Inhibition of adenosine 3',5'-monophosphate phosphodiesterase by nicotinamide and its homologues in vitro.

Inhibition of cAMP phosphodiesterase from rat liver by nicotinamide and its homologues was studied. Among the several compounds tested, such agents as nicotinamide, N2-ethylnicotinamide, N2-methylnicotinamide, N,N-diethylnicotinamide, 3-acetylpyridine, methylnicotinate, and ethylnicotinate showed potent inhibition of cAMP phosphodiesterase, with an over 90% inhibition by 5 mM ethylnicotinate when cAMP was used as substrate at a 0.48 x 10(-7) M concentration. A comparison of the inhibitory curves of theophylline, papaverine, and ethylnicotinate on enzyme activity showed them to be approximately coincident. Furthermore, the plots with abscissa of equal increments per concentration of ethylnicotinate in the presence of theophylline or papaverine coincided with that in the absence of these agents.