The effect of L-leucine on the absorption of levodopa, studied by regional jejunal perfusion in man.

1. A new method for perfusing a 10 cm segment of jejunum in humans has been used in seven subjects to study the effect of the amino acid L-leucine (40 mM) on the intestinal absorption of levodopa (2.5 mM). The tube contains six channels and has two inflatable balloons, which enable a perfusion of a closed and defined segment of the proximal small intestine. 2. L-leucine decreased the intestinal absorption of levodopa from 40 +/- 19 to 21 +/- 15% but was without effect on the absorption of antipyrine, benserazide and D-glucose. 3. We confirm that levodopa is absorbed by the active transport system normally responsible for the absorption of large neutral amino acids (LNAA) in humans. Oral absorption by passive diffusion, probably by the paracellular route, might also occur for levodopa in the proximal part of the small intestine.