Small intestinal development in growth-retarded fetal sheep.

The functional maturity of the gastrointestinal system is essential for the survival of the neonate. The effects of reducing placental size and the ensuing fetal growth retardation on the development of the small intestine (SI) of the sheep fetus were investigated. At 140 days of gestation (term is 147 days), fetal body weight, gastrointestinal weight (from the abomasum to the rectum, i.e., the gut), SI weight, and SI length in the growth-retarded fetuses (n = 6) were significantly reduced (p less than 0.05) when compared with age- and breed-matched control fetuses. The SI weight was disproportionately reduced as a fraction of the gut weight or SI length (p less than 0.01). The proximal SI showed marked reductions in the thickness of the wall, muscularis externa, mucosa, villus height, and crypt depth (p less than 0.003). Densities of villi and crypts were also reduced (p less than 0.02). The crypt-to-villus ratio was maintained. Glycogen was accumulated basally in the villus epithelial cells, and their nuclei were located apically. These characteristics are comparable to those of much younger fetuses. In the distal SI, interanimal variation was large; however, the mean thickness of the wall, the muscularis externa, the mucosa, and the villus height were all reduced (p less than 0.05). In this region, the density of villi and crypts, the pattern of glycogen accumulation, and the position of the nuclei did not markedly differ between growth-retarded and control fetuses. Villus cell density was increased (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)