitussive agent, on airway inflammation in guinea-pigs in vivo.

Cough is a common symptom of respiratory diseases associated with irritation or inflammation of the airways, and symptomatic antitussive drugs are frequently prescribed to control an abnormal cough reflex. Our aim was to evaluate the effects of moguisteine, a novel, peripheral, nonnarcotic antitussive agent, on airway inflammation induced in guinea-pigs with a variety of stimuli. These stimuli included exposure to tobacco smoke for 10 min, to elicit airway hyperreactivity, eosinophil recruitment in bronchoalveolar lavage (BAL), airway epithelial damage and plasma exudation; graded platelet-activating factor (PAF) infusion (600 ng.kg-1 over one h), to induce airway hyperreactivity; 2% ovalbumin (OA) aerosol challenge in 1% OA-sensitized animals, to induce late-phase (17 and 72 h) airway leucocyte accumulation. We also assessed the activity of moguisteine on plasma leakage induced by capsaicin, on bronchoconstriction induced by acetylcholine (ACh), histamine (H) and PAF, and on leukotriene mediated allergic bronchospasm in OA-sensitized guinea-pig. Moguisteine (p.o. and i.m.) and dexamethasone (p.o. and i.m.) dose-dependently reduced tobacco smoke-induced bronchial hyperreactivity. Moguisteine and dexamethasone abolished eosinophil recruitment in BAL, prevented the sloughing of the epithelium and significantly reduced airway microvascular leakage. Both agents were also highly effective in reducing bronchial hyperreactivity elicited by PAF infusion. In addition, moguisteine was active in inhibiting airway neutrophil and eosinophil accumulation in BAL observed 17 and 72 h after OA challenge in sensitized guinea-pigs. In contrast to dexamethasone, moguisteine did not prevent capsaicin-induced plasma leakage. It was also ineffective against bronchoconstriction as induced by ACh, H, and PAF and failed to inhibit leukotriene-dependent bronchospasm. Our data suggest that moguisteine represents an antitussive compound endowed with interesting airway anti-inflammatory properties in guinea-pigs in vivo. Its mechanism of action remains to be elucidated.

Antitussive activity of moguisteine enantiomers in guinea-pigs and rats.

The antitussive effect of the R-(+)- and S-(-)-enantiomers of moguisteine were evaluated in comparison with the racemate in cough induced by 7.5% citric acid and 30 microM capsaicin aerosol in conscious guinea-pigs. No difference in potency was observed between moguisteine and the enantiomers. The oral ED50 values (with 95% confidence limits) for moguisteine, R-(+)- and S-(-)-enantiomers were respectively: 20.4 (12.9-26.6), 20.9 (14.9-26) and 21.6 (11.8-30.0) mg/kg-1 in cough provoked by citric acid and 17.7 (12.5-29.8), 18.9 (14.1-30.1) and 20.5 (15.1-36.6) mg/kg-1 in cough induced by capsaicin. The acute oral and intraperitoneal toxicities of the enantiomers and moguisteine in the rat are very similar. These findings suggest that the use of either enantiomer does not offer any advantage over the racemate.

N-acyl-2-substituted-1,3-thiazolidines, a new class of non-narcotic antitussive agents: studies leading to the discovery of ethyl 2-[(2-methoxyphenoxy)methyl]-beta-oxothiazolidine-3-propanoate.

The synthesis of a novel class of antitussive agents is described. The compounds were examined for antitussive activity in guinea pig after cough induction by electrical or chemical stimulation. Ethyl 2-[(2-methoxyphenoxy)methyl]-beta-oxothiazolidine-3-propanoate (BBR 2173, moguisteine, 7) and other structurally related compounds showed a significant level of activity, comparable to that of codeine and dextromethorphan. The compounds presented in this paper are characterized by the N-acyl-2-substituted-1,3-thiazolidine moiety, which is a novel entry in the field of antitussive agents. The serendipitous discovery of the role played by the thiazolidine moiety in determining the antitussive effect promoted extensive investigations on these structures. This optimization process on N-acyl-2-substituted-1,3-thiazolidines led to the initial identification of 2-[(2-methoxypheoxy)methyl]-3-[2-(acetylthio)acetyl]- 1,3-thiazolidine (18a) as an interesting lead compound. The careful study of the rapid and very complicated metabolism of 18a provided further insights for the design of newer related derivatives. The observation that the metabolic oxidation on the lateral chain's sulfur of 18a to sulfoxide maintained the antitussive properties suggested the introduction of isosteric functional groups with respect to the sulfoxide moiety. Subsequent structural modifications showed that hydrolyzable malonic residues in the 3-position of the thiazolidine ring were able to assure high antitussive activity. This optimization ultimately led to the selection of moguisteine (7) as the most effective and safest representative of the series. Moguisteine is completely devoid of unwanted side effects (such as sedation and addiction), and its activity was demonstrated also in clinical studies.

Moguisteine: a novel peripheral non-narcotic antitussive drug.

1. The antitussive effects of moguisteine have been compared with codeine in several experimental models of cough in guinea-pigs and dogs. 2. Moguisteine and codeine dose-dependently (respective ED50 values are given in parentheses) inhibited cough induced in guinea-pigs by 7.5% citric acid aerosol (25.2 and 29.2 mg kg-1, p.o.), by 30 microM capsaicin aerosol (19.3 and 15.2 mg kg-1, p.o.), by mechanical stimulation (22.9 and 26.4 mg kg-1, p.o.) and by tracheal electrical stimulation (12.5 and 13.9 mg kg-1, p.o.). 3. Moguisteine was effective against cough induced by tracheal electrical stimulation in dogs (ED50 17.2 mg kg-1, p.o.); codeine was not tested because of its emetic effect. 4. After repeated dosing (12-15 days), moguisteine did not induce tolerance in either guinea-pigs or dogs. 5. Moguisteine did not interact with opiate receptors, since it did not show affinity for [3H]-naloxone binding sites and furthermore naloxone (5 mg kg-1, s.c.) did not antagonize its antitussive effects. 6. Moguisteine had no antitussive effect after i.c.v. administration (20 micrograms), whilst codeine (2-10 micrograms) and dextromethorphan (2.5-20 micrograms) were highly effective. 7. Our findings demonstrate that moguisteine is a novel peripherally acting non-narcotic antitussive agent, the mode of action of which remains to be elucidated fully.

Airway hyperreactivity induced by active cigarette smoke exposure in guinea-pigs: possible role of sensory neuropeptides.

Exposure to cigarette smoke is associated with increased airway responsiveness to different stimuli, both in human and animal studies. However, the mechanisms involved in the pathogenesis of smoke-induced airway hyperreactivity are less clear. We investigated the development of airway hyperreactivity induced by active cigarette smoke exposure in anaesthetised guinea-pigs and the possible mechanisms involved. Active inhalation of cigarette smoke (15 s/min for 10 min) potentiated the broncho-contractile effect of acetylcholine (Ach), indicating the occurrence of airway hyperreactivity. This phenomenon appeared within 5 min and lasted up to 50 min after smoke exposure. Smoke induced airway hyperreactivity was a non-specific phenomenon, involving an enhanced responsiveness to both Ach and histamine (Hist). Recruitment of proinflammatory cells into the airway lumen, as revealed by the analysis of bronchoalveolar lavage fluid, paralleled the development of the hyperreactive phenomenon, suggesting a relationship between the inflammatory reaction and the genesis of smoke-induced airway hyperreactivity. Cervical bilateral vagotomy did not modify either the degree and the time-course of smoke induced airway hyperreactivity. Moreover, atropine treatment did not affect the increase in Hist response due to smoke inhalation. On the other hand, depletion of substance P due to capsaicin pretreatment almost completely prevented the capacity of cigarette smoke to potentiate Ach induced bronchoconstriction. Cyclo-oxygenase inhibition, by indomethacin pretreatment, reduced the time course of the hyperreactivity induced by smoke inhalation. Our results clearly demonstrate the occurrence of airway hyperreactivity triggered by active cigarette smoke exposure. Moreover, the data obtained suggest a predominant role for substance P and related peptides in the pathogenesis of smoke induced increase in airway responsiveness.

Benzodiazepine receptor ligands. Synthesis and preliminary pharmacological evaluation of 2-aminoalkyl-8-chloro- and 2-aryl-1,2,4-triazolo[3,4-a]phthalazine-3(2H)-ones.

Some 2-aminoalkyl-8-chloro- and 2-aryl-1,2,4-triazolo[3,4-a]-phthalazine-3-(2H)-ones were synthesized and preliminarily tested in vitro and in vivo as potential benzodiazepine-receptor (BZRs) ligands. 2-Aryl-1,2,4-triazolo[3,4-a]-phthalazine-3(2H)-ones displaced in vitro 3H-diazepam (3H-DZ) from rat brain specific binding sites with Ki (nM) comparable to DZ and chlordiazepoxide used as reference compounds. The specific binding of the triazolones of this study was not enhanced in vitro by 4-aminobutyric acid (GABA) and in vivo they did not show any activity in counteracting the pentylenetetrazole (PTZ) induced convulsions (mice). One of these compounds (IV a) antagonized the effects of DZ in the bicuculline (BIC) induced convulsions test (mice) and the DZ induced muscle relaxant effects in the horizontal wire test.

6-(Alkylamino)-3-aryl-1,2,4-triazolo[3,4-a]phthalazines. A new class of benzodiazepine receptor ligands.

Some 6-(alkylamino)-3-aryl-1,2,4-triazolo[3,4-a]phthalazines have been shown to displace diazepam from rat brain specific binding sites, in vitro, with Ki (nM) values comparable to those of reference benzodiazepines and to have anticonvulsant (pentylenetetrazole test, mice) and anticonflict activity (Vogel test, rat) in vivo. Separation between the doses causing anticonflict effects (Vogel test, rat) and those impairing motor coordination (rotarod test, rat) has been shown for N,N-bis(2-methoxyethyl)-3-(4-methoxyphenyl)-1,2,4-triazolo[3,4-a] phthalazin-6-amine (80). This compound, unlike diazepam, was inactive in counteracting the strychnine (mouse) and maximal electroshock (mouse) induced convulsions and in the "aggressive monkey" model. These differences from the classical benzodiazepines in the animal tests indicate that 80 may have some selective anxiolytic activity.

3-(1-Iminoethyl)-4,5-cycloalkylpyridine-2,6-diol derivatives. A novel class of benzodiazepine receptor antagonists and partial agonists.

A series of 3-(1-iminoethyl)-4,5-cycloalkylpyridine-2,6-diol derivatives have been prepared from isoxazolo [5,4-b] pyridones. Some of these compounds had affinity for the benzodiazepine receptors in vitro and in vivo radioligand displacement assays. These compounds did not have any anticonvulsant properties and were not active in pharmacological tests predictive of antianxiety activity, but antagonised the anticonvulsant and muscle-relaxant effects of diazepam and had proconvulsant properties.

Heterocyclic GABA analogues. Displacement of radiolabelled 3H-GABA from rat brain membrane preparations.

2,5-Dimethyl-1H-pyrrol-1-yl-butanoic acid (I) and 2,5-diethyl-1H-pyrrol-1-yl-butanoic acid (V) were synthesised as non basic analogues of 4-aminobutanoic acid (GABA) to investigate the influence of the pKa of the 4-nitrogen on the in vitro binding to GABA receptors. (I) displaced 3H-GABA from specific binding sites of synaptosomal membrane preparations from rat cerebellum with an IC50 of 0.5 microM and (V) with an IC50 of 0.4 microM. (I) was inactive in vivo in the bicuculline anticonvulsant test (mice i.p.). The authors conclude that a basic nitrogen is not necessary for the binding to the GABAergic receptors although the ensuing complex is likely to be pharmacologically ineffective.

Benzodiazepine receptor binding and anticonflict activity in a series of 3,6-disubstituted pyridazino[4,3-c]isoquinolines devoid of anticonvulsant properties.

A series of 3,6-disubstituted pyridazino[4,3-c]isoquinolines were synthesized and tested for their ability to inhibit the binding of [3H]diazepam to rat brain receptors in vitro. Compounds bearing a phenyl, 4-methoxyphenyl, or methyl group at position 3 and a dialkylamino group at position 6 showed the highest affinity in the binding assay and were subsequently evaluated for their anticonflict and anticonvulsant effects. All of these compounds (5a-1 and 5q) were active in the Vogel rat conflict procedure, but none prevented convulsions in mice induced either by metrazol or bicuculline. 3-Phenyl-6-pyrrolidinylpyridazino[4,3-c]isoquinoline (5d) with a Ki = 11.4 nM in the binding assay exhibited the best potency in the anticonflict assay (MED 5 mg/kg ip) and did not produce neuromuscular impairment at the highest dose tested (50 mg/kg ip).

MDL-646, a new synthetic E1-prostaglandin with local protective effects on the gastric mucosa.

The gastric protection, diarrheogenic and arterial hypotensive effects of MDL-646, a PGE1 derivative, have been studied in rats. The compound administered p.o. or i.v. was able to inhibit the macroscopic damage to gastric mucosa produced by noxious stimuli (ethanol and indomethacin). In the stomach perfusion test with the anesthetized rat, intravenously administered MDL-646 reduced histamine- or pentagastrin-stimulated gastric secretion. After intraduodenal administration (i.d.) doses at least 40-50 times greater were necessary for an antisecretory effect. In conscious rats with chronic gastric fistulas, intragastrically administered (i.g.) MDL-646 affected both acid concentration and volume of unstimulated gastric secretion. In experimental models for gastric lesions, MDL-646 was much more potent after oral (p.o.) (15-30 times) than after i.v. administration. (ED50 micrograms/kg: vs. alcohol lesions, 0.05 p.o. and 0.7 i.v.; vs. indomethacin ulcers, 7.0 p.o. and 195 i.v.). Our data would fit the hypothesis that it was a local effect on the gastric mucosa. The mechanism of this effect is not known. The supposed local activity coupled with the antisecretory effects and the good tolerability make it interesting to test MDL-646 as an anti-ulcer agent in man.

Synthesis and antifertility activity of 13-aza 14-oxo-prostaglandins.

Some 13-aza-14-oxo prostaglandin analogues of PGF2 alpha, PGE2 and PGA2 have been synthetized in optically active form, starting from Corey's intermediate and evaluated for antifertility activity in the hamster. The C-15 absolute configuration was established and found critical for the biological activity, but unexpectedly the highest potency was always associated with the 15 epi derivatives. Among the PGF2 alpha analogues the 15 epi derivative was about one tenth as potent as PGF2 alpha. The preparation of a few 16-phenoxy 17,18,19,20 tetranor-derivatives led to more potent compounds with the p-fluorophenoxy analogue having the same potency as PGF2 alpha.

Synthesis and pregnancy terminating activity of 2-arylimidazo [2,1-a]isoquinolines and isoindoles.

A series of 2-arylimidazo[2,1-a]isoquinolines (1-21), some 5,6-dihydro derivatives (22-28) and 2-phenyl-5H-imidazol[2,1]isoindole (29) were synthesized and tested for the pregnancy terminating activity in hamsters and rats. An efficient preparation of 2-arylimidazo[2,1-a]isoquinolines was devised. The isoquinolines having a 4-chlorophenyl (8), 4-bromophenyl (9), or a biphenylyl group (12) in the 2-position were the most potent compounds after subcutaneous administration. Compound 12 also showed good oral activity. The data obtained with the title compounds are compared with those of the corresponding triazolo [5,1-1]isoquinolines and isoindoles. The structure-activity relationships are discussed.

In vitro and ex vivo binding to uterine progestin receptors of the rat as a tool to assay progestational activity of glucocorticoids.

The competition of some widely employed glucocorticoids with the binding of [3H]-promegestone, a highly potent synthetic progestagen, to uterine cytosol progestin receptors of the immature rat has been studied both in in vitro and ex vivo experiments. The relative binding affinities (RBA's) to progesterone were determined in vitro: fluocinolone acetonide greater than triamcinolone acetonide greater than betamethasone 17-valerate greater than prednisolone, betamethasone, triamcinolone and cortisol. After pretreating rats in vivo with progesterone or chlormadinone acetate (subcutaneously), a dose-dependent decrease in in vitro binding of [3H]-promegestone to uterine cytosol was evident. Similar decreases were obtained after pretreatment with some of the other glucocorticoids tested. Potency ratios to progesterone, arbitrarily set at 1.0, were: fluocinolone acetonide 86.7, triamcinolone acetonide 5.6, betamethasone valerate 4.1, chlormadinone acetate 2.6. Prednisolone, betamethasone, triamcinolone and cortisol were inactive. Both the in vitro and the ex vivo results clearly indicate that glucocorticoids interact with the uterine cytosol progestin receptor system, depending on their chemical structures; this interaction may account for some of their unwanted side-effects in the endocrine system. Moreover, this experimental system may prove to be a useful tool for evaluation of the progestational activities of glucocorticoids and other steroids, using the rat as an animal model.

A new non-hormonal pregnancy-terminating agent.

DL 111-IT, 3-(2-ethylphenyl)-5-(3-methoxyphenyl)-1H-1,2,4 triazole, a compound belonging to a new class of non-hormonal antifertility agents, when given subcutaneously, intramuscularly, intravaginally or orally terminates pregnancy in the rat, the mouse, the hamster and the dog. Time-course and dose-activity studies indicate that its effectiveness is dependent on dose, vehicle, route and time of pregnancy. DL 111-IT has no pre-implantation activity. The most effective time for treatment is the early post-implantation period. The compound has an antifertility effect through a slow and continuing action that results in the degeneration and subsequent resorption or expulsion of conceptuses. As a result, there must be sustained availability of active principle to arrest the pregnancy. Administered parenterally in a proper vehicle (oily) and with a suitable schedule of treatment (x 2-5 days), it demonstrates a very high pregnancy terminating activity (ED50: 0.04-0.7 mg/kg/day). Multiple intravaginal and oral administrations are also effective but the daily doses required are 10-20 and 40-100 times higher than the parenteral ones. Studies of the mechanism of action indicate that the site of action is the utero-placental complex. In fact, in pregnant rats, mice, hamsters and dogs, both plasma progesterone levels and the ineffectiveness of progesterone therapy rule out luteolysis as a basis for the activity. Moreover in hypophysectomized, ovariectomized animals whose pregnancies were maintained with proper hormonal treatments, DL 111-IT terminates pregnancy and adrenalectomy does not prevent its effect, which suggests that pituitary, ovaries and adrenals are not required for the antifertility action.

Pregnancy terminating activity of a new non-hormonal anti-fertility agent, 2-(3-ethoxy-phenyl)-5,6-dihydro-s-triazole [5,1-a] isoquinoline (DL 204-IT) in the rat and the hamster. Studies on the factors affecting its activity.

The biological and the pharmacokinetic profiles of 2-(3-ethoxy-phenyl)-5,6-dihydro-s-triazole [5,1-a]isoquinoline (DL 204-IT) were explored in rats and hamsters at different stages of gestation (1st--11th day) after single and multiple (5 days) doses given in different vehicles (oily and aqueous) and by different routes of administration (s.c., i.m., i.v.). The effectiveness of the compound was demonstrated to be dependent on time of gestation, dose and vehicle. DL 204-IT did not show any pre-implantation activity. The optimal time for treatment was found to be immediately after the implantation of blastocysts. Time-course studies demonstrated that the anti-fertility action is slow and progressive with subsequent degeneration and reabsorption (rats and hamsters), or expulsion (only hamsters) of conceptuses. The biological and pharmacokinetic data show that with prolonged presence of the compound at the site of action (the utero-placental complex) lower doses are far more active in interrupting embryonal development than are much higher ones for shorter time periods.