Distribution of Lipase Activity in Selected Tissues of Rainbow Trout (Oncorhynchus mykiss)

Abstract

Lipases (EC 3.1.1.3.) are water-soluble enzymes that catalyze the hydrolysis of ester bonds in water–insoluble, lipid substrates. Although the distribution and properties of various lipases from many tissues of human, laboratory and domestic animals have been studied, little is known about the pattern of distribution and physiological roles of these enzymes in the rainbow trout. The aim of the present study was to examine and compare the distribution of lipase in different tissues of the rainbow trout. A selection of tissue samples was assayed for lipase using the olive oil splitting method for the determination of formed free fatty acids. Significant activity of this enzyme was found throughout digestive system, which provokes that the pyloric caecal mass has the highest specific activity of lipase followed by the liver, kidney, stomach, spleen, distal intestine, proximal intestine, gill, heart, abdominal muscle and brain. High activity of lipase in the pyloric caecal mass of rainbow trout indicates its primary role in fat digestion. However, its wide tissue distribution suggests that this enzyme might perform other functions beside gastrointestinal fat digestion. The lipase activity in pyloric caecal mass seems to be dependent to bile salts under our assay conditions, resulting in a significant activity in the presence of natural bovine bile. The results of this study will be discussed in terms of the involvement of lipase in several biochemical and physiological functions in this species.