Plasma Na+-ion concentration or pH as regulator of pancreatic HCO-3secretion

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Abstract
Pancreatic HCO2 secretion is caused by proton flux from pancreatic cells to interstitial fluid which, hypothetically, may be driven by a Na-pump or a proton pump. A Na-pump would reabsorb protons from pancreatic duct in proportion with plasma Na+ concentration (PNa+). A proton pump would cause passive HCO3 flux into pancreatic ducts that would vary with pancreatic juice HCO3 concentration (CHCO3-). Because pancreatic ducts are waterpermeable, CHCO3- varies with plasma osmolarity. This phenomenon allows testing of the 2 hypotheses. I.v. infusion of hypotonic salt solution to 5 anesthetized, secretin infused pigs (2.7 C.U./kg b.wt. H-1) lowered PNa by 20 .+-. 2 mmol/l and CHCO3- by 20 .+-. 4 mmol/l and increased pancreatic HCO3- secretion by 71 .+-. 15 .mu.mol/min. I.v. infusion of hypertonic salt solutions to 5 other pigs raised PNa+ by 52 .+-. 3 mmol/l and CHCO3- by 54 .+-. 3 mmol/l and reduced HCO3- secretion by 86 .+-. 26 .mu.mol/min. Isotonic glucose infusion lowered PNa by 27 .+-. 2 mmol/l and did not change CHCO3- nor HCO3 secretion rate in 5 pigs. These findings comply with the proton pump hypothesis and are at variance with the Na-pump hypothesis of pancreatic HCO3 secretion.