Effect of chronic drug treatment on intestinal membrane transport of 14 C-L-dopa.

1. By the use of the everted jejunal sac it was shown that chronic oral treatment of rats with various drugs can either increase or decrease the mucosal transport of (14)C-L-DOPA or alter its serosal/tissue ratio.2. (14)C-L-DOPA transport was significantly increased in rats that were chronically treated with L-DOPA and diminished in those that were treated with chlorpromazine and phenobarbitone.3. Chronic treatment with amantadine and neomycin did not affect (14)C-L-DOPA intestinal transport, although direct addition of amantadine to the medium, significantly increased (14)C-L-DOPA transport in everted sacs of nontreated rats. Addition of neomycin directly to the medium did not affect (14)C-L-DOPA transport.4. The possible mechanisms of these findings and their clinical significance are discussed.