Metabolism in vivo of C14-Labelled Pyrethrin I and Cinerin I by House Flies with Special Reference to the Synergistic Mechanism1

Abstract

Randomly labeled C14-pyrethrin I (PI*) and C14-cinerin I (CI*) were used alone and in combination with sesamex in the study of their metabolism by house flies, Musca domestica L., in vivo. The metuholisms of PI* and of CI* follow a similar pattern and the difference is quantitative rather than qualitative. The difference in potency of PI* and CI* was due to the rate of detoxification. There is no difference in the absorption rate. More than 96% of the absorbed dose of CI* or PI* was detoxified 4 hours after topical application. The mechanism of synergism was explained by the fact that the synergist prevents the detoxification of the absorbed pyrethroids although the absorption of pyrethroids is less in the presence of sesamex than in its absence. Five metabolites plus chrysanthemic acid each from PI* and CI* have been isolated and partially characterized. The amount of free chrysanthemic acid never exceeds 2.6% of the applied dose. The direct hydrolysis of the ester linkage in either molecule is not a major detoxification mechanism. Of 5 metabolites, 3 showed an intact chrysanthemic acid moiety and ester linkage. The detoxification process is apparently initiated or the ketoalcohol moiety while the acid moiety and the ester linkage are still intact. Further breakdown of the altered molecule into more polar compounds is indicated.