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Gastric emptying is delayed in patients receiving postoperative pain relief with epidural morphine compared to patients receiving epidural bupivacaine. The electrophysiological basis for this effect is unknown. The aim of this study was to compare the effects of epidural morphine with epidural bupivacaine on gastroduodenal myoelectric activity (EMG) in patients after surgery.Fourteen patients with epidural analgesia who underwent open cholecystectomy were randomly assigned to receive either epidural morphine (EM) or epidural bupivacaine (EB) for postoperative pain relief. During surgery EMG electrodes were placed in the subserosa in the antrum and duodenum and the EMG registration started 3.5 hours after the end of surgery. Gastric emptying measured with the acetaminophen test was studied in the morning the day after surgery.The spike activity in the antrum was significantly lower 160-340 minutes after the administration of morphine in the EM-group compared to the activity in the EB-group (P<0.04). The incidence of regular slow wave rhythm in the antrum was significantly lower 160-520 minutes after the administration of morphine in the EM-group compared to the EB-group (P<0.03). Duodenal Phase III activity measured with EMG was significantly more frequent during 160-520 minutes after the morphine administration in the EM-group compared to the EB-group (P<0.02). The acetaminophen absorption was significantly delayed in the epidural morphine group compared to the epidural bupivacaine group.Gastroduodenal electromyographic activity was significantly changed during epidural morphine compared to epidural bupivacaine. The delayed gastric emptying during epidural morphine may be explained by decreased and uncoordinated contractile activity in the antrum, shown by decreased spike activity and irregular slow wave rhythm. The increased pressure activity in the duodenum, shown by increased Phase III activity, may also impair gastric emptying.