SPECIFIC ADAPTATION OF GASTRIC-EMPTYING TO DIETS WITH DIFFERING PROTEIN-CONTENT IN THE RAT - IS ENDOGENOUS CHOLECYSTOKININ IMPLICATED

Background-Recent studies indicate that gastric emptying may be influe nced by patterns of previous nutrient intake. Endogenous cholecystokin in (CCK), whose synthesis and release can be affected by dietary intak e, has a major role in the regulation of gastric emptying. Aims-To eva luate 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 gas tric emptying is modified after long term intake of diets with differi ng protein content. Methods-Rats were fed for three weeks with high pr otein, medium protein (regular), or low protein diet. On day 22 gastri c emptying of a peptone meal was studied. In addition, basal and postp randial 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 gast ric emptying was studied at the end of the adaptation period (three we eks). Results-Feeding the animals with a high protein diet for three w eeks 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)%) in the emptying rate . When the time course of the effect of dietary adaptation on gastric emptying was studied, it appeared that at least two weeks are required for dietary protein to be effective. The regulatory effect of dietary protein on gastric emptying proved to be dependent on meal compositio n. Only the emptying rate of a protein containing meal (40% peptone) w as significantly modified by previous dietary intake. No significant ( p>0.05) changes were observed with glucose and methylcellulose meals w hose emptying rates were similar in rats receiving a high protein or l ow protein diet. A peptone meal strongly and significantly (p<0.05) in creased plasma CCK levels in rats fed a medium protein (regular) diet. Results were similar in rats receiving a low protein diet (p<0.05) bu t not in rats on a high protein diet (p>0.05). As a consequence, postp randial plasma levels of CCK 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. In rats on high and low protein diets, dose respon se curves to CCK-8 were virtually identical, suggesting that dietary p rotein intake has no influence on the effect of exogenous CCK. Conclus ions-These results clearly show that gastric emptying of a protein con taining meal can be modified by previous dietary protein intake. This effect, which is time dependent and meal specific, may be related to c hanges in endogenous CCK release which will affect emptying rate. Whil e the exact mechanisms underlying this adaptive response need to be st udied and clarified further, these results emphasise the importance of dietary history in the evaluation and interpretation of gastric empty ing data.