Manometric patterns of rat colonic motor activity and defecation

We investigated in conscious and unrestrained rats, the major patterns of colonic pressure waves, as related to defecation. A manometric low compliance perfusion system, which was set at a very low flow rate (0.03 ml/min), permitted simultaneous recordings of intraluminal pressure in the proximal, transverse, and distal colon. Pressure waves in control rats reflected two types of motor activity: short-duration waves (<15 sec), that were frequent throughout the colon (about 40–90/hr with aborally decreasing frequency), and propulsive, long-duration, high-amplitude waves (>15 sec, >15 mm Hg) that occurred only occasionally (1/hr or less) in the transverse and distal, but not in the proximal colon; these waves appeared to migrate aborally and were associated with defection. The serotonin 5HT_1A agonist 8-OH-DPAT dramatically and dose-dependently increased the frequency of long-duration, high-amplitude waves in the transverse and distal colon, and concurrently promoted defecation; these effects were prevented by the putative 5HT_1A antagonist pindolol. We conclude that 5HT_1A agonists such as 8-OH-DPAT may promote defecation and occurrence of propulsive waves through the same serotoninergic mechanism.A preliminary account of this work was presented at the 13th International Symposium on Gastrointestinal Motility, Kobe, Japan, Abstract 172. J Gastrointest Motil 3, 1991.