Ultrastructural properties of collagen fibrils in rat intestine.

Collagen fibers (bundles of fibrils) of rat small intestine as observed by Nomarski differential interference contrast microscopy were densely packed in parallel undulating arrays. At the electron microscopical level the diameters of intestinal collagen fibrils increased gradually from 50 nm at three weeks of age to 80 nm at 12 months of age. At each age the fibril diameters were fairly uniform in size. At three weeks or six months of age collagen fibrils from stretched, salted samples were somewhat larger in diameter (12-16%) than those from unstretched, unsalted samples. A biaxial orientation existed between bundles of collagen fibrils at angles that varied from 32 degrees to 81 degrees with a mean of 60 degrees. Thus, intestinal collagen at the fibril level is aligned at varying angles to the longitudinal and circular directions of the intestine.