Thiamine uptake in isolated schizonts of Eimeria tenella and the inhibitory effects of amprolium.

The uptake of thiamine by isolated second-generation schizonts of Eimeria tenella and 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 microM) and parasite (Km = 0.07 microM) and found to be significantly different. Both systems were competitively inhibited by amprolium but showed different affinities for the drug. (Host Ki = 323 microM; parasite Ki = 7.6 microM). Further differences were observed in schizonts of a drug-resistant line of E. tenella. These findings are discussed in terms of the inhibition of thiamine uptake being the basis of the anticoccidial activity of amprolium.