Community Research and Development Information Service - CORDIS

Effects of lipids on gastro-intestinal function in rainbow trout and regulation of feed intake by peptides and hormones

The data generated from the present project suggest that rainbow trout are able to regulate their feed intake in relation to energy content, and that their decreased food intake at high lipid diets may also reflect a compromise between reduced protein intake and increased lipid intake. Vegetable oils may accelerate the gastric emptying rate, with linseed oil having the strongest effect, which suggests that the regulation of gastric emptying is not functioning optimally. In addition, gastric emptying time increased with increasing dietary lipid levels, but at higher levels the effect levelled off. Thus, it appears that the regulation of gastric emptying may somehow break down at extremely high lipid levels, indicating a higher energy throughput and lower energy utilization. The postprandial regulatory mechanisms behind these effects need to be addressed in future studies.

Among CCK, GRP and ghrelin, only GRP was effective in regulating food intake, potently suppressing food intake. Thus, GRP is a candidate satiety factor in rainbow trout. As plasma GRP levels did not change after feeding, the most likely pathway for GRP action on food intake would be a local action at afferent nerves, being effective at low concentrations to terminate a meal. The RIA-analysis also revealed that the circulating GRP levels are generally very low. As GRP accelerated gastric emptying, the suggestion that GRP decreases feed intake at the gastrointestinal level by slowing the gastric emptying rate is not supported (Himick and Peter 1994b).

From our data, it is hypothesized that CCK could be related to gastrointestinal function regulating the proper processing of food in the intestine at different diet composition rather that having a role in the feedback inhibition of food intake. Alternatively, CCK may have a transient acute effect on food intake, or regulates the time between meals, that could not be detected in the present experimental set-up. It can be speculated that CCK delays gastric emptying time and possibly also mediates the decreased food intake at high lipid levels, which is supported by the CCK levels being elevated at high dietary lipid levels. The physiological role of CCK needs to be clarified and further studies should be designed to take into account rapid effects of CCK on food intake and its effect on interfeeding period duration as well as its functional relation to dietary lipids. Although a role for ghrelin in food intake regulation in rainbow trout is not supported by the obtained data, it may well be linked to nutritional status.

Finally, this part of the GUTINTEGRITY project has established a number of new techniques to study voluntary food intake and gastrointestinal passage of food and the regulation of these processes by different substances, along with the methods to measure CCK and GRP in plasma. This has generated important basic knowledge that significantly contributes to our understanding of gastrointestinal physiology in relation to food intake and appetite regulation, and also raises a number of interesting scientific issues that may be addressed in future studies. The gained information will help for a better design of diet compositions by increasing the usefulness of lipids of vegetable origin. Feed waste and release to the environment will be reduced by a better matching between feed distribution and fish appetite.

These data will be published in the scientific literature. The developed methodologies of RIA assessment of CCK and GRP levels in fih, as well as the method of intraperitoneal cannulation, will be used in further research applications and projects.

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