The role of sodium ions in pancreatic fluid secretion in the rabbit.

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Abstract
NaCl in the bathing medium of the isolated rabbit pancreas was gradually replaced by isotonic amounts of sucrose, choline chloride or KCl. The replacement of NaCl always leads to a reduction in pancreatic flow. This reduction is largest with sucrose as replacing agent and smallest with KCl. The Na+ concentration in the secreted fluid decreases only slightly when NaCl is replaced by sucrose. In the experiments with choline chloride, the Na+ concentration in the secreted fluid decreases slightly when less than 60 mM-NaCl was replaced, but decreases markedly after more extensive NaCl replacement. Upon replacement of NaCl by KCl, the Na+ concentration in the secreted fluid is always equal to that in the bathing medium. The K+ concentration in the secreted fluid increases by 8 mM upon replacing NaCl by sucrose or choline chloride. Upon replacement by KCl the K+ concentration in the secreted fluid is always approximately equal to that in the bathing medium. The secreted fluid is always isotonic with that of the bathing medium; in the case of an extensive replacement of NaCl by sucrose or choline chloride, isotonicity is maintained by a higher cation concentration and an increased appearance of the replacing agents in the secreted fluid. Extracellular Na+ is evidently essential for pancreatic fluid secretion. The monovalent cations apparently reach the secreted fluid through a paracellular pathway. A model for the electrolyte movements involved in the pancreatic fluid secretion by ductular as well as by acinar cells is discussed.