THE PRENATAL DEVELOPMENT AND GLUCOCORTICOID CONTROL OF BRUSH-BORDER HYDROLASES IN THE PIG SMALL-INTESTINE

The development of brush-border enzymes and the possible regulatory ro le of cortisol were investigated in the small intestine of the fetal a nd neonatal pig. With the sows under pentobarbitone anesthesia, osmoti c minipumps containing either saline or cortisol were inserted s.c. in to 25 fetuses from 10 pregnant sows (82-96 d gestation). Six d later, the infused fetuses were removed by cesarean section and samples of th e proximal, middle, and distal intestine taken for analysis. Samples w ere also obtained from 48 piglets that did not undergo an operation (c ontrols) and that were removed at intervals from 82 d gestation until term (114 +/- 2 d). In the proximal and middle intestine, the mean lev els of lactase-phlorizin hydrolase (EC 3.2.1.23-62), maltase-glucoamyl ase (EC 3.2.1.20), aminopeptidase N (EC 3.4.11.2), and aminopeptidase A (EC 3.4.11.7) increased during the last 10-15 d before term, correla ted positively with log(10) plasma cortisol values, and were higher in cortisol-infused than in saline-infused fetuses (p < 0.05). Activity of sucrase-isomaltase (EC 3.2.1.48-10) was low in fetal pigs, and this enzyme and dipeptidyl peptidase IV (EC 3.4.14.5) were not significant ly affected by fetal age or exogenous cortisol. Maltase (EC 3.2.1.48-1 0 and EC 3.2.1.20) activity was significantly decreased in the middle and distal intestine of cortisol-infused fetuses. The results suggest that the prepartum rise in endogenous cortisol secretion stimulates th e prenatal expression of certain brush-border enzymes in the pig small intestine at this critical time. However, the effects of cortisol on the developing intestine were highly idiosyncratic for particular enzy mes and intestinal regions.