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Postheparin plasma lipase activities and plasma lipoproteins in newborn infants
Insights
In newborn infants, hepatic lipase activity is significantly higher than lipoprotein lipase activity. This finding suggests that postheparin lipolytic activity is not a reliable measure of lipoprotein lipase in this age group.
Area of Science:
- Biochemistry
- Pediatric Medicine
- Lipid Metabolism
Background:
- Newborn infants undergoing exchange transfusion require careful monitoring of metabolic parameters.
- Lipoprotein lipase and hepatic lipase are key enzymes in lipid metabolism, but their activity in newborns is not fully understood.
- Postheparin lipolytic activity is commonly used to assess lipoprotein lipase function.
Purpose of the Study:
- To measure and compare lipoprotein lipase and hepatic lipase activities in newborn infants undergoing exchange transfusion.
- To evaluate the validity of using postheparin lipolytic activity as a surrogate marker for lipoprotein lipase in neonates.
Main Methods:
- Blood samples were analyzed for glucose, insulin, apolipoproteins, triglycerides, and cholesterol.
- Lipoprotein and hepatic lipase activities were measured using specific assays after heparin administration.
- Enzyme activities were assessed at various time points and during exchange transfusion.
Main Results:
- Lipoprotein lipase activity in infants was comparable to adult levels after a heparin bolus.
- Hepatic lipase activity was significantly higher in infants than in adults.
- Hepatic lipase activity decreased during exchange transfusion, while lipoprotein lipase activity remained stable.
- Hepatic lipase activity was 3.4 times higher than lipoprotein lipase activity in infants.
Conclusions:
- Hepatic lipase plays a more dominant role in lipolysis in newborn infants compared to adults.
- Postheparin lipolytic activity is not a suitable measure of lipoprotein lipase in newborn infants due to high hepatic lipase contribution.
- Further research is needed to establish appropriate methods for assessing lipase activity in neonates.
Abstract:
We measured blood glucose, serum insulin and apoprotein A-I and A-II, and triglycerides and cholesterol contained in serum lipoprotein fractions of 24 full-term newborn infants who underwent exchange transfusion with heparinized blood for hematological reasons. The values were similar to those previously reported for healthy newborn infants. We also measure lipoprotein and hepatic lipase activities with specific methods. Fifteen minutes after an intravenous heparin bolus of 100 IU/kg, mean lipoprotein lipase activity in infants (16.0 mumol free fatty acids/ml/h) was as in adults. In contrast, hepatic lipase activity was significantly higher in infants (54.3 mumol free fatty acids/ml/h) than in adults. There was no sex difference in the infant lipase activities. Lipoprotein and hepatic lipase activities were also measured 5 and 15 min after a heparin bolus of 10 and 50 IU/kg: 10 IU/kg released only part of the lipase activities. In addition, the two lipases were measured during the exchange transfusion. Although 92% of the original infant blood was removed, lipoprotein lipase activity remained constant. In contrast, hepatic lipase activity decreased considerably. In infants, postheparin lipolytic activity is a conventional measure of lipoprotein lipase. Lipoprotein and hepatic lipases comprise 95% of postheparin lipolytic activity. In our infants, hepatic lipase activity was 3.4 times higher than lipoprotein lipase activity. Hence, it seems unjustified to use postheparin lipolytic activity as a measure of lipoprotein lipase.