| Abstract: | We compared the circadian patterns of pancreatic and biliary secretions in fasting rats. For this purpose, indwelling plastic catheters were placed in 10 male Wistar rats (300-320 g) for the collection of biliary and pancreatic secretions. After small samples were taken for analysis, pancreatic and biliary secretions were recirculated into the duodenum by an additional connecting system. The rats were adapted to an inverse night-day cycle by artificial light during the night (8 pm-8am) and by darkroom housing at daytime (8 am -8 pm ). During a 24-h fasting period, samples of bile (100 μL) and pancreatic juice (20 μL) were taken every hour for determination of the following parameters: pancreatic and biliary flow rate, protein, amylase, lipase, trypsin, and bile acid output. Peak pancreatic flow rate (1.96 ± 0.05 mL/h-kg) was achieved toward the end of the dark period at 7 pm. A significant increase of pancreatic secretion could be achieved merely by turning the lights off, a significant decrease by turning the lights on. Similar circadian patterns were found for pancreatic protein, amylase, and lipase output with peak secretions at 7 PM. An increase of nearly 5x was found between minimal (15.64 ± 0.65 mg/h-kg) and maximal (72.43 ± 2.83 mg/h-kg) pan-creatic protein output. The amplitude was highest for amylase; peak amylase output (13740 ± 832 U/h-kg) was about 18-fold above minimal output (758 ± 44.3 U/h-kg). Conversely, the peak of trypsin concentration in pancreatic juice (1095 ± 17.8 U/mL) occurred during the light period when flow rates were lowest. Circadian patterns of biliary vol flow rate and bile acid output were also present, with peak secretions after 4 and 5 h of the dark phase, respectively (9.22 ± 0.31 mL/h-kg; 440 ± 9,53 μmol/h-kg). No acute alterations in biliary secretion resulted from turning the lights on or off. We conclude that pancreatic and biliary secretions are nonparallel in fasting rats and that distinct mechanisms are likely to be involved in the regulation of these different circadian patterns. |
