Intake of a palatable sucrose solution modifies the actions of spiradoline, a kappa opioid receptor agonist, on analgesia and feeding behavior in male and female rats

Previous research has shown that rats consuming a sucrose solution and chow are more sensitive to the analgesic actions of morphine, a selective mu opioid agonist, and the anorectic actions of opioid antagonists, than rats eating only chow. However, from these data, it cannot be determined if sucrose intake only modifies the behavioral consequences of drugs that act at the mu opioid receptor, or if the sugar also alters the actions of opioid drugs that act at other opioid receptor subtypes. Thus, the present experiments examined the effects of sucrose intake on the actions of spiradoline, a selective kappa opioid agonist? on analgesia and food intake in male and female Long-Evans rats. In Experiment I, male and female rats consumed either chow, a 32% sucrose solution and water, or only chow and water. After 3 weeks, antinociceptive responses on the tail-flick test were determined after spiradoline injections (0.0, 0.3, 1.0, and 3.0 mg/ kg, SC). Rats fed sucrose were more sensitive to the analgesic actions of spiradoline than rats fed only chow. In Experiment 2, drug-naive male and female rats were maintained under the same dietary conditions as in Experiment 1. Food intake was measured 1, 2, 4, and 6 h after spiradoline injections (0.0, 0.3, 1.0, and 3.0 mg/kg, SC). Spiradoline led to significant dose-related decreases in food intake for males and females in both dietary conditions. However, the anorectic effects of the drug were more pronounced in rats fed sucrose than in those eating only chow. These results support the hypothesis that intake of palatable foods and fluids alters the activity of the endogenous opioid system. (C) 1999 Elsevier Science Inc.