Mechanism of hepatic bicarbonate secretion and bile acid independent bile secretion

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Abstract
To examine hepatic bicarbonate transport and bile acid independent bile secretion, bile was sampled via a T-tube inserted into the common bile duct of anesthetized pigs. Secretin was infused i.v. at a rate of 2.7 C.U.[clinical unit]/kg body wt h-1 (large dose) or 0.45 C.U./kg body wt h-1 (small dose). Hepatic water and electrolyte secretion were studied during systemic acid-base disturbances while secretin was continuously administered. Systemic acidosis reduced the rate of NaHCO3 secretion which fell in proportion to changes in plasma pH, by 9% and 2% per 0.1 pH unit for the large and small dose of secretin, respectively. Plasma pCO2 [partial pressure of CO2] and bicarbonate concentration had little influence on NaHCO3 secretion. Consequently, plasma pH appeared to be the main determinant of hepatic NaHCO3 secretion during acid-base changes. Secretion of 1 mol NaHCO3 was accompanied by an isotonic solution containing water and 0.25 mol NaCl. After secretin infusion, 14C-erythritol clearance increased in proportion to bile flow. Bicarbonate secretion is determined by a gradient limited H+-pump at the contraluminal cell. During secretin stimulation bile acid independent bile secretion is osmotically driven by bile NaHCO3 flux.