EFFECTS OF D-ALA(2)-D-LEU(5)-ENKEPHALIN, MICROINJECTED INTO THE SUPRAOPTIC AND PARAVENTRICULAR NUCLEI, ON URINE OUTFLOW RATE

The effects Of D-Ala2-D-Leu5-enkephalin (DADL, a delta-opioid agonist) , microinjected directly into the hypothalamic supraoptic (SON) and pa raventricular (PVN) nuclei, on urine outflow rate, urinary osmotic pre ssure, blood pressure, heart rate, respiratory rate and rectal tempera ture were investigated in water-loaded and ethanol-anesthetized rats. The microinjection of DADL into both the nuclei decreased urine outflo w rate in a dose-dependent manner with an increase in urinary osmotic pressure, but did not change the other recorded parameters. The DADL-i nduced antidiuretic effect in the SON was inhibited by naloxone, but n ot by atropine, phenoxybenzamine, timolol nor a vasopressin antagonist , d(CH2)5-D-Tyr(Et)VAVP. The effect in the PVN was inhibited by naloxo ne, atropine, timolol and d(CH2)5-D-Tyr(Et)VAVP, but not by phenoxyben zamine. These results suggest that DADL causes antidiuretic effects me diated through opioid receptors in both the SON and PVN, and the under lying mechanisms are different between them. Involvement of delta-opio id receptors in the DADL-induced antidiureses was discussed.