Bombesin stimulates colonic motility via muscarinic cholinergic pathway in isolated, vascularly perfused rat colon

Abstract

Although bombesin (BN) regulates colonic motility, the associated mechanism of action remains unclear. The objective of this study was to investigate the effect of BN on colonic motility using isolated rat colon. An isolated rat colon was perfused with Krebs solution via the superior mesenteric artery. Intraluminal pressure was measured via microtip catheter pressure transducers at both proximal and distal portions of the isolated colon. After a control period, BN was administered intraarterially in concentrations of 13, 26, 130 and 260 pM. After pretreatment with hexamethonium (10 -3 M), atropine (10 -5 M) or tetrodotoxin (10 -6 M), BN was administered at a concentration of 260 pM (proximal colon) or 130 pM (distal colon), and then the intraluminal pressure was monitored. The motility changes were expressed as the percentage change of motility index (MI) over basal period. As a result, BN increased colonic motility and showed dose-dependent increase on proximal colonic motility. The stimulant effect of BN was almost completely abolished by atropine and tetrodotoxin at both proximal and distal colon. But BN was not inhibited by hexamethonium at both proximal and distal colon. Therefore, the stimulant action of BN may be mediated by local cholinergic muscarinic receptors.