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Gastric lipolysis in the developing rat. Ontogeny of the lipases active in the stomach
Insights
Lingual lipase is the primary enzyme for fat digestion in newborn rats, compensating for immature pancreatic function. Its activity increases with age, supporting significant stomach fat hydrolysis from birth through weaning.
Area of Science:
- Biochemistry
- Developmental Biology
- Gastroenterology
Background:
- Fat digestion initiates in the stomach, hydrolyzing triacylglycerols.
- Newborns rely on preduodenal fat digestion due to immature pancreatic and hepatic functions.
- Lingual and gastric lipases are potential contributors to stomach fat digestion.
Purpose of the Study:
- To investigate the developmental pattern of lingual and gastric lipase activity in rats.
- To quantify the contribution of these enzymes to intragastric fat digestion.
- To determine the primary lipase responsible for fat digestion in newborns.
Main Methods:
- Assessed lipase activity in lingual glands and gastric mucosa homogenates from rats (birth to 60 days).
- Measured lipase activity using medium-chain and long-chain triacylglycerols.
- Analyzed triacylglycerol hydrolysis in stomach contents post-feeding.
Main Results:
- Lingual lipase activity increased steadily from birth to 50 days.
- Gastric lipase activity peaked at 17-20 days and declined post-weaning.
- Lingual lipase exhibited higher activity than gastric lipase throughout the study period.
- Significant triacylglycerol hydrolysis occurred in the stomach, correlating with lingual lipase levels.
Conclusions:
- Lingual lipase is the major digestive enzyme in newborn rats.
- Lingual lipase activity compensates for immature pancreatic function in neonates.
- Lingual lipase plays a crucial role in early-life fat assimilation.
Abstract:
The first step in fat digestion occurs in the stomach, where 10-30% of dietary triacylglycerols are hydrolyzed to partial (di- and mono-) acylglycerols and free fatty acids. Preduodenal fat digestion is an important compensatory mechanism in the newborn because of immature pancreatic (lipase) and hepatic (bile acid synthesis) function. Since hydrolysis of fat in the stomach can be catalyzed by enzymes of lingual (Hamosh, M. (1979) Pediatr. Res. 13, 615-622) and possibly gastric origin, we have studied the developmental pattern and quantitative contribution of these two enzymes to intragastric fat digestion by measuring lipase activity in homogenates of lingual glands and gastric mucosa of rats from birth until 60 days of age. Total lipolytic activity in rat gastric mucosa was only 2-10% of that in the lingual glands throughout the entire period studied. Lingual lipase activity increased steadily from birth until day 50, whereas the activity in the gastric mucosa reached peak levels at 17-20 days and declined sharply after weaning. Throughout the period of study--suckling, weaning, and young adulthood--lingual and gastric lipase had very similar characteristics: pH optimum in the range of 5.0-6.0 and 2.5-5.0-fold higher activity on medium-chain (tri[14C]octanoin) than long-chain (tri[3H]olein) triacylglycerols. In the lingual glands, lipase activity was higher during fasting, probably because of accumulation of enzyme (without depletion during meals), whereas in the gastric mucosa lipase levels were higher after feeding, suggesting adsorption of lingual lipase (which reaches the stomach with the ingested food) onto the gastric mucosa. From birth to weaning, there was rapid and extensive hydrolysis of triacylglycerol in the stomach (decrease from 98 mol% in rat milk to 33.6-48.9 mol% in the stomach contents half an hour after feeding). The intragastric lipolysis remained almost constant from birth until day 20, in spite of a marked increase in food consumption, probably because of the continued rise of lingual lipase levels. The direct relationship between high intragastric lipolysis and high lingual lipase activity suggests that lingual lipase is the major digestive enzyme in the newborn.