Inhibition of noradrenaline release from cerebrocortical synaptosomes and stimulation of synaptosomal Na+, K+-ATPase activity by morphine in rats

Abstract

Abstract The effects of morphine on noradrenaline (NA) release from rat cerebrocortical synaptosomes and on the synaptosomal Na+, K+-ATPase activity were determined. Morphine (10−3-10−5 M) caused a dose-related inhibition of enhanced prelabelled [3H]NA release evoked by a high concentration of K+ from synaptosomes and this inhibitory action of morphine was antagonized by the specific antagonist naloxone (10−4, 10−5 M). Morphine dose-dependently stimulated the synaptosomal Na+, K+-ATPase activity but not Ca2+-ATPase activity in the incubation medium containing 2.2 × 10−6 4.7 × 10−7 M free Ca2+, and this stimulatory effect was antagonized by naloxone. These results suggest that morphine may have some role in the suppression of membrane depolarization and/or the release of NA through its stimulatory action on the Na+, K+-ATPase activity in rat cerebral cortex.