Thiamine uptake in isolated schizonts ofEimeria tenellaand the inhibitory effects of amprolium

Abstract

SummaryThe uptake of thiamine by isolated second-generation schizonts ofEimeria tenellaand by host intestinal cells was found to consist of two components. One was passive and the other apparently an active process. The kinetic constants of the latter were compared in host (Km= 0·36 μm) and parasite (Km= 0·07 μm) and found to be significantly different. Both systems were competitively inhibited by amprolium but showed different affinities for the drug. (HostKi= 326 μm; parasiteKi= 7·6 μm). Further differences were observed in schizonts of a drug-resistant line ofE. tenella. These findings are discussed in terms of the inhibition of thiamine uptake being the basis of the anticoccidial activity of amprolium.