Drug Absorption VI: Water Flux and Drug Absorption in an In Situ Rat Gut Preparation

The influence of net water transfer on drug absorption occurring in an in situ rat intestinal preparation was studied using hypotonic, hypertonic, and isotonic intestinal lumenal solutions composed of sodium phosphate and sodium chloride. It was found that the tonicity of the lumenal solution tended to change to a slightly hypertonic value when the initial solutions were isotonic or hypertonic and to isotonicity when the lumenal solution was initially hypotonic. Net water flux occurred from hypotonic solutions and into hypertonic solution. Water loss from isotonic solutions ranged between 7 and 17% in 3.0 hr. The results indicated that the intestinal water loss or gain which occurred with the different tonicity solutions altered the apparent rate constant for sulfaethidole absorption. It was found that the changes could be accounted for by correcting the rate constant for volume and relative available surface area and that when this was done there were no differences between permeability constants for sulfaethidole from the iso‐and hypotonic solutions for absorption. However, the hypertonic solution had a reduced permeability constant.