A new method to measure intestinal activity of P-glycoprotein in avian and mammalian species

Permeability-glycoprotein (Pgp) actively exports numerous potentially toxic compounds once they diffuse into the cell membrane of intestinal epithelial cells. We adapted the everted sleeve technique to make the first measures of intestinal Pgp function in an avian species ( chicken) and in wild mammalian species, and compared them to laboratory rats. Tissues maintained both structural and functional integrity, and our method offers advantages over other in vitro techniques by using smaller intestinal sections ( 1 cm), and shorter incubation times ( 8 - 12 min). To determine Pgp function, we compared accumulation of [H-3]- digoxin in sleeves incubated in Ringer solution with and without a transport-saturating concentration of a competitive inhibitor, cyclosporin A. We demonstrated significant variation in Pgp activity within individuals along the intestine, between populations fed different diets, and between species ( laboratory rats had one-third to one-fifth the Pgp activity of wild rodents). In chicken, we also tested the effect of natural metabolites on digoxin accumulation. We found that among flavonoids, genistein ( 200 muM), found in soy and other legumes, but not quercetin ( 10, 30, 100, 330 muM) or the 3-beta-glycoside isoquercetrin ( 100 muM), significantly increased digoxin accumulation. Among fungal metabolites, sterigmatocystin ( 5 muM), but not aflatoxin B1 ( 5 muM), significantly increased digoxin accumulation.