Intrauterine growth retardation (IUGR) affects almost 10% of infants born in the United States. It may be responsible for delayed gastrointestinal function and is an important cause of perinatal morbidity and mortality. The New Zealand White rabbit provides an optimal model for the study of naturally occurring IUGR. At term, birth weight is determined by fetal position within the bicornuate uterus. The small intestinal disaccharidase enzymes are indicators of bowel maturity and function. To examine potential differences in disaccharidase development between normal and IUGR fetuses, this rabbit model was investigated. Jejunum was harvested at multiple stages in rabbit development including the third trimester fetus, neonate, and adult. Lactase, maltase, and sucrase enzyme activity, as well as total protein content, was determined. Results were analyzed by the 2-tailed t test and ANOVA. Lactase activity appeared in the mid-third trimester, peaked in the early neonatal period, then declined to adult levels. Maltase activity appeared in the early third trimester and gradually rose to adult levels. Sucrase remained at trace levels until the mid-neonatal period, reaching adult levels by weaning. Both lactase and maltase activity were depressed in IUGR fetuses compared with their normal littermates. This pattern of disaccharidase depression continued into the neonatal period until catch-up growth occurred at 2 wk when levels equalized. This report describes differential small intestinal disaccharidase development between normal and growthretarded rabbit fetuses in a naturally occurring model of IUGR. The third trimester is a critical period in the maturation of the fetal gut for the postnatal functions of nutrient propulsion and absorption. The terminal stages of digestion are accomplished by the disaccharide hydrolases, disaccharidases, which are located on the enterocyte brush-border membrane. Disaccharidase activity parallels the digestive needs of the animal and is indicative of intestinal function and maturity. Disaccharidase ontogeny has been described in human (1) and animal models, including fetal and neonatal rabbits (2). Developmental delays in fetal disaccharidase activity have been reported in rat models of surgically created intrauterine growth retardation (IUGR) (3) and fetal rabbit gastroschisis (our unpublished observation).The pregnant New Zealand White rabbit has a bicornuate uterus containing multiple fetuses within individual amniotic cavities ( Fig. 1). By convention, the fetus at the ovarian end is numbered 1. At term, the weight ratio of the growth-retarded fetus (position 3) to the ipsilateral normal fetus (position 1) is consistently 0.85, an example of naturally occurring IUGR (4). We hypothesize that IUGR rabbits are not only small but also have immature gastrointestinal development that impairs postnatal bowel function. To test this hypothesis, we studied the development of small intestinal disaccharidase enzymes. These enzymes are indicators of intestinal maturity and function in both norma...
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