Movement of wax particles by contractions in the isolated opossum esophagus

We investigated whether the contractions of the isolated smooth muscle opossum esophagus can propel luminal contents. Wax particles were placed into the esophagus in vitro, and esophageal contractions were evoked by stimulating either primarily the intrinsic esophageal nerves (using electrical pulses of 0.5 ms) or the esophageal muscle directly (using pulses of 0.5 s). Direct muscle stimulation and neural stimulation produced circular muscle contractions of similar amplitude, but only neural stimulation was associated with a propagating ring contraction and longitudinal muscle contraction. Movement of the wax particle occurred after 21% of all stimulus responses. Aborad movement of the wax particle was 10 times as common as was its orad movement. Wax movement occurred less commonly and over shorter distance with muscle as compared with neural stimulation. The distance the wax moved was enhanced when the esophagus was allowed to shorten in its longitudinal axis. Movement occurred late during the contraction response and at velocities less than that of the ring contraction. Also, the ring contraction passed over the particle. The amplitude of circular muscle contractions had no predictive value for the occurrence of propulsion. The finding that the isolated esophagus can propel luminal contents in the aborad direction supports the thesis that peristalsis is primarily a function of the intrinsic neuromuscular organization of the smooth muscle esophagus.