Food restriction and recovery of nonabsorbed indicators from the small intestine of the rat.

Indicators of net water movement are used in a variety of intestinal transport studies. Such indicators should be virtually unabsorbed under study conditions. The effects of stimuli that alter intestinal mass on indicator recovery have not been examined. We used the male albino rat to study the effects of food restriction (50%) and fasting on recovery of indicators perfused intraluminally through the entire small intestine. Recovery of PEG 4000 and phenol red was essentially complete (98-100%) from control and restricted groups, but was 96% from the fasted group. PEG 400, consisting of a homologous series of polymers of which seven were measured (MW 242-506), was also perfused. The lower-molecular-weight polymers were absorbed. Absorption decreased with increasing molecular weight, and the slope of the relation of absorption to molecular weight was the same for all groups.