Effects of clonidine and sumatriptan on postprandial gastric volume response, antral contraction waves and emptying: an MRI study M. A. KWIATEK,* M. R. FOX,*,** A. STEINGOETTER,  D. MENNE, à A. PAL,§ H. FRUEHAUF,* E. KAUFMAN,* Z. FORRAS-KAUFMAN,* J. G. BRASSEUR,§ O. GOETZE,* G. S. HEBBARD, – P. BOESIGER,  ,** M. THUMSHIRN,* M. FRIED*,** & W. SCHWIZER*,** *Division of Gastroenterology & Hepatology, University Hospital Zurich, Zurich, Switzerland  Institute of Biomedical Engineering, Swiss Federal Institute of Technology (ETH) Zurich, Zurich, Switzerland àMenne Biomed, Tuebingen, Germany §Department of Mechanical Engineering, The Pennsylvania State University, University Park, Pennsylvania, USA –Department of Gastroenterology, The Royal Melbourne Hospital, Melbourne, VIC, Australia **Zurich Centre for Integrative Human Physiology (ZIHP), Zu ¨ rich University, Switzerland Abstract Gastric emptying (GE) may be driven by tonic contraction of the stomach (Ôpressure pumpÕ) or antral contraction waves (ACW) (Ôperistaltic pumpÕ). The mechanism underlying GE was studied by con- trasting the effects of clonidine (a 2 -adrenergic agonist) and sumatriptan (5-HT 1 agonist) on gastric function. Magnetic resonance imaging provided non-invasive assessment of gastric volume responses, ACW and GE in nine healthy volunteers. Investigations were per- formed in the right decubitus position after ingestion of 500 mL of 10% glucose (200 kcal) under placebo [0.9% NaCl intravenous (IV) and subcutaneous (SC)], clonidine [0.01 mg min )1 IV, max 0.1 mg (placebo SC)] or sumatriptan [6 mg SC (placebo IV)]. Total gastric volume (TGV) and gastric content volume (GCV) were assessed every 5 min for 90 min, inter- spersed with dynamic scan sequences to measure ACW activity. During gastric filling, TGV increased with GCV indicating that meal volume dictates initial relaxation. Gastric contents volume continued to in- crease over the early postprandial period due to gastric secretion surpassing initial gastric emptying. Cloni- dine diminished this early increase in GCV, reduced gastric relaxation, decreased ACW frequency com- pared with placebo. Gastric emptying (GE) rate in- creased. Sumatriptan had no effect on initial GCV, but prolonged gastric relaxation and disrupted ACW activity. Gastric emptying was delayed. There was a negative correlation between gastric relaxation and GE rate (r 2 = 49%, P < 0.001), whereas the associa- tion between ACW frequency and GE rate was inconsistent and weak (r 2 = 15%, P = 0.05). These findings support the hypothesis that nutrient liquid emptying is primarily driven by the Ôpressure pumpÕ mechanism. Keywords gastric accommodation, gastric emptying, antral contraction waves, magnetic resonance imaging, clonidine, sumatriptan. Abbreviations: ACW, antral contraction wave; AD pres- sure gradient, antroduodenal pressure gradient; GCV, gastric contents volume (meal plus secretion volume); GE R , gastric emptying rate (volume/time); GE R,max , max- imum gastric emptying rate (volume/time); j, regression- estimated coefficient for TGV increase after V 0 ; T 50 , half emptying time of gastric emptying; TGV, total gastric volume (GCV plus air volume); V 0 , TGV immediately after meal; V max , maximum TGV during the study time period; DV 0 fi max , defined as V max )V 0 ; Dt 0 fi max , defined as t max )t 0 , where t max is a time of V max . The control of gastric emptying in humans is incom- pletely understood partly due to the interactive mechanical contributions of gastric tone on the one hand, and peristaltic antral contraction waves (ACWs) on the other. Although distinct, tonic and phasic Address for correspondence Dr Mark R Fox, Division of Gastroenterology & Hepatology, University Hospital Zurich, Zurich, Switzerland. Tel: +41 44 255 9631; fax +41 44 255 4503; e-mail: dr.mark.fox@gmail.com Received: 23 September 2008 Accepted for publication: 5 March 2009 Neurogastroenterol Motil (2009) 21, 928–e71 doi: 10.1111/j.1365-2982.2009.01312.x Ó 2009 Blackwell Publishing Ltd 928