Pancreatic interstitial pH regulation: effects of secretory stimulation

Bicarbonate secretion by pancreatic ducts presumably releases an equivalent amount of acid into the parenchyma. The purpose of this study was to determine the effects of this acid load on pancreatic interstitial pH (pHI). In addition, we examined the relationship of pHI to changes in pancreatic blood flow (PBF), which may be important in acid disposal.

After validation of a microelectrode method for measurement of pHI in anesthetized cats, the effects of secretin (2 IU/kg intravenously) and cholecystokinin (0.08 microgram/kg intravenously) were examined. PBF was measured simultaneously by the H2 gas clearance technique.

Secretory stimulation with secretin produced an increase in pancreatic bicarbonate secretion (146 +/- 23 microEq/15 minutes, p < 0.01). This secretion was associated with a fall in pHI from 7.36 +/- 0.02 to 7.31 +/- 0.02 (p < 0.001), which returned to baseline after 25 minutes. There was an accompanying increase in PBF from 118 +/- 32 to 148 +/- 35 ml/min/100 gm (p < 0.01). In contrast, stimulation with cholecystokinin only slightly increased pancreatic secretion (49 +/- 19 microliters/15 minutes) and had no significant effects on pH or blood flow.

These results suggest that pancreatic secretion of bicarbonate, but not protein, releases H+ into the interstitium, an acid tide comparable to the alkaline tide during acid secretion by the stomach. This interstitial acidosis was accompanied by an increase in PBF. The increase in blood flow may be important in pH homeostasis, contributing to the disposal of this acid.