Pancreatic triglyceride lipase is a unique digestive enzyme in its requirement for colipase to reverse the marked inhibition of lipolytic activity by intraluminal bile salts. Together these two pancreatic secretory proteins are essential for digestion of dietary fat and are required in equimolar amounts to produce maximal lipolytic activity in the intestinal lumen. Without adequate intraluminal pancreatic lipase or colipase activity, such as occurs in the premature infant and in disease states associated with exocrine pancreatic insufficiency, steatorrhea invariably is present. This requirement for parallel secretion for optimal lipolytic underscores the need for a clear understanding of the events that regulate their expression and secretion. Almost nothing is known about the relative rates of secretion of lipase and colipase under basal and stimulated conditions, in part because functional assays are difficult to reproduce. Colipase has been reported to be secreted in a proform, but its mechanism of activation is unknown. Activation may play a physiological role in regulating bile-salt inhibited lipase activity. We propose initially to quantitatively assay the relative rates of secretion of lipase and colipase from the rat pancreatic duct under basal conditions and in response to specific secretagogues, using monoclonal antibodies already developed. If we confirm that colipase is secreted in proform, the intraluminal events controlling its activation will also be examined. Subsequent studies will focus on the developmental changes that occur in the expression of lipase and colipase in the rat using CDNAS encoding each of these proteins. Monoclonal antibodies against each of these proteins will be used for immunocytochemical co-localization. Using dispersed rat pancreatic acinar lobules from fetal and newborn rates, we will also determine the effect of hormones (i.e., corticosteroids) in regulating the expression of these proteins during development, and on inducing conversion of the fetal constitutive secretory pathway to a regulated one perinatally. The effect of corticosteroids and other hormones in regulating their coordinate or incoordinate expression will also be studied in the intact animal following continuous infusion of the putative agent in the adult rat. Finally, we propose to identify the nucleotide sequences regulating expression of each lipase and colipase gene by isolating and characterizing the genes encoding lipase and colipase from a genomic library and transfecting selected portions of each gene into cultured cells.
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