A study was undertaken to investigate the effects of surgical procedures on food and water intake and spontaneous locomotor activity in laboratory rats. The influence of anaesthesia with halothane and administration of the opioid analgesic nalbuphine was investigated in normal rats and in animals which underwent either unilateral nephrectomy or jugular vein cannulation. Both nephrectomy and jugular cannulation were associated with a significant reduction in food and water consumption and a depression in locomotor activity levels. The reduction in activity following nephrectomy was reversed by administration of 6 doses of nalbuphine at 4 hourly intervals. Administration of nalbuphine at the same dose rate following halothane anaesthesia in normal rats resulted in a stimulation of activity. The prevention of the depressant effects of surgery by this opioid appears to be due to its stimulatory effect rather than a specific analgesic action. The degree of depression of food and water consumption after nephrectomy was significantly reduced following 6 doses of nalbuphine. This beneficial effect of repeated administration of an opioid may be related to the compound's analgesic action.

Locomotor activity and food and water consumption are potentially indices of post-operative pain in laboratory rodents, but it is important to establish whether these variables are directly affected by opioid analgesics or by halothane anaesthesia in normal rats. The effects of three opioids, buprenorphine, nalbuphine and butorphanol administered alone or following halothane anaesthesia, were studied in groups of normal non-operated adult Wistar rats. All 3 analgesics affected food intake and activity levels, but had little or no effect on water intake. Buprenorphine caused a significant elevation of activity levels and a reduction in food intake at clinical doses (0·01 and 0·05 mg/kg s/c). Nalbuphine (0·5, 1 and 2 mg/kg s/c) caused a reduction in food intake but had a smaller stimulatory effect on locomotion. Butorphanol (0·4 mg/kg s/c) caused a reduction in food intake and elevation in activity. These results suggest that water consumption is likely to be a more reliable variable to use when assessing post-operative pain and the efficacy of analgesics in rats.