Postnatal development of intestinal villi in the rat. Determination of villus size gradient

The existence of the so called "Villus Size Gradient" (VSG) which defines the proportional decrease in height of intestinal villi from duodenum to ileum is well documented in adult animals and man. The aim of this study is to define whether the VSG is present since birth or, if not, when and why it appears. We have measured the height of intestinal villi in 25 rats: 5 at 1 day from birth, 5 at 5 days, 5 at 8 days, 5 at 15 days and 5 at 30 days. We have prepared histological slides of a duodenal, jejunal and ileal tract of each animal and measured the height of villi on microphotographs. At day 1 we observed a higher size of duodenal villi statistically significant with respect to jejunum and ileum, while at day 5 no differences were observed between the various intestinal tracts. The VSG become evident 8 days after birth progressively increasing to day 30. The predominance of duodenum present at birth is therefore probably due to the fetal developmental growth which is known to be more precocious in duodenum than in more distal tracts. Five days after birth the intestinal villi are equally developed, while in later ages the VSG appears. So we can conclude that the VSG is a consequence of luminal and humoral factors and not a predetermined event.