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SUMMARY Ranitidine bismuth citrate is a novel compound formed from ranitidine and a bismuth citrate complex. In conscious dogs, ranitidine bismuth citrate had similar activity to ranitidine hydrochloride as an inhibitor of histamine-induced gastric acid secretion when oral doses containing equivalent amounts of ranitidine base (0.1 or 0.3 mg/kg) were compared. In the rat, ranitidine bismuth citrate (3–30 mg/kg p.o.) prevented gastric mucosal damage induced by ethanol (fundic damage) and indomethacin (antral damage). Ranitidine hydrochloride and tripotassium dicitrato bismuthate were also effective against indomethacin induced damage, but were both significantly less potent than ranitidine bismuth citrate in this model. Ranitidine hydrochloride was inactive against ethanol-induced damage. In vitro, ranitidine bismuth citrate (1 mmol/L) inhibited human pepsin isoenzymes 1, 2, 3 and 5. Pepsin 1 was inhibited to a similar extent by ranitidine bismuth citrate, bismuth citrate and tripotassium dicitrato bismuthate at concentrations equivalent to 1 mmol/L bismuth, but ranitidine (1 mmol/L) was inactive. Ranitidine bismuth citrate was more potent than tripotassium dicitrato bismuthate as an inhibitor of pepsins 2, 3 and 5. Ranitidine bismuth citrate inhibited both Helicobacter pylori (effective concentration 4–32, μg bismuth/ml) and H. mustelae (1–4,μg bismuth/ml); similar results were obtained with tripotassium dicitrato bismuthate. Bismuth citrate was slightly less effective, and ranitidine hydrochloride was inactive (> 125, μg/ml). In ferrets naturally colonized with H. mustelae, oral treatment with ranitidine bismuth citrate, 12 or 24 mg/kg twice daily for 4 weeks, caused a dose related clearance of H. mustelae. Qualitatively similar results were obtained in a small study with tripotassium dicitrato bismuthate and bismuth citrate.

Replacement of the isothiourea moiety of known histamine H 3 antagonists by certain 5-membered heteroaromatic systems can give compounds with an improved activity profile. One of these, 3-[(4-chlorophenyl)methyl]-5-[2-(1H-imidazol-4-yl)ethyl] 1,2,4-oxadiazole (GR175737) is a potent, selective, orally active and centally penetrating H 3 antagonist.

Replacement of the isothiourea moiety of known histamine H 3 antagonists by certain 5-membered heteroaromatic systems can give compounds with an improved activity profile. One of these, 3-[(4-chlorophenyl)methyl]-5-[2-(1H-imidazol-4-yl)ethyl] 1,2,4-oxadiazole (GR175737) is a potent, selective, orally active and centally penetrating H 3 antagonist.

The muscarinic activities and rates of hydrolysis by acetylcholinesterase of the optical isomers of the acetyl-α- and acetyl-β-methylcholines of known configuration have been determined. The results have been correlated and the possible characteristics of muscarinic receptors outlined.

The absolute configurations of the (+)-acetyl-α- and -β-methyl-choline iodides have been established, being related to D(−)-alanine hydrochloride and L(+)-lactic acid respectively. The (+)-, (−)- and racemic forms of the precursor amino-alcohols have been converted to the succinyl esters and these quaternised.

ALTHOUGH the main function of acetylcholinesterase (AChE) at the synapses of cholinergic nerves has been fairly well established, the biological role of pseudo-cholinesterase (PsChE) has not1–3,13. It has been proposed, however, that the latter enzyme is concerned with relatively slow nerve conduction processes2, and that the blood cholinesterases might be important in limiting responses to hydrolysable cholinergic agents4.