Transductal Fluxes of Anions in the Rat Pancreas

Recent studies of the rat pancreas (1) have shown that during stimulation of the gland with exogenous secretin, the primary secretory fluid which was produced in the acini-intercalated ducts was isotonic to plasma. The concentrations of Na and K of this fluid were identical to those of plasma while the concentrations of Cl and HCO3 were higher. Simultaneous measurements of the concentrations of these ions in the primary secretory fluid and in the final pancreatic juice revealed that exchanges of Cl and HCO3 took place across the ducts of the gland while there were no net transductal fluxes of Na and K. The present experiments demonstrate that the transductal fluxes of anions in the rat pancreas during stimulation with exogenous secretin are regulated by this hormone. In the absence of exogenous secretin in the unstimulated gland or during stimulation of secretion with pilocarpine or pancreozymin (CCK-PZ) there are no transductal fluxes of anions both in the whole gland or in segments of the interlobular ducts perfused by the split-oil droplet method of stationary microperfusion. Under these conditions, the ionic composition of the final pancreatic juice is identical to that of the primary secretory fluid. During stimulation of secretion with porcine secretin, infused intravenously, activation of a transductal mechanism of exchange of anions against concentration gradients appears to regulate the final anionic composition of the rat pancreatic juice. Methods and Materials. Male, albino rats of the Sprague-Dawley strain, weighing approximately 200 g were used in these experiments. The methods of surgical preparation of the animals, stimulation of pancreatic secretion, collection of samples, and calculation of the flow rates have been described in previous publications (1, 2). The method of split-oil droplet stationary microperfusion developed by Shipp et al. (3) as modified by Gertz et al. (4) was used for the study of chloride fluxes in segments of the pancreatic ducts in situ. The ducts perfused were interlobular ducts of 60–90 μm external diameter.