Opiates inhibit adenylate cyclase by stimulating GTP hydrolysis.

Specific, GTP hydrolysis catalyzed by membranes prepared from neuroblastoma--glioma (NG108-15) hybrid cells can be measured in the presence of adenosine-5'-[beta, gamma-imido] triphosphate (p[NH]ppA), ATP, and a nucleotide triphosphate-regenerating system. Opiates and opioid peptides stimulate low Km GTP hydrolysis when measured in the presence of Na+ and Mg2+. Opiate stimulation is rapid, stereospecific, and reserved by the antagonist naloxone. Potencies of opiates as stimulators of GTP hydrolysis and as inhibitors of adenylate cyclase are closely correlated. Agents that stimulate adenylate cyclase, including prostaglandin E1, 2-Cl-adenosine, secretin, and NaF, have little or no effect upon the rate of GTP hydrolysis. Opiates have no effect upon either adenylate cyclase or GTPase activity in membranes prepared from C6-BU1 glioma cells, which lack opiate receptors. In view of the pivotal role of GTP in the activation of adenylate cyclase, we conclude that receptor-mediated stimulation of GTP hydrolysis is the mechanism by which opiates and other inhibitory hormones lower adenylate cyclase activity in NG108-15 cell membranes.