A comparison of two opioid analgesics for relief of visceral pain induced by intestinal resection in rats

While developing a rat model for human short bowel syndrome, we noted that untreated rats as well as rats administered buprenorphine after intestinal resection exhibited behavior and appearance consistent with visceral pain a nd distress. To provide appropriate analgesics, we developed criteria to as sess pain-related behavioral changes and conducted an experiment to evaluat e the effectiveness of buprenorphine versus oxymorphone to alleviate the pa in induced by intestinal resection. Rats underwent either small-bowel resec tion or transection surgery; in addition, animals received jugular catheter ization for the delivery of total parenteral nutrition (TPN). Rats treated with buprenorphine received 0.5 mg/kg every 6 h subcutaneously, and rats tr eated with oxymorphone received 0.03 mg/kg hourly for 32 h via continuous i ntravenous (i.v.) infusion with TPN solution. Rats treated with buprenorphi ne exhibited behavior and appearance consistent with pain and distress for as long as 32 h postoperatively, whereas animals treated with oxymorphone e xhibited behavior and appearance similar to their preoperative state. Thus, oxymorphone alleviated the pain-related behavioral changes after intestina l resection far better than did buprenorphine. Of interest, we observed tha t the buprenorphine was associated with a decrease in the volume of urine c ollected, whereas oxymorphone was associated with urine volumes similar to those of nonresected rats maintained with TPN. Because oxymorphone appeared to be a superior analgesic, we also evaluated three routes for administeri ng this drug. Pain-related behavior changes were alleviated by the administ ration of oxymorphone by either Alzet mini-pump, bolus i.v. injection, or c ontinuous i.v. infusion. We conclude that compared with buprenorphine, oxym orphone is a superior analgesic for the alleviation of visceral pain due to intestinal resection.