Opiates modulation of cAMP levels and PGE2 binding in mammalian sympathetic ganglia.

The effects of opiates on cyclic adenosine monophosphate (cAMP) levels have been studied in sympathetic ganglia of guinea-pig, rat and rabbit. D-[Ala2]-Met-enkephalinamide inhibits cAMP synthesis in guinea pig and rat but not in rabbit ganglia, while morphine is always ineffective. In the presence of the enkephalin plus prostaglandin E2 (PGE2) a synergistic increase of the nucleotide levels is observed in guinea pig. This effect is not induced by morphine plus PGE2 and is not shared by rat and rabbit. In guinea pig alpha-endorphin inhibits both basal and PGE2-stimulated cAMP synthesis. In the same preparation the enkephalin increases [3H]PGE2 binding. In guinea pig ganglia a cooperative effect of the enkephalin and PGE2 on the cAMP system is suggested.