Clearing Factor Lipase Activity Research Articles

The storage and synthetic pools of heparin-releasable lipoprotein lipase and hepatic triacylglycerol lipase in the growing puppy.

Age-related changes in the activities of extrahepatic lipoprotein lipase and hepatic triacylglycerol lipase were determined during a primed/constant-rate infusion of heparin for 2 h in puppies between birth and 18 weeks of age. The early (storage) and late (synthetic) phases were measured. Both phases of hepatic triacylglycerol lipase activity were well developed in the first week, reflecting the metabolic maturity of the liver at birth. During the 18 weeks of study, the activity remained relatively unchanged except for a sharp peak at 12 weeks. Extrahepatic lipoprotein lipase activity was low in the first 4 weeks of suckling. Its storage pool increased 6-fold in the next 14 weeks, with a less marked rise in its late (synthetic) pool. Sustained increases in the activity of this enzyme were first noticed during weaning, when the insulin-secretory response matured. Endogenous insulin-secretory capacity rather than the fat content of the feed appeared significant in the postnatal development of lipoprotein lipase (Clearing-factor lipase) activity.

The lipoprotein lipase (clearing-factor lipase) activity of cells isolated from rat cardiac muscle.

The total lipoprotein lipase activity recovered in suspension of cells prepared from adult rat hearts was unaffected by the nutritional state of the animals used. The enzyme activity present in the cell suspensions was almost exclusively associated with the cardiac muscle cells present as the major cell type.

Changes in the lipoprotein lipase (clearing-factor lipase) activity of white adipose tissue during development of the rat

The lipoprotein lipase (clearing-factor lipase) activity of the white adipose tissue from rats aged between 1 and 145 days was determined. Five adipose-tissue sites (epididymal, uterine, subcutaneous, perirenal and intramuscular) together with serum concentrations of triacylglycerol, cholesterol and glucose were studied. The pattern of enzyme-activity change was remarkably similar in all the sites studied, although the growth of the tissues proceeded non-uniformly. After a peak of activity early in suckling, lipoprotein lipase activity fell to low values by 20 days of age. At weaning (21 days) the activity increased sharply and within 5 days high values were regained. The serum triacylglycerol and cholesterol concentrations were low at birth and reached peaks of concentration coincidentally with the minima of white-adipose-tissue lipoprotein lipase activities, seen late in suckling. The changes in enzyme activity were related to other metabolic changes in adipose tissue and with the known changes in plasma insulin concentrations occurring during development.

Effects of clofibrate treatment on plasma triglyceride concentration, plasma post-heparin clearing factor lipase (lipoprotein lipase) activity and serum clearing factor lipase activating ability in maturity-onset diabetes

The effects of clofibrate on plasma triglyceride concentration, plasma post-heparin clearing factor lipase activity and serum clearing factor lipase activating ability were studied in a group of maturity-onset diabetic patients. Significant falls in both triglyceride concentration and in activating ability occurred within 2 weeks of beginning clofibrate treatment and, when treatment was stopped after 4 weeks, these changes were reversed within a further 4 weeks. Plasma post-heparin clearing factor lipase activity, on the other hand, was significantly increased during clofibrate administration and fell again when the treatment was stopped. The possible interrelationships of these findings are discussed.

The inhibition in vivo of lipoprotein lipase (clearing-factor lipase) activity by triton WR-1339

1. Lipoprotein lipase activity was measured in heart homogenates and in heparin-releasable and non-releasable fractions of isolated perfused rat hearts, after the intravenous injection of Triton WR-1339. 2. In homogenates of hearts from starved, rats, lipoprotein lipase activity was significantly inhibited (P less than 0.001) 2h after the injection of Triton. This inhibition was restricted exclusively to the heparin-releasable fraction. Maximum inhibition occurred 30 min after the injection and corresponded to about 60% of the lipoprotein lipase activity that could be released from the heart during 30 s perfusion with heparin. 3. Hearts of Triton-treated starved rats were unable to take up and utilize 14C-labelled chylomicron triacylglycerol fatty acids, even though about 40% of heparin-releasable activity remained in the hearts. 4. It is concluded that Triton selectively inhibits the functional lipoprotein lipase, i.e. the enzyme directly involved in the hydrolysis of circulating plasma triacylglycerols. 5. Lipoprotein lipase activities measured in homogenates of soleus muscle of starved rats and adipose tissue of fed rats were decreased by 25 and 39% respectively after Triton injection. It is concluded that, by analogy with the heart, these Triton-inhibitable activities correspond to the functional lipoprotein lipase.

Effect of nutritional status on rat adipose tissue, muscle and post-heparin plasma clearing factor lipase activities: their relationship to triglyceride fatty acid uptake by fat-cells and to plasma insulin concentrations.

1. In rats in a variety of nutritional states, the adipose tissue clearing factor lipase activity is strongly, positively correlated with fat-cell triglyceride fatty acid uptake. 2. In the same animals, muscle clearing factor lipase activity is inversely correlated with the activity of the enzyme in adipose tissue and with the plasma insulin concentration. 3. In starved animals that are given glucose, adipose tissue clearing factor lipase activity is positively correlated with the plasma insulin concentration. 4. The effect of changes in nutritional status on the activity of clearing factor lipase in rat post-heparin plasma depends on the heparin dosage used. The administration of glucose, but not of fructose or sucrose, to starved rats alters the response to heparin injection towards that found in rats in the fed state.

Colchicine inhibition of the heparin-stimulated release of clearing-factor lipase from isolated fat-cells.

When isolated fat-cells are incubated at 25 degrees C in serum-based media containing glucose, insulin and heparin, the rise that occurs in the clearing-factor lipase activity of the incubation medium is inhibited by colchicine. The rise in the fat-cell clearing-factor lipase activity that occurs during similar incubations in the absence of heparin is not affected by colchicine.

The clearing-factor lipase activity of isolated fat-cells.

1. When fat-cells are isolated from the epididymal adipose tissue of 24h-starved rats and incubated at 25 degrees C in the presence of dialysed serum, glucose, insulin, amino acids and heparin, the total clearing-factor lipase acitivity of the incubation system increases progressively over a period of several hours. 2. All of the increase in activity is accounted for by the appearance of enzyme in the appearance of enzyme in the incubation medium and the fat-cell activity does not change significantly. Cycloheximids, at a concentration that prevents protein synthesis, does not affect the appearance of enzyme in the incubation medium, but the fat-cell enzyme activity is decreased in its presence. 3. The magnitude of the increase in total clearing factor lipase activity is unaffected by the omission of heparin from the medium. However, less enzyme is extracted in tis absence and the fat-cell activity increases. Cycloheximide again only affects the rise in cell activity and does not alter the activity in the incubation medium. 4. When serum in the incubation medium is replaced by casein, the distribution of enzyme between the cells and the medium is changed, but the magnitudes of the increases in total enzyme activity are similar. 5. These characteristics of the clearing-factor lipase response of isolated fat-cells differ in several respects from those observed earlier with intact adipose tissue from 24h-starved rats (Robinson & Wing, 1971; Cryer et al., 1973). The differences could be due, in part, to changes in the relative amounts of two different molecular forms of the enzyme that occur during the isolation of the fat-cells.

Hormonal control of adipose tissue clearing factor lipase activity

Hormonal control of adipose tissue clearing factor lipase activity

Effects of fructose, sucrose and glucose feeding on plasma insulin concentrations and on adipose-tissue clearing-factor lipase activity in the rat.

The rise in adipose-tissue clearing-factor lipase activity that results from feeding glucose to starved rats cannot be duplicated by giving equicaloric amounts of fructose or sucrose. An inability of the administered fructose and sucrose to raise the plasma insulin concentration probably accounts for this failure in enzyme response.

Effects of cold exposure on heart clearing factor lipase and triglyceride utilization in the rat

The clearing factor lipase activity of the rat heart was measured in animals kept at 4 degrees C for several hours and was compared with that in control animals kept at 25 degrees C. The total activity of the enzyme in the heart increased markedly on exposure to the low temperature, whether the animals were in a fed or a fasted state. The activities of both the heparin-releasable and the heparin-nonreleasable enzyme fractions were usually raised. However, only increases in the former could be correlated satisfactorily with corresponding increases in the capacity of the heart to utilize chylomicron triglyceride fatty acids perfused through it. Cold exposure also raised the plasma clearing factor lipase activity and reduced the plasma triglyceride concentration. These changes may have been due, at least in part, to the alterations in the activity of the tissue enzyme.

The action of protamine on clearing factor lipase and on plasma triglyceride metabolism

The effects of protamine on plasma triglyceride concentrations and on clearing factor lipase activity have been studied in rats. When protamine is injected intravenously, the removal of triglyceride from the plasma is inhibited and this causes a rise in the plasma triglyceride concentration. Such inhibition of triglyceride removal does not appear to be due to a direct effect of the protamine on the plasma lipoproteins since 90 % of the injected dose is removed from the blood within 10 min and the residual plasma concentration is probably too low to affect lipoprotein behaviour. It seems likely, therefore, that protamine interferes with the hydrolysis of the plasma triglycerides at the site of clearing factor lipase action in the tissues. The stability of clearing factor lipase in solution is markedly reduced in the presence of low concentrations of protamine. Such increased instability, rather than an inhibitory effect of protamine on the release of the enzyme from the tissues, probably explains why animals injected with protamine and then with heparin display lower plasma clearing factor lipase activities than animals injected with heparin alone.

The effect of cycloheximide on adipose-tissue clearing-factor lipase.

The progressive increase in clearing-factor lipase activity that occurs during the incubation of adipose tissue from starved rats in an appropriate medium at 25 degrees C is shown to occur in two stages. The first of these is not inhibited by cycloheximide, whereas the second is.

Effect of sodium hydrodextran sulfate on experimental arteriosclerosis in spontaneously hypertensive rats

In order to examine the effect of sodium hydrodextran sulfate (HDS) on experimental atherosclerosis spontaneously hypertensive rats (SHR) and normotensive Wistar rats (NR) were fed a high-fat diet with and without the drug. Blood samples were collected for 5 months to measure serum levels of cholesterol, triglyceride and clearing factor lipase activity. Effect of HDS on certain blood factors were as follows: 1) HDS inhibited the increase of serum cholesterol levels in rats. 2) HDS did not change the triglyceride concentration. 3) HDS elevated the clearing factor lipase activity. 4) A high-fat diet increased the intimal thickening of arteries in SHR. 5) Intimal thickening of arteries decreased slightly in the HDS treated group.

Clearing-factor lipase in obese hyperglycaemic mice (ob-ob).

1. Clearing-factor lipase was assayed in acetone-ether-dried powders of heart and epididymal fat-pads of lean and genetically obese mice (ob/ob). In both tissues the enzyme activity in the adult was higher in the obese mice. 2. In heart the enzyme activity was unchanged from 8 to 48 weeks of age in lean mice, but in obese mice it increased between 8 and 12 weeks of age and remained elevated. 3. Starvation produced changes in the heart clearing-factor lipase activity in obese, but not lean, mice. 4. The clearing-factor lipase activity of epididymal fat-pads decreased rapidly during 24h starvation in both lean and obese mice, but the activity in the obese mice remained higher than that in lean mice. 5. Plasma triglyceride and cholesterol concentrations were determined in both lean and obese mice. Triglyceride concentrations were not greatly different, but the obese mice were hypercholesterolaemic. Plasma cholesterol concentrations were not correlated with changes in clearing-factor lipase activity.

Dosage semi-automatique de l'activité lipolytique du plasma post-héparine. Bilan des premiéres applications cliniques

An automated method for measurement of glycerol is presented for the determination of post-heparin plasma clearing factor. The method has been found to have advantages over previous manual methods with regard to both speed of estimation and accuracy. Clearing factor lipase activity is significantly lower in atherosclerotic subjects than in normal subjects.

Release of clearing factor lipase (lipoprotein lipase) in vivo and from isolated perfused hearts of alloxan diabetic rats.

The release of clearing factor lipase (CFL) into the blood stream after heparin injection and from hearts during perfusion with a heparin-containing fluid was studied using normal and alloxan diabetic rats. In addition, the effect of alloxan diabetes on heart tissue lipase activity and the “repletion” of this enzyme in previous “depleted” animals by pre-injection of heparin were also investigated. The results show that the plasma CFL activity after an injection of a standard dose of heparin and that of the medium incubated with heart slices or homogenates in the presence of heparin was significantly decreased in alloxan diabetic rats. CFL release from isolated perfused hearts of alloxan diabetic rats was comparable to that from hearts of normal animals during the short perfusion period of five to ten minutes. However, the enzyme release from hearts of alloxan diabetic rats was considerably decreased during prolonged perfusion. Addition of insulin and glucose to the fluid perfusing hearts of diabetic animals did not correct the defect. Insulin treatment restored the CFL activity in plasma, heart slices, homogenates, and perfusates to normal levels. The CFL release into the blood stream or from perfused hearts of rats previously treated with heparin was decreased when rats were given a second injection of this agent or when rats were killed and hearts were perfused less than two hours after the first heparin administration. This decrease was more marked in diabetic than in normal rats. The “repletion” of CFL in hearts of normal rats was completed in three hours with an overshoot four hours after heparin injection. The CFL release from perfused hearts of diabetic rats remained at a low, depleted level even eight hours after heparin administration. The heart tissue lipase activity in rats with heparin pretreatment was also decreased; this decrease was more marked in diabetic than in normal animals. The “repletion” of tissue lipase was also much slower in diabetic rats. Omission of heparin in the incubation medium of heart slices and the perfusion fluid markedly decreased the lipase release especially that from the perfused heart; the decrease was very slight in the incubation medium of heart homogenates. Tissue and perfusate lipase were inhibited by sodium chloride and protamine.

Effect of fasting on the clearing factor lipase (lipoprotein lipase) activity of fresh and defatted preparations of rat heart muscle

The clearing factor lipase (lipoprotein lipase) activities of homogenates of fresh tissue and of acetone-ether powders have been compared in hearts from fed and starved rats. The activity of the enzyme measured in homogenates of acetone-ether powders is generally higher than that in homogenates of the fresh tissue. Activation is due to an effect of the acetone-ether treatment on enzyme which is associated with the tissue residue in fresh tissue homogenates. A similar activation occurs when the tissue residue is treated with deoxycholate. When rats are fasted, a marked increase in the clearing factor lipase activity of the heart occurs. Peak activities are reached after 10-24 hr, and thereafter the activity falls slowly. This pattern of activity is observed in homogenates of fresh tissue and of acetone-ether powders. The activity of clearing factor lipase in diaphragm muscle also increases in rats starved for 8 or 24 hr. The importance of the change in muscle clearing factor lipase activity on fasting in relation to triglyceride fatty acid utilization by this tissue is emphasized.

The effect of fasting on the utilization of chylomicron triglyceride fatty acids in relation to clearing factor lipase (lipoprotein lipase) releasable by heparin in the perfused rat heart

Hearts from rats that have been starved for 10 or 24 hr oxidize (14)C-labeled chylomicron triglyceride fatty acids perfused through them at a higher rate than do hearts from rats in the fed state. Starvation for such periods increases the total clearing factor lipase activity of the heart. It is suggested that most of this increase may be accounted for by a rise in that portion of the total enzyme activity of the tissue that is released on perfusion with heparin. In rats starved for 48 hr, removal of this portion by heparin preperfusion reduces the capacity of the heart to oxidize (14)C-labeled chylomicron triglyceride fatty acids perfused subsequently by more than 80%. It is concluded that correlations between triglyceride fatty acid utilization and clearing factor lipase activity in the heart should be sought only with that portion of the total enzyme activity which is released from the intact organ by heparin.

Clearing-factor lipase in adipose tissue. Distinction of different states of the enzyme and the possible role of the fat cell in the maintenance of tissue activity.

1. Incubation of intact epididymal adipose tissue from fed rats at 37 degrees in an albumin solution at pH7.4 in vitro results in rapid loss of clearing-factor lipase activity until a low activity, stable to prolonged incubation, is attained. The clearing-factor lipase activity of intact tissue from starved rats, which is initially much less than that of tissue from fed rats, is mainly stable to incubation at 37 degrees . 2. Much of the clearing-factor lipase activity of intact epididymal adipose tissue from fed rats is inactivated by collagenase. The enzyme activity of intact tissue from starved rats is not inactivated by collagenase. 3. The clearing-factor lipase activity of fat cells isolated from the epididymal adipose tissue of fed rats is stable to prolonged incubation at 37 degrees . It represents only a small proportion of the total activity of the intact tissue. In starved rats, the isolated fat cells contain a much higher proportion of the activity of the intact tissue. Their activity is also stable at 37 degrees . 4. Incubation of isolated fat cells in a serum-based medium leads to a progressive rise in clearing-factor lipase activity. Actinomycin increases the extent of this rise in activity. No rise in clearing-factor lipase activity occurs when stromal-vascular cells isolated from epididymal adipose tissue are incubated in the medium. 5. The findings indicate that less than 20% of the activity of intact adipose tissue from fed rats is retained when fat cells are isolated from the tissue by collagenase treatment. The activity that is lost could be that which normally functions in the uptake of triglyceride fatty acids by the tissue.