5-ht induced jejunal motor activity: enteric locus of action and receptor sub-types. Graf, Stefanie, and Sushil K. Sarna. Departments of Surgery, Physiology and Digestive Disease Research Center, Medical College of Wisconsin and Zablocki VA Medical Center, Milwaukee, WI
APStracts 3:0008G, 1996.
The role of 5-HT, its enteric locus of action and receptor sub-types involved in the regulation of jejunal contractions, was investigated by close-intraarterial infusions in conscious dogs. Close -intraarterial infusions of 5-HT in short segments of the jejunum stimulated phasic contractions that were blocked completely by atropine, partially by tetrodotoxin, and not affected by hexamethonium. This response was also blocked significantly by 5-HT2A and 5-HT2C receptor antagonists, but not affected by 5-HT1A/5-HT1B, 5-HT 3 and 5-HT 4 receptor antagonists. Spontaneous phase III contractions were inhibited significantly by 5-HT2A and 5-HT2C receptor antagonists, not affected by 5-HT1A/5-HT1B, 5-HT3 receptor antagonists, but enhanced by 5-HT 4 receptor antagonists. Repeated close-intraarterial infusions of 5-HT over several days stimulated giant migrating contractions (GMCs). We conclude that in the conscious state, 5-HT acts on 5-HT2A and 5-HT2C receptors located on postsynaptic cholinergic neurons in the canine jejunum to stimulate phasic contractions and phase III activity. The 5-HT4 receptors in the canine small intestine may be localized on non-adrenergic non -cholinergic (NANC) inhibitory neurons; these receptors suppress the amplitude and duration of phase III activity. 

Received 8 May 1995; accepted in final form 21 November 1995.
APS Manuscript Number G192-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96