Effect of intrahypothalamic injection of [D-Ala2,D-Leu5]enkephalin on feeding and temperature in the rat.

The effectiveness of the delta-opioid agonist [D-Ala2,D-Leu5]enkephalin (DADLE) in eliciting alterations in feeding and core temperature in rats was compared to morphine. When injected into the ventromedial hypothalamus this peptide caused a dose-related increase in feeding which was rapid in onset and of short duration, and a short-lived increase in temperature. Neither of these effects was blocked by the intrahypothalamic injection of naloxone. The alpha-adrenoreceptor antagonist phentolamine significantly reduced DADLE-stimulated feeding, although it did not counteract the hyperthermia. Since the delta-opioid agonist DADLE is more potent than the mu-agonist, morphine, and produces its effect more rapidly, the delta-opiate receptor may have an influence on the regulation of feeding.