Effects of enprofylline and theophylline on purified human basophils

Extracts from purified human basophils revealed activity of cAMP-phosphodiesterase with a km-value of 0.59 microM. The enzyme was not activated by Ca-ions. Enprofylline and theophylline inhibited the enzyme in a competitive manner. Enprofylline was more potent than theophylline. These drugs did also inhibit the anti-IgE-induced histamine release from the basophils. These results favour the hypothesis that inhibition of histamine release of enprofylline is caused by an inhibition of phosphodiesterase. Although accumulating data have indicated that theophylline, at therapeutic concentrations, is a weak inhibitor of cAMP-phosphodiesterase activity, there is reason to believe that enprofylline, at therapeutic concentrations, may act at least partly as a phosphodiesterase inhibitor.