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

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-fold increase in the overall protein synthesis following 5 days of lipid diet consumption, 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 adaptive mechanism. The pancreatic 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 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.