title: Chronic sucrose intake reduces the antagonist effect of beta-funaltrexamine on morphine-induced antinociception in female but not in male rats.
abstract: Chronic ingestion of a sweet-tasting sucrose solution enhances the pain relieving actions of opioid agonists. These results, taken in conjunction with research demonstrating that sucrose stimulates the production and release of endogenous opioid peptides, have led to the hypothesis that the effects of palatable foods and fluids on pain sensitivity are mediated by the endogenous opioid system. To assess this hypothesis, two studies determined if chronic sucrose intake would block the antagonist effects of the micro-selective opioid antagonist beta-funaltrexamine (beta-FNA) on morphine-induced antinociception. Female and male Long-Evans rats were maintained on chow and water, or chow, water and a 32% sucrose solution. In Experiment 1, after four weeks on the diets, female rats received 0 or 10 mg/kg (subcutaneously (s.c.)) beta-FNA, while in Experiment 2, male and female rats received 0, 5 or 20 mg/kg beta-FNA. Six days later, rats were tested for morphine-induced antinociception using the hot-water tail-withdrawal test. Morphine, administered using a cumulative dose regime (1.0, 3.0, 5.6, 10.0 and 31.0 mg/kg s.c.), led to dose-dependent increases in tail-withdrawal latencies in male and female rats. Males were more sensitive to the pain relieving properties of morphine than females. Sucrose intake increased, while beta-FNA decreased the analgesic actions of morphine in males and females. beta-FNA was less effective in blocking the antinociceptive actions of morphine in sucrose-fed female rats than in females fed only chow. In contrast, diet had minimal effects on responses to beta-FNA in male rats.
authors.affiliation: Department of Psychology, Tufts University, Medford, MA 02155, USA.
authors.forename: R Todd
authors.initials: RT
authors.lastname: Coy
authors.forename: Robin B
authors.initials: RB
authors.lastname: Kanarek
mesh_terms: D000818:Animals; D019422:Dietary Sucrose; D002149:Energy Intake / Q000187:drug effects*; D005247:Feeding Behavior / Q000187:drug effects*; D005260:Female; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009619:Nociceptors / Q000502:physiology; D051381:Rats; D020318:Rats, Long-Evans; D012727:Sex Characteristics
chemical_list: D019422:Dietary Sucrose; D009292:Narcotic Antagonists; D009271:Naltrexone; C024524:beta-funaltrexamine; D009020:Morphine