Antonio Schiavone

The gastrointestinal motor effect of benzamide derivatives is unrelated to 5-HT3 receptor blockade

The prokinetic properties of a number of 5-HT3 antagonists containing the benzamide moiety (metoclopramide, cisapride, BRL 24924, zacopride) were compared with those of the chemically unrelated antagonist, ICS 205-930. Their 5-HT3 antagonistic potency was evaluated using the Bezold-Jarisch test. All compounds accelerated gastric emptying of beads in the rat, with potencies comparable to those found for inhibiting the Bezold-Jarisch reflex. Metoclopramide, cisapride and zacopride potentiated the twitch contraction of guinea pig ileum and contracted the isolated guinea pig colon in a concentration-dependent manner. Furthermore, they increased the contractility of the gastric Heidenhain pouch in the conscious dog. In contrast, ICS 205-930 was devoid of agonist or antagonist activities in all models except gastric emptying in the rat. Two findings, (1) that benzamide derivatives showed high efficacy in all models of gastrointestinal motility in contrast to ICS 205-930 that was active only to increase gastric emptying, and (2) the different potency order of benzamides in the Bezold-Jarisch test as compared to the in vitro motility tests, indicate that 5-HT3 receptors are involved in gastric emptying, whereas a different receptor operates in the other models used.

DAU 6285: A novel antagonist at the putative 5-HT4 receptor

The antagonistic properties of DAU 6285, an azabicycloalkyl benzimidazolone derivative, at putative 5-hydroxytryptamine4 (5-HT4) receptors were investigated in in vitro preparations of guinea-pig ileum and human atrium, in comparison to ICS 205-930. DAU 6285 behaved as a competitive antagonist in all the preparations examined. Its affinity (pA2) ranged between 6.50 and 7.12 in the test models considered. The affinity of ICS 205-930 was 2-3 fold lower. At variance with ICS 205-930, DAU 6285 displayed a weak affinity for 5-HT3 receptors (pKi = 6.1, rat cortex; pA2 less than 5, guinea-pig ileum). In the guinea-pig ileum, DAU 6285 (10 microM) did not exert antimuscarinic, antihistaminic, antinicotinic or myolytic activity. Moreover, it did not bind to other 5-HT receptor subtypes, or to adrenergic, dopaminergic, benzodiazepine, nicotine, GABA receptors. DAU 6285 may represent a suitable tool for studies in the field of 5-HT4 receptors.

Pharmacological properties of a novel class of 5-HT3 receptor antagonists

The pharmacological profile of six representative members of a novel class of 5-HT3 receptor antagonists is described. The compounds are esters and amides of benzimidazolone-1-carboxylic acid with a basic azabicycloalkyl moiety (compounds 1-3) and their respective ethyl derivatives (compounds 4-6). In isolated preparations (rabbit heart and guinea pig ileum) all compounds antagonized the 5-HT3 receptor-mediated effects of serotonin, with potencies comparable with those of the reference compounds, ICS 205.930 and GR 38032F (-log IC50 9.30-11.9 and 6.8-8.20, in heart and ileum, respectively). In the anaesthetised rat, all agents potently inhibited the Bezold-Jarisch reflex whether given i.v. or i.d. I.v. administration of compounds prevented cisplatin-induced emesis in dogs (ID50 ranging from 3.7 to 147 micrograms/kg). All agents accelerated gastric emptying of solids in rats (ED50 about 10-160 micrograms/kg i.p.). In addition, compounds 4 and 5 were able to stimulate 5-HT4 receptors in the isolated guinea pig ileum, as well as enhance contractile activity in the Heidenhain gastric pouch of dogs, showing clearcut prokinetic properties.

Gastroprokinetic properties of the benzimidazolone derivative BIMU 1, an agonist at 5-hydroxytryptamine4 and antagonist at 5-hydroxytryptamine3 receptors

We have investigated the in vivo motor stimulating and gastroprokinetic properties of the azabicycloalkyl benzimidazolone derivative BIMU 1 (3-ethyl-2,3dihydro-N-(8-methyl-8-azabicyclo [3.2.1] oct-3-yl)-2-oxo 1H-benzimidazole-1-carboxamide hydrochloride) and its binding profile at 5-hydroxytryptamine3 and 5-hydroxytryptamine4 receptors, in an attempt to assess the serotonergic mechanism underlying its prokinetic action.BIMU 1 dose-dependently (0.01–0.3 mg/kg iv.) increased the motility of a denervated pouch of canine stomach. This excitatory action was sensitive to muscarinic blockade. A similar stimulatory effect was exerted by the benzamidic prokinetic agent cisapride (0.03–0.3 mg/kg i.v.) but not by the 5-HT3 receptor antagonist ondansetron (up to 1 mg/kg i.v ). The significance for propulsive efficacy of the motor stimulating activity of BIMU 1 was evaluated in a model of gastric emptying of liquids in the conscious dog. The emptying rate of a non-caloric liquid meal instilled through a gastric fistula was accelerated by both BIMU 1 (0.01–1 mg/kg i.v. and 0.1–3 mg/kg p.o.) and cisapride (0.03–1 mg/kgiv.and0.3–10 mg/kgp.o.).Ondansetron (1 mg/kg i.v.) did not show any effect. The activity of the 5-HT4 receptor antagonist DAU 6285 was evaluated in the gastric emptying model per se and in interaction experiments on the accelerating action of BIMU 1 (0.3 mg/kg L v.). At 1 mg/kg iv., DAU 6285 was ineffective on its own and failed to antagonize BIMU 1-induced prokinetic action;at the dose of 3 mg/kg i.v., it depressed the gastric emptying rate per se by 15% and totally abolished the accelerating effect of BIMU 1.In the binding assay, BIMU 1 exhibited an appreciable affinity for 5-HT3 receptors in NG 108-15 cells (KD: 0.8 nmol/l) and for 5-HT4 receptors in pig striatum (KD: 26.5 nmol/l). Compared to BIMU 1, cisapride bound with a similar affinity to 5-HT4 (KD: 35.2 mnol/l) and a much lower affinity to 5-HT3 receptors (KD: 155 nmol/l). By contrast, ondansetron was highly selective for 5-HT3 sites (KD: 4.7 nmol/l), being ineffective in the assay for 5-HT4 receptors (KD > 10000).Our results show that BIMU 1, like cisapride and unlike ondansetron, is an effective stimulant of gastric motility and propulsion. The action of BIMU 1 appears to depend on 5-HT4 receptor stimulation and to involve the activation of cholinergic nerve pathways.

Himbacine discriminates between putative muscarinic M1 receptor-mediated responses

This study describes the antagonistic properties of himbacine, in comparison with those of pirenzepine, at muscarinic receptors mediating the depolarization of rat superior cervical ganglion, the inhibition of electrically-induced twitch contractions of rabbit vas deferens and the contraction of dog saphenous vein, currently classified as putative muscarinic M1 sites. The affinity of himbacine for the vas deferens site (pA2 8.08) was nearly ten times higher than those for the M1 receptors of rat ganglion and dog saphenous vein (pA2 7.14 and 7.16, respectively); affinity estimates for pirenzepine were similar throughout the different preparations. The present data are consistent with the allocation of ganglion and saphenous vein receptors into the M1 subclass; the profile of the vas deferens site, conversely, appears to be different, and possibly more closely related to that reported for the M4/m4 receptor.

Cimetropium bromide: in vitro and in vivo evaluation of spasmolytic activity on human and dog colon.

The present study investigates the spasmolytic properties of cimetropium bromide, compared to atropine, on human and canine large bowel. The drug behaved as a competitive antagonist of muscarinic-mediated contractions in isolated colonic preparations from both species, with affinity values (pA2) ranging between 7.41 and 7.82. When administered intravenously to conscious dogs provided with a colonic Thiry fistula, cimetropium was a potent inhibitor of large bowel motility evoked by both exogenous and endogenous stimuli. The compound (10-100 micrograms/kg) counteracted colonic motor response to neostigmine administration with an ID50 of 27.9 micrograms/kg; both tonic and phasic components of contractile response were affected. In a comparable range of doses (3-100 micrograms/kg), the drug inhibited motor activity elicited by intraluminal distension.

Affinitu profile of the novel muscarinic antagonist guanylpirenzepine

The study reports the functional affinity of an amidino derivative of pirenzepine, guanylpirenzepine, for muscarinic receptors mediating relaxation of rat duodenum, inhibition of rabbit vas deferens twitch contraction (both receptors previously classified as M1), guinea pig negative inotropism (M2) and ileal contraction (M3). Unlike pirenzepine, guanylpirenzepine discriminated between duodenum and vas deferens receptors, with a 30-fold greater affinity for the former subtype. The unique selectivity pattern of guanylpirenzepine (duodenum greater than vas deferens greater than ileum greater than atrium) renders it a promising tool for the classification of muscarinic receptor subtypes.

Effect of propionyl-L-carnitine on rats with experimentally induced cardiomyopathies

Congestive heart failure (CHF) is the functional definition of a clinical syndrome with a heterogeneous underlying aetiology, but a common manifestation characterised by the “exhaustion of the reserve force of the heart” [1]. Despite the different classes of drugs employed in its treatment, CHF maintains a poor prognosis [2] and is considered a malignant disease. It is noteworthy that some recent editorials published in leading medical journals emphasise the “failure to treat heart failure” [3, 4]. Thus, despite the progress that has unequivocally been achieved in recent years with the development of pharmacological classes of agents acting through novel mechanisms, the need to develop effective and safe drugs remains strong [5].