Effect of Head Upward Tilting on Unidirectional Na and H 2 O Fluxes Across the Canine Ileum 1

Abstract

Summary

Head upward tilting and subsequent return to the supine position were both associated with increased net Na and/or H₂O absorption but decreased unidirectional Na and H₂O fluxes across the gut and decreased arterial blood pressure and blood flow through the ileum. The cardiovascular changes correlated significantly with the unidirectional H₂O fluxes both into and out of the lumen but not with net Na or H₂O absorption nor with the unidirectional Na fluxes. It was suggested that vasoconstriction could reduce the capillary surface area available for diffusion and thus reduce the unidirectional fluxes but that additional factors must be affecting Na fluxes.