ABSORPTION OF RETINOL FROM THE RETINOL-RETINOL-BINDING PROTEIN COMPLEX BY SMALL-INTESTINAL GUT SHEETS FROM THE RAT

Absorption of retinol by the absorptive cells of the small intestine i s a necessary first step in the metabolism of vitamin A. Previous stud ies had suggested that absorption of retinol from the retinol:retinol- binding protein complex (retinol:RBP) might be receptor mediated. We i nvestigated the specificity of this process by determining the absorpt ion of retinol from retinol:RBP by small intestinal sheets obtained fr om the suckling rat. We found that the absorption of retinol from reti nol:RBP was a saturable process. Unlike the absorption of free retinol , absorption of retinol from retinol:RBP was not inhibited by N-ethyhn aleimide. The absorption was specifically competable by unlabeled reti nol:RBP and by both apo- and holocellular retinol-binding protein, but not by beta-lactoglobulin. This suggests that a specific mechanism is present for the absorption of retinol bound to REP. (C) 1997 Academic Press.