María A. Ruiz Martínez

Plasma peptide YY and pancreatic polypeptide in dogs after long-term adaptation to dietary fats of different degrees of saturation : Olive and sunflower oil

Abstract Mongrel dogs from weaning to 6 months of age were fed on one of two diets that differed only in the type of fat content (virgin olive oil or sunflower seed oil) to compare plasma levels of peptide YY (PYY) and pancreatic polypeptide (PP) in the basal period and in response to food. Under resting conditions, blood concentrations of both peptides, measured by specific radioimmunoassays, were significantly higher in the olive oil group. Food intake was not followed by any marked or significant changes in PYY or PP circulating levels, although some rises were observed. On the other hand, plasma PYY reached significantly greater values throughout the postprandial period in the dogs fed on the diet containing olive oil, whereas no differences were recorded between the groups as far as PP is concerned. Our results demonstrate that long-term intake of diets enriched in monounsaturated fatty acids (olive oil) produces significantly higher basal levels of PYY and PP, as well as significantly higher PYY levels in response to food compared with diets containing sunflower oil. The differences, traceable to the composition of the two types of dietary fat supplied, explain the attenuated pancreatic secretory activity observed by us previously in this animal species. This mechanism may be responsible, at least in part, for the adaptation of pancreatic secretion to the quality of dietary fat.

Comparison of the effects of dietary sunflower oil and virgin olive oil on rat exocrine pancreatic secretion in vivo

The aim of this study was to investigate the functional consequences in vivo of adapting the rat exocrine pancreas to different dietary fats. Weanling rats were fed diets containing 10 wt% virgin olive oil or sunflower oil for 8 wk. We then examined resting and cholecystokinin-octapeptide (CCK-8)-stimulated pancreatic secretion in the anesthetized animals. To confirm a direct influence of the type of fat upon the gland, the FA composition of pancreatic membranes as well as tissue protein and amylase content were determined in separate rats. The membrane FA profile was profoundly altered by the diets, reflecting the type of dietary fat given, although this was not paralleled by variations in the pancreatic content of protein or amylase. Nevertheless, dietary intake of oils evoked different effects on in vivo secretory activity. Resting flow rate and amylase output were significantly (P<0.05) enhanced by sunflower oil feeding. Time course changes in response to CCK-8 infusion also showed a different pattern in each group. Secretion of fluid, protein, and amylase increased markedly in all animals, reaching a maximum within 20–40 min of infusion that was followed by a dramatic decline in both groups. In the sunflower oil group, this resulted in values reaching the resting level as soon as 60 min after CCK-8 infusion was begun. However, after the initial decline, olive oil group values showed a prolonged plateau elevation above the baseline (P<0.05) that was maintained for at least the infusion time. In addition, a positive correlation between flow rate and both protein concentration and amylase activity existed in the olive oil group, but not in the sunflower oil group. The precise mechanism by which these effects are produced remains to be elucidated.

Dietary-induced changes in the fatty acid profile of rat pancreatic membranes are associated with modifications in acinar cell function and signalling

The effects of dietary lipids on the fatty acid composition of rat pancreatic membranes and acinar cell function were investigated. Weaning rats were fed for 8 weeks on one of two diets which contained 100 g virgin olive oil (OO) or sunflower-seed oil (SO)/kg. Pancreatic plasma membranes were isolated and fatty acids determined. Amylase secretion and cytosolic concentrations of Ca(2+) and Mg(2+) were measured in pancreatic acini. Membrane fatty acids were profoundly affected by the diets; the rats fed OO had higher levels of 18 : 1n-9 (42.86 (sem 1.99) %) and total MUFA compared with the animals fed SO (25.37 (sem 1.11) %). Reciprocally, the SO diet resulted in greater levels of total and n-6 PUFA than the OO diet. The most striking effect was observed for 18 : 2n-6 (SO 17.88 (sem 1.32) %; OO 4.45 (sem 0.60) %), although the levels of 20 : 4n-6 were also different. The proportion of total saturated fatty acids was similar in both groups, and there was only a slight, not significant (P=0.098), effect on the unsaturation index. Compared with the OO group, acinar cells from the rats fed SO secreted more amylase at rest but less in response to cholecystokinin octapeptide, and this was paralleled by reduced Ca(2+) responses to the secretagogue. The results confirm that rat pancreatic cell membranes are strongly influenced by the type of dietary fat consumed and this is accompanied by a modulation of the secretory activity of pancreatic acinar cells that involves, at least in part, Ca(2+) signalling.

Membrane Lipid Composition of Pancreatic AR42J Cells: Modification by Exposure to Different Fatty Acids

Dietary fat type influences fatty acids in rat pancreatic membranes, in association with modulation of secretory activity and cell signalling in viable acini. We aimed to confirm whether AR42J cells are a valid model to study the interactions between lipids and pancreatic acinar cell function. For this purpose we have (i) compared the baseline fatty acid composition of AR42J cells with that of pancreatic membranes from rats fed a standard chow; (ii) investigated if fatty acids in AR42J membranes can be modified in culture; and (iii) studied if similar compositional variations that can be evoked in rats when dietary fat type is altered occur in AR42J cells. Weaning Wistar rats were fed for 8 weeks either a commercial chow (C) or semi-purified diets containing virgin olive oil (VOO) or sunflower oil (SO) as fat source. AR42J cells were incubated for 72 hrs in medium containing unmodified fetal calf serum (FCS, AR42J-C cells), FCS enriched with 18:1 n-9 (AR42J-O cells), or FCS enriched with 18:2 n-6 (AR42J-L cells). Fatty acids in crude membranes from rat pancreas and AR42J cells were determined by gas–liquid chromatography. Differences in membrane fatty acids between C rats and AR42J-C cells can be explained in part by variations in the amount of fatty acids in the extracellular environment. Supplementation of FCS with 18:1 n-9 or 18:2 n-6 changed the fatty acid spectrum of AR42J cells in a manner that resembles the pattern found, respectively, in VOO and SO rats, although AR42J-L cells were unable to accumulate 20:4 n-6. The AR42J cell line can be a useful tool to assess the effect of membrane compositional changes on acinar cell function. However, differences in baseline characteristics, and perhaps fatty acid metabolism, indicate that results obtained in AR42J cells should be confirmed with experiments in the whole animal.

Adaptation of the exocrine pancreas to dietary fats

This article reviews studies on the adaptation of the exocrine pancreas to dietary fat. We include all the latest information about the mechanisms that underlie the adaptation of the secretory mechanism of the exocrine pancreas to the amount and the type of dietary fat. We review the kinetics of pancreatic adaptation and the mediators of the adaptive response of the pancreas including cellular and molecular mechanisms (modulation of intracellular messengers and gene expression of the different enzymes and secretagogues involved in the adaptation process). At the same time we include our results in this field in dogs and humans.ResumenEsta revisión recoge los estudios que tratan sobre la adaptación del páncreas exocrino a la grasa de la dieta. Se incluye la última información disponible acerca de los mecanismos implicados en la adaptación de los mecanismos secretores del páncreas exocrino a la cantidad y tipo de grasa de la dieta. Se revisa la cinética de la adaptación pancreática y los mediadores de la respuesta adaptativa del páncreas incluyendo los mecanismos celulares y moleculares (modulación de los mensajeros intracelulares y expresión génica de los diferentes enzimas y secretagogos implicados en el proceso de adaptación). Al mismo tiempo, incluimos nuestros resultados en este campo obtenidos en perros y humanos.