Ingestive behavior following central [D-Ala², Leu⁵, Cys⁶]-Enkephalin (DALCE), a short-acting agonist and long-acting antagonist at the delta opioid receptor

DALCE (1-40 μg, ICV), a short-acting agonist and long-acting antagonist at the delta opioid receptor, was examined for its effects upon food intake in rats under spontaneous, deprivation,glucoprivic and palatable conditions. DALCE (10 μgt) significantly stimulated free feeding for up to 10 h but only minimally decreased (40 μg) food intake and body weight after 24-72 h. DALCE, administered prior to food deprivation (24 h), failed to affect subsequent 24-h intake and sporadically decreased intake and body weight change after 48-72 h. 2-Deoxy-D-glucose (650 mg/kg, IP) hyperphagia was transiently (2 h) decreased by long-term DALCE (10 μg) pretreatment. Hyperphagia following exposure to a high-fat diet was significantly potentiated by long-term DALCE (1 μg) pretreatment. DALCE (10 μg) hyperphagia (2-10 h) was eliminated by central pretreatment with either naltrexone (20 μg) or the kappa antagonist, nor-binaltorphamine (20 μg) but was minimally affected by central pretreatment with the mu antagonist, beta-funaltrexamine (20 μg) or long-term DALCE (40 μg). The general inability of the antagonist actions of DALCE to alter these forms of feeding argues againts a role for the delta opioid receptor in these responses.