Lipoprotein lipase and lipogenic enzyme activities in adipose tissue from rats fed different lipid sources

This work was designed to study the effect of different lipid sources on the activities of lipoprotein lipase and lipogenic enzymes in adipose tissue from rats fedad libitum or energy-controlled diets. Male Wistar rats were fed diets containing 40% of energy as fat (olive oil, sunflower oil, palm oil or beef tallow), for 4 wk. Underad libitum feeding no differences were found among dietary fat groups in final body weight, adipose tissue weights and total body fat. Under energy-controlled feeding, despite isoenergetic intake, rats fed the beef tallow diet gained significantly less weight than rats fed the other three diets. Beef tallow fed rats showed the lowest values for adipose tissue weights and total body fat. When rats had free access to food no effect of dietary lipid source on lipogenic enzyme activities was found. In contrast, under energy-controlled feeding rats fed the beef tallow diet showed significantly higher activities of glucose-6-phosphate dehydrogenase and fatty acid synthase than rats fed the other three diets. Heparin-releasable lipoprotein lipase activity in perirenal and subcutaneous adipose tissues was not different among rats fed olive oil, safflower oil, palm oil or beef tallow. When comparing both adipose tissue anatomical locations, significantly higher activities were found in subcutaneous than in perirenal fat pad independently of dietary fat. In conclusion, under our experimental protocol, lipogenesis in rat adipose tissue does not seem to be affected by dietary fat type.     

Activity of lipoprotein lipase in thyroidectomized rats

Total plasma postheparin lipolytic activity as well as lipoprotein lipase activity in plasma was higher after heparin injection in thyroidectomized rats than in controls. In contrast, the activity of liver lipase was lower in thyroidectomized rats. Adipose tissue from thyroidectomized rats contained more lipoprotein lipase activity than adipose tissue from controls as measured both in extracts of tissue homogenates and medium from in vitro incubations of tissue pieces. There were no differences between control and hypothyroid rats in the disappearance of intravenously injected 125I-labeled lipoprotein lipase, but when a low dose of heparin was injected before the labeled enzyme, the disappearance of 125I-labeled lipoprotein lipase was more retarded in thyroidectomized rats. The elimination of heparin itself was slightly retarded by thyroidectomy.     

The role of glucagon in the regulation of myocardial lipoprotein lipase activity

The role of glucagon in regulating the lipoprotein lipase activities of rat heart and adipose tissue was examined. When starved rats were fed glucose, heart lipoprotein lipase activity decreased while that of adipose tissue increased. Glucagon administration to these animals at the time of glucose feeding prevented the decline in heart lipoprotein lipase activity, but had no effect on the adipose tissue enzyme. When glucagon was administered to fed rats, heart lipoprotein lipase activity increased to levels found in starved animals but there was no change in the adipose tissue enzyme. It is suggested that the reciprocal lipoprotein lipase activities in heart and adipose tissue of fed and starved animals may be regulated by the circulating plasma insulin and glucagon concentrations.     

Influence of some gastrointestinal hormones on adipose tissue lipoprotein lipase activity in vitro: Evidence of a stimulatory effect of pancreozymin and gastrin

At concentrations corresponding to the levels usually reported in the blood of different species in the fed state, gastrin and pancreozymin but not secretin and vasoactive intestinal peptide, stimulate the lipoprotein lipase activity of adipose tissue from fasted rats. The enzyme response to gastrin is, like that to insulin, dependent on the presence of glucose and is not additive with the enzyme response to insulin. On the contrary, the effect of pancreozymin on lipoprotein lipase is glucoseindependent and is additive with the enzyme response to insulin. Both the effects of gastrin and pancreozymin depend on protein synthesis as shown by their suppression by cycloheximide. With isolated fat cells, gastrin increases both the releasable and non-releasable lipase activities whereas pancreozymin increases almost exclusively the non-releasable activity. The mechanisms and the possible physiological significance of these findings are discussed in relationship with the influence of insulin and the nutritional state on adipose tissue lipoprotein lipase.     

Tissue-specific effects of rapid tumour growth on lipid metabolism in the rat during lactation and on litter removal.

1. The effect of tumour burden on lipid metabolism was examined in virgin, lactating and litter-removed rats. 2. No differences in food intake or plasma insulin concentrations were observed between control animals and those bearing the Walker-256 carcinoma (3-5% of body wt.) in any group studied. 3. In virgin tumour-bearing animals, there was a significant increase in liver mass, blood glucose and lactate, and plasma triacylglycerol; the rate of oxidation of oral [14C]lipid to 14CO2 was diminished, and parametrial white adipose tissue accumulated less [14C]lipid compared with pair-fed controls. 4. These findings were accompanied by increased accumulation of lipid in plasma and decreased white-adipose-tissue lipoprotein lipase activity. 5. In lactating animals, tumour burden had little effect on the accompanying hyperphagia or on pup weight gain; tissue lipogenesis was unaffected, as was tissue [14C]lipid accumulation, plasma [triacylglycerol] and white-adipose-tissue and mammary-gland lipoprotein lipase activity. 6. On removal (24 h) of the litter, the presence of the tumour resulted in decreased rates of lipogenesis in the carcass, liver and white and brown adipose tissue, decreased [14C]lipid accumulation in white adipose tissue, but increased accumulation in plasma and liver, increased plasma [triacylglycerol] and decreased lipoprotein lipase activity in white adipose tissue. 7. The rate of triacylglycerol/fatty acid substrate cycling was significantly decreased in white adipose tissue of virgin and litter-removed rats bearing the tumour, but not in lactating animals. 8. These results demonstrate no functional impairment of lactation, despite the presence of tumour, and the relative resistance of the lactating mammary gland to the disturbance of lipid metabolism that occurs in white adipose tissue of non-lactating rats with tumour burden.     

Zinc deficiency and the activities of lipoprotein lipase in plasma and tissues of rats force-fed diets with coconut oil or fish oil

The present study was performed to investigate the effect of zinc deficiency on the activities of lipoprotein lipase in postheparin serum and tissues of rats fed diets containing either coconut oil or fish oil as dietary fat, using a bifactorial experimental design. To ensure an adequate food intake, all the rats were force-fed by gastric tube. Experimental diets contained either 0.8 mg zinc/kg (zinc-deficient diets) or 40 mg zinc/kg (zinc-adequate diets). The effects of zinc deficiency on the activities of lipoprotein lipase in postheparin serum and postprandial triglyceride concentrations and distribution of apolipoproteins in serum lipoproteins depended on the type of dietary fat. Zinc-deficient rats fed the coconut oil diet exhibited a reduced activity of lipoprotein lipase in postheparin serum and adipose tissue, markedly increased concentrations of triglycerides in serum, and a markedly reduced content of apolipoprotein C in triglyceride-rich lipoproteins and high density lipoproteins compared with zinc-adequate rats fed coconut oil. By contrast, zinc-deficient rats fed the fish oil diet did not exhibit reduced activities of lipoprotein lipase in postheparin serum and adipose tissue and increased concentrations of serum lipids compared with zinc-adequate rats fed the fish oil diet. This study suggests that a reduced activity of lipoprotein lipase might contribute to increased postprandial concentrations of serum triglycerides observed in zinc-deficient animals. However, it also demonstrates that the effects of zinc deficiency on lipoprotein metabolism are influenced by dietary fatty acids.     

Intra- and extracellular forms of lipoprotein lipase in adipose tissue.

The location of lipoprotein lipase activity in rat adipose tissue was studied using intact epididymal fat pads, isolated adipocytes, and lipoprotein lipase activity secreted from adipocytes as enzyme sources. The enzyme activities of these preparations were characterized by gel filtration. The method used for isolation of adipocytes had been modified to minimize activation of lipoprotein lipase during the procedures. Extracts of intact adipose tissue separated into two major lipoprotein lipase activity peaks, designated "a" and "b", the "a" fraction representing about 30 (fasted rats) to 50% (fed rats) of the total enzyme activity. An intermediate fraction (designated "i") was frequently observed. Extracts of isolated adipocytes from fed rats contained about 35% and those from fasted rats about 65% of the lipoprotein lipase activity present in intact tissue. The "b" fraction constituted 80--97% of the adipocyte lipoprotein lipase activity. In contrast, the enzyme activity secreted from the adipocytes contained only the "a" and "i" fractions. These data implicate the existance of one intracellular form of lipoprotein lipase (corresponding to the "b" fraction), different from extracellular forms of the enzyme (corresponding to fractions "a" and "i"). A transformation of the intracellular to the extracellular forms appears to occur in conjunction with secretion of enzyme from the fat cell.     

The activities of lipoprotein lipase and of enzymes involved in triacylglycerol synthesis in rat adipose tissue. Effects of starvation, dietary modification and of corticotropin injection.

1. The effects of dietary modification, including starvation, and of corticotropin injection on the activities of acyl-CoA synthetase, glycerol phosphate acyltransferase, dihydroxyacetone phosphate acyltransferase, phosphatidate phosphohydrolase, diacylglycerol acyltransferase and lipoprotein lipase were measured in adipose tissue. 2. Lipoprotein lipase activities in heart were increased and those in adipose tissue were decreased when rats were fed on diets enriched with corn oil or beef tallow rather than with sucrose or starch. The lipoprotein lipase activity was lower in the adipose tissue of rats fed on the sucrose rather than on the starch diet. 3. Rats fed on the beef tallow diet had slightly higher activities of the total glycerol phosphate acyltransferase in adipose tissue than did rats fed on the sucrose or starch diet. The diacylglycerol acyltransferase and the mitochondrial glycerol phosphate acyltransferase activities were higher for the rats fed on the tallow diet than for those fed on the corn-oil diet. 4. Starvation significantly decreased the activities of lipoprotein lipase (after 24 and 48 h), acyl-CoA synthetase (after 24 h) and of the mitochondrial glycerol phosphate acyltransferase and the N-ethylmaleimide-insensitive dihydroxyacetone phosphate acyltransferase (after 48 h) in adipose tissue. The activities of the microsomal glycerol phosphate acyltransferase, diacylglycerol acyltransferase and the soluble phosphatidate phosphohydrolase were not significantly changed after 24 or 48 h of starvation. 5. The activities of lipoprotein lipase and phosphatidate phosphohydrolase in adipose tissue were decreased 15 min after corticotropin was injected into rats during November to December. No statistically significant differences were found when these experiments were performed during March to September. These differences may be related to the seasonal variation in acute lipolytic responses. 6. These results are discussed in relation to the control of triacylglycerol synthesis and lipoprotein metabolism.     

Expression of lipoprotein lipase in different human subcutaneous adipose tissue regions

Steady state expression of lipoprotein lipase was compared in abdominal and gluteal subcutaneous adipose tissue of nonobese men and women. In both regions enzyme activity and lipoprotein lipase mRNA levels were significantly higher in women than in men. In men the enzyme activity was higher in abdominal than in gluteal adipose tissue (P less than 0.01) whereas the opposite was observed in women (P less than 0.05). In both sexes, however, lipoprotein lipase mRNA levels were threefold higher in the abdominal as compared to the gluteal site, whether they were determined in isolated fat cells or in fat segments (P less than 0.01). This regional difference persisted when the mRNA values were expressed as a function of the mRNA concentration for beta-actin. There was a correlation between the two adipose tissue regions as regards the values for enzyme activity and mRNA level (r = 0.6-0.8). Northern blot analysis revealed two mRNA species of 3.5 and 3.7 kilobases, respectively. It is concluded that there are regional variations in the steady state expression of lipoprotein lipase in human subcutaneous adipose tissue. This involves site variations in gene expression as well as posttranslational modification of lipoprotein lipase enzyme activity and may contribute to the characteristic variations in adipose tissue mass and distribution between men and women.     

Effect of nutrition on subcellular localization of rat fat-cell lipoprotein lipase.

This study supports the possibility for multiple subcellular forms of lipoprotein lipase. 1. The total activity of lipoprotein lipase per g of intact epididymal adipose tissue from fed rats is much higher than that from starved rats. 2. The isolated fat-cells of fed and of starved rats have lipoprotein lipase of almost the same activity per g of fat-pads. The isolated fat-cells of starved rats have a much higher proportion of total activity per g of the intact tissue than do those of fed rats. 3. Under the conditions of homogenization used, only a small proportion of the total activity per g of intact tissue from fed rats was associated with the fat layer which floated to the top of the homogenate during low-speed centrifugation. The different proportions of the specific enzyme activity found in each subcellular fraction are described. 4. Lipoprotein lipase from plasma membranes and microsomal fractions from starved and fed rats was purified by affinity chromatography. 5. The total activity of microsomal lipoprotein lipase per g of intact adipose tissue is enhanced by a normal diet. 6. In intact epididymal adipose tissue from fed rats, the activity per g of tissue of lipoprotein lipase of plasma membranes is much higher than that in the same fraction from starved rats. By contrast, the activities per g of tissue in plasma membranes obtained from starved or from fed rats by collagenase treatment were similar.     

Rapid downregulation of adipose tissue lipoprotein lipase activity on food deprivation: evidence that TNF-alpha is involved

When food was removed from young rats in the early morning, adipose tissue tumor necrosis factor (TNF)-alpha activity increased 50% and lipoprotein lipase (LPL) activity decreased 70% in 6 h. There was a strong negative correlation between the TNF-alpha and LPL activities. Exogenous TNF-alpha further decreased LPL activity. Pentoxifylline, known to decrease production of TNF-alpha, had no effect on LPL activity in fed rats but almost abolished the rise of TNF-alpha and the decrease of LPL activity in rats deprived of food. The specific activity of LPL decreased from 0.92 mU/ng in fed rats to 0.35 and 0.24 mU/ng in rats deprived of food given saline or TNF-alpha, indicating a shift in the LPL molecules toward an inactive state. Lipopolysaccharide increased adipose tissue TNF-alpha and decreased LPL activity. Both of these effects were strongly impeded by pretreatment of the rats with pentoxifylline, or dexamethasone. Pretreatment of the rats with actinomycin D virtually abolished the response of LPL activity to food deprivation or exogenous TNF-alpha. We conclude that food deprivation, like lipopolysaccharide, signals via TNF-alpha to a gene whose product causes a rapid shift of newly synthesized LPL molecules toward an inactive form and thereby shuts down extraction of lipoprotein triglycerides by the adipose tissue.     

Effect of pantethine on post-heparin plasma lipolytic activities and adipose tissue lipoprotein lipase in rats

The lipid-lowering effect of pantethine, a new drug affecting lipid metabolism, had been evaluated in carbohydrate-induced hyperlipidemic rats. Administration of the drug raised post-heparin lipolytic activities, the change being due to an increase in lipoprotein lipase activity, whereas hepatic lipase activity remained virtually unchanged. Total lipoprotein lipase activity per g of adipose tissue increased in pantethine-treated rats compared with controls. Furthermore, the soluble lipoprotein lipase of fat-pads was fractionated by heparin-Sepharose affinity chromatography. The first active peak, originated from the microsomal fractions, significantly increased after the drug treatment, while the second one, originated from the plasma membranes, remained unchanged. The increase in the microsomal lipoprotein lipase activity may be due to an increase in intracellular synthesis of lipoprotein lipase enzyme proteins. The heterogeneity of lipoprotein lipase of rat adipose tissues was ensured using affinity chromatography on heparin-Sepharose.     

Involvement of an NAD(P)H oxidase as a pO2 sensor protein in the rat carotid body.

Selenium (Se) deficiency for 5 weeks in rats produced changes in the activity of a number of hepatic, renal and plasma enzymes. In animals whose food intake was restricted to 75% of normal for 2 weeks, Se deficiency produced significant increases in the activity of hepatic cytosolic 'malic' enzyme and mitochondrial alpha-glycerophosphate dehydrogenase (GPD), two enzymes that are particular sensitive to the thyroid-hormone concentrations in tissue. Propylthiouracil-induced hypothyroidism produced significant decreases in 'malic' enzyme and GPD activities. The effect of hypothyroidism on the activity of 'malic' enzyme, GPD and other enzymes studied in liver and plasma was often opposite to that seen in Se deficiency. Glutathione S-transferase (GST) activity was increased by both Se deficiency and hypothyroidism, but in hypothyroid animals further significant increases in GST were produced by Se deficiency. These data suggest that the changes in enzyme expression observed in Se deficiency are not caused by decreased tissue exposure to thyroid hormones.     

Modulation of lipoprotein lipase activity in the rat by the beta 2-adrenergic agonist clenbuterol.

This study evaluated the effects of beta 2-adrenoceptor stimulation on some determinants of triglyceride metabolism. Male Sprague-Dawley rats were injected twice daily with clenbuterol (30 micrograms.kg-1) for 7 days, or with an equivalent volume of vehicle. Serum triglycerides, hepatic triglyceride secretion rate, and lipoprotein lipase activity in white and brown adipose tissues as well as in red vastus lateralis muscle and heart were evaluated in the fasting state and following a fat-free, high-sucrose meal, 3 h after the last agonist injection. In rats killed in the fasting and postprandial states, clenbuterol reduced the mass of white adipose tissue (-25 and -12%, respectively; p < 0.02), whereas it increased the mass of vastus lateralis muscle (+11 and +7%; p < 0.002) and heart (+13 and %; p < 0.0001). In vehicle-injected animals, the fasting state was associated with lower lipoprotein lipase activity in white and brown adipose tissues, and higher enzyme activity in vastus lateralis and heart, compared with the postprandial state. Postprandially, treatment with clenbuterol reduced lipoprotein lipase activity in white adipose (-24%), whereas it increased enzyme activity in brown adipose (+107%) as well as in vastus lateralis (+35%). In fasted animals, no significant variation of enzyme activity in these tissues was observed following clenbuterol treatment, whereas in the heart, a decrease of lipoprotein lipase activity was observed (-22%). Clenbuterol lowered serum triglycerides significantly (-23%), but not their rate of secretion, whereas the agonist decreased the insulin to glucagon ratio only in the postprandial state.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of lipoprotein lipase. Induction by insulin.

Lipoprotein lipase activity in intact epididymal adipose tissue of fasted rats increased rapidly after treatment with insulin in vivo. In contrast, lipoprotein lipase activity in adipocytes isolated from the contralateral fat pads remained essentially unchanged. When adipocytes were incubated for 30 min at ambient temperature in vitro, about 2 times more lipoprotein lipase activity was found in the medium of cells from insulin-treated rats than in medium from cells of control animals. Following insulin treatment, extracts of tissue acetone powders separated by gel chromatography showed increases in both enzyme activity fractions obtained (designated lipoprotein lipase a and b). However, no consistent differences were observed between fractions derived from adipocyte acetone powders of insulin-treated and control animals. All the observed effects of insulin on lipoprotein lipase activity were abolished by cycloheximide treatment in vivo. These data indicate that following insulin treatment, increased lipoprotein lipase activity in adipose tissue results from enhanced enzyme secretion by the fat cell and subsequent accumulation in the tissue, thus implicating the adipocyte secretory mechanism as a major site of regulation of lipoprotein lipase activity in adipose tissue.     

Influence of age and exercise training on lipid metabolism in Fischer-344 rats

The influence of training on fatty acid and glyceride synthesis by liver and adipose tissue homogenates of young and old Fischer-344 rats was examined. Four groups of rats (10 animals/group) were studied: young untrained, young trained, old untrained, and old trained. Training of each group was for 10 wk at 75% maximal O2 uptake. Young rats were killed at 6 mo of age and old rats were killed at 27 mo of age. Fatty acid synthesis was assessed by measuring the activities of acetyl-CoA carboxylase, fatty acid synthase, ATP citrate-lyase, "malic" enzyme, and glucose-6-phosphate dehydrogenase. Glyceride synthesis was evaluated by determining the rate of incorporation of [14C]glycerol 3-phosphate into lipids. In addition, lipoprotein lipase activity was measured in acetone-ether powders of adipose tissue from the four groups of rats. In liver, training had no effect on fatty acid or glyceride synthesis in either group. However, aging caused a significant decrease in the activities of four of the lipogenic enzymes but had no effect on glyceride synthesis. Training caused an increase in fatty acid synthase and glyceride synthesis in adipose tissue, and aging decreased lipoprotein lipase activity. It was concluded that training enhances the synthetic capacity of lipids by adipose tissue but that aging had a more profound effect in that the activities of the enzymes involved in these processes were lower in the old rats. Furthermore, the decreased activity of lipoprotein lipase in the older rats may explain the higher plasma triglyceride levels that were observed in these animals.     

Reduced brown adipose tissue thermogenesis of obese rats after ovariectomy

Brown adipose tissue (BAT) thermogenesis was assessed by measuring mitochondrial guanosine diphosphate (GDP) binding, cytochrome oxidase activity and oxygen consumption in ovariectomized (OVX) and sham-operated rats. The food intake and body weight of OVX rats increased more than those of controls and OVX rats became obese. Mitochondrial GDP binding, as an indicator of thermogenic activity, cytochrome oxidase activity, as a marker of mitochondrial abundance, and mitochondrial respiration of BAT in OVX rats were significantly reduced compared with those in controls. And, also, even when OVX rats were restricted in food intake (pair-gained) to produce comparable changes in body weight with sham-controls, or matched in food intake (pair-fed) with sham-controls, these parameters in both pair-gained and pair-fed OVX groups were decreased markedly compared to those in sham-controls. As expected, body weight in pair-fed OVX rats increased significantly more than that in sham-controls. In response to cold exposure, these parameters of OVX rats increased as much as those of controls did. These results suggest that reduced brown adipose tissue thermogenesis might be one of the important factors that are responsible for the development of obesity after OVX.     

Nutritional regulation of lipoprotein lipase in guinea pig tissues

Glucose transport in guinea pig adipocytes has been shown to be markedly resistant to stimulation by insulin. Lipoprotein lipase is another transport catalyst in adipose tissue which is believed to be regulated by insulin. We have therefore studied how feeding-fasting affects lipoprotein lipase activity in guinea pig tissues. There was an even more marked decrease in adipose tissue lipoprotein lipase activity on fasting in guinea pigs (10-20 fold) than in rats or mice (4-5 fold). In adipocytes, the activity decreased only 2.5-4.5 fold; most of the change was in extracellular lipoprotein lipase. On glucose refeeding, the activity was rapidly restored. In the first 4 hours after glucose administration extracellular lipoprotein lipase activity increased to more than 10 times the amount present in adipocytes. After cycloheximide, lipoprotein lipase activity decreased with a half-life of 22 min. It is concluded that lipoprotein lipase is rapidly produced and turned over in guinea pig adipose tissue, and that the system is quite sensitive to feeding-fasting. In contrast to adipose tissue, there was no significant change in lipoprotein lipase activity in any other tissue on fasting. There was a strong correlation between the activities in heart and diaphragm muscle, but this correlation was independent of feeding-fasting.     

Lipoprotein lipase and cholesterol transfer activities of lean and obese Zucker rats.

Adult female lean and obese Zucker rats maintained under standard conditions were used for the estimation of plasma, liver and white adipose tissue (WAT) activity of lipoprotein lipase, plasma and liver hepatic lipase and plasma lecithin-cholesterol acyltransferase. No differences in plasma or tissue levels of lipoprotein lipase between lean and obese rats were detected, but the larger WAT size of the obese rats resulted in higher lipase activity per unit of rat weight. Hepatic lipase levels in plasma were higher in the obese, but in liver, the higher activity was found in lean rats. No significant differences were found for lecithin-cholesterol acyltransferase activity, except when the levels in the HDL fraction were expressed per unit of protein weight, showing lower activity in the obese rats. In conclusion, the essentially maintained enzyme activities in obese rat tissues suggest that they cannot explain the deficient lipoproteins processing of obese rats, and, consequently their dislipidaemia.     

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.