Release Of Lipoprotein Lipase Research Articles

Effects of heparin and a semi-synthetic heparin analogue on platelet aggregation, lipoprotein lipase and other laboratory tests in surgical patients

Platelet aggregation, lipoprotein lipase activity, coagulation parameters and routine blood chemistry were measured in a randomised study of 21 surgical patients before, immediately after and 3 months after operation. Sodium heparin 5000 IU was given subcutaneously to 11 patients every 12 hours for 7 days, the first injection 2 hours preoperatively; 10 patients received a semisynthetic heparin analogue (SSHA 75 mg) in the same manner. The groups were sex and age matched. No conclusive changes were found in platelet aggregation. The increase in lipoprotein lipase activity in SSHA patients 2 hours after injection was significantly greater than in heparin patients. Neither of the two drugs induced significant chages in coagulation parameters or routine blood chemistry. The results indicate a difference in the effect on lipoprotein lipase release between heparin and SSHA at the used dosage schedules.

The response of plasma triglyceride, cholesterol, and lipoprotein lipase to treatment in non-insulin-dependent diabetic subjects without familial hypertriglyceridemia.

The effects of treatment on plasma total triglyceride, total cholesterol, and plasma postheparin lipase activities have not been evaluated in non-insulin-dependent diabetic (NIDD) subjects without a coexisting familial lipid disorder. In 49 untreated NIDD subjects, there was a linear relationship between glycosylated hemoglobin (GHb) and triglyceride (r = 0.35, P less than 0.02). This correlation was improved after adjusting for the effects of obesity by a partial correlation analysis. After therapy, there was a significant relationship between the change in GHb and the change in triglyceride. To determine whether changes in lipid removal from plasma may contribute to the decrease in plasma lipid concentrations during treatment, the plasma postheparin lipoprotein lipase and hepatic lipase activities were evaluated in a subgroup (N = 8) of these NIDD subjects before and after 1 and 3 mo of therapy. Plasma postheparin hepatic lipase activity in the NIDD subjects was not different from that observed in six normal control subjects and did not change during therapy. In contrast, plasma postheparin lipoprotein lipase activity was lower in the untreated NIDD subjects than in the control subjects. Analysis of the two phases (early and late) of the postheparin lipoprotein lipase activity in plasma showed that the abnormal early phase in untreated NIDD corrected to normal values in less than a month, but the late phase was not corrected until the 3-mo measurement. These findings suggest that some NIDD subjects have a defect in heparin releasable lipoprotein lipase activity, which is reversed with improved glycemic control.(ABSTRACT TRUNCATED AT 250 WORDS)

Simple, reproducible procedure for selective measurement of lipoprotein lipase and hepatic lipase.

Existing methods for determining the release of lipoprotein lipase (EC 3.1.1.34) and hepatic lipase (EC 3.1.1.3) into plasma after heparin injection give highly variable results, primarily traceable to errors in the isolation of labeled oleate from the substrate, triolein. Methods involving anion-exchange resin to bind oleate show high variability and have a low yield. Introducing a strong base in the last step of the assay may spuriously increase the counts from oleate, whereas a detergent such as Triton X-100, used to minimize this problem, has a strong quenching effect. We report a simple and rapid method in which we eliminate rather than correct for the sources of variation. The substrate, tri[1-14C]oleoyl-glycerol, is sonicated under strictly standardized conditions with gum arabic, 50 g/L. Incubation is stopped by addition of a benzene/chloroform/methanol mixture and NaOH, 0.2 mol/L. Labeled oleic acid is extracted with hexane after acidification of the alkaline aqueous (upper) phase, so that no alkali is introduced into the scintillation liquid. For lipoprotein lipase measurement, hepatic lipase is inactivated by a specific antiserum, whereas hepatic lipase is measured after lipoprotein lipase is inactivated by NaCl, 1.0 mol/L. The method is efficient and specific, and quenching and chemiluminescence artifacts are avoided.

Triacylglycerol hyrolysis in the isolated, perfused rat lung

We have studied the mechanism of hydrolysis of labeled long-chain triacylglycerols in the isolated, ventilated, perfused rat lung. Hydrolysis of emulsified tri[ 3H]oleate or doubly labeled [ 3H]glyceryl, tri[ 14C]oleate was measured by quantitation of [ 3H]oleate or of [ 14C]oleate and [ 3H]glycerol released into the perfusate. Hydrolysis was directly proportional to the initial triacylglycerol concentration of the perfusate in the range of 0.30 to 2.2 mM. The release of free fatty acids was linear after an initial lag period, the length of which was inversely proportional to the triacylglycerol concentration. Studies with doubly labeled [ 3H]glyceryl, tri[ 14C]oleate showed that, during triacylglycerol hydrolysis, the molar ratio of free fatty acid to glycerol released is close to 1, suggesting that about one-third of the fatty acids hydrolyzed is released into the pulmonary circulation. The earlier appearance of free fatty acid than glycerol in the venous effluent indicates that the first step in triacylglycerol hydrolysis occurs at the endothelial surface. In order to investigate the role of lipoprotein lipase in this process, we administered heparin, which leads to immediate release of lipoprotein lipase from the endothelium to the circulation in vivo, 10 min and 4 h before isolation and perfusion of the lungs. Heparin administration 10 min prior to perfusion led to marked release of lipoprotein lipase from the lungs and completely abolished the subsequent hydrolysis of circulating triacylglycerols. Perfusions carried out 4 h after heparin administration show that in the lung, endothelial lipoprotein lipase levels did not return to normal within 4 h after heparin administration. The data show that circulating triacylglycerols are hydrolyzed by endothelial lipoprotein lipase during passage through the lung.

Binding of lipoprotein lipase to the cell surface is essential for the transmembrane transport of chylomicron cholesteryl ester

Four cell types, F 1 rat heart cells, rat preadipocytes, human skin fibroblasts and bovine endothelial cells, were used to investigate whether surface binding of lipoprotein lipase was essential in the transmembrane transport of chylomicron cholesteryl ester. Exposure of F 1 heart cells to colchicine resulted in decrease in endogenous surface-bound lipoprotein lipase and a concomitant fall in the uptake of chylomicron cholesteryl linoleyi ether, a nondegradable analog of cholesteryl ester. Uptake of chylomicron cholesteryl linoleyi ether was enhanced by addition of milk lipoprotein lipase and this enhancement also persisted in the presence of colchicine. The drug did not reduce surface binding of the enzyme. Milk lipoprotein lipase was bound to the cell surface of the different cell types and its fate during chase in enzyme-free medium was determined. The t 1 2 of surface-bound enzyme in endothelial cells and in F 1 heart cells was about 2h; it was 4 h in skin fibroblasts. The decrease in surface-bound lipoprotein lipase was accompanied by a parallel fall in the binding and uptake of chylomicron cholesteryl linoleyi ether by the various cell types examined. This decrease in the uptake of cholesteryl linoleyl ether occurred even though lipoprotein lipase activity in the medium was present, as evidenced by the hydrolysis of [ 14C]triacylglycerol. Release of surface-bound endogenous or exogenous lipoprotein lipase by heparin was accompanied by almost complete elimination of uptake of cholesteryl linoleyl ether in presence of complete hydrolysis of [ 14C]triacylglycerol. The present results indicate that the transmembrane transport of cholesteryl ester is catalyzed by lipoprotein lipase only when the enzyme is bound to the cell membrane.

Involvement of cell surface heparin sulfate in the binding of lipoprotein lipase to cultured bovine endothelial cells.

It has been postulated that lipoprotein lipase, an enzyme important in the uptake of fatty acids into tissues, is bound to the vascular endothelial cell surface and that this binding occurs through attachment to heparinlike glycosaminoglycans. Furthermore, it is thought that heparin releases the enzyme from its attachment to the endothelium into the circulation. These hypotheses have never been tested directly in cell systems in vitro. In the present study we have directly evaluated the interaction of lipoprotein lipase, purified from bovine skim milk with monolayer cultures of endothelial cells, isolated from bovine pulmonary artery. Endothelial cells in primary culture had no intrinsic lipoprotein lipase activity but were able to bind lipoprotein lipase quantitatively. The binding reached equilibrium and was saturable at 0.24 nmol of lipoprotein lipase/mg of cell protein. The concentration of lipoprotein lipase at half-maximal binding was 0.52 microM. Bound lipoprotein lipase could be detached from cultured cells by increasing concentrations of heparin, and at and above 0.6 microgram/ml of heparin, 90% of the cell-bound lipoprotein lipase activity was released. Heparan sulfate and dermatan sulfate released the enzyme to a lesser extent and chondroitin sulfate caused little, if any, release of lipoprotein lipase. The release of lipoprotein lipase with heparin was not associated with a release of [3S]glycosaminoglycans from 35S-prelabeled cells. Reductions of lipoprotein lipase binding to endothelial cells and of cell surface-associated [3S]glycosaminoglycans in 35S-prelabeled cells occurred in parallel both when cells were pretreated with crude Flavobacterium heparinum enzyme before lipoprotein lipase binding and when cells were treated with this enzyme after lipoprotein lipase binding. The removal of heparan sulfate from the cell surface by purified heparinase totally inhibited the binding of lipoprotein lipase by endothelial cells, but the removal of chondroitin sulfate by chondroitin ABC lyase had no effect on this binding. These results provide direct evidence for lipoprotein lipase attachment to endothelial cells through heparan sulfate on the cell surface, and provide evidence for the release of lipoprotein lipase by heparin through a detachment from this binding site.

Selective release of extrahepatic lipoprotein lipase by polymetaphosphate

We have studied the lipase released into the circulation by polymetaphosphate injection into rats. Lipase release was in proportion to the dose injected. The post-polymetaphosphate lipase was almost completely inhibited by high salt concentrations or by addition of protamine sulfate to the assay system suggesting that this compound released lipoprotein lipase and not hepatic triglyceride lipase. The lipases released by polymetaphosphate and by heparin were compared using a heparin-sepharose affinity column technique which separates lipoprotein lipase from hepatic triglyceride lipase. While heparin released both lipoprotein lipase and hepatic triglyceride lipase, polymetaphosphate released almost exclusively lipoprotein lipase. Other experiments showed that neither polymetaphosphate nor heparin inhibited the hepatic lipase when added to the assay. These results suggest that lipoprotein lipase may be released by the negative charge on these high-charge polymers while hepatic triglyceride lipase release may require the specific sugar configuration of heparin.

Isolation and pharmacological activities of heparin and other sulfated mucopolysaccharides from thymus

The anticoagulant, antithrombic, antilipemic and antihemolytic activities of heparin, chondroitin sulfates A, B and C, and heparitin sulfate from beef thymus are reported. The heparin fraction extracted from beef thymus was more active on the release of lipoprotein lipase (LPL) than on the coagulation process (APTT) when compared with commercial heparin prepared from beef or pork intestinal mucosa. The physical and clinical properties of the different mucopolysaccharide fractions are also reported. All the results obtained suggest that heparin is a family of compounds, some with a prevailing activity on hemocoagulation, others on the lipoprotein lipase system, and others on the cytolytic system of complement.

Post-heparin lipolytic activity with no hepatic triacylglycerol lipase involved in a mammalian species

It was found that lipolytic activity in bovine post-heparin plasma differed from that of other mammalian species by the fact that intravenous heparin induced the release of lipoprotein lipase but not hepatic triacylglycerol lipase. Initially, this fact was strongly suspected when no remaining lipolytic activity could be found after whole bovine post-heparin plasma had been tested with either 1 M NaCl or antiserum against lipoprotein lipase. This was further confirmed by using heparin-Sepharose affinity chromatography when the entire lipolytic activity was eluted with 1.5 M NaCl but none with 0.4 or 0.7 M NaCl. The active fraction had lipoprotein lipase characteristics i.e it required serum activators to produce optimum activity and was fully inhibited by NaCl of high molarity and by anti-lipoprotein lipase antiserum. Neither the different doses of heparin nor the various times of sampling altered the results. This raises the question whether hepatic triacylglycerol lipase is absent from the bovine liver or whether this enzyme is present but cannot be released by heparin.

Studies of biologic properties of a polysulfated chondroitin, A73025.

AbstractThe chemical composition of a “heparin analog” (A73025) was studied and its biologic properties were compared with those of a heparin preparation from intestinal mucosa. A73025 was characterized as a polysulfated chondroitin with a molecular weight of about 10,000 Mr. Unlike heparin, A73025 showed poor anticoagulant activity in vitro by Stypven clotting time, partial thromboplastin time, and thrombin time assays. A73025, like heparin, although to a lesser extent, inhibited thrombin induced platelet aggregation, released lipoprotein lipase when injected into rabbits, and complexed with serum low and very low density lipoproteins.

Interaction of lipoprotein lipase with native and modified heparin-like polysaccharides.

1. Lipoprotein lipase (EC 3.1.1.34), which was previously shown to bind to immobilized heparin, was now found to bind also to heparan sulphate and dermatan sulphate and to some extent to chondroitin sulphate. 2. The relative binding affinities were compared by determining (a) the concentration of NaCl required to release the enzyme from polysaccharide-substituted Sepharose; (b) the concentration of free polysaccharides required to displace the enzyme from immobilized polysaccharides; and (c) the total amounts of enzyme bound after saturation of immobilized polysaccharides. By each of these criteria heparin bound the enzyme most efficiently, followed by heparan sulphate and dermatan sulphate, which were more efficient than chondroitin sulphate. 3. Heparin fractions with high and low affinity for antithrombin, respectively, did not differ with regard to affinity for lipoprotein lipase. 4. Partially N-desulphated heparin (40-50% of N-unsubstituted glucosamine residues) was unable to displace lipoprotein lipase from immobilized heparin. This ability was restored by re-N-sulphation or by N-acetylation; the N-acetylated product was essentially devoid of anticoagulant activity. 5. Partial depolymerization of heparin led to a decrease in ability to displace lipoprotein lipase from heparin-Sepharose; however, even fragments of less than decasaccharide size showed definite enzyme-releasing activity. 6. Studies with hepatic lipase (purified from rat post-heparin plasma) gave results similar to those obtained with milk lipoprotein lipase. However, the interaction between the hepatic lipase and the glycosaminoglycans was weaker and was abolished at lower concentrations of NaCl. 7. The ability of the polysaccharides to release lipoprotein lipase to the circulating blood after intravenous injection into rats essentially conformed to their affinity for the enzyme as evaluated by the experiments in vitro.

Lipoprotein lipase and adipose tissue and plasma triglyceride clearance in patients with primary hypertriglyceridaemia.

1. The activity of lipoprotein lipase (E.C.3.1.1.3) extracted and released from adipose tissue has been measured in obese subjects with mild or severe hypertriglyceridaemia. The Intralipid tolerance test has been studied as a measure of in vivo clearance of exogenous triglyceride from plasma. 2. Plasma triglyceride clearance was reduced in patients with severe hypertriglyceridaemia (> 4 mmol/l) and this was associated with reduced activities of extracted lipoprotein lipase in adipose tissue compared to patients with mild hypertriglyceridaemia (2--4 mmol/l). 3. A course of insulin therapy (20 u/day) for 1 week increased the extracted, but not the released component of the enzyme from adipose tissue of hypertriglyceridaemic patients. 4. Serum (25% v/v) potentiated the release of lipoprotein lipase from adipose tissue of normo- but not hypertriglyceridaemic patients. 5. The effect of serum on enzyme release was abolished if lipoprotein-deficient serum was used. Addition of very low density lipoprotein (VLDL) or high density lipoprotein (HDL) restored the ability of delipidated serum to augment release of enzyme from adipose tissue, but this was not observed with low density lipoprotein (LDL). 6. It is suggested that a defect in the release of lipoprotein lipase activity in adipose tissue may contribute to the development of hypertriglyceridaemia in this group of patients.

Effects of metabolic inhibitors on the synthesis and release of lipoprotein lipase in cultured cells derived from the stromal-vascular fraction of rat adipose tissue

Cultured cells derived from the stromal-vascular fraction of rat epididymal adipose tissue have been used to study the release of lipoprotein lipase in response to heparin. In the presence of heparin, lipoprotein lipase appeared in the medium biphasically, with an initial rapid rise followed by a slower linear release. The initial increase in activity in the medium was paralleled by a decrease in cell-associated activity. Over the course of the slower phase of release, cell-associated lipoprotein lipase levels remained constant. Treatment of cultures with cycloheximide or 2-deoxyglucose eliminated the second phase of release as well as cell-associated lipoprotein lipase activity. Treatment of cultures with Colcemid decreased the second phase of release but increased cell-associated lipoprotein lipase activity. These data suggest that exposure to heparin results in a rapid release of pre-formed enzyme and that continued release is dependent on both protein synthesis and transport of the enzyme to the cell surface.

Effects of immune complexes on plasma triglycerides in rabbits

The effect of immune complexes on plasma lipids, especially triglycerides (TG) was studied in rabbits. After a single intravenous dose of bovine serum albumin (BSA), serological aberrations suggestive of immune complexes appeared around the 14th day. Changes in the plasma TG or cholesterol values were not observed within a follow-up period of 4 weeks. However, reimmunization with a second dose of BSA 2 months later led to a significant decrease in plasma TG ( P < 0.01). In fat tolerance tests TG emulsion was given intravenously to rabbits immunized 14 days earlier with BSA. The elimination curve of exogenous TG (followed for 100 min) was in its first phase exponential and in its second phase linear in all experimental groups. The significance of the second phase, however, has to be interpreted with some caution because of the possible recirculation of TG into the blood stream. In the rabbits immunized with one dose of BSA the fractional removal rate of TG did not differ from that of the controls. However, in the rabbits reimmunized with a second dose of BSA 2 months later the fractional removal rate of TG was greater than in the controls ( P < 0.01). It was concluded that immune complex lesions under certain circumstances may affect the TG metabolism. The mechanism concerned may be increased permeability of the injured vascular endothelial cells, possibly through the increased release of lipoprotein lipase (LPL).

In vivo release of anti-Xa clotting activity by a heparin analogue

The parenteral injection of a semi-synthetic heparin analogue (SSHA) releases anti-Xa clotting activity, lipoprotein lipase activity and PF 4 antigen. The increased anti-Xa activity is not neutralized by PF 4 or protamine sulphate. A second injection of the drug after 90 minutes, or an increase in dose, does not increase the level of induced anti-Xa clotting activity. Possible mechanisms of action include the release by SSHA of endogenous glycosaminoglycans with anti-Xa activity, and interference by released lipoprotein lipase of a modulator of anti-Xa activity. It is concluded that a drug with weak anticoagulant activity in vitro may nevertheless have significant antithrombotic potential.

Effect of heparin on the utilization in vitro of labelled glycerides from triglyceride-rich lipoproteins in rat adipose tissue.

Triglyceride-rich lipoproteins from adult rat plasma were labelled in vivo with 3H in the esterified fatty acids and 14C in the labelled glyceride glycerol of neutral lipids by injecting i.v. sodium 9-10 (n)-[3H] palmitate and [U-14C] glycerol, after which the prelabelled lipoproteins were purified by ultracentrifugation and dialysis. The lipoproteins were incubated in vitro, in the presence or not of heparin, with pieces of epididymal fat pads or isolated adipocytes from fed rats. The disappearance of both [3H]- and [14C] lipids from the media was greater when incubations were performed with adipocytes than with fat-pad pieces and it increased with heparin in both preparations. More 3H-label than 14C was found in the tissue lipids, a higher percentage being present in adipocytes than in fat-pad pieces, and the amount of label in tissue lipids was always enhanced by heparin. Some 14C-label appeared as esterified fatty acids in both tissue preparations and it also was enhanced by the presence of heparin. These findings are in agreement with the recognized influence of heparin on the release of lipoprotein lipase and show the direct relationship between heparin action and tissue ability to take up products of lipoprotein triglyceride breakdown. They also demonstrate the ability of adipose tissue to metabolize glycerol coming from the hydrolysis of lipoprotein glycerides.

Studies on the effect of hepatectomy on pig post-heparin plasma lipases

The effect of different amounts of heparin injected intravenously in swine on lipoprotein lipase and hepatic lipase activities in post-heparin plasma was studied using an immunochemical method. After the injection of 50 I.U. of heparin/kg body weight the apparent half-life of lipoprotein lipase and hepatic lipase activity measurable in post-heparin plasma was 15 min. This was prolonged to more than 60 min after the injection of 1000 I.U./kg body weight. It is concluded that the higher the heparin dose injected the longer can lipolytic activities be measured in plasma. A possible explanation for these findings is that the amount of circulating heparin governs the distribution of lipoprotein lipase and hepatic lipase between an endothelial-bound form and a circulating form and thus determines the apparent ‘half-life’ of lipase activity measurable in plasma. The apparent half-life of radioactively labelled heparin in normal swine was not different from that observed in hepatectomized animals. After hepatectomy no immunoreactive hepatic lipase activity could be demonstrated in post-heparin plasma confirming our previous findings that the liver is the only source of hepatic lipase. To study the role of the liver in the clearance of plasma lipoprotein lipase activity after the administration of heparin normal and hepatectomized pigs were given 200 I.U./kg body weight followed by a heparin infusion of 100 I.U./ h per kg body weight. In the control pigs the heparin injection caused a rapid release of lipoprotein lipase and hepatic lipase activities. These activities were maintained in the circulation during the 3-h infusion at a level of about 60% of the levels measurable 30 min after the injection. In hepatectomized pigs the lipoprotein lipase activity rose during the infusion to about six times the activity recorded 30 min after heparin administration. From these experiments we conclude that after heparin injection the liver is involved in the clearance of post-heparin plasma lipolytic activity.

Quantitative aspects of lipoprotein lipase release by heparin in mice.

Although heparin has been known to release lipoprotein lipase (diacylglycerol acylhydrolase, EC 3.1.1.34) since 1943 (1), the quantitative aspects related to dosage have never been fully determined. Furthermore, only the data of Robinson et al. (2) are available concerning the half-life of enzyme action, once released into the blood. Olsson et al. (3) and Estes et al. (4) published data on the volume of distribution of heparin and kinetic data on heparin's anticoagulant action in man. More recently, McAvoy (5) determined the biologic half-life of heparin. In this paper, we present quantitative dose-response data on the release of lipoprotein lipase by heparin in mice, as well as information on time-duration action of released lipoprotein lipase in serum.Materials and Methods. Seventy male Swiss-Webster mice (weighing 20–30 g) were used in this investigation. Heparin sodium was injected intravenously in the tail vein in a volume of 0.1 ml. Axillary blood was obtained from etherized mice, allowed to clot, a...

Insulin regulation of lipoprotein lipase activity and release in 3T3-L1 adipocytes. Separation and dependence of hormonal effects on hexose metabolism and synthesis of RNA and protein.

Insulin regulation of lipoprotein lipase was studied in fully differentiated 3T3-Ll fat cells. Insulin at low concentrations (10e7 to 10-l’ M) elicited a rapid and maximal increase (-lo-fold) in lipoprotein lipase release from the cells to the medium within 30 min and caused a 2to lo-fold increase in total cellular lipoprotein lipase activity over a a-day period. Insulin had no effect on cell lipoprotein lipase activity during the first 4 h of treatment. Prolonged exposure to insulin (% to 4 days) resulted in additional increases in enzyme release rate, and increased the fractional release rate per h approximately lo-fold. Stimulation of cellular lipoprotein lipase activity was dependent on the presence of glucose in the incubation medium. Although half-maximal increases in cell activity required 12 h of insulin treatment in glucose-containing medium, removal of either glucose or insulin resulted in loss of more than 50% of the stimulation in enzyme activity within 90 min. Addition of glucose to cells incubated 20 h with insulin in carbohydrate-free medium elicited a rapid and full response to insulin in 2 h. Fructose, mannose, and glucosamine could substitute for glucose in supporting this rapid response in insulin-pretreated cells, but only glucose, mannose, and fructose would support the effect in 24-h incubations with hormone. Induction of the increase in lipoprotein lipase activity by glucose in insulin-pretreated cells was prevented by cycloheximide, but not by actinomycin D. In contrast, inhibitors of either protein (cycloheximide, puromycin) or RNA (a-amanitin, actinomycin D) synthesis completely blocked the response when added with insulin to cells incubated in medium containing glucose. We propose that insulin regulates lipoprotein lipase in fat cells by three major actions: 1) it elicits a rapid release of enzyme from the cell through mechanisms which are independent of energy metabolism and protein synthesis; 2) it stimulates gene expression and synthesis of RNA independently of effects on hexose and amino acid transport; 3) it stimulates expression of the nuclear effects of the hormone at the translational level by increasing hexose uptake and the levels of regulatory glycolytic metabolites within the cells. Induction of the enzyme and its release thus appear

Lipoprotein lipase and acid lipase activity in rabbit brain microvessels.

A preparation of cerebral microvessels was used to demonstrate the presence of lipoprotein lipase and acid lipase activity in the microvasculature of rabbit brain. Microvessels, consisting predominantly of capillaries, small arterioles, and venules, were islated from rabbit brain. Homogenates were assayed for lipolytic activity using a glycerol-stabilized trioleoylglycerol-phospholipid emulsion as substrate. Lipoprotein lipase activity was characterized with this substrate by previously established criteria including an alkaline pH optimum, increased activity in the presence of heparin and heat-inactivated plasma, and reduced activity in the presence of NaCl and protamine sulfate. A different substrate, containing trioleoylglycerol incorporated into phospholipid vesicles, was used to reveal acid lipase activity that was not affected by heparin, plasma, NaCl, or protamine sulfate. Lipoprotein lipase did not show activity with the vesicle preparation as substrate. Intact microvessels, when incubated in the presence of heparin, release lipoprotein lipase into the incubation solution. In contrast, release of acid lipase activity from intact microvessels was not dependent on heparin. The data show the presence of both lipoprotein lipase and acid lipase in brain microvessels and suggest that lipoproteins are metabolized within the cerebral vasculature.