The intestine as a site of absorption, elimination, and action of toxins in vertebrates

KARASOV, W. H.; CAVIEDES VIDAL, E

Salvador

Congreso; 7th Internactional Congress of Comparative Physiology; 2007

It is generally accepted that permeability of the intestinal apical membrane to plant secondary metabolites (PSMs) is a positive function of their lipophilicity.  It is not so well appreciated that absorption of hydrosoluble PSMs can be considerable through the paracellular pathway between intestinal cells.  We review the capacity for absorption of water soluble compounds through the intestine by nonmediated pathways (not involving transporters).  Birds tend to have a greater capacity for passive absorption of hydrosoluble compounds than do mammals or reptiles. Because hydrosoluble PSMs are potentially absorbed along this pathway, there could be differences among these taxa in sensitivity to these compounds.  Also, PSMs that affect intestinal nutrient transporters may be less potent in birds that rely more on passive absorption.  It is known that a variety of flavonoids inhibit intestinal glucose transport in vitro, including phloridzin and phloretin the potent inhibitors of SGLT1 and GLUT2, respectively.  As expected, flavonoids (phloridzin, phloretin, isoquercetin) significantly depressed D-glucose absorption in intact laboratory rats, which rely more on transporters for D-glucose absorption, whereas they did not significantly depress D-glucose absorption in intact American robins, which rely more on passive absorption.  The intestinal membrane also includes transporter(s) that can expel toxins, including a membrane-bound phosphoglycoprotein called P-glycoprotein (Pgp) that apparently binds many lipophilic compounds that have diffused into the lipid bilayer and expels them.  We measured its functional activity in intact intestinal sleeves of mammals that eat varying amounts of lipophilic PSMs, both among closely related species and within one species eating two diets.  We review the extent to which Pgp might play a role in dietary adaptation to diet.