Plasma osmolality and exocrine pancreatic secretion.

To confirm the influence of plasma osmolality on exocrine pancreatic secretion, hypertonic saline (4% saline) was given intravenously to dogs with gastric and pancreatic fistulae. Intravenous administration of hypertonic saline caused a reduction of pancreatic juice flow and bicarbonate output, but did not alter protein output stimulated by secretin and cerulein. The changes of pancreatic juice flow(X) exhibited negative correlations with the changes in plasma osmolality(Y) (Y = -2.2X + 6.4, r = -0.74, p less than 0.01). Plasma osmolality and plasma vasopressin level were measured simultaneously. Plasma osmolality was elevated from 292 to 315 mOsm/kg with concurrent increase of plasma vasopressin level from 2.4 to 19.6 pg/mL. On the other hand, exogenous administration of vasopressin inhibited pancreatic juice flow and bicarbonate output dose-dependently. In conclusion, elevation of plasma osmolality decreased exocrine pancreatic secretion stimulated by secretin and cerulein, and vasopressin may play an important role in its mechanism.