Lipoprotein Lipase Activity In Liver Research Articles

Starvation enhances lipoprotein lipase activity in the liver of the newborn rat

To determine to what extent lipoprotein lipase activity in the liver of the newborn rat depends on milk ingestion, its changes were studied during different nutritional conditions. Newborns were placed with nurse rats with or without ligated nipples and they were killed at 0, 8 or 24 h of life. Lipoprotein lipase in newborns liver was characterized by its inhibition in the presence of 1.0 M NaCl, its specific elution at 1.5 M NaCl on heparin-Sepharose 4B column and its requirement for serum in the assay mixture to manifest its activity. In fed animals lipoprotein lipase activity and triacylglycerol content in liver as well as circulating triacylglycerols and ketone bodies increased progressively after birth. When newborns were kept starved the change in enzyme activity was significantly enhanced, whereas the increase found after birth in the other parameters disappeared. Starvation produced reduction in circulating RIA-insulin levels in the newborn rats. Results show that liver lipoprotein lipase activity in the newborn rat is controlled by a mechanism which resembles that of the enzyme in the adult heart and indicate that its presence facilitates the uptake by the liver of fatty acids from circulating triacylglycerols for their oxydation rather than deposit.

Liver lipoprotein lipase activity in Intralipid-injected rats

Liver lipoprotein lipase activity in Intralipid-injected rats

Increase with starvation in the pregnant rat of the liver lipoprotein lipase activity

Increase with starvation in the pregnant rat of the liver lipoprotein lipase activity

Circulating triacylglycerols, lipoproteins, and tissue lipoprotein lipase activities in rat mothers and offspring during the perinatal period: Effect of postmaturity

Mammary gland and adipose tissue lipoprotein lipase activities have been implicated in the changes of circulating triacylglycerol levels which occur in the mother at late gestation. In the newborn the temporal accumulation of triacylglycerols in the liver coincides with the appearance of a lipoprotein lipase peak. The relationships of these changes with the rise in circulating prolactin in the mother before parturition and the extrauterine nutritional status in the offspring were studied in a postmaturity model produced in the rat by subcutaneous injection of 7 mg progesterone/day to pregnant animals from the 20th day of gestation. Pregnant controls received the medium. Parturition occurred at day 21.5 of gestation in pregnant controls while it did not occur before the 23rd day in those receiving progesterone. At the 20th day of gestation, plasma triacylglycerol concentrations and all lipoprotein fractions (especially VLDL) were much higher in mothers not receiving progesterone than in age-matched virgins, and these differences disappeared at the 21st day of gestation. Lipoprotein lipase activity was maintained low in control mothers' adipose tissue until the 23rd postfecundation day while it greatly increased in mammary gland from parturition time. In progesterone treated mothers, both triacylglycerol and lipoprotein fractions (especially VLDL) in plasma were maintained elevated until the 23rd postfecundation day and adipose tissue and mammary gland lipoprotein lipase activities were maintained low until this time. Circulating prolactin levels increased around parturition in control mothers while they did not change in the progesterone treated mothers at any of the times studied. In offspring from control mothers, plasma triacylglycerols were low and their most abundant circulating lipoprotein fraction appeared to be LDL. In contrast to mother's liver, in offspring liver a marked lipase activity with all the inhibitory characteristics of lipoprotein lipase in the presence of both NaCl and protamine sulfate appeared around birth, coinciding with a sharp increase in liver triacylglycerol concentration and plasma ketone body levels. In postmature fetuses, liver lipoprotein lipase activity and triacylglycerol content decreased from the 20th to the 23rd postfecundation day while levels of both acetoacetate and beta-hydroxybutyrate rose in blood. Results indicate that increased mammary gland lipoprotein lipase in the mother may play a role in the decline of hypertriglycerolemia before parturition and that the initial change is driven by the rise in circulating prolactin at that time. On the contrary, the reduction in adipose tissue lipoprotein lipase activity in late gestation is not associated with the increase in circulating prolactin levels. We speculate that in offspring from control mothers, the high fat content of the mother's milk produces a substrate induction mechanism on liver lipoprotein lipase converting the liver of the newborn into a temporary lipid storage organ. Consumption of endogenous resources and maintenance of maternal ketone bodies transfer through the placenta ensure development of postmature fetus.

Lipoprotein lipase activity in liver of the rat fetus

Lipoprotein lipase activity was determined in tissue from pregnant and post-partum rats and virgin adult controls and in liver from fetuses and pups. A glycerol-based emulsion of tri-(1- 14C)-oleoyl-glycerol was used as substrate. According to the inhibitory characteristics in the presence of protamine and NaCl, the measured activity corresponded to the extrahepatic lipoprotein lipase of the adults. Compared to control values, the lipoprotein lipase activity was reduced in the mother's adipose tissue in late gestation and during the first days after parturition while it did not change in heart. Liver activity was negligible in mothers and controls while in the fetus it increased until the time of birth. The presence of this enzyme may allow the fetus liver to remove circulating triglycerides and to store them in preparation for early extrauterine life.

Identification of an adipose tissue-like lipoprotein lipase in perfusates of chicken liver

The nature of the lipolytic activity released from chicken livers perfused with Krebs-Ringer buffer (pH 7.0) containing heparin (50 or 10 U/ml), fraction V albumin (3%), and glycerol (20%) was investigated. The nonrecirculating perfusates contained both previously described NaCl-resistant "liver lipase" as well as an apoLp-Gluactivated lipoprotein lipase (LPL). Crude perfusate lipolytic activity was separated on heparin-Sepharose columns into two enzymatic peaks which were eluted at mean NaCl molarities of 0.75 M (liver lipase) and 1.2 M (LPL). The liver LPL activity was stimulated 7-fold by human apoLp-Glu (half maximal activity at 1.5 microgram/ml) and inhibited by apoLp-Ala, apoLp-Ser, apoLp-GlnI, and apoLP-GlnII. Liver LPL was fully inhibited by anti-adipose LPL immunoglobulins. The "liver lipase" was not affected by apoLp-Glu (3-34 microgram/ml) or anti-adipose LPL immunoglobulins. The data demonstrate the presence in liver perfusates of a LPL with properties similar to adipose tissue lipoprotein lipase.