The contribution of exocrine pancreatic secretions to fat digestion

Fat digestion occurs in the small intestine and absorption of fatty acids, as mono- and diacylglycerols, is nearly complete at the distal ileum. The whole process of fat digestion is dependent on the exocrine pancreas and without pancreatic secretions, fat digestion would be severely impaired. There are three enzymes: lipase, carboxyl ester hydrolase and phospholipase A(2) and one cofactor: colipase, which act in concert to digest dietary fat. The exocrine pancreas of both the monogastric animal and the ruminant animal secretes these enzymes. The existence of carboxyl ester hydrolase in sows' milk remains to be demonstrated; the activity of this enzyme in pancreatic tissue increases very rapidly during the suckling period, and it is suggested that the pig may compensate for the missing enzyme in the milk by secreting more carboxyl ester hydrolase from the pancreas during the suckling period. Exocrine pancreatic secretion responds to changes in the level of fat in the diet and lipase secretion increases with an increase in the level of dietary fat. The exocrine pancreas also responds to changes in the fatty acid profile of dietary fat and these changes may have implications for fat digestion and digestive function. We observed significant effects of the type of fat on the total activities of chymotrypsin and carboxyl ester hydrolase, when the catheter method was used to collect pancreatic juice. Recently, additional research has been conducted in weanling pigs to further investigate the effect of dietary fat source on exocrine pancreatic secretions, and it has been found that the secretion of carboxyl ester hydrolase is increased by the inclusion of fish oil in the diet. We have applied the ileal analysis method to study the digestion of different sources of fat, which were also used in studies designed to investigate the nutritional regulation of exocrine pancreatic secretions. Different batches of the same sources of fat were used and both ileal and faecal digestibilities of fat and fatty acids were determined. The secretion and action of pancreatic lipolytic enzymes is not only dependent on the amount and type of dietary fat; the amount and type of protein, carbohydrates, minerals and antinutritional compounds may influence the digestion and absorption of fat as well. Fat digestion is a complex process and involves many different factors. The amount and type of dietary fat is probably the most important factor affecting the secretion of lipolytic enzymes. When the content of dietary fat in the diet is increased an increased secretion of lipase follows. Lipase is the most thoroughly studied lipolytic enzyme and future studies will have to elucidate whether there is a parallel increase in the other lipolytic enzymes, i.e. carboxyl ester hydrolase and phospholipase A(2) and in the cofactor colipase, when there is an increase in dietary fat. In addition, the quantitative role of specific enzymes in the process of fat digestion needs to be investigated.