Alimentary tract motility

Drugs affecting alimentary tract motility 88 Secretion and absorption 91 Summary 95... 

Several drugs are used for alimentary tract motility disorders in humans and there are excellent reviews on their mechanisms of action and clinical use (Longo Vemava 1993, McCallum 1999, Tonini 1996). 

In the periphery, 5-HT4 receptor mRNA is found in vascular smooth muscle. Newly developed drugs that activate 5-HT4 receptors are of interest for their potential in treating cardiac arrhythmia. The 5-HT4 receptor is also located on neurons of the alimentary tract, for example the myenteric plexus of the ileum, and on smooth muscle cells and secretory cells of the gastrointestinal tract, where they evoke secretions and the peristaltic reflex. 5-HT4 receptor agonists (e.g. cisapride, prucalopride, tegaserod) are used therapeutically in the treatment of constipation-predominant irritable bowel syndrome and in functional motility disorders of the upper gastrointestinal tract. 

Diarrhoea results from an imbalance between secretion and reabsorption of fluid and electrolytes it has numerous causes, including infections with enteric organisms (which may stimulate secretion or damage absorption), inflammatory bowel disease and nutrient malabsorption due to disease. It also commonly occurs as a manifestation of disordered gut motility in the absence of demonstrable disease (see below). Rarely it is due to secretory tumours of the alimentary tract, e.g. carcinoid tumour or vipoma (a tumour which secretes VIP, vasoactive intestinal peptide). 

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