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Pancreatic Secretion; Bicarbonate Secretion; H+ Ion Transport Buffer Secretion
Abstract:
The isolated cat pancreas was perfused with solutions containing different concentrations of bicarbonate- or glycodiazine buffer. The concentrations of the different buffer components were varied in order to determine the rate-limiting component. 1. The rates of bicarbonate and fluid secretion were proportional to the respective concentrations of the bicarbonate anion and total bicarbonate in the perfusate. 2. In only 2 of 9 experiments could the secretory rate of fluid and bicarbonate be varied by altering the CO2- pressure of the perfusate. 3. Glycodiazine (Redul®) can partially replace the bicarbonate CO2 buffer in its ability to promote water and solute secretion. 4. The rate-limiting step for the enhancement of the glycodiazine and concomitant fluid secretion is the anion concentration in the perfusate, whereas by increasing concentrations of the undissociated acid of this buffer the secretory flow rate and total buffer secretion can be decreased.
Considering also earlier findings with sulfamerazine buffer a model is proposed where a H+/OH− ion separation takes place at the luminal cell border of the exocrine pancreas cells. Undissociated acid as well as buffer anions neutralize the H+ resp. the OH− ions thereby promoting the buffer secretion.
The rate-limitation with each buffer component seems to be dependent on its concentration and permeation properties. The inhibition of pancreatic secretion by the undissociated glycodiazine is presumably caused by its effects on the mitochondrial energy production.
