EFFECTS OF BETA-ENDORPHIN, MORPHINE AND NALOXONE ON ARGININE VASOPRESSIN SECRETION AND THE ELECTROENCEPHALOGRAM

β-Endorphin injected into the third ventricle of conscious rabbits resulted in a sustained elevation of the concentration of arginine vasopressin in blood plasma. Tenfold greater doses of morphine were required to produce a comparable response. The secretion of arginine vasopressin appears not to be a consequence of respiratory depression or hemodynamic alterations induced by β-endorphin or morphine. Most pharmacological effects of β-endorphin and morphine were reversed by naloxone but the effects on the secretion of arginine vasopressin were not. Furthermore, pretreatment with naloxone failed to prevent the rise in plasma levels of arginine vasopressin after administration of morphine. Paroxysmal seizure discharges were recorded on the electroencephalogram after injection of β-endorphin into the lateral ventricle, but not after injection into the third ventricle. Frequency analysis revealed slowing and reduced power in all frequency bands of the electroencephalogram. Both morphine and the endogenous peptide β-endorphin have similar effects on the release of arginine vasopressin and these effects appear to be independent of naloxone-sensitive opiate receptors. © 1979.