Extrapancreatic lipases.
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Gastric Mucosa↗
Biomedical subjects
S J DeNigris
Publications and source records attributed to S J DeNigris.
Lingual and gastric lipases: species differences in the origin of prepancreatic digestive lipases and in the localization of gastric lipase.
The source of the lipase(s) acting in the stomach was investigated in five animal species: rat, mouse (rodents), rabbit (lagomorphs), guinea pig (caviidae), baboon and human (primates). The activity of lingual and gastric lipases was quantitated in homogenates of lingual serous glands and of gastric mucosa, respectively, by the hydrolysis of tri[3H]oleylglycerol and is expressed in units/g (1 U = 1 mumol [3H]oleic acid released/min) per g tissue wet weight, mean +/- S.E. There were marked differences in the activity level of lingual and gastric lipases among species: mouse and rat had high levels of lingual lipase activity (250 +/- 20 and 824 +/- 224 U/g) and only traces of gastric lipase activity (4.5 +/- 0.9 and 0.04 U/g, respectively), whereas rabbit and guinea pig had no lingual lipase activity and only gastric lipase activity (78 +/- 48 and 27 +/- 7.4 U/g, respectively). In the baboon and human, gastric lipase was the predominant enzyme (109 +/- 20 U/g and 118 +/- 8.8 U/g, respectively), whereas lingual lipase activity was present in trace amounts only (0.04 U/g and 0.3 U/g, respectively). In addition to species differences in the origin of the preduodenal lipases, there were also species differences in the distribution of gastric lipase in the stomach. Thus, while in the rabbit, gastric lipase was localized exclusively in the cardia and body of the stomach, it was diffusely distributed in the entire stomach of the guinea pig and baboon. A comparison between the level of activity of lipase and pepsin (the two chief digestive enzymes secreted by the stomach), showed differences in their localization in the species studied. The difference in source (tongue vs. stomach) and site (cardia-body vs. entire stomach) of lipase secretion must be taken into account in future studies of these digestive enzymes. Although the exact contribution of lingual and gastric lipases individually to fat digestion in species which contain both enzymes cannot yet be evaluated, the markedly higher levels of gastric lipase activity in the baboon and human suggests that, in primates, gastric lipase is probably the major non-pancreatic digestive lipase.
Animals↗
Secretion of human gastric lipase from dispersed gastric glands.
The presence of a triacylglycerol lipase in human gastric juice was described in previous studies. Its source and role in intragastric lipolysis was, however, uncertain. Our study presents definitive evidence for gastric origin of a lipase and its release by secretagogues. Both carbachol and cholecystokinin-8 stimulate release of this enzyme for dispersed human gastric glands. While the two secretagogues had similar efficacies, with nearly a 3-fold stimulation over basal rates, cholecystokinin-8 was about four orders of magnitude more potent in releasing lipolytic activity than carbachol (maximum stimulation at concentrations of 1 X 10(-9) and 1 X 10(-5) M, respectively). Lipolytic activity measured against triolein (18:1), tricaprylin (8:0) and tributyrin (4:0) emulsions was 1.18 +/- 0.12, 4.48 +/- 0.64, and 12.17 +/- 0.88 units (1 unit = 1 mumol free fatty acid released/min per mg protein), respectively. Characterization of the pH optimum for each substrate showed maximum lipolysis at 4.5 for tributyrin, and at 5.5 for tricaprylin and triolein. These results indicate that a lipase which hydrolyzes long-, medium- and short-chain triacylglycerols is secreted by human gastric mucosa. At pH 6.0, the pH of the duodenum, there is appreciable lipolytic activity in the presence of bile salts. This suggests that gastric lipase, in addition to initiating lipolysis in the stomach, might also aid in the digestion of lipids in the duodenum. It remains to be determined whether gastric lipase is distinct from lingual lipase, or is the same enzyme secreted by the lingual serous glands and the gastric mucosa.
Bile Acids and Salts↗
Lipase secretion from dispersed rabbit gastric glands.
We have measured gastric lipase activity in dispersed glands of rabbit stomach by quantitating the hydrolysis of tri[3H]olein. Lipase activity in isolated gastric glands was 200-400 nmol [3H]oleic acid released per milligram dry weight per minute. The percentage of lipase activity released during incubation for 30 min at 37 degrees C under basal conditions was 1.5-4.5%. Lipase release was stimulated by secretagogues: 10 nM cholecystokinin octapeptide (CCK-8) and 100 microM carbachol led to four- to sixfold and two- to threefold higher enzyme secretion, respectively, while histamine had no effect. Carbonyl cyanide m-chlorophenylhydrazone (30 microM) completely inhibited the CCK-8-induced lipase release, indicating that lipase secretion is dependent on mitochondrial oxidative energy; dibutyryl cGMP (1 mM) inhibited 1 nM CCK-8-stimulated but not 100 microM carbachol-stimulated secretion; atropine (1 microM) had the opposite effect. These studies suggest that secretion of lipase from isolated gastric glands is stimulated by at least two receptor mechanisms. These studies show that a lipase that hydrolyzes long-chain triglyceride is secreted by rabbit stomach mucosa and that the secretion of gastric lipase is stimulated by two different receptor mechanisms.
Animals↗