Micropuncture techniques have been used to study electrolyte secretion by the spontaneously secreting in vitro rabbit pancreas over a wide range of environmental conditions. Pancreatic secretion does not have a strong requirement for HCO3 and secretion continues at nearly normal rates when exogenous HCO3 is replaced by acetate. Acetate concentration in the juice averages 70 meq/liter, nearly three times the environmental concentration. The similar characteristics exhibited by HCO3 and acetate secretion indicate that they are secreted by a common mechanism involving active H transport. In vitro acid-base alterations demonstrate that the secretion rate is controlled by the environmental HCO3 concentration and to a much lesser extent by the pCO2. Secretion also requires active Na transport across the mucosal membrane. The effects of ouabain and a low Na environment strongly suggest coupling between the transport of Na and H and a cellular mechanism for electrolyte secretion is proposed involving Na-H exchange mechanisms at both the mucosal and serosal membranes.

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