Specific adaptation of gastric emptying to diets with differingprotein content in the rat: is endogenous cholecystokinin implicated?

摘要

Background—Recent studies indicate that gastric emptying may be influenced by patterns of previous nutrient intake. Endogenous cholecystokinin (CCK), whose synthesis and release can be affected by dietary intake, has a major role in the regulation of gastric emptying.
Aims—To evaluate the influence of diets with differing protein content on gastric emptying of differing liquid test meals and plasma CCK levels in the rat and to check whether the inhibitory effect of exogenous CCK on gastric emptying is modified after long term intake of diets with differing protein content.
Methods—Rats were fed for three weeks with high protein, medium protein (regular), or low protein diet. On day 22 gastric emptying of a peptone meal was studied. In addition, basal and postprandial CCK levels after the different dietary regimens were measured by bioassay. The time course of dietary adaptation was studied and its specificity assessed through the use of different (peptone, glucose, and methylcellulose) test meals. The effect of exogenous CCK-8 on gastric emptying was studied at the end of the adaptation period (three weeks).
Results—Feeding the animals with a high protein diet for three weeks resulted in a significant (p<0.05) acceleration (by 21.2(8.2)%) of gastric emptying while feeding with a low protein diet was followed by a significant (p<0.05) delay (by 24.0 (6.2)%) inthe emptying rate. When the time course of the effect of dietary adaptation on gastric emptying was studied, it appeared that at leasttwo weeks are required for dietary protein to be effective. Theregulatory effect of dietary protein on gastric emptying proved to bedependent on meal composition. Only the emptying rate of a proteincontaining meal (40% peptone) was significantly modified by previousdietary intake. No significant (p>0.05) changes were observed withglucose and methylcellulose meals whose emptying rates were similar inrats receiving a high protein or low protein diet. A peptone mealstrongly and significantly (p<0.05) increased plasma CCK levels inrats fed a medium protein (regular) diet. Results were similar in ratsreceiving a low protein diet (p<0.05) but not in rats on a highprotein diet (p>0.05). As a consequence, postprandial plasma levels ofCCK in rats fed with a medium or low protein diet were significantly(p<0.05) higher than those in rats receiving a high protein diet. Inrats on high and low protein diets, dose response curves to CCK-8 werevirtually identical, suggesting that dietary protein intake has noinfluence on the effect of exogenous CCK.
Conclusions—These results clearly show thatgastric emptying of a protein containing meal can be modified byprevious dietary protein intake. This effect, which is time dependentand meal specific, may be related to changes in endogenous CCK release which will affect emptying rate. While the exact mechanisms underlying this adaptive response need to be studied and clarified further, theseresults emphasise the importance of dietary history in the evaluationand interpretation of gastric emptying data.

Keywords:diet; protein content; gastric emptying; cholecystokinin