Are delta-opioid receptors involved in the regulation of food and water intake?

The effect of the delta-opioid antagonists ICI 154,129 (1-100 micrograms, i.c.v.) and ICI 174,864 (1-100 micrograms, i.c.v.) and of the delta-agonist D-Ala2-D-Leu5-enkephalin (DADL; 1-10 micrograms, i.c.v.) on the intake of food and water of non-deprived rats was investigated. Animals treated with either ICI 154,129 or ICI 174,864 ate and drank significantly less than vehicle-treated controls over a 3 hr test period. The suppressant effects of these peptides on appetite were similar to those observed with the more commonly-used opioid antagonists, naltrexone and Mr 2266. In contrast, the delta-agonist DADL produced an increase in both the consumption of food and water in the 3 hr following administration of drug. The findings presented in this study lend further support to the hypothesis that an endogenous enkephalin/delta-receptor system may play a role in the tonic induction of ingestive behaviour.