Effects of feeding and lighting regimes on sugar transport in the rat small intestine.

1. The use of a controlled feeding regime which restricted rats to feeding during the 12 h dark period reduced the variability of sugar transport measurements made with the vascularly perfused intestine. 2. When the timing of the 12 h feeding or lighting periods was shifted by 12 h, pronounced changes in the rate of D-galactose and L-glucose transport were observed. 3. These variations were shown most clearly when the data were expressed as the ratio of the rate of appearance of the actively transported D-galactose to that of the poorly transported L-glucose in the vascular perfusate. This ratio was reduced in those animals studied during their feeding period. The lower ratios in these animals were attributable mainly to an increased rate of transport of L-glucose. 4. Significant reductions in D-galactose/L-glucose ratios were also found when the lighting period was shifted by 12 h, indicating that sugar transport is influenced by the lighting regime as well as by the feeding pattern. 5. An examination of the tissue sugar concentrations under the different feeding and lighting regimes revealed that the variations in sugar transport were associated with changes in the selectivity of the process responsible for the exit of sugars from the mucosa into the vascular bed. This phase of transepithelial transport appeared to be influenced mainly by the lighting cycle.