Abstract
Inhibitory effects on low Km cyclic AMP-phosphodiesterase (PDE) obtained from guinea-pig ileum and rat cardiac muscle were studied using papaverine (Pap) and its related moiety compounds which were classified into group I : isoquinoline derivatives, group II : 2-veratrylpyridine derivatives and group III : 1-veratryl-veratrylamine derivatives. 3, 4-Dimethyl-2-veratryl-pyridine (P-3, 4M) belonging to group II was more effective than 1-methyl-6, 7-dimethoxy-isoquinoline (IQ) belonging to group I, but not so as Pap. Compounds in group III were little effective inhibitors. Pap and P-3, 4M seemed to be a competitive type and IQ to be a non-competitive type of compound. In the steric configuration of Pap molecule, an aphorphine type compound was more effective than a berberine type compound. Barium chloride did not exert any antagonistic effect upon low Km cyclic AMP-PDE inhibited by Pap. Potentiation effects on dose-relaxation curve induced by cyclic AMP in guinea-pig taenia coli fell into the order of Pap>P-3, 4M>IQ, being parallel with the potency order of cyclic AMP-PDE inhibition.
