Kappa-opioid agonists do not inhibit adenylate cyclase

Morphine, levorphanol and D-Ala2, Met enkephalin, but not bremazocine, pentazocine, U-50 488H and U-69 593, were found to inhibit adenylate cyclase activity dose-dependently in bullfrog brain membranes. The inhibition of the enzyme activity was abolished by naloxone. These results suggest that the signalling transduction of mu- and delta-agonists is partially mediated by the adenylate cyclase system coupled with opioid receptors, but that kappa-receptors may not be associated with adenylate cyclase.