Antagonism by Opiates Against Prostaglandin E2-Stimulated Adenylate Cyclase in the Corpus Striatum
The actions of opiates on the elevation of cyclic AMP (cAMP), induced by prostaglandin E2 (PGE2), were studied in slices of the rat striatum. Morphine (2μM) antagonized the PGE2-induced elevation of cAMP, while an equimolar concentration of naloxone inhibited morphine’s effect. The action of morphine was mimicked by met-enkephalin (100μM, in presence of 0.2 mM bacitracin) and by levorphanol (10μM), but not by an equimolar concentration of its stereoisomer dextrorphan. Adenosine (1mM) or an elevation of K+ -ions to 54 mM raised the cAMP concentration, and PGE2 induced a further elevation, which however, was not antagonized by morphine under these conditions.