MOTILITY PATTERN OF ISOLATED RAT PROXIMAL COLON AND EXCITATORY ACTIONOF NEUROTENSIN

The investigation concerned the effects of neurotensin on mechanical a ctivity of isolated rat proximal colon. An isometric-isovolumic prepar ation was used. Colonic segments showed spontaneous contractile activi ty, consisting of regular changes in both endoluminal and isometric te nsion. Neurotensin (1 pM to 0.1 mu M) induced a concentration-dependen t tonic contraction of both circular and longitudinal muscle accompani ed by high frequency oscillatory activity. Desensitization of the neur otensin receptors antagonized the contractile activity of neurotensin. The excitatory effects of neurotensin were partially blocked to the s ame degree by tetrodotoxin and atropine, indicating that a component o f the neurotensin-mediated contraction involves the release of endogen ous acetylcholine. The tetrodotoxin-resistant component of the neurote nsin-induced effect seems to be due to a direct action on the smooth m uscle cells.