The herbal preparation STW 5 (Iberogast Ò ) desensitizes intestinal afferents in the rat small intestine 1 C.-Y. LIU,* ,  M. H. MU ¨ LLER,* J. GLATZLE,* D. WEISER, à O. KELBER, à P. ENCK,* D. GRUNDY* & M. E. KREIS* *Department of Surgery, Ludwig-Maximilians University, Hospital Großharden, Munich, Germany  Department of Physiology, Medical School, Shandong University, Shandong, China àSteigerwald Arzneimittelwerk GmbH, Darmstadt, Germany Abstract Introduction: Visceral hypersensitivity in the upper gastrointestinal tract is a potential pathomecha- nism of functional dyspepsia. The herbal preparation STW 5 (Iberogast Ò ) provides symptomatic relief for this condition. We aimed to investigate whether STW 5 modulates intestinal afferent sensitivity. Methods: The herbal preparation STW 5 or vehicle (30.8% ethanol) were administered orally in male Wister rats. After 2 h animals were anaesthetized and extracellular multi-unit intestinal afferent nerve recordings were secured from the neurovascular bun- dle of the mesentery in the proximal jejunum. Afferent discharge to ramp distension of the intestinal loop (0–60 cm H 2 O) and dose–response curves for i.v. bra- dykinin (10, 20 and 40 lg kg )1 ) and 5-HT (5, 10, 20 and 40 lg kg )1 ) were recorded. Results: Baseline discharge was not different between the vehicle and treatment group. Ramp distension was followed by a pressure dependent increase in afferent nerve discharge that was decreased following STW 5 pretreatment for all distending pressures reaching 147 ± 8 impulses s )1 (imp s )1 ) following STW 5 vs 171 ± 5 imp s )1 following vehicle at 60 cm H 2 O (mean ± SEM; P < 0.05). A dose-dependent increase in afferent discharge was observed for 5-HT and brady- kinin. Following STW 5 pretreatment, afferent dis- charge was reduced at all doses of 5-HT to 110 ± 5 at the maximum dose after STW 5 and 128 ± 3 imp s )1 in controls (all P < 0.05). Afferent discharge to bradyki- nin was similarly reduced at 20 and 40 lg kg )1 but not at 10 lg kg )1 of bradykinin with a discharge rate of 176 ± 7 imp s )1 following STW 5 and 200 ± 6 imp s )1 in controls at 40 lg kg )1 (P < 0.05). Conclusions: The preparation STW 5 reduces intesti- nal afferent nerve discharge following chemical and mechanical stimuli, while baseline discharge is not affected. This effect of STW 5 on afferent sensitivity may contribute to its therapeutic relief of dyspeptic symptoms. Keywords afferents, functional dyspepsia, hypersen sitivity, STW 5, visceral sensitivity. INTRODUCTION Functional dyspepsia and irritable bowel syndrome are the two most commonly seen functional gastrointes- tinal disorders. While functional dyspepsia involves upper gastrointestinal symptoms, patients with irrit- able bowel syndrome present with symptoms that have been attributed to the colon. 1,2 Functional bowel disorders are characterized by the absence of morpho- logical or histological alterations in the gastrointesti- nal tract. Thus, the diagnosis of functional dyspepsia and irritable bowel syndrome are based on patientsÕ symptoms and the clinical impression rather than on objective findings. 3,4 The early observation that patients who suffer from irritable bowel syndrome are more sensitive to rectal distension than healthy controls 5,6 was more recently confirmed in a large number of patients with more sophisticated technology. 7 Thus, it appears that in patients with irritable bowel syndrome mechanical stimuli from the gastrointestinal tract cause painful sensations that are not perceived as painful in healthy individuals. This led to the conclusion that these patients are characterized by rectal hypersensitivity. 1 This work was presented as a poster at the Meeting of the American Gastroenterological Association in New Orleans, May 16, 2004 and published in abstract form in the journal Gastroenterology 2004; 126 (Suppl.): 2 S1106. Address for correspondence PD Dr Martin E. Kreis, Department of Surgery, Ludwig- Maximilians University, Marchioninistrasse 15, D-81377 Munich, Germany. Tel.: +49 (0) 89 7095 6564; fax +49 (0) 89 7095 8893; e-mail: martin.kreis@med.uni-muenchen.de Received: 28 April 2004 Accepted for publication: 20 July 2004 Neurogastroenterol Motil (2004) 16, 759–764 doi: 10.1111/j.1365-2982.2004.00576.x Ó 2004 Blackwell Publishing Ltd 759