The reversibility of the inhibition of intestinal amino-acid transport by harmaline.

The inhibitory aciton of harmaline on L-phenylalanine uptake by guinea-pig intestinal rings is fully reversible provided only low concentrations of the inhibitor are used; if the concentration is raised to a sufficient extent to enable the drug to interfere with sodium pumping or cellular metabolic reactions, as witnessed by its effect on tissue oxygen consumption, then the inhibition of L-phenylalanine uptake is only reversible if short contact times are employed.