Physiological studies of exocrine pancreatic secretion in conscious rats. 5. Communication: circadian rhythms of flow rate and composition of pancreatic juice.

1. In conscious rats provided with indwelling pancreatic and biliary catheters, the circadian variations of flow rate, electrolyte- and protein concentrations are followed. 2. Individual enzymes are separated by Polyacrylamid-Gelelectrophoresis and quantitatively determined by photometry after evaluation of the coloured bands. 3.) Volume flow rate increases towards the evening and reaches maximal values in the early morning hours (2-4 a. m.). 4. A similar nocturnal maximum can be observed for the concentrations and elimination rates of total protein, potassium and bicarbonate, while the concentration of sodium is fairly constant and only slightly decreasing in very high flow rates. 5. Typical circadian variations can be observed for the individual enzyme fractions: at night, the part of amylase is higher and the amount of chymotrypsinogen is lower, together with the increased nocturnal protein elimination. At day time these relations are inversed. 6. This rhythm is also existing in fasting animals, although with reduced basal values and smaller amplitude of variation. 7. In fasting animals the relative part of amylase is smaller compared with that of chymotrypsinogen, probably in relation to the reduced elimination of total protein. 8. The circadian variations of exocrine pancreatic secretion may be primarily inaugurated by hormonal action of hormones, whose release is controlled by nervous centers in the brain.