Secretion of electrolytes by the pancreas of the anaestetized rat.

1. HCO-3, Na+ and K+ concentrations were measured in bile-free pancreatic juice collected from fasted and fed anaesthetized rats. 2. Resting flow rates averaged 0.62 mul. g-1 .min-1 (fasted) and 2.8 mul. g-1. min-1 (fed) and the mean HCO-3 concentrations, respectively, were 25.8 and 33.3 mM. 3. In fasted rats, instillation of HCl into the duodenum caused flow rate to increase threefold and HCO-3 concentrations to double (66 mM). Intravenous infusion of pure natural (GIH) secretin caused a fivefold increase in flow rate; HCO-3 concentrations, again, doubled (67.5 mM). Infusion of synthetic secretin produced effects essentially the same as those produced by GIH secretin. 4. Infusion of Boots secretin caused a thirteenfold increase in flow rate (8.32 mul.g-1. min-1) but HCO-3 concentrations rose only slightly (43.3 mM). However, following cessation of infusion, when flow rate approximated the maximum obtained with pure secretin, the HCO-3 concentration was much higher (57.2 mM at 3.19 uml.g-1.min-1). In fed animals the responses were similar but maximum flow rates were greater (12 mul. g-1. min-1). 5. Infusion of caerulein produced a secretory rate slightly less than with Boots secretin (5.06 mul. g-1.min-1) and HCO-3 concentrations were plasmalike (30.2 mM); infusion of the synthetic octapeptide of cholecystokinin (OP-CCK) gave similar flow rates and HCO-3 concentrations. 6. Infusion of a mixture of caerulein and GIH secretin mimicked closely the effect of Boots secretin. At maximum flow rates (7.6 mul. g-1. min-1) the HCO-3 concentration was 43.7 mM and at lower flow rates (3.90 mul.g-1. min-1) it rose to 54.2mM. 7. It is concluded that the response of the rat pancreas to secretin is qualitatively similar to that of all other vertebrates so far studied, but, relative to other animals, the response is sluggish. In contrast, the rat pancreas responds well to cholecystokinin (CCK) stimulation, yielding a juice with plasma-like HCO-3 concentration. Boots secretin, which is heavily contaminated with CCK, causes a mixed response resembling that of CCK at high secretory rates and that of pure secretin at lower rates. 8. An unexplained feature of rat pancreatic juice was that K+ concentrations, although plasma-like in unstimulated samples, rose to about 8mM when flow rate increases as a result of secretin, but not CCK, stimulation. In all other animals so far studied, the K+ concentration has been found to be independent of flow rate.