AN ESTIMATE OF TURNOVER TIME OF INTESTINAL MUCUS GEL LAYER IN THE RAT INSITU LOOP

A method is described to estimate the turnover time of the mucus gel layer in chronically isolate intestinal loops in the rat during perfusion with isotonic saline. Measuring the concentration of a marker substance (total hexose) in the perfusion solution allowed calculation of the volume of produced mucus (V(p)) to be in the range between 0.03 and 0.16-mu-1 min-1 cm-1. The volume of the adhering mucus gel layer (V(a)) was calculated using anatomical data from the literature to be 7.78 +/- 0.32-mu-1 cm-1. Hence, the turnover time of the mucus gel layer as given by the quotient of V(a)/V(p) could be estimated to vary in the range between 47 and 270 min. This time scale is well comparable with the mean residence time found for mucoadhesive microspheres in earlier experiments using the same animal model. It is concluded that mucus turnover probably represents a crucial physiological factor for the concept of mucoadhesive dosage forms.