Role Of Lipoprotein Lipase Research Articles

Role of lipoprotein lipase and apolipoprotein E secretion by macrophages in modulating lipoprotein uptake. Possible role in acceleration of atherosclerosis in diabetes.

Because the accumulation of lipid in macrophages is a characteristic feature of atherosclerosis, the mechanisms by which this lipid accumulation occurs have been intensively studied. This paper reviews the receptor- and non-receptor-mediated pathways that promote lipid accumulation in macrophages. Particular emphasis is placed on the contributions of two secretory products of macrophages, lipoprotein lipase and apolipoprotein E, to both receptor- and non-receptor-mediated uptake of triglyceride-rich lipoproteins by macrophages. The hormonal, lipid, and immunological factors that regulate the secretion of LpL and apoE by macrophages are discussed, as are how changes in the secretion of apoE and LpL that can modulate the uptake of triglyceride-rich lipoproteins by macrophages might influence the atherosclerotic process in people with diabetes.

Metabolism of very-low-density lipoprotein triglyceride by human placental cells: The role of lipoprotein lipase

Several studies have shown lipoprotein lipase (LPL) activity in human placenta, but the quantitative significance and cellular specificity of LPL in this organ are unknown. The objective of this report is to investigate the metabolism of very-low-density lipoprotein triglycerides (VLDL-TG) by the placenta, the role of LPL in this process, and the types of cells involved. Placental cells were obtained by enzymatic digestion (collagenase, hyaluronidase, and DNA-ase) and separated on a 40% Percoll gradient. The trophoblasts were the predominant cell type (80% to 85% pure) isolated at d = 1.033 to 1.048 and macrophages were predominant at d = 1.077 to 1.100 (>95% pure), as characterized by eight immunocytochemical assays using cell protein-specific monoclonal antibodies. Macrophages represented 50% to 60% of cells isolated, and trophoblasts, 40% to 50%. LPL activity was assessed by VLDL-TG hydrolysis in primary 3- to 4-day tissue culture. In a representative experiment, LPL activity (nmol fatty acids (FA)/mg protein/24h) was 101.3 ± 5.3 in macrophages and 29.9 ± 6.5 in the predominant trophoblast cell types, with approximately 20% of these amounts incorporated and reesterified. VLDL-TG hydrolysis and cell lipid uptake in both placental cell types was essentially abolished by a monoclonal anti-LPL antibody. When compared with a model of hepatocytes (Hep G2 cells), the hydrolysis of VLDL-TG was almost undetectable in these cells. In contrast, free fatty acids (FFA) uptake by Hep G2 cells was fourfold to sixfold greater than that by macrophages and trophoblasts, respectively. In conclusion, macrophages and trophoblasts are the two predominant placental cells isolated by enzymatic digestion. The majority of VLDL-TG hydrolysis activity in tissue culture of placental cells arises from macrophages and is LPL-mediated. Compared with a cell model of hepatocyte function, VLDL-TGFA predominate as a source of FA for placental cells, while FFA predominate for the hepatocyte. Placental macrophages may play a role in the uptake of triglyceride-rich lipoprotein FA for placental storage, oxidation, and transfer to the fetus.

Lipoprotein lipase is synthesized by macrophage-derived foam cells in human coronary atherosclerotic plaques.

Lipoprotein lipase (LPL), hydrolyzes the core triglycerides of lipoproteins, thereby playing a role in their maturation. LPL may be important in the metabolic pathways that lead to atherosclerosis, since it is secreted in vitro by both of the predominant cell types of the atherosclerotic plaque, i.e., macrophages and smooth muscle cells. Because of uncertainty concerning the primary cellular source of LPL in atherosclerotic lesions, in situ hybridization assays for LPL mRNA were performed on 12 coronary arteries obtained from six cardiac allograft recipients. Macrophages and smooth muscle cells were identified on adjacent sections with cell-specific antibodies and foam cells were identified morphologically. LPL protein was localized using a polyclonal antibody. LPL mRNA was produced by a proportion of plaque macrophages, particularly macrophage-derived foam cells, but was not detected in association with any intimal or medial smooth muscle cells. These findings were confirmed by combined immunocytochemistry and in situ hybridization on the same tissue sections. LPL protein was detected in association with macrophage-derived foam cells, endothelial cells, adventitial adipocytes, and medial smooth muscle cells, and, to a lesser extent, in intimal smooth muscle cells and media underlying well-developed plaque. These results indicate that macrophage-derived foam cells are the primary source of LPL in atherosclerotic plaques and are consistent with a role for LPL in the pathogenesis of atherosclerosis.

Role of lipoprotein lipase in the regulation of high density lipoprotein apolipoprotein metabolism. Studies in normal and lipoprotein lipase-inhibited monkeys.

Mechanisms that might be responsible for the low levels of high density lipoprotein (HDL) associated with hypertriglyceridemia were studied in an animal model. Specific monoclonal antibodies were infused into female cynomolgus monkeys to inhibit lipoprotein lipase (LPL), the rate-limiting enzyme for triglyceride catabolism. LPL inhibition produced marked and sustained hypertriglyceridemia, with plasma triglyceride levels of 633-1240 mg/dl. HDL protein and cholesterol and plasma apolipoprotein (apo) AI levels decreased; HDL triglyceride (TG) levels increased. The fractional catabolic rate of homologous monkey HDL apolipoproteins injected into LPL-inhibited animals (n = 7) was more than double that of normal animals (0.094 +/- 0.010 vs. 0.037 +/- 0.001 pools of HDL protein removed per hour, average +/- SEM). The fractional catabolic rate of low density lipoprotein apolipoprotein did not differ between the two groups of animals. Using HDL apolipoproteins labeled with tyramine-cellobiose, the tissues responsible for this increased HDL apolipoprotein catabolism were explored. A greater proportion of HDL apolipoprotein degradation occurred in the kidneys of hypertriglyceridemic than normal animals; the proportions in liver were the same in normal and LPL-inhibited monkeys. Hypertriglyceridemia due to LPL deficiency is associated with low levels of circulating HDL cholesterol and apo AI. This is due, in part, to increased fractional catabolism of apo AI. Our studies suggest that variations in the rate of LPL-mediated lipolysis of TG-rich lipoproteins may lead to differences in HDL apolipoprotein fractional catabolic rate.

ApoA-IV metabolism in the rat: role of lipoprotein lipase and apolipoprotein transfer.

Factors influencing the association of apoA-IV with high density lipoproteins (HDL) were investigated by employing a crossed immunoelectrophoresis assay to estimate the distribution of rat plasma apoA-IV between the lipoprotein-free and HDL fractions. Incubation of rat plasma at 37 degrees C resulted in the complete transfer of lipoprotein-free apoA-IV to HDL within 45 min. When plasma obtained from fat-fed rats was incubated at 37 degrees C in the presence of postheparin plasma as a source of lipolytic activity, there was a complete transfer of HDL apoA-IV to the lipoprotein-free fraction within 30 min. With extended incubation (120 min), lipoprotein-free apoA-IV began to transfer back to HDL. Similar patterns of apoA-IV redistribution were seen when plasma from fat-fed rats was incubated with postheparin heart perfusate or was perfused through a beating heart. Incubations conducted with plasma obtained from fasted rats showed similar but markedly attenuated apoA-IV responses. Similar observations were found in vivo following intravenous heparin administration. To determine whether the transfer of apolipoproteins from triglyceride-rich lipoproteins to HDL was partially responsible for the lipolysis-induced redistribution of apoA-IV, purified apoA-I, apoE, and C apolipoproteins were added to plasma from fasted rats. When added to plasma, all of the apolipoproteins tested displaced apoA-IV from HDL in a dose-dependent manner. Conversely, apolipoproteins were removed from HDL by adding Intralipid to plasma from fasted rats. With increasing concentrations of Intralipid, there was a progressive loss of HDL apoC-III and a progressive increase in HDL apoA-IV. Intravenous injection of a bolus of Intralipid to fasted rats resulted in a transient decrease of HDL apoC-III and concomitant increase in HDL apoA-IV. From these studies, we conclude that the binding of apoA-IV to HDL is favored under conditions that result in a relative deficit of HDL surface components, such as following cholesterol esterification by LCAT or transfer of apolipoproteins to nascent triglyceride-rich lipoproteins.

The role of lipoprotein lipase in metabolism of normolipidemic very low density lipoprotein by macrophages.

It was demonstrated by using lipoprotein lipase (LPL) inhibitor benzene boronic acid (BBA) that LPL played a major role in the accumulation of triglycerides (TG) in mouse peritoneal macrophages exposed to rabbit normal very low density lipoproteins (N-VLDL). There wwere less free fatty acids (FFA) and much more N-VLDL-TG left in the media containing BBA than in the controls. TG accumulation in the cells was greatly diminished or even prohibited by BBA. Thus, we obtained direct evidence that LPL played a more important role than the receptor did in the uptake of N-VLDL-TG by mouse macrophages. The mechanisms of LPL action were discussed.

Uptake and Metabolism of Intralipid by Rat Liver: An Electron-Microscopic Study

The metabolism of Intralipid (intravenously injected) was studied in rats fasted for 48 h. At all doses used, the Intralipid triacylglycerols disappeared rapidly from circulation and concomitantly the hepatic content of triacylglycerols and the level of circulating ketone bodies increased, indicating an active metabolism of Intralipid by the liver. To study this possibility further we used an ultrastructural approach. In rats given Intralipid we detected numerous lipid particles in the spaces of Disse, retained in the interdigitations of the hepatocyte. There were also lipid particles attached to the luminal surface of the endothelial cells. Small lipid particles were seen in close contact with endocytic vesicles internalized into hepatocytes but were present mainly in endothelial cells. Inside the endothelial cells, the endocytic vesicles were detected in contact with lysosomes. Inside hepatocytes, a process of sterification seemed to occur in the endoplasmic reticulum as deduced from the presence of small lipid droplets with ill-defined outlines. Large lipid droplets were seen in close contact with mitochondria, indicating a mitochondrial uptake and metabolism of fatty acids to synthesize and release ketone bodies. The possible role of lipoprotein lipase in the liver for the hepatic uptake of Intralipid particles is discussed.

Effects of alpha-adrenergic and beta-adrenergic receptor blockade on lipid metabolism

The role of lipoprotein lipase in the pathophysiology of lipid changes during alpha-receptor or beta-receptor blockade was evaluated in this clinical trial. Thirty hypertensive patients were given 2 mg of prazosin twice daily or 100 mg of metoprolol twice daily for 10 weeks, according to an open, randomized protocol. Both drugs were effective in reducing arterial blood pressure (from 153 ± 16/102 ± 6 mm Hg to 146 ± 12/92 ± 8 mm Hg with prazosin and from 158 ± 17/103 ± 8 to 144 ± 14/94 ± 10 mm Hg with metoprolol). Prazosin significantly reduced total plasma cholesterol from 202 ± 39 to 188 ± 36 mg/dl and increased high-density lipoprotein cholesterol from 36 ± 8 to 40.5 ± 11 mg/dl. Prazosin did not affect plasma triglycerides levels, whereas patients taking metoprolol had a slight rise in these levels, from 122 ± 42 to 142 ± 57 mg/dl, along with a decrease in high-density lipoprotein cholesterol from 37 ± 10 to 31 ± 8 mg/dl. The concentration of apoprotein B did not change significantly with either treatment. Lipoprotein lipase activity increased in the prazosin group from 28.4 ± 16 to 37.7 ± 14 μmol/liter per minute (p <0.01), but did not change significantly (29.9 ± 12 versus 32.8 ± 8 μmol/liter per minute) in patients treated with the beta blocker. These data, which confirm previous reports of serum lipid changes during antihypertensive therapy, suggest that alpha 1 blockers may interfere with lipoprotein lipase, possibly by reducing its catecholamine-mediated inactivation.

酵素法によるPostheparin lipolytic activityの測定

Two kinds of lipase, lipoprotein lipase (LPL) and hepatic triglyceride lipae (H-TGL) are released into plasma by intravenous administration of heparin. LPL is believed to play an important role in the degradation of triglyceride rich lipoprotein, and is also suggested to be engaged in the metabolism of HDL. On the other hand, the physiological role of H-TGL was undefined for a long time, but recently the deficiency of H-TGL was discovered and it's abnormalities in lipoprotein composition resembled Type III hyperlipoproteinemia associated with apo E3 deficiency, suggesting this enzyme may be essential for the metabolism of IDL or remnants of TG-rich lipoproteins.Considering these roles of LPL and H-TGL in the lipoprotein metabolism, the precise measurement of postheparin lipolytic activity (PHLA) is very important.PHLA is now commonly measured by using radioisotopically labeled substrate, but we had better restrict the use of RI if possible in order to avoid the environmental pollution. In non-RI method, PHLA was measured by using Ediol as substrate and titration method of Dole for the determination of released free fatty acid. because of its low sensitivity, we must use much more volume of postheparin plasma (PHP) for incubation than that in the RI method. Considering the property of H-TGL, which is inhibited by serum in vitro, the activity measured by this method is not accurate.In this work, we established a new non-radioisotopic method for the measurement of LPL and H-TGL in postheparin plasma, using NEFA KitK (NIPPON SHOJI, Osaka, Japan) for the deterurination of released free fatty acid. The selective measurement of LPL and H-TGL was performed as described by M. L. Baginsky and W. V. Brown. Using this measurement system, we examined LPL and H-TGL activity of postheparin plasma (50units/kg Body Weight) in normal control group and type III hyperlipoproteinemia with apo E3 deficiency and discussed the contribution of LPL and H-TGL to lipoprotein metabolism.Following results were obtained.1) Extracted free fatty acid by Dole's method can be measured with linearity up to about 300nmol/tube for LPL and about 400nmol/tube for H-TGL by NEFA Kit-K. Thus, we can measure PHLA with lenearity up to about 60μmol/ml/hr for LPL and about 80μmol/ml/hr for H-TGL, since 5μl of postheparin plasma was used for the measurement of PHLA in our system.2) H-TGL was inhibited almost completely after 10min pre-incubation of PHP with an equal volume of 100mM SDS at 26°C. The remaining activity (LPL activity) was plateau till 70min of preincubation.3) The addition of hyperlipidemic serum up to 10μl did not interfere the purified H-TGL activity.4) The mean activities of LPL and H-TGL of normal males are 9.4 and 20.1μmol/ml/hr respectively which are nearly equal to those reported by J. Boberg and M. Boberg.5) The relationships between PHLA (LPL and H-TGL) and lipid composition in VLDL, IDL, LDL, HDL2 and HDL3 were not statistically significant in this study.6) After clofibrate treatment with apo E3 deficient patient, LPL activity increased, cholesterol and triglyceride in VLDL, IDL, LDL and HDL3 decreased, and HDL2 cholesterol increased.These results suggested that this non-radioisotopic method is accurate and useful for clarifing the etiology of various hyperlipidemia and the contribution of abnormalities of lipoprotein metabolism to atherosclerotic diseases.

Mechanisms of energy balance in obesity.

The proper understanding of obesity requires a multifaceted approach. Behavioral considerations of eating and activity patterns do not account for the large between- and within-subjects variance associated with the energy-balance equation. Sources of adaptive and dispositional variance in metabolic rates are reviewed and suggested to be a likely source of importance for the proper conceptualization and intervention of obesity. Five proposed mechanisms of metabolic variation are reviewed with consideration of the supporting evidence for each mechanism. The generalizability of some of the proposed mechanisms is limited because of the scope of past research. However, the roles of lipoprotein lipase in fat storage and brown adipose tissue in thermogenesis are intriguing possibilities for future research with humans.

Uptake and degradation of human chylomicrons by macrophages in culture. Role of lipoprotein lipase.

Because macrophages secrete lipoprotein lipase (LPL), we sought to determine if LPL activity would influence the metabolism of chylomicrons by macrophages. In initial studies, we showed that normal chylomicrons were a substrate for the macrophage's LPL activity. Uptake of normal chylomicrons occurred in a saturable fashion and was effectively competed for by human chylomicrons, very low density lipoproteins (VLDL), and rabbit beta-VLDL, but not by acetyl-low density lipoprotein (LDL), and only modestly by native LDL. When apoprotein C-II-deficient chylomicrons were incubated with macrophages, no hydrolysis of triglyceride occurred, yet saturable uptake of chylomicron protein and lipid occurred, demonstrating that LPL activity is not a prerequisite for saturable uptake. However, addition of apo C-II led to marked hydrolysis and enhanced uptake of protein and lipid moieties. When albumin was present in the medium, there was approximately equal enhancement of cellular content of triglyceride and cholesteryl ester, despite the fact that chylomicrons are triglyceride-rich. This was due to uptake of a triglyceride-depleted particle produced by LPL, as well as a preferential re-release of triglyceride. These studies suggest potential pathways by which triglyceride-rich lipoproteins could contribute to accumulation of cholesteryl esters in macrophages, even while only small amounts of triglyceride accumulate.

The role of lipoprotein lipase in the metabolism of triglyceride-rich lipoproteins by macrophages.

We have previously shown that cultured macrophages secrete lipoprotein lipase (LPL) into the culture medium. The purpose of these experiments was to determine the role of LPL in the uptake of very low density lipoproteins (VLDL). Both J774 cells and mouse peritoneal macrophages took up and degraded normotriglyceridemic VLDL in a saturable manner. Uptake of VLDL was effectively competed for by rabbit beta-VLDL, human VLDL, but not by native LDL or acetyl LDL. LPL activity accelerated saturable uptake of VLDL but was not a prerequisite for it. This was most clearly seen in experiments with apo-C-II-deficient VLDL. Although no hydrolysis of VLDL triglyceride occurred, saturable uptake and degradation of the C-II-deficient lipoprotein occurred. However, addition of apo-C-II enhanced saturable uptake. Normal VLDL also promoted cellular accumulation of both triglycerides and cholesteryl esters. Accumulation of triglyceride occurred by uptake of intact VLDL particles, by uptake of a triglyceride-depleted particle produced by the action of LPL, and by the direct uptake of free fatty acids generated by the activity of LPL. In turn, the latter process was influenced by the amount of albumin in the medium capable of being an acceptor for free fatty acids. Finally, we have shown that when albumin is present in the medium, the macrophage is capable of mobilizing most of its stored triglyceride over 24 h, even as its cholesteryl ester content remains constant. These studies may be relevant to the ability of VLDL to promote macrophage accumulation of cholesteryl ester, even as triglyceride accumulation is minimized.

Conversion of low density lipoprotein 1 (LDL1, 1.019 less than d less than 1.045) to low density lipoprotein 2 (LDL2, 1.045 less than d less than 1.063) by hepatic triglyceride lipase.

The role of lipoprotein lipase and hepatic lipase in the conversion of LDL1 (1.019 less than d less than 1.045) to LDL2 (1.045 less than 1.063) were investigated on the basis of incubation of 125I-LDL1 with postheparin plasma (PHP) at NaCl concentrations of both 0.15 M and 1.0 M. Insignificant small increments of radioactivity and apoprotein B specific activity of LDL2 were observed even when 125I-LDL1 was incubated with preheparin plasma as the control. When 125I-LDL1 was incubated with PHP, the LDL1 radioactivity decreased and the LDL2 radioactivity increased significantly. the apoprotein B specific activity was also increased in the LDL2 fraction. One molar NaCl did not inhibit these changes. It is concluded that hepatic triglyceride lipase was the major mediator in the conversion of LDL1 to LDL2.

Possible role of lipoprotein lipase in the regulation of endogenous triacylglycerols in the rat heart.

1. Adrenaline has a biphasic effect on intracellular lipoprotein lipase activity and on endogenous triacylglycerol content in heparin-perfused heart. 2. A high concentration of adrenaline (1 microM in the perfusion buffer) activated endogenous lipoprotein lipase activity and, at the same time, decreased intracellular triacylglycerol stores. 3. In contrast, a low concentration (0.005 microM-adrenaline) inhibited intracellular lipoprotein lipase activity. Under these conditions, cardiac triacylglycerol content was elevated above control values. 4. Perfusing the heart with high and low concentrations of 3-isobutyl-1-methylxanthine elicited a biphasic effect on endogenous lipoprotein lipase activity and triacylglycerol content similar to that seen with adrenaline treatment. 5. The effect of adrenaline on intracellular lipoprotein lipase activity appears to be mediated by cyclic AMP through protein kinase. 6. A possible role for intracellular lipoprotein lipase in the regulation of endogenous triacylglycerol in rat heart is proposed.

Plasma lipoprotein changes resulting from immunologically blocked lipolysis

The role of lipoprotein lipase (LPL) in the generation of low density lipoprotein (LDL) and high density lipoprotein (HDL) was investigated. Intravenous injections of high titer goat antiserum against highly purified chicken LPL into fasted roosters quantitatively blocks the removal of plasma VLDL triglyceride (1976. J. Lipid Res. 17: 498-505). Analyses of the chemical components of lipoproteins after 8 hr of LPL inhibition showed that the very low density lipoprotein (VLDL) concentration increased over 10-fold, while LDL and HDL concentrations decreased by 5-fold and 48%, respectively. LDL and HDL cholesterol levels decreased logarithmically over the 8-hr period, with half-lives of 2.4 and 6 hr, respectively. The composition of these lipoprotein fractions on a percent weight basis changed significantly. Experimental LDL contained 37% less phospholipid, 64% less cholesterol, and 2.3-fold more triglyceride than control LDL. Experimental HDL contained 3.1-fold more triglyceride and 50% less unesterified cholesterol than control HDL. The Stokes' radii of HDL were determined by gel filtration on Biogel A5M and Ultrogel AcA 22: the radius of experimental HDL (44.9 A) was smaller than that of control HDL (55.4 A). These measurements were confirmed by electron microscopy (43 and 54 A, respectively). After rate zonal ultracentrifugations of plasma samples, control LDL was clearly resolved, while no LDL could be detected in the experimental samples. Rate zonal ultracentrifugations of plasma samples also indicated that control HDL had a higher flotation rate than experimental HDL. Equilibrium zonal ultracentrifugation showed experimental HDL to be more dense than control HDL with hydrated densities of 1.118 and 1.113 g/ml, respectively. These experiments provide in vivo evidence that LDL is a direct metabolic product of VLDL and that LPL plays a role in the transfer of surface constituents from VLDL to HDL.-Behr, S. R., J. R. Patsch, T. Forte, and A. Bensadoun. Plasma lipoprotein changes resulting from immunologically blocked lipolysis.

Role of lipoprotein lipase in regulating endogenous triacylglycerols in rat heart

Administration of glucagon (10 μg/rat) to the intact animal increased the levels of lipoprotein lipase activity by 92% in the heparin-non-releasable fraction of the heart. At the same time, cardiac levels of triacylglycerols were reduced 47% and free fatty acids were increased about 2-fold. In contrast, the administration of a lower dose of glucagon (0.5 μg/rat) resulted in an 80% reduction in lipoprotein lipase activity in the heparin perfused myocardium. At the same time, triacylglycerols were increased 44% and free fatty acids were decreased 69%. These results provide circumstantial evidence that lipoprotein lipase is involved in the regulation of endogenous triacylglycerols such that higher levels of enzyme activity result in cardiac lipolysis and, conversely, lower levels result in triacylglycerol production.

Lipoprotein lipase and uptake of chylomicron triacylglycerol and cholesterol by perfused rat mammary tissue

The role of lipoprotein lipase in the uptake of chylomicron triacylglycerol and cholesterol from blood was studied in perfused inguinal-abdominal mammary tissue of rats lactating 10–15 days. Lipoprotein lipase activity in the tissue was reduced, from 0.47 to 0.10 units/g, by removing the anterior pituitary gland from lactating rats 2 days before the experiment. Perfused mammary tissue of normal lactating rats took up 12% of the chylomicron triacylglycerol infused, whereas the tissue of hypophysectomized lactating rats took up less than 1%. About two-thirds of the triacylglycerol taken up was retained as glyceride, and the rest was hydrolyzed and released to the perfusing fluid as fatty acids and glycerol. Autoradiographic studies of perfused tissues of normal lactating rats showed that both the acyl and glycerol moieties derived from chylomicron triacylglycerol were incorporated into milk lipid droplets. Perfused mammary tissue of normal lactating rats also took up 15% of the chylomicron cholesterol infused, whereas the tissue of hypophysectomized lactating rats took up less than 1%. The findings demonstrate that chylomicron cholesterol is taken up with triacylglycerol by lactating mammary tissue, and that uptake of both lipids is markedly suppressed when lipoprotein lipase activity is low, as in tissue of hypophysectomized rats. It is proposed that uptake of triacylglycerol from chylomicrons by mammary tissue requires the action of lipoprotein lipase, while uptake of cholesterol is dependent on reduction of the triacylglycerol core, resulting from action of the enzyme on the core and uptake of lipolytic products by the tissue.

Lipoprotein lipase activity in adipose tissues of the domestic duck: The effect of age, sex, and nutritional state

1. 1. Lipoprotein lipase activity was investigated in inguinal and peritoneal adipose tissues of the domestic duck. 2. 2. Optimal conditions for the assay of this enzyme m tissue extracts were determined. 3. 3. Differences in nutritional state or sex did not alter enzyme activity. 4. 4. A marked decline in enzyme activity in peritoneal and inguinal adipose tissues occurred during the first 8 weeks of postembryonic life. 5. 5. The role of lipoprotein lipase in the regulation of fat accretion in adipose tissue during growth is discussed.