Changes in mRNA levels of rat pancreatic lipase in the early days of consumption of a high‐lipid diet

Abstract

The time-course response of rat pancreatic enzymes to a diet containing 25% sunflower oil was investigated. A 1.2-fold enhancement in lipase specific activity was observed as early as the first day of diet consumption and was further increased up to 1.9-fold on the 5th day. On the other hand, colipase activity was slightly decreased during the first two days of high-lipid diet intake and then increased. An immediate and direct effect was also exerted by the 25% lipid diet on lipase biosynthesis. Both fractional synthetic rate and specific activity of lipase were comparably induced. Due to a 1.6-Sold increase in the overall protein synthesis following 5 days of lipid diet comsumption, the absolute synthesis of lipase and amylase was increased by 3.5-fold and 0.98-fold, respectively, as compared to control animals. By contrast, the synthesis of procarboxypeptidases and serine proteases did not increase before day 5, probably as the result of a distinct adaptative mechanism. The pancreactic mRNA levels in control and adapted animals, which were determined by dot-blot hybridization with amylase and lipase cDNAs, were consistent with a biphasic induction of lipase synthesis since a first increase in the level of the enzyme-specific mRNA during the first two days of diet intake (4-fold on day 1) was followed by a second increase after the fourth day (6.5-fold on day 5). On the other hand, amylase mRNA level was unchanged during the dietary manipulation. Thus, hyperlipidic diets exerted an immediate effect on both lipase activity and synthesis but a delayed effect on procarboxypeptidase and serine protease synthesis. In a similar manner, the immediate induction of lipase mRNA level by dietary fat, followed by another increase a few days later, suggested that at least two different mechanisms are involved in lipase mRNA induction.The concentration of pancreatic lipase is readily increased by fat-rich diets, the adjustment magnitude being governed by factors such as the amount [l -41 and type [4, 51 of lipids, as well as the total percentage of calories as fat in the diet [6]. Although the causal mechanisms still remain elusive, recent animal experiments suggested that secretion might play a major part in this adaptation since ingestion of fat resulted in the release of secretin [7 -91. Furthermore, the adaptative response patterns of pancreatic enzymes to dietary fat [I] and secretin [lo, 111 were found to be similar.Pancreatic lipase adaptation is a rapid process since a fourfold increase in the enzyme specific activity could be measured in the pancreas of just-weaned rats after the ingestion of a lard-rich diet for two days only [12]. The most significant adjustment in lipase specific activity, a six-fold increase as compared with control rat, occurred after the fourth day. It was therefore interesting to try to define better the early response of pancreatic enzymes to dietary Sat in adult rats in terms of activity and levels of the corresponding mRNAs. The purpose of the present report was to study the time-course r...

Pancreatic Lipase and Its Related Protein 2 Are Regulated by Dietary Polyunsaturated Fat during the Postnatal Development of Rats

“…This is also the first report of dietary regulation of PL in the preweaned rat, as previous studies on adaptation of PL to dietary fat all have been in weaned or adult animals. The parallel changes found in PL mRNA levels and activity in the weanling and adult rat in this study are concordant with previous studies (20,22,37) and suggest that the dietary regulation of PL postweaning is pretranslational or transcriptional. PL exhibited the previously reported (9) developmental regulation, independent of diet; PL activity and mRNA levels were low at d9 and d15 and increased to maximal levels by d28.…”

“…The different amount of polyunsaturated fat in the milk and the diet did not affect expression of PLRP1. The lack of influence of amount of fat in diet on PLRP1 expression in weanling rats in this work is surprising and differs from other studies (16,20,22,37), in which PLRP1 was shown to be transcriptionally regulated by dietary fat. However, the introduction of different amounts of PUFA, started earlier during the tertiary phase of pancreatic development, may alter the long-term regulation of PLRP1.…”

Regulation of Pancreatic Lipase by Dietary Medium Chain Triglycerides in the Weanling Rat

“…The regulation of PLRP1 by the amount of dietary fat is transcriptional, as demonstrated by increased nuclear transcript run-on assay (15). The parallel changes in PL mRNA levels (16) and synthetic rates (14) suggest that the regulation of PL is pretranslational and likely to be transcriptional. However, such transcriptional regulation has yet to be conclusively documented.…”

“…The rats were fed for 7 d ad libitum purified low-(LF; 11% of energy), moderate-(MF; 40% of energy) and high-(HF; 67% of energy) fat diets with MCT (trioctanoate/tridecanoate, Neobee 1053, Stepan, Maywood, NJ) or low-fat (11% of energy) diet with safflower oil (control). The period of 7 d was selected because maximal adaptation and new steady-state levels are seen in PL content, synthesis, and mRNA levels after 5 d (14). The composition of the diets is shown in Table 1.…”

“…When a high-fat diet is introduced to rats, PL protein synthesis and content and PLRP1 mRNA levels increase within 24 h (36%, 20%, and 412%, respectively) (14). After 5 d, PL content and synthesis and PLRP1 mRNA levels reach steady-state maximal levels (191%, 217%, and 650%, respectively) (14). The regulation of PLRP1 by the amount of dietary fat is transcriptional, as demonstrated by increased nuclear transcript run-on assay (15).…”