Reefs in experimental gastroenterology--cyclic activities of the gastrointestinal tract.

The activity of the upper gastrointestinal tract is periodic. It concerns the gastrointestinal and gallbladder motility, gastrointestinal blood flow, gastric, intestinal, pancreatic and biliary secretions, rate of nutrient absorption, and many other physiological events. Nowadays, the periodic activity of the gastrointestinal tract is considered as a basic physiological pattern in conscious animals and humans. Unfortunately, there are considerable species- and age-related as well as individual differences, therefore experimental protocols should consider first describing the individual periodic pattern in the examined animals. A lot of confusion may appear with data interpretation if the periodic activity is neglected, in particular when low physiological-like doses of test substances are used. For instance, the effect of CCK or VIP administration on the exocrine pancreas may differ from negligible effect to strong one depending of the phase of pancreatic secretion. The action of secretagogues on the gastrointestinal tract will also be discussed in terms of the ultradian and circadian cycles.