Figure 1
Original recordings of the effect of racemic and (+)-tramadol on peristalsis. (A) Luminal perfusion of isolated segments of the guinea pig small intestine slowly increased the intraluminal pressure; when the peristaltic pressure threshold (PPT, marked by an arrow in the inset of A was reached, a peristaltic wave shown as a spike-like increase of intraluminal pressure was triggered. Increasing concentrations of racemic tramadol were cumulatively added to the bath. Peristaltic activity was constant during a control period and remained uninfluenced by 1 μM racemic tramadol. PPT was concentration-dependently increased by 10 and 30 μM racemic tramadol and peristalsis was completely abolished by 100 μM of the drug. (B) The concentration of 30 μM (+)-tramadol added singly to the bath caused an increase in PPT and peristalsis ceased for about 10 min. Thereafter peristaltic contractions returned, however, with a markedly higher PPT. (C) Peristaltic contractions were completely abolished by 100 μM (+)-tramadol added singly to the bath, so that despite an intraluminal pressure of 400 Pa no peristalsis took place. The high-frequency oscillations of intraluminal pressure in the later part of the tracing represent uncoordinated gut wall motions without any propulsion of the intraluminal contents.