OPIOIDS, NORADRENALINE AND GTP ANALOGS INHIBIT CHOLERA-TOXIN ACTIVATED ADENYLATE-CYCLASE IN NEURO-BLASTOMA X GLIOMA HYBRID-CELLS

D-Ala2-Met5-enkephalin, morphine and noradrenaline [norepinephrine] inhibit the adenylate cyclase in homogenates of mouse neuroblastoma .times. rat glioma hybrid 108CC15 cells in a dose-dependent manner even after the enzyme has been preactivated by cholera toxin. Half-maximal inhibition and extent of inhibition are the same with native or cholera toxin-activated enzyme. The inhibitions caused by opioids or noradrenaline are antagonized by naloxone or phentolamine, respectively. The effect of D-Ala2-Met5-enkephalin on cholera toxin-activated enzyme is immediate in onset and rapidly reversed by the addition of naloxone. Guanyl-5''-yl-imidodiphosphate stimulates basal activity but inhibits the enzyme activated by cholera toxin or prostaglandin[PG]E1. Stimulation occurs at a concentration of 100 .mu.M or above, inhibition even at 0.1 .mu.M. The inhibitory effect of the non-hydrolyzable GTP analog is antagonized by GTP. Guanyl-5''-yl-methylenediphosphonate, another nonhydrolysable GTP analog, inhibits basal as well as cholera toxin-stimulated or PGE1-stimulated adenylate cyclase. Other guanine derivatives such as GDP, GMP, cGMP, guanyl-5''-yl-phosphoric acid amide and guanosine have no effect under the same conditions. The results may be taken as a piece of evidence for 2 separate guanyl nucleotide-binding sites accompanying the adenylate cyclase in the hybrid cells and mediating, respectively, stimulation and inhibition of the enzyme by hormones.