Determination of the intravenous fat tolerance test with intralipid by nephelometry

Accelerated Hypertriglyceridemia in Patients on Continuous Ambulatory Peritoneal Dialysis - A Preventable Abnormality

Increasing hypertriglyceridemia is a recognised complication of CAPD. To investigate the etiology lipid clearance studies using the intravenous fat tolerance test were performed in control subjects and in uremic patients before and after six months CAPD treatment. Oral carbohydrate intake was restricted and the use of hypertonic dialysate kept to a minimum. Although serum triglycerides were elevated in the uremic patients before CAPD (3.1 ± 0.3 mMol/L) no further increase occurred during therapy. Oral carbohydrate intake was restricted to 240–250 Gms/24 hrs and hypertonic dialysate to 5.7 ± 4.1% of the total. There were no significant changes in fractional removal rate of lipid. Therefore further increases in serum triglycerides in CAPD may be prevented by simple dietary manoeuvres.

Postprandial triglyceridemia after single dose of alcohol in healthy young men

BACKGROUND AND AIMS

Moderate alcohol consumption provides protection against cardiovascular disease primarily due to increase of HDL-cholesterol. However, it also has some adverse effects on metabolism of triglycerides (TG). Therefore, we addressed the question how a single dose of alcohol affects postprandial lipemia and activities of two enzymes playing a critical role in regulation of triglyceridemia, lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL).

METHODS AND RESULTS

Eight healthy volunteers were given a single dose of alcohol (vodka; 0.6 g of ethanol/kg of body weight) together with a fat load (0.7 g of fat/kg of body weight) in an experimental breakfast or together with dinner 12 h before the experimental breakfast. In comparison to control experiment, alcohol given with breakfast induced increased and prolonged postprandial response of triglyceride-rich lipoproteins (TRL; d < 1.006 g/ml). At the same time TG accumulated also in intermediate density lipoproteins (IDL; d 1.006-1.019 g/ml). Alcohol given in the evening before the experiment increased fasting TG concentration but did not affect changes in TRL and IDL concentrations. LPL activity measured both in vivo using intravenous fat tolerance test and in vitro and HTGL activity were determined at the end of experiments (after 7.5 h of postprandial lipemia study). Neither was affected by a single dose of alcohol.

CONCLUSIONS

Single dose of alcohol induces immediate and profound changes in metabolism of TRL and IDL. The same dose of alcohol given 12 h before meal does affect baseline TG concentration but not the postprandial changes of triglyceridemia.

Fractional removal rate of fat emulsion (K2) remains to be low in APOE3/3 phenotype subjects with serum triglyceride level above 180mg/dl

The relation between fractional catabolic rate (K2) of an intravenously injected fat emulsion, Intralipid, and the level of serum triglyceride (TG) was evaluated to cast light on TG-rich lipoprotein metabolism in 182 subjects who were homozygotes for the most common form of apoE3/3. Both normolipidemic individuals and primary hyperlipidemic patients were included. To assess the influence of variation in the apoE phenotype on fat emulsion metabolism, 25 subjects with the apoE 4/3 phenotype and 21 with apoE 3/2 phenotype were also evaluated. In the apoE 3/3 subjects, K2 decreased with increasing TG level up to 180mg/dl, but above 180mg/dl, K2 remained at a constant level. This TG value was therefore concluded to be a cut off beyond which the TG-dependent decrease in K2 disappeared. No apparent correlation between K2 and serum TG was observed in subjects with apoE 4/3 or 3/2 phenotypes. In subjects with TG above 180mg/dl, presumably both accelerated synthesis and limited removal are involved in the development of their hypertriglyceridemia. Since K2 demonstrated little change with increase of TG over 180mg/dl in apoE 3/3 subjects, we concluded that the capacity to catabolize fat emulsion reaches a kinetic saturation. The TG value of 180mg/dl may be a physiological significance. The relation between K2 and TG was specific in apoE 3/3, as it was not observed in subjects having apoE 4/3 or 3/2 phenotypes.

Dietary fish oil normalize dyslipidemia and glucose intolerance with unchanged insulin levels in rats fed a high sucrose diet

The aim of this study was to investigate the relationship between the lipid-lowering effects of fish oils and concomitant consequences on glucose tolerance and insulin sensitivity in an experimental animal model of hypertriglyceridemia induced by high sucrose intake. To achieve this goal, male Wistar rats were fed a semi-synthetic sucrose rich diet (SRD) (w/w: 62.3% sucrose, 8% corn oil, 17% protein) for 90 days. At the time, a well established and permanent hypertriglyceridemia accompanied by glucose intolerance was present. After that, one half of the animals continued on the SRD up to 120 days. The other half received an SRD in which the source of fat was substituted by cod liver oil (w/w 7% CLO plus 1% corn oil) from day 90 to 120 (SRD+CLO). Control rats were fed a semi-synthetic diet (CD) (w/w: 62.5% corn starch, 8% corn oil, 17% protein) throughout the 120 days experimental period. Results obtained after the experimental period show that the hypertriglyceridemia and glucose intolerance ensuing long term feeding normal rats with a sucrose-rich diet could be completely reversed mediating no change in circulating insulin levels by shifting the source of fat in the diet from corn oil to cod liver oil. These findings suggest that manipulation of dietary fats may play a role in the management of the lipid disorders associated with glucose intolerance and insulin resistance.

Hyperlipidemia in acute pancreatitis. Cause or epiphenomenon?

Whether hyperlipidemia is a pre-existing metabolic disorder or a consequence of acute pancreatitis is still debated. Mild to moderate elevation of serum triglyceride levels are likely to be an epiphenomenon of the pancreatic disease. A marked hyperchylomicronemia and hypertrygliceridemia would be needed to trigger acute pancreatitis; a relevant defect in the lipid catabolism and clearance should therefore pre-exist. The aim of the present study was to investigate whether patients with acute pancreatitis and marked hyperlipidemia have an impaired clearance capacity of exogenous lipids, which would define the hyperlipidemia as a preexistent abnormality and therefore a potential cause of the pancreatic disease. With this aim, the kinetics of the removal of exogenous triglycerides from the circulation have been analyzed. Twenty patients with acute pancreatitis have been studied. Ten of them suffered from an episode of acute pancreatitis with marked hyperlipidemia (serum triglyceride levels > 20 mmol/L). Four to six months after recovery from the pancreatitis, a two-stage infusion of Intralipid 20% was carried out and the fractional removal rate (K2) and the maximal clearance capacity (K1) of exogenous triglycerides were calculated. At low infusion rates a first order kinetics for removal was observed, whereas at high infusion rates a zero order kinetics was operating. All patients with a previous attack of normolipidemic acute pancreatitis had normal K2 and K1 values. Five patients with previous hyperlipidemic acute pancreatitis had an abnormally low clearance capacity of exogenous triglycerides, whereas the remaining five had normal removal values. The present study provides new information in the association between hyperlipidemia and acute pancreatitis by showing that even a marked elevation of serum lipid levels should not be invariably considered as the etiological factor of the pancreatic disease, even if other potential causes are not evident.

Excess parathyroid hormone adversely affects lipid metabolism in chronic renal failure

Hyperlipidemia is common in chronic renal failure (CRF), but the underlying mechanisms are not clearly defined. Certain data points toward a potential role for the state of secondary hyperparathyroidism of CRF in its pathogenesis. We examined the effects of parathyroid hormone (PTH) on lipid metabolism utilizing intravenous fat tolerance test (IVFTT) and post-heparin lipolytic activity in five normal dogs, in six animals with CRF and secondary hyperparathyroidism (NPX) and in six normocalcemic-thyroparathyroidectomized dogs (NPX-PTX) with comparable degree and duration of CRF. NPX dogs had fasting hypertriglyceridemia (82 + 6.0 mg/dl vs. 49 +/- 2.7 mg/dl in normal dogs, P less than 0.01), abnormal IVFTT, and reduced post-heparin plasma LPL activity (151 +/- 10 vs. 275 +/- 15 mumol fatty acids/ml/min in normal dogs, P less than 0.01). The NPX-PTX dogs had normal fasting levels of serum triglycerides (42 +/- 0.6 mg/dl), normal IVFTT, and normal post-heparin plasma LPL (317 +/- 19 mumol fatty acids/ml/min) despite CRF. Post-heparin HL activity in plasma was not different between NPX and NPX-TPX dogs. The results show that excess blood levels of PTH and not other consequences of CRF are mainly responsible for the abnormalities in lipid metabolism. The data are consistent with the notion that excess PTH reduces post-heparin LPL activity in plasma, which in turn results in impaired lipid removal from the circulation and consequently hyperlipidemia.

Serum lipids, lipoproteins and macrovascular disease in non-insulin-dependent diabetics: a possible new approach to prevention

The relationship between macrovascular disease and serum lipids, low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL), and subfraction cholesterol, and apolipoproteins has been examined in 53 female and 95 male patients with non-insulin-dependent diabetes mellitus (NIDDM). In males, those with macrovascular disease had higher serum and LDL cholesterol concentrations than those without. In females, those with macrovascular disease had higher levels of serum triglyceride, cholesterol, LDL cholesterol, as well as lower HDL, HDL2, and HDL3 cholesterol and apoprotein A-1, than those without. On multivariate analysis, LDL cholesterol was the most important association with macrovascular disease in males and apoprotein A-1 in females. In a subgroup of 36 patients, a double-blind placebo controlled study using bezafibrate or placebo, in addition to conventional oral hypoglycaemic therapy over 4 months, showed falls in serum and LDL cholesterol and in serum triglyceride and a rise in HDL cholesterol in the treated group. These changes should reduce the incidence of macrovascular disease in NIDDM and we suggest further prospective studies of such therapy in addition to conventional oral hypoglycaemic agents.

Exogenous lipid clearance in compensated liver cirrhosis

The tolerance to exogenous fats has been evaluated in patients with liver cirrhosis. A three-stage lipid clearance test with continuous infusion (3 hr) of a triglyceride emulsion, Intralipid, was performed on 10 patients with well compensated liver cirrhosis and 10 normolipidemic volunteers. During the infusion, blood samples were collected for the measurement of particulate triglycerides (TG) by nephelometry; samples were also collected for total TG, free fatty acids (FFA) and free tryptophan (TRP) determinations. Plasma endogenous triglycerides were calculated as the total minus exogenous, particulate, TG. The fractional removal rate (K2) and the maximal clearing capacity (K1) for exogenous TG were lower in patients than in controls, though a significant difference (p less than 0.05) was found only for K1. Endogenous TG and FFA showed a comparable rise in patients and controls during Intralipid infusion. A significant increase in free TRP was noted in cirrhotics upon maximal infusion rate. It is concluded that: in patients with well compensated liver cirrhosis the maximal clearing capacity (K1) for exogenous TG is impaired. Nonetheless, moderate amounts of fat may be removed at a normal rate from the bloodstream; a normal synthesis rate of exogenous TG may be maintained even in a severely damaged liver; considering the possible role of free TRP in the pathogenesis of hepatic encephalopathy (HE), the use of large amounts of lipids should be discouraged in patients with decompensated liver cirrhosis, or even avoided in those with impending or overt HE.

The effect of apolipoprotein A on in vitro apolipoprotein C binding and in vivo removal of artificial triacylglycerol-rich particles

Although the presence of apolipoprotein A on the surface of chylomicrons and its exchange for apolipoprotein C in the mesenteric lymph is known, the functional role of apolipoprotein A in triacylglycerol transport has not been elucidated. Mimicking the in vivo situation, artificial triacylglycerol rich particles (TGRP) with which apolipoprotein AI had been associated, were incubated with high-density lipoproteins (HDL). It was found that apo AI-TGRP bound approximately twice as much apolipoprotein C from HDL as nonprotein-containing TGRP, losing 75% of the apolipoprotein AI originally present. To test whether an increased apolipoprotein C binding in vitro implicated an increased removal rate in vivo, boluses of apolipoprotein AI preincubated and control TGRP were given intravenously (IV) to six hypertriacylglycerolemic patients. The fractional catabolic rate was 35% (range 6% to 65%) higher for apolipoprotein AI preincubated TGRP than for control TGRP. In accordance with the in vitro incubations, the molar ratio of apolipoprotein C to phospholipid on TGRP reisolated 30 minutes after injection was 39% (range 12% to 115%) higher for apo AI triacylglycerol rich particles (TRP) than for control TGRP. The maximal removal capacity of apo AI-TRP, tested in one patient by constant infusion, was increased 53% as compared to control TGRP. Thus, the function of apolipoprotein AI in triacylglycerol transport may be to enhance apolipoprotein C binding to chylomicrons, which are comparable to TRP, and in doing so to enhance their removal from the plasma compartment.

The short term effects of bezafibrate on the hypertriglyceridaemia of moderate to severe uraemia

Hypertriglyceridaemia, an atherogenic risk factor, is a well recognised complication of uraemia, and is present in the earliest stages of the disease. Bezafibrate is an effective hypolipidaemic agent, and its effect in moderate to severe uraemia is documented in this study. Significant reductions in serum triglyceride and cholesterol have been achieved after 1 month's therapy with a reduced dosage of bezafibrate. A reduction in the hyperinsulinaemia was also seen, but no change in the fractional removal rate of injected lipid emulsion (K2) was observed. An accelerated decline in some patients' renal function was observed, which was partially reversed on cessation of treatment. Reversible elevations in the serum creatinine phosphokinase were also seen, but no patient exhibited the myositis-like syndrome associated with clofibrate.

Clearance rate of intravenously administered lipid emulsion in canine endotoxemia

The effect of endotoxemia on the initial catabolism of intravenously given lipid emulsion was investigated in dogs. Two types of endotoxemia were prepared. One was produced by peritonitis which was established by ligation of the artery and vein of an isolated intestine (group 1, n = 6). The other was made by an intravenous injection of Escherichia coli lipopolysaccharide in a dose of 1.5 mg/kg of body weight (group 2, n = 6). Group 1 showed evident peritonitis with a positive limulus test 48 hr after the procedure, but no significant changes of blood sugar level and lactate/pyruvate ratio, while group 2 demonstrated profound hypoglycemia, significant elevation of lactate/pyruvate ratio, and low arterial pressure 3 to 5 hr after the injection of lipopolysaccharide. The clearance rate of intravenously administered lipid emulsion (K value) of group 1 before the peritonitis was 0.0105 +/- 0.0017 and after the peritonitis it was 0.0105 +/- 0.0019. The difference was not significant, while the K value of group 2 which was 0.0133 +/- 0.0056 before the injection of lipopolysaccharide decreased significantly to 0.0069 +/- 0.0024 after the injection of lipopolysaccharide. These results suggest that, in case of endotoxemia with normally maintained oxidation-reduction potential, the initial catabolism of intravenously given lipid emulsion is kept in a normal level, while oxidation-reduction potential is impaired, it is inhibited.

Effects of ethyl-CPIB (clofibrate) on tissue lipoprotein lipase and plasma post-heparin lipolytic activity in rats

The role of LPL in reducing the serum triacylglycerol concentration was investigated in rats fed a high sucrose diet containing 0.25% (w/w) ethyl-CPIB. Compared with sucrose-fed controls, drug treatment resulted in a fall in adipose tissue LPL activity and a rise in enzyme activity in thigh and heart muscle. Serum post-heparin lipoprotein lipase activity after a high dose of heparin was lower in ethyl-CPIB-treated rats than controls, but after a low dose of heparin the values were similar. The amount of LPL activator was decreased by the drug. Thus, the low serum triacylglycerol concentration observed in the ethyl-CPIB-treated rats cannot be explained by changes in functional LPL activity. The plasma triacylglycerol-lowering effect of the drug could be explained by the observed decrease in triacylglyerol output by the liver.

Adrenergic mechanisms in the control of plasma lipids in man

The effects on plasma lipids of beta-blocking antihypertensive agents with differing degrees of selectivity and intrinsic sympathomimetic activity were studied. The interrelationship between changes in lipid factors, lipoprotein lipase function, the degree of response, and pretreatment characteristics were examined. Beta-adrenergic blockade increased plasma triglycerides but decreased high-density lipoprotein cholesterol. Cardioselective drugs (atenolol and metoprolol) had less effect on triglyceride and very low-density lipoprotein cholesterol than the nonselective beta blockers (propranolol and oxprenolol). Inhibition of lipoprotein lipase was suggested by a reduction of the fractional removal rate of triglyceride in conjunction with increased total and very low-density lipoprotein cholesterol levels and reduced high-density lipoprotein cholesterol. Consistent decreases in free fatty acids lend argument against elevated triglyceride synthesis.

Effects of hemodynamic changes induced by hyper- or hypothermia on intravenous lipid clearance rate and lipoprotein lipase activity in dogs

Hyper- and hypothermia was induced in dogs by peritoneal perfusion with warm or cold Lactate-Ringer's solution, the objective being to alter cardiac output. Changes in cardiac index, intravenous lipid clearance rate (K-value), and lipoprotein lipase (LPL) activity, concomitantly with changes of the temperature of the mixed venous blood were investigated. The cardiac index increased significantly with the hyperthermia and there was a close correlation between the cardiac index and the K-value. The LPL activity did not change significantly with changes in blood temperature, and the correlation between the LPL activity and the K-value was not significant. The hemodynamics has to be considered when attempting to discuss the intravenous lipid clearance rate.

Effects of hypertonic glucose on the rates of plasma clearance and CO2 production of intravenously administered intralipid emulsion in dogs

Simultaneous infusion of glucose and Intralipid was carried out on dogs to evaluate the effect of glucose on utilization of the fat emulsion. For control experiments, normal saline was used in place of glucose. Results of these studies revealed that clearance of Intralipid and also of triglyceride and free fatty acid (FFA) from the plasma did not differ between the dogs receiving glucose and those receiving saline infusion. The rates of Intralipid clearance were 0.049 +/- 0.003 and 0.047 +/- 0.003 per minute (n = 16), respectively. Study with radioactive [14C]Intralipid also gave similar rates of 14C clearance from the plasma, 0.037 +/- 0.003 and 0.040 +/- 0.003 per minute (n = 4), respectively for the two groups. These suggested that clearance of Intralipid from the plasma was not affected by glucose. However, data on expired 14CO2 revealed that oxidation of the fat, which yielded CO2 as end product, was inhibited by glucose. The amount of 14CO2 expired in 2 hours was 10.4 +/- 1.4% for the saline group, which was significantly reduced to 3.0 +/- 0.4% (n = 4; p less than 0.01) for the glucose group. In each group, CO2 production was much delayed as compared to fat clearance from the plasma. Thus, the rate of clearance of Intralipid from plasma does not reflect the actual utilization of fat emulsion. In accordance with an experiment with insulin, it appears that suppression of CO2 production is directly related to plasma insulin levels.

Adrenergic mechanisms in control of plasma lipid concentrations

The mechanisms of the changes in plasma lipids concentrations observed after beta-blockade were examined in 53 patients with hypertension receiving treatment with atenolol, metoprolol, propranolol, and oxprenolol in a randomised cross-over trial. Significant increases in mean plasma total and very-low-density lipoprotein (VLDL) triglyceride and reductions in high-density lipoprotein (HDL) cholesterol and free fatty acids concentrations wer observed with all four drugs, the increase in plasma triglyceride concentration being greatest after propranolol and oxprenolol. No significant changes were observed in total of LDL cholesterol concentrations, but HDL:LDL ratios and HDL cholesterol as a proportion of total cholesterol fell significantly. Thus plasma lipid concentrations should be monitored after three to six months of long-term treatment. Changes in triglyceride, HDL cholesterol and free fatty acid concentrations were associated with a highly significant reduction in clearance of soya oil (Intralipid) in 25 patients studied but were unrelated to changes in blood pressure. The fall in HDL cholesterol and rise in free fatty acid concentrations were significantly less in those with initially reduced HDL cholesterol or raised free fatty acid concentrations respectively. It is proposed that unopposed alpha stimulation inhibits lipoprotein lipase with a subsequent rise in plasma triglyceride and fall in HDL cholesterol concentration. Analysis of the relation between pretreatment concentrations and subsequent changes suggests that excessive alpha stimulation may impair production of HDL cholesterol in those with low HDL cholesterol concentrations before treatment. Subtle catecholamine-mediated changes in plasma lipid concentrations might provide a mechanism for the relation between stress and the development of cardiovascular events.

Fat emulsion catabolism in vitro and in vivo--sex related differences

The removal rates of an intravenously administered 10% fat emulsion (Intralipid) from plasma in male and female conscious rats are described. The plasma concentration of fat emulsion particles at various time intervals following a bolus administration (0.2 g/kg) was measured by nephelometry. At the dose employed, the removal of fat emulsion from the plasma followed first order kinetics, ie, a constant fraction was removed from the plasma per unit of time, K2 (%/min). Females exhibited a significantly greater fractional removal rate (K2) than comparably aged males (21.0 +/- 1.0 vs 15.0 +/- 1.4, p less than 0.05). Postheparin lipoprotein lipase, measured using fat emulsion as substrate, also was significantly greater in female rats compared with males. Our results demonstrate that, in rats, fat emulsion (Intralipid) is catabolized more rapidly in females than in males and a greater lipoprotein lipase activity in female rats may be the causative factor.

Lipodystrophy with hyperlipidaemia: the role of insulin in very low density lipoprotein over-synthesis

A patient with partial lipodystrophy is described in whom hypertriglyceridaemia was accompanied by marked hyperinsulinaemia. The hyperlipidaemia was due to increased plasma levels of very low density lipoprotein (VLDL). Kinetic studies, performed after injection of autologous radioiodinated VLDL, indicated that the raised VLDL levels were associated with over-production of this lipoprotein. Administration of diazoxide led to a substantial fall in serum insulin levels, accompanied by reduction in VLDL production and in serum triglyceride concentration. The possible role of insulin in inducing hyperlipidaemia by causing over-production of VLDL is discussed.

Intravenous fat tolerance in obese Africans with varying grades of carbohydrate tolerance

An intravenous fat tolerance test (IVFTT) was performed and fasting plasma lipid values determined in 12 healthy normal weight, 18 obese non-diabetic, 9 obese chemical diabetic and 10 obese symptomatic diabetic African subjects. Their insulin responses to an oral glucose load were also determined. Mean plasma triglyceride levels were similar in the normal weight and obese non-diabetic groups but were significantly raised in the two diabetic groups, being highest in the symptomatic diabetics. The fractional removal-rate of an intravenous injection of the fat emulsion Intralipid was significantly less in each of the obese diabetic groups compared with the normal weight or obese non-diabetic group. There was a significant negative correlation in all but the symptomatic diabetic group between the fasting triglyceride level and the rate constants for the IVFTT. These results suggest that the rate of triglyceride clearance is an important determinant of the basal plasma triglyceride concentration in urban African subjects.

Intravenous fat tolerance. Correlation with very low density lipoprotein apoprotein B kinetics in man

The intravenous fat tolerance test (IVFTT) has been introduced as a measure of the fractional catabolic rate of the endogenous triglyceride of plasma. To assess the validity of this test we have compared this test in 21 normal and hyperlipidaemic subjects with direct measurement of the fractional catabolic rate of autologous radio-iodinated VLDL. There was a strong positive correlation between the rate constant K2 of the IVFTT and the fractional catabolic rate of VLDL-apolipoprotein B (r=+0.87). The two rates were considerably different in magnitude. The IVFTT appears to be a valid index of the fractional catabolic rate of VLDL. Its limitations and uses are discussed.

Differences among hyperlipoproteinaemic subjects in the response of lipoprotein lipids to resin therapy

Ih has been reported that cholesterol turnover is raised when hypercholesterolaemia occurs in association with elevated levels of very low density lipoprotein, but normal when hypercholesterolaemia reflects an increase in the concentration of low density lipoprotein alone. The relationship of plasma lipoprotein levels to cholesterol metabolism has been further investigated in the present experiments, in which the acute effects on lipoprotein lipids of stimulating cholesterol turnover with a bile acid-sequestering resin, colestipol, have been compared in normal subjects and in patientw with four types of hyperlipoproteinaemia. Very low density lipoprotein (VLDL) lipids increased in every subject. The increase was greatest in patients with type IV or type V hyperlipoproteinaemia, least in normal subjects and in those with type IIa hyperlipoproteinaemia, and intermediate in patients with type IIb hyperlipoproteinaemia. The induced increments in VLDL cholesterol and triglyceride mass were accordingly positively correlated with the pre-treatment concentrations. Low density lipoprotein (LDL) lipids decreased during resin therapy in all subjects, except those with type IV or type V hyperlipoproteinaemia in whom there was a transient rise. The reductions in LDL cholesterol were significantly greater in patients with type II hyperlipoproteinaemia than in the normal volunteers, and in both groups of subjects were proportionately greater than those in LDL triglyceride. These findings demonstrated clear differences among the hyperlipoproteinaemias in the response of lipoprotein lipids to resin therapy, and profide further evidence for the heterogeneity of cholesterol metabolism in these conditions. The colestipol-induced changes in type UV and type V patients could be partially reproduced in normal subjects during the consumption of high carbohydrate diets, which might be expected to increase VLDL synthesis. It is suggested, therefore, that the synthesis of VLDL cholesterol may be enhanced in such patients, and that any rise in LDL cholesterol observed during resin therapy reflected subsequent metabolism of VLDL to LDL rather than diminished LDL cholesterol clearance.

Removal of exogenous triglycerides in human forearm muscle and subcutaneous tissue

The removal of exogenous triglyceride (TG) in forearm muscle and subcutaneous tissue of 7 healthy male volunteers has been studied by nephelometric determinations of arterial-deep venous (a-dv) and arterial-superficial venous (a-sv) differences in concentration of fat particles. Exogenous TG was administered as a constant i.v. infusion of Intralipid over a period of 30 min at reat and another 15 min during forearm work. At rest a significant positive a-dv difference in fat particle concentration of 121 plus pr minus 21 mumol TG/l (mean plus or minus S.E.M.) was found, which correspondens to a fractional extraction of 1093 plus or minus 2.0%. Also the a-sv difference was significant, 81 plus or minus 14 mumol TG/l, 5.7 plus or minus 0.8% of the arterial concentration. During exercise no further significant removal was found. Thus both skeletal muscle and subcutaneous tissue seem to be able to remove exogenous TG in substantial amounts under resting conditions. In the exercising muscle, however, the direct removal of exogenous TG does not seem to be of significant importance.

Plasma lipoproteins and the synthesis and turnover of plasma triglyceride in normal and genetically obese mice

1. Lipoproteins in the plasma of mice were characterized by agarose-gel chromatography and polyacrylamide-gel electrophoresis: genetically obese (ob/ob) mice exhibited hyperlipoproteinaemia (compared with lean mice), largely owing to an increase in the concentration of cholesterol in high-density lipoprotein. Plasma concentrations of triglyceride and phospholipid were not markedly increased in genetically obese mice. 2. The formation of glycerolipids in liver and plasma was investigated with (14)C-labelled precursors. The synthesis of hepatic triglyceride and phospholipid from glucose or palmitate was enhanced in ob/ob mice, compared with lean mice. The rate of entry of triglyceride into plasma, calculated from the time-course of incorporation of (14)C from [(14)C]palmitate into plasma triglyceride, was increased in ob/ob mice (0.5mumol of fatty acid/min, compared with 0.2 in lean mice). 3. The removal from plasma of murine lipoprotein triglyceride-[(14)C]fatty acid was increased in ob/ob mice (half-time 2.2min, compared with 7.2min in lean mice). Similar results were obtained with an injected lipid emulsion (Intralipid). 4. From these measurements, estimates of the rates of turnover of plasma triglyceride in mice (fed on a mixed diet, female, 3 months old) are about 1.0mumol of fatty acid/min in ob/ob mice, and 0.25 in lean mice. 5. The major precursor of hepatic and plasma triglyceride in lean and ob/ob mice was calculated to be plasma free fatty acid. 6. These results are discussed, in connexion with the role of the liver in triglyceride metabolism in mice, especially in relation to genetic obesity.