Pharmacological Research 58 (2008) 297–301 Contents lists available at ScienceDirect Pharmacological Research journal homepage: www.elsevier.com/locate/yphrs Potentiation by cholinesterase inhibitors of cholinergic activity in rat isolated stomach and colon Emma M. Jarvie b , Selim Cellek a , Gareth J. Sanger a,∗ a Immuno-Inflammatory Centre of Excellence for Drug Discovery, GlaxoSmithKline, Stevenage, Hertfordshire, UK b Neuroscience Centre of Excellence for Drug Discovery, GlaxoSmithKline, Harlow, Essex, UK article info Article history: Accepted 1 September 2008 Keywords: Itopride Donepezil Neostigmine Tegaserod Gastric motility Cholinesterase abstract Acetylcholinesterase (AChE) inhibitors stimulate gastrointestinal (GI) motility and are potential treat- ments of conditions associated with inadequate GI motility. The ability of itopride to facilitate neuronally (predominantly cholinergic) mediated contractions of rat isolated stomach, evoked by electrical field stimulation (EFS), has been compared with other cholinesterase inhibitors and with tegaserod, a clinically effective prokinetic and non-selective 5-HT 4 receptor agonist which also facilitates GI cholinergic function. Neostigmine greatly increased EFS-evoked contractions over a narrow concentration range (0.01–1 M; 754 ± 337% facilitation at 1 M); higher concentrations (1, 3 M) also increased muscle tension. Donepezil increased EFS-evoked contractions gradually over the full range of concentrations (0.01–10 M; maximum increase 516 ± 20% at 10 M). Itopride increased the contractions even more gradually, rising to 188 ± 84% at 10 M. The butyrylcholinesterase inhibitor iso-OMPA 0.01–10 M also increased EFS-evoked contrac- tions, to a maximum of 36 ± 5.0% at 10 M, similar to that caused by tegaserod (35 ± 5.2% increase at 1 M). The effects of tegaserod, but not itopride were inhibited by the 5-HT 4 receptor antagonist SB-204070A 0.3 M. In rat isolated colon, neostigmine was again the most efficacious, causing a defined maximum increase in EFS-evoked contractions (343 ± 82% at 10 M), without changing muscle tension. Maximum increases caused by donepezil and itopride were, respectively, 57.6 ± 20 and 43 ± 15% at 10 M. These data indicate that the abilities of different AChE inhibitors to increase GI cholinergic activity differ markedly. Understanding the reasons is essential if AChE inhibitors are to be optimally developed as GI prokinetics. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction Within the enteric nervous system acetylcholinesterase (AChE) inhibitors prevent the degradation of acetylcholine (ACh) [1], increasing the availability of ACh and thereby increasing gastroin- testinal (GI) motility. This action has been used therapeutically with inhibitors such as neostigmine successfully treating conditions such as intestinal pseudo-obstruction [2,3], post-operative ileus [4], refractory and opioid-induced constipation in cancer patients [5] and constipation resulting from spinal injury [6]. However, side effects associated with AChE inhibition are common. These may reach an incidence of 53% (nausea) or 12% (diarrhoea) with neostigmine, with bradycardia also reported when used to relieve constipation [7,8]. Interestingly the incidence of these adverse events may be lower with the selective, long-lasting AChE inhibitor donepezil [7], used for the treatment of Alzheimer’s disease [9]. Fur- ther, good tolerance has been reported for the AChE inhibitor and ∗ Corresponding author. Tel.: +44 1438 763191. E-mail address: Gareth J Sanger@gsk.com (G.J. Sanger). dopamine D 2 receptor antagonist itopride [10,11], evaluated as a potential new treatment of GI disorders associated with inadequate motility of the gut (e.g. [12,13]). The recent withdrawal of the lower bowel prokinetic and non-selective 5-HT 4 receptor agonist tegaserod, following a revised benefit/risk analysis (http://www.fda.gov/cder/drug/ advisory/tegaserod.htm), is likely to increase the use of AChE inhibitors in patients with severe GI motility disturbance, given the poor availability of alternative GI prokinetic agents. Since there may be major differences in the side-effect profiles and perhaps, in the efficacy of these agents, it is now important to compare the effects of different AChE inhibitors on GI function. For this purpose, we measured and compared the abilities of neostigmine, donepezil and itopride to exert GI prokinetic-like activity in rat isolated stomach, a model proven to detect prokinetic activity [14,15] and also in rat colon. In the stomach, comparisons were made with tegaserod, to provide a clinical benchmark of activity, and with the butyrylcholinesterase (BuChE) inhibitor iso-OMPA [16]. Our results indicate that marked differences in GI prokinetic activity exist between these compounds and that such differences could be exploited to generate new types of therapy. 1043-6618/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.phrs.2008.09.001