INTESTINAL BRUSH-BORDER MEMBRANE ENZYME-ACTIVITIES AND TRANSPORT FUNCTIONS DURING PRENATAL DEVELOPMENT OF PIGS

Enzyme activities and rates of leucine and glucose uptake were measure d using brush-border membrane vesicles prepared from the small intesti ne of 7- 8-, 10-, and 12-week fetal (43, 49, 61, and 74% of gestation) and unsuckled, neonatal pigs. Lactase was detected in 7-week fetuses, with a large increase in activity between 10 weeks of gestation and b irth. gamma-Glutamyltranspeptidase activity was stable throughout gest ation, whereas sucrase activity was not detected. Active L-leucine upt ake was already present at 7 weeks of gestation, with an increasing di stal-to-proximal gradient observed at birth. D-glucose uptake was low at 7 weeks, but by 8 weeks it exhibited a typical overshoot phenomenon and established a decreasing proximal-to-distal gradient by 12 weeks. D-glucose uptake at all ages was directly related to incubation tempe rature, but less so for 7- and 10-week fetuses. By 12 weeks strict Na-dependency of D-glucose uptake was observed along the entire length o f the small intestine. Kinetic analysis of Na+-D-glucose cotransport s howed a shift from the presence of both high- and low-affinity systems at 8 weeks of gestation to a single high-affinity Michaelian componen t at birth. In light of similarities with human fetuses, the pig may b e a valuable model for studying development of intestinal transport du ring gestation, particularly during the final trimester, when availabi lity of human tissue is limited.