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

Pancreatic HCO-3 secretion is caused by proton flux from pancreatic cells to interstitial fluid which, hypothetically, may be derived 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 HCO-3 flux into pancreatic ducts that would vary with pancreatic jice HCO-3 concentration (CHCO-3). Because pancreatic ducts are water-permeable, CHCO-3 varies with plasma osmolarity. This phenomenon allows testing of the two hypotheses. Intravenous 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 CHCO-3 by 20 +/- 4 mmol/l and increased pancreatic HCO-3 secretion by 71 +/- 5 mumol/min. Intravenous infusion of hypertonic salt solutions to 5 other pigs raised PNa+ by 52 +/- 3 mmol/l and CHCO-3 by 54 +/- 3 mmol/l and reduced HCO-3 secretion by 86 +/0 26 mumol/min. Isotonic glucose infusion lowered PNa+ by 27 +/- 2 mmol/l and did not change CHCO-3 nor HCO-3 secretion rate in 5 pigs. These findings comply with the proton pump hypothesis and are at variance with the Na-pump hypothesis of pancreatic HCO-3 secretion.