Relationship between plasma pH and pancreatic HCO3- secretion at different intravenous secretin infusion rates

The relationship between pancreatic HCO₃^- secretion and plasma pH during acute systemic acid-base changes was investigated in 6 anesthetized, artificially ventilated pigs (20–25 kg) at 2 different, i.v. secretin infusion rates. At 0.45 C.U./kg b.wt. h^-1 secretin infusion and plasma pH 7.40±0.01 pancreatic HCO₃^- secretion averaged 61±12 μmol/min. Stepwise lowering of plasma pH through i.v. infusion of HCI and CO₂ administration to inspired air proportionately reduced secretion rate; estimated zero HCO₃^- secretion occurring at plasma pH 7.01. Subsequent i.v. secretin infusion at 2.70 C.U./kg b.wt. h^-1 increased HCO₃^- secretion to 249±42 μmol/min at plasma pH 7.33+0.04; stepwise lowering of plasma pH proportionately reduced HCO₃^- secretion to estimated zero at plasma pH 6.71. A reduction of plasma pH by 0.1 pH unit reduced HCO₃^- secretion during low and high rate of i.v. secretin infusion by 18±3 μmol/min and 35±8 μmol/min, respectively. Secretin infusion rate did not affect pancreatic chloride excretion. These findings support the view that secretin increases HCO₃^- secretion, and hence proton transport to the interstitial fluid, by augmenting the proton motive force developed by HCO₃^- secreting cells.