MANOMETRIC PATTERNS OF RAT COLONIC MOTOR-ACTIVITY AND DEFECATION EFFECT OF SELECTIVE 5HT(1A) AGONIST 8-OH-DPAT

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 pressur e in the proximal, transverse, and distal colon. Pressure waves in con trol rats reflected two types of motor activity: short-duration waves (<15 sec), that were frequent throughout the colon (about 40-90/hr wit h 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 co lon; these waves appeared to migrate aborally and were associated with defecation. The serotonin 5HT(1A) agonist 8-OH-DPAT dramatically and dose-dependently increased the frequency of long-duration, high-amplit ude waves in the transverse and distal colon, and concurrently promote d defecation; these effects were prevented by the putative 5HT(1A) ant agonist 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.