Recovery, reproducibility, and usefulness of polyethylene glycol, iodine-labelled rose bengal, sulphobromophthalein, and indocyanine green as non-absorbable markers.

Non-absorbable reference markers are widely employed in investigations of gastrointestinal absorption either to estimate the fluid content of a segment of gut or to compare the concentration of the markers to that of an unknown (Cooper, Levitan, Fordtran, and Ingelfinger, 1966; Clifton and Schedl, 1963; Fordtran, Levitan, Bikerman, Burrows, and Ingelfinger, 1961; Schedl, 1966). The reliability of both estimations has been questioned (Worning and Amdrup 1965). The need in our laboratory for a highly precise determination of the fluid content of the rat intestine led to this re-evaluation. Data in the literature on recovery of the indicator and the reproducibility upon serial sampling of the intestinal contents from the same site are limited (Cooper et al., 1966; Schedl, 1966). The total recovery and constancy