DIETARY MODULATION OF MU-OPIOID AND KAPPA-OPIOID RECEPTOR-MEDIATED ANALGESIA

Research has demonstrated that intake of palatable carbohydrates and f ats enhanced morphine-induced analgesia (MIA) in Sprague-Dawley rats. To determine if the effects of palatable foods an nociceptive response s would generalize to other strains of animals and other opioid agonis ts, the present experiments investigated whether intake of palatable f oods would: a) alter MIA in Long-Evans rats, and b) alter analgesia pr oduced by drugs acting at kappa opioid receptors. In experiment I, adu lt male Long-Evans rats were fed Purina chow alone or chow and either a 32% sucrose solution, a 0.15% saccharin solution, or hydrogenated ve getable fat. Using a tail-flick apparatus, nociceptive responses, meas ured as percent maximal possible effect (%MPE), were examined after mo rphine administration [0.0, 1.0, 3.0, and 6.0 mg/kg subcutaneously (SC )]. %MPEs varied directly as a function of dose and were significantly greater for rats fed chow and either sucrose or fat than-for rats fed chow alone or chow and saccharin. Experiment 2 compared the analgesic effect of the kappa opioid receptor agonist U50,488H (0, 5.0, 10.0, a nd 20.0 mg/kg SC) in rats fed chow alone or chow and a 32% sucrose sol ution. Administration of U50,488H led to analgesia. However, %MPEs did not vary directly as a function of dose. %MPEs of rats fed chow and s ucrose were significantly greater than those of rats fed chow alone af ter injections of 10.0 and 20.0 mg/kg U50,488H. Experiment 3 compared the analgesic effect of U50,488H (5.0, 10.0, 15.0, and 20.0 mg/kg SC) in rats fed chow alone or chow and either a 0.15% saccharin solution o r hydrogenated vegetable fat. Administration of U50,488H led to analge sia. However, %MPEs did not vary directly as a function of dose or as a function of diet. %MPEs of rats fed chow and fat were significantly greater than those of rats fed chow alone after injection of 5.0 mg/kg U50,488H. (C) 1997 Elsevier Science Inc.