Effect of sodium taurodeoxycholate, CaCl 2 and albumin on the action of pancreatic lipase on droplets of trioleoylglycerol and the release of lipolytic products into aqueous media

Abstract

1. 1. Effects of various substances on the activity of pancreatic lipase and on the release of lipolytic products into aqueous media were studied with droplets of trioleoylglycerol suspended from a membrane filter at the top of a flow-through chamber. The droplets were perifused for 7 min with a commercial preparation of pancreatic lipase in 0.15 M NaCl solution at pH 6.5 and then perifused for 60 min with lipase-free media, either 0.15 M NaCl at pH 6.5 or basal medium at pH 7.4 (70 mM sodium barbital) containing different additives. 2. 2. About 6% of the trioleoylglycerol in droplets was hydrolyzed during the perifusion with lipase. Another 15% was hydrolyzed in 30 min, but none thereafter, when the droplets were perifused with 0.15 M NaCl alone. The rate of hydrolysis was doubled and prolonged when droplets were perifused with basal medium at pH 7.4. Lipolytic products formed at pH 7.4 were 62% oleic acid, 20% monooleoylglycerol and 18% dioleoylglycerol, yet only 4% of the lipolytic products were released into the perifusate. 3. 3. Sodium taurodeoxycholate (TDC) (17 mM) added to basal medium increased 18 × the amount of lipolytic products released into the perifusate but increased lipolysis only 13%. The molar ratio of oleic acid to monooleoylglycerol in the perifusate was 5.7 during the first 30 min and 4.0 during the last 30 min. 4. 4. Ca 2+ (3.3 mM) added to basal medium increased lipolysis 87% but did not affect the amount (4%) of lipolytic products released into the perifusing medium. 5. 5. TDC and Ca 2+ added to basal medium produced the largest increase in lipolysis, with 59% of trioleoylglycerol hydrolyzed in 15 min and 91% in 60 min. The amount of lipolytic products released into the perifusing medium, however, was not increased above that released into medium containing TDC alone. 6. 6. Serum albumin (0.6 mM) and Ca 2+ added to basal medium increased 14 × the amount of lipolytic products released into the perifusate without affecting the basal lipolytic rate. Albumin, however, suppressed by 40% the stimulatory effect of Ca 2+ on pancreatic lipase activity. 7. 7. The findings show that Ca 2+ enhanced the activity of pancreatic lipase on triacylglycerol without affecting release of lipolytic products into the medium, whereas TDC increased release without affecting formation of lipolytic products. TDC did increase, however, the stimulatory effect of Ca 2+ on lipolysis. Thus, bile salts could facilitate fat digestion in vivo, in the presence of Ca 2+, by enhancing the action of pancreatic lipase and dispersing lipolytic products into the surrounding aqueous phase.