Circadian rhythmicity in rat intestinal villus length and cell number.

Circadian rhythmicity has been reported in various small intestinal digestive-absorptive functions and in the mitotic activity of intestinal crypt cells. These functional activity rhythms and perhaps the mitotic rhythms are cued by the feeding schedule. We now report that circadian rhythms also occurred in both the villus height and cell number in rats maintained on morning or afternoon feeding schedules for 7 days. Villus width was constant. In afternoon-fed rats both villus height and cell number were 50% greater just before feeding than 12 h later. The amplitudes of the two rhythms in the morning fed rats were decreased, the general shape of the cycles were changed and the average number of cells was increased. These changes between morning and afternoon feeding are attributed to incomplete phase shifting due to an insufficient adaptation span for the morning fed rats. We conclude that circadian rhythms occurring in villus height and cell number are affected by the feeding schedule. Similarities to some previously reported functional rhythms suggest that fluctuations in cell number and/or villus length might be related to the functional changes.