Fig. (1) Typical tracing of opioid withdrawal on guinea-pig ileum. A. 3 similar acetylcholine response (A), electrical stimulation, injection of the opioid agonist (OA) followed after 4 min of contact period by naloxone (N) which induces contraction (1° opioid withdrawal). After washout (█), it was performed another A response.B: After 30 min resting period under electrical stimulation, a further 4 min exposure of the ileum to the OA and N elicited reproducible response (2° opioid withdrawal).C: After another 30 min resting period under electrical stimulation, the ileum responded again to the OA and N with the same intensity (3° opioid withdrawal).