Physiological studies of exocrine pancreatic secretion in conscious rats. 7th communication: short-term kinetics of adaptation of digestive enzymes to different nutritional stimuli.

In conscious rats provided with appropriate indwelling catheters the kinetic period of adaptation (short-term adaptation) of digestive enzymes was investigated in response to a rapid change of diet and to intraduodenal infusions of different food components. Flow-rate and total protein concentration of pancreatic juice were measured. Enzyme-separation by PAA-Gel-Electrophoresis and quantitative analysis of amylases I and II, lipase, chymotrypsins I and II and trypsin were performed. The specific enzymatic activity was characterized by the enzyme fraction in percent of total protein. Rapid "change of diet" in rats, previously adapted for two weeks to a certain diet, caused increasing and decreasing concentrations of the corresponding enzymes respectively. The kinetic of this adaptation could well be described by exponential functions. Intraduodenal perfusion of starch, soy-bean oil or amino acids revealed similar changes in enzyme secretion as seen in the dietary experiments; i. e. intraduodenaL perfusion of starch caused mainly an increase in amylase secretion, soy-bean oil in lipase secretion and amino acids in the secretion of proteases. The kinetics could be described as a definite transfer function to a rectangular stimulus. The time lag between the duodenal "stimulation" and "response" in pancreatic enzyme secretion was only a few hours. After a period of rapid change in enzyme secretion during the initial 5 hours, the secretion rises more slowly to reach steady-state level after 18-22 hours. The results of this study allow a more detailed formal description of the kinetics of pancreatic short-term adaptation to nutritional stimuli without clarifying the involved mechanisms.