Restraint stress has no effect on morphine-induced inhibition of gastrointestinal transit in the rat

Stress in the rat has been reported to enhance the analgesic and thermic effects of opioids, drug effects that are mediated centrally. We examined whether this stress-induced enhancement of response to opioids could also be demonstrated for a drug effect mediated largely in the periphery, morphine-induced inhibition of gastrointestinal transit. Restrained (stressed) and unrestrained (unstressed) rats were injected with saline or morphine and then administered orally a charcoal suspension; after sacrifice, the distance the charcoal traveled through the intestine was determined. After the administration of saline, restrained rats had significantly lower gastrointestinal transit than did unstressed rats; however, both groups were comparably sensitive to inhibition of gastrointestinal transit by morphine.