STIMULATION OF INTRAMURAL SECRETORY REFLEX BY LUMINAL DISTENSION PRESSURE IN RAT DISTAL COLON

The effects of distension on epithelial transport were examined by increasing intraluminal pressure in the rat distal colon in vitro. Two kinds of preparation, one with the musculature intact (intact preparation) and the other with the musculature and the myenteric neurons detached (mucosa-submucosa preparation), were used and the transmural potential difference (PD) changes were measured. In the intact preparation, distension with a luminal pressure of 15 cmH2O for 15 s caused a transient increase in PD (the lumen being more negative) of 3.7 +/- 0.6 mV. The distension-induced increase in PD was largely sustained when the pressure was applied for 10 min. Distension caused by intraluminal pressure, if it is of a similar degree to that caused by fecal pellets, is enough to elicit a PD increase. The distension-induced PD increase was largely abolished by the removal of Cl- from the bathing solution, or by the addition of furosemide or bumetanide. In the mucosa-submucosa preparation, distension with a luminal pressure of 15 cmH2O for 15 s caused an increase in PD of 5.8 +/- 0.6 mV. The distension-induced increase in PD was partially inhibited by atropine and was further decreased in the presence of tetrodotoxin both in the intact and mucosa-submucosa preparation. Indomethacin reduced the distension-induced PD increase in both preparations. These results suggest that distension by increased intraluminal pressure elicits the activation of Cl- secretion, which is mediated by submucosal plexus neurons. In addition, this distension-induced reflex is likely to be activated by normal fecal pellets.