Concentration and pH dependency of alpha-methyldopa absorption in rat intestine

The intestinal absorption of alpha-methyldopa from perfused segments of rat intestine was determined. Jejunal and ileal segments were studied at pH 4.5, 6.0 and 7.4 at an alpha-methyldopa concentration of 0.01 mM, and at pH 6.0 at concentrations of 0.01, 0.10 and 10 mM. Intestinal absorption was found to depend on both concentration and pH but not on segment. A weak positive correlation (r = 0.5) was observed between net water absorption and alpha-methyldopa absorption, similar to that observed for amino acids. The low intestinal wall permeability of alpha-methyldopa under normal intestinal pH conditions (pH 7.4) is consistent with the incomplete oral bioavailability of this drug.