Noninvasive in vivo analysis of human small intestinal paracellular absorption: Regulation by Na+-glucose cotransport

Activation of intestinal Na+-glucose cotransport increases paracellular mov ement of inert tracers in cultured monolayers, isolated rodent intestinal m ucosae, and in rodents in vivo. However, not all studies have demonstrated comparable effects on human intestinal paracellular absorption. We sought t o assess the effects of Na+-glucose cotransport on paracellular absorption in human beings using a simple noninvasive assay. Study subjects drank six 200-ml doses of test solution, composed of 0.8% w/v creatinine (sufficient to overwhelm endogenous creatinine) in 277 mM glucose or mannitol and urine was collected. Intestinal creatinine absorption is paracellular. Once abso rbed, creatinine is cleared into the urine. Therefore, urinary creatinine r ecovery reflects intestinal paracellular creatinine absorption. Total urina ry creatinine recovery was 55% +/- 4% of creatinine ingested with glucose a nd 38% +/- 9% of creatinine ingested with mannitol (p < 0.001). Thus, intes tinal paracellular absorption of creatinine is increased by the presence of luminal glucose. Our results are consistent with in vivo human regulation of mucosal permeability by Na+-glucose cotransport.