Water flux across the rat jejunum and ileum

¹ New York University Research Service, Goldwater Memorial Hospital, Welfare Island, New York 10017; and Department of Medicine, New York University School of Medicine, New York, New York 10016

The flux of tritiated water from mucosa to serosa and from serosa to mucosa was measured across the rat ileum and rat jejunum in an in vitro perfusion system. The rate at which the specific activity of tritiated water decreased with time was an almost linear logarithmic function in the ileal serosal bath, whereas under identical conditions the rate of decrease was plainly curvilinear in the jejunal serosal bath. In comparing the first 40 min to the subsequent 60–100 min, the flux from mucosa to serosa across the ileum increased by 6.7 ± 5.6% in 12 comparisons, while the flux across the jejunum decreased by 21.O ± 9.9% in 7 comparisons. These observations illustrate the pitfall in determining flux rates based on a single determination at the beginning and end of an observation period. They illustrate the necessity of setting experimental conditions to be able to obtain intervening determinations to have some assurance that flux has not changed during the period of measurement.

Submitted on December 11, 1969