Feeding pattern and gastrointestinal transit rate of rats under different room lighting schedules

Food consumption, fecal production, and excretion of an orally administered, nonabsorbed fecal marker were measured in rats housed in continuously-lighted animal quarters or in a room with alternating 12-hour light and dark periods. After a 3-week adaptation period, animals kept in alternate-lighting consumed 75% of their 24-hour food intake and produced 61% of their 24-hour fecal output during the 12 dark hours. In rats subjected to continuous-lighting, food intake and fecal output during the 12 hours corresponding to the dark in alternate-lighting were only 39% and 46% of the 24-hour totals, respectively. A radioactive chromic chloride fecal marker was presented for voluntary consumption to half of the animals in the morning and to the other half in the evening in each lighting situation. Rats offered the 51Cr dose at the beginning of their more active feeding period excreted about 40% of the radioactivity in each of the first two 12-hour collection periods. When the fecal marker was offered at the beginning of the less active feeding period, less than 10% of the 51Cr appeared in the first 12-hour collection, and over 70% was excreted during the second 12-hour collection. Thus, changes in food consumption patterns that occurred with alteration of room lighting were accompanied by parallel changes in fecal production and gastrointestinal transit rates.