DEVELOPMENT OF COLONIC TRANSPORT PROCESSES IN EARLY CHILDHOOD: EVIDENCE OF REDUCED ANION EXCHANGE

Studies of colonic electrolyte transport in adults and children suggest that anion (movement in vivo is only in part mediated by Cl−/HCO3− exchange mechanism. Using the technique of non-equilibrium dialysis of the rectum we have investigated anion (exchange by incubating solutions of differing electrolyte composition in children (2 premature infants and 1 neonate, age 33-42 weeks gestation = A, and 3 children aged 5-18 months =B). Using a plasma-like solution, absorption of Cl− and HCO− was greater in A compared with B (see table). As in B HCO3− secretion might have been expected, we investigated the effect of the electrochemical gradient on HCO3− movement by using a Cl− - free solution to remove anion exchange, and a Na+ -free solution to remove the etetrical drive for HCO3− absorption. With a Cl− - free solution HCO3− absorption increased in both A and B. With no electrical gradient, Cl− absorption decreased in both groups but only in B did HCO3− secretion occur. These data support our previous view that anion exchange is poorly developed in infancy, only accounting for 15% of Cl− absorption in infants and accounting for virtually no Cl− absorption in the preterm neonate. In addition it is clear that, in vivo, Cl− is absorbed by electrical coupling as well as anion exchange.