Figure 5From: The enantiomers of tramadol and its major metabolite inhibit peristalsis in the guinea pig small intestine via differential mechanismsNaloxone (Nalox) attenuates the inhibitory effect of tramadol on peristalsis. The increase in PPT due to 100 μM (-)-tramadol, (+)-tramadol and O-desmethyltramadol was significantly reduced by pre-treatment with the pan-opioid receptor antagonist naloxone (0.5 μM). The bars represent means with SEM, n = 6 segments, *P < 0.05 as compared with vehicle (Tyrode's solution).Back to article page