Studies on myoinositol. Effects of caffeine and theophylline on incorporation of myoinositol into phosphatidylinositol in rat liver homogenate.

Both caffeine and theophylline, which were known to be potent inhibitors of cyclic-AMP phosphodiesterase, stimulated the incorporation of myoinositol into phosphatidylinositol in rat liver homogenate. However, cyclic-AMP had no effect. The effect of dibutyryl-cyclic-AMP differed with different concentrations. These results suggest that the stimulation cannot be explained by the increase in the amount of cyclic-AMP. This view was supported by the fact that papaverine, cyclic-AMP phosphodiesterase inhibitor, did not stimulate the incorporation and imidazole, the phosphodiesterase stimulator, did not inhibit the incorporation, and that adenylcyclase stimulators, epinephrine and glucagon, did not stimulate the incorporation.