Sodium transport by the small intestine of new-born and suckling pigs.

1. Sodium transport has been measured across in vitro preparations of pig ileum taken at birth or during the first 10 days of post-natal life.2. Both the unidirectional and net fluxes of sodium fell shortly after colostrum was ingested by the new-born piglet. These changes were associated with falls in short-circuit current, open-circuit voltage and tissue conductance and with the appearance of protein-filled vacuoles within the mucosal epithelium.3. Overnight fasting of piglets following a period of suckling caused all sodium fluxes to revert to values similar to those found in the new-born animal. The short-circuit current also increased on fasting but the magnitude of this effect decreased with age.4. The suckling-dependent inhibition of sodium transport was not associated with any change in the level of adenine nucleotides within the mucosa. However the rate at which sodium entered the intestinal mucosa of suckled pigs was found to be only half that of the new-born.5. It is suggested that pinocytosis might use up or chemically modify the microvillar membrane making it less permeable to sodium. Subsequent fasting would, by replenishment or further modification of existing membrane surface, allow the epithelium to recover its original permeability to sodium and possibly regain the ability to undergo a further cycle of pinocytotic activity.