EFFECTS OF BETA-ENDORPHIN AND D-ALANINE2 ENKEPHALINAMIDE ON URINE PRODUCTION AND URINARY ELECTROLYTES IN THE RAT

The intracerebro-ventricular administration of human β-Endorphin (β-EP, 0.1-3 μg/rat) or D-alanine2 methionine enkephalinamide (D-ala, 0.3-30 μg/rat) caused a dose dependent reduction in the urine volume. The oliguria was associated with a decrease in the concentration of Na+ and K+ in the urine of rats previously hydrated by oral administration with 25 ml/kg tap water plus 50 ml/kg 0.5% NaCl. On a molar basis, β-EP proved to be about 5-7 times more potent than D-ala. The effects caused by the peptides were antagonized by the simultaneous intraperitoneal administration of 1 mg/kg naloxone. In rats treated chronically with morphine, no cross-tolerance was demonstrated to the antidiuretic effect of β-EP, but clear cross-tolerance was evident to the changes in urine electrolytes induced by β-EP. Results suggest that morphine and the opiate peptides share a similar mechanism of action. © 1979.