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PubMed2004

Systemic and forearm triglyceride metabolism: fate of lipoprotein lipase-generated glycerol and free fatty acids.

Little is known about the fate of the lipolytic products produced by the action of lipoprotein lipase (LPL) on circulating triglyceride-rich lipoproteins in humans. We studied eight lean, healthy male subjects after an overnight fast. Subjects received infusions of lipid emulsions containing triolein labeled with (3)H on both the glycerol backbone and the fatty acid portion of the molecule; (14)C glycerol and (14)C oleate were coinfused to quantify the systemic and forearm release of (3)H glycerol and (3)H oleate resulting from LPL action. There was significant forearm uptake of both whole plasma triglyceride (presumed to represent primarily VLDL; extraction fraction 2.6 +/- 0.6%, P < 0.005 vs. zero) and radiolabeled triglyceride derived from the lipid emulsion (a surrogate for chylomicrons; extraction fraction 31 +/- 4%, P < 0.005 vs zero). Systemic clearance and forearm fractional extraction of glycerol was greater than that of oleate (P < 0.001 and P < 0.02, respectively). The systemic and forearm fractional release of LPL-generated glycerol were similar at 51 +/- 4 and 59 +/- 1%, respectively (NS). In contrast, the forearm fractional release of LPL-generated oleate was less than systemic fractional release (14 +/- 2 vs. 36 +/- 4%, P < 0.0001). These results indicate that there is escape, or spillover, of the lipolytic products of LPL action on triglyceride-rich lipoproteins in humans. They further suggest that LPL-mediated fatty acid uptake is an inefficient process, but may be more efficient in muscle than in adipose tissue.

Adipose Tissue↗
PubMed2001

Skeletal muscle triglyceride. An aspect of regional adiposity and insulin resistance.

Recent evidence derived from four independent methods indicates that an excess triglyceride storage within skeletal muscle is linked to insulin resistance. Potential mechanisms for this association include apparent defects in fatty acid metabolism that are centered at the mitochondria in obesity and in type 2 diabetes. Specifically, defects in the pathways for fatty acid oxidation during postabsorptive conditions are prominent, leading to diminished use of fatty acids and increased esterification and storage of lipid within skeletal muscle. These impairments in fatty acid metabolism during fasting conditions may be related to a metabolic inflexibility in insulin resistance that is not limited to defects in glucose metabolism during insulin-stimulated conditions. Thus, there is substantial evidence implicating perturbations in fatty acid metabolism during accumulation of skeletal muscle triglyceride and in the pathogenesis of insulin resistance. Weight loss by caloric restriction improves insulin sensitivity, but the effects on fatty acid metabolism are less conspicuous. Nevertheless, weight loss decreases the content of triglyceride within skeletal muscle, perhaps contributing to the improvement in Insulin action with weight loss. Alterations in skeletal muscle substrate metabolism provide insight into the link between skeletal muscle triglyceride accumulation and insulin resistance, and they may lead to more appropriate therapies to improve glucose and fatty acid metabolism in obesity and in type 2 diabetes.

Adipose Tissue↗
PubMed2004

Association of triglyceride-to-HDL cholesterol ratio with heart rate recovery.

OBJECTIVE: Insulin resistance is associated with autonomic dysfunction. An attenuated decrease in heart rate after exercise (or heart rate recovery [HRR]) predicts all-cause mortality and is believed to reflect decreased parasympathetic activity. Utilizing triglyceride/HDL cholesterol concentration as a marker of insulin resistance, we sought to assess the association between insulin resistance and HRR. RESEARCH DESIGN AND METHODS: Our study population included 4,963 healthy adults who participated in the Lipid Research Clinics Prevalence Study and underwent exercise testing. HRR was considered abnormal if it did not drop > or = 42 bpm 2 min after completion of exercise. Fasting blood specimens were drawn. RESULTS: Individuals in the highest quartile of triglyceride/HDL cholesterol had a significantly higher prevalence of abnormal HRR (40 vs. 30%, multivariable-adjusted prevalence ratio 1.18, 95% CI 1.01-1.39; P = 0.04). As a continuous variable, an increase in 1 SD of triglyceride-to-HDL cholesterol ratio was associated with a greater likelihood of an abnormal HRR, even after adjusting for >20 covariates (adjusted OR 1.16, 95% CI 1.07-1.25; P < 0.001). During 12 years of follow-up, there were 284 deaths. In age- and sex-adjusted analysis, participants with an abnormal HRR and high triglyceride-to-HDL cholesterol ratio had significantly higher mortality than those with a normal HRR and high triglyceride-to-HDL cholesterol ratio (hazard ratio = 1.49, 95% CI 1.08-2.04; P = 0.015). CONCLUSIONS: HRR is associated with triglyceride-to-HDL cholesterol ratio and identifies patients with insulin resistance who are at increased risk of death.

Adult↗
PubMed1999

Effects of saturation and esterification of fat sources on site and extent of digestion in steers: digestion of fatty acids, triglycerides, and energy.

Five steers (mean BW 526 kg) fitted with ruminal, duodenal, and ileal cannulas were used in a 5 x 6 Youden square design with 14-d periods. Diets contained chopped alfalfa hay, corn silage, and concentrate (25:35:40, DM basis). Treatments were 1) control (no added fat); 2) tallow (T), iodine value (IV) = 51.5; 3) partially hydrogenated tallow (PHT), IV = 30.7; 4) hydrogenated tallow (HT), IV = 6.9; 5) blend (1: 1) of HT and hydrogenated free fatty acids (HTHFA), IV = 9.0; and 6) hydrogenated free fatty acids (HFA), IV = 11.2. Fats replaced cornstarch in the control diet to supply 5% added fatty acids. Intake was restricted to 90% of ad libitum; DMI was similar among diets (mean 9 kg/d). Total fatty acid intake averaged 170, 500, 506, 525, 489, and 491 g/d for treatments 1 to 6, respectively. Flows of total C16, total C18, and total fatty acids to the duodenum were increased by supplemental fat; flows of total C18 and total fatty acids were greater than their intake for all treatments. Flow of total fatty acids associated with ruminal bacteria accounted for 50 and 17% of the total duodenal fatty acid flow for the control and fat-supplemented diets, respectively. Digestibility of total fatty acids entering the small intestine (74, 71, 62, 39, 53, and 63% for treatments 1 to 6, respectively) was greater for the control diet than for fat-supplemented diets and decreased as either saturation (T < PHT < HT) or esterification (HFA < HTHFA < HT) increased. Digestibilities of fatty acids in the total tract followed similar patterns. Ruminal lipolysis of dietary triglycerides decreased linearly as the degree of saturation of fat sources increased. Small intestinal disappearance of triglycerides (89, 75, 51, 44, 64, and 73% of duodenal flow for treatments 1 to 6, respectively) decreased linearly as either saturation or esterification increased. Flows and digestion of gross energy followed patterns similar to those for fatty acids and triglycerides. Resistance to ruminal and small intestinal lipolysis is a major factor contributing to the poor digestibility of highly saturated triglycerides.

Animal Feed↗
PubMed1982

Morphological fatty changes and function of the liver, serum free fatty acids, and triglycerides during parenteral nutrition.

Morphological fatty changes and function of the liver and serum free fatty acids and triglycerides were investigated in 37 catabolic patients (22 men, 15 women) given different parenteral nutrition regimens. In the glucose group energy was supplied as carbohydrate alone, in the lipid group as carbohydrates and fats, and in addition both groups received amino acids. In the amino acid group amino acids were given in excess and less energy was supplied as carbohydrates. Each patient served as his own control. During parenteral nutrition liver steatosis rose from 5% to 35% (p less than 0.001) in the glucose group and from 7% to 23% (p less than 0.01) in the amino acid group, but no increase occurred in the lipid group. Liver fat accumulation was associated with the rises in serum aminotransferase activities and with the lack of or a poor rise in serum prothrombin and proconvertin. The conjugation function of the liver was not disturbed. No cholestatis was found. During lipid infusion serum free fatty acids increased to 4.41 mmol/l (p less than 0.01) and serum triglycerides to 3.06 mmol/l (p less than 0.01), but they decreased to normal range 12 h after lipid infusion was stopped. In the glucose and amino acid groups serum free fatty acid levels fell, as expected, below the normal range. Serum triglycerides rose 1.4-fold (p less than 0.05) in the amino acid group. On the basis of liver tests and histological examination steatosis in the liver caused only a minor disturbance in hepatocellular integrity. The very high levels of serum free fatty acids and triglycerides during lipid infusion may be harmful in certain pathological states.

Adult↗
PubMed1982

In vitro synthesis of triglycerides and cholesterol in human gallbladder mucosa.

Triglyceride and sterol synthesis was investigated in vitro in the gallbladder mucosa from control subjects and patients with acalculous cholesterolosis. The incorporation rate of 14C-acetate was 1.6 +/- 0.2 nmol/g/h into cholesterol (sum of squalene, methyl sterols, and cholesterol) and 5.7 +/- 0.8 nmol/g/h into triglycerides. The rates were significantly correlated with each other (r = 0.667). The conversion of 3H-mevalonate into cholesterol (49 +/- 10 nmol/g/h) and triglycerides (4.7 +/- 1.2 nmol/g/h) indicated a high activity in the postmevalonate cholesterol synthesis and an active shunt pathway of mevalonate metabolism. The synthesis rates of cholesterol, triglycerides, and sterol esters were closely interrelated, were unaltered in cholesterolosis, and were not correlated with the serum, biliary, and mucosal lipid concentrations. Thus, despite marked lipid accumulation the lipid synthesis proceeds effectively in the gallbladder mucosa with cholesterolosis.

Cholesterol↗
PubMed1988

Intestinal absorption of phosphatidylcholine and triglyceride after ileal resection.

The intestinal absorption of (14C)oleoyl moieties in triglyceride and phospholipid was investigated by means of (14C)phosphatidylcholine and (14C)triolein breath tests. In patients who had undergone ileal resection the absorption of both phosphatidylcholine and triglyceride was subnormal, as reflected by a lower production of 14CO2. In healthy subjects the production of expiratory 14CO2 after oral administration of (14C)phosphatidylcholine was slightly higher than after administration of (14C)triolein. This was also observed in the patient group, indicating that the absorption of both triglyceride and phospholipid was decreased to similar extents, although triglyceride absorption tended to be more affected after major ileal resection. In patients with lipid malabsorption the proportion of linoleic acid in serum phosphatidylcholine was subnormal, and the decrease was correlated to the decrease in lipid absorption. The concentration in serum of selenium, alpha-tocopherol, and carotene but not of ascorbic acid and retinol was subnormal after ileal resection.

Adolescent↗
PubMed1995

Serum cholesterol and triglyceride levels in weight reduction program dropouts.

Dropouts of a weight reduction program are not evaluated for the lasting effects of weight reduction. This study was an attempt to learn about the benefits of weight reduction received and sustained by the dropouts of the program. Ninety-seven males and females dropping out of a dietary weight management program after 16-18 weeks of treatment, and after 9-9.4kg weight loss and wishing to rejoin the program for a second time after at least 9 months' absence from it, were considered for the study. Their body weight, serum cholesterol, serum triglyceride, and blood sugar levels at the beginning of the second attempt, were compared with the respective values at the beginning of the first attempt. All patients had regained the weight lost during their first attempt when they reported for a second attempt. However, serum cholesterol and triglyceride values were 15% and 26% less for females, and 17% and 24% less for males, compared to their respective values on the first attempt, in the subgroup of patients with normal blood sugar levels. In the subgroup with above normal blood sugar levels, however, serum cholesterol and triglyceride values showed an increase by 12% and 17% respectively, for females, and by 2% and 7% respectively, for males, compared to their baseline values on their first attempt. The mechanism responsible for this observation was not uncovered. However, the observation that even an incomplete attempt at weight reduction appears to contribute in maintaining lower levels of serum cholesterol and triglyceride of at least those with normal blood sugar levels, is useful in nutritional counseling for emphasizing the health benefits of the weight reduction.

Adult↗
PubMed1976

Changes in plasma triglyceride fatty acids during lactation.

Total blood plasma lipid and plasma triglyceride fatty acids were analyzed at an average of 33, 89, and 139 days of lactation (ranges 20 to 57, 52 to 129, and 122 to 157 days for periods I, II, and III) for 35 Holstein cows in their second or later lactation. Average milk production in the test periods was 35.7, 30.3, and 25.5 kg/day. Lipid analysis was part of a study comparing methionine hydroxy analog or sulfur for lactating cows with effects of treatment and time separated statistically. Cows fed methionine analog had a lower percent palmitate in the triglyceride fatty acid, but there was no other treatment effect. There were significant changes with time in percent total lipid and triglyceride fatty acid. Total lipid averaged 424, 526, and 529 mg/dl. Average percents of measured triglyceride fatty acid and differences with stage of lactation were: myristic, 2.96; palmitic, 27.52, I greater than II or III; palmitoleic, 2.83, I greater than II or III; stearic, 38.58 I greater than II greater than III, oleic, 20.75, I greater than II or III; and linoleic, 4.59.

Animals↗
PubMed1978

Formation of intracellular fat droplets: interrelation of newly synthesized phosphatidylcholine and triglyceride in milk.

The lipogenic system of fresh goat milk was used to investigate the relationship of lipid synthesis to formation of fat droplets. The skim milk phase was incubated with [1-carbon-14] palmitate and incorporation of activity into the glycerolipids was assayed. In two representative experiments, 44 and 56% of the label was incorporated into the lipids. Most of this activity (78 to 84%) was in triglycerides. Of 12 and 10% activity in the phospholipids, about 60% was contained in phosphatidylcholine with substantially smaller amounts in the other phospholipids. The synthesis of triglyceride and phosphatidylcholine was further investigated in relation to distribution of labeled lipids in a cream layer and a sedimenting fluff (membrane) fraction derived by centrifuging the skim milks following incubation. The correlation coefficient for the amounts of activity in phosphatidylcholine and triglyceride in the cream layer was .97. The data are consistent with synthesis of phosphatidylcholine and triglyceride to meet the requirements of surface and volume expansion, respectively, in formation of fat droplets. Our findings suggest the interesting working hypothesis that phosphatidylcholine synthesis regulates development of fat droplets.

Animals↗
PubMed1988

Triglyceride accumulation and very low density lipoprotein secretion by rat and goat hepatocytes in vitro.

Utilization of [1-14C] oleate by freshly isolated rat and goat hepatocytes was compared. Intracellular [14C] triglyceride accumulation by hepatocytes did not differ between species. At 2 h of incubation, rat hepatocytes secreted approximately 25 times more [14C] triglyceride than goat hepatocytes. Very low density lipoprotein secretion was greatest by hepatocytes incubated in media containing 4:1 oleate:bovine serum albumin. Rat hepatocytes converted three to four times more [1-14C] oleate to 14CO2 and acid-soluble products than goat hepatocytes. Rate of 14CO2 formation by both rat and goat hepatocytes increased as incubation time increased and as rate of cellular triglyceride accumulation decreased. The ratio of 14CO2:[14C] acid-soluble products formed was greater for rat than goat hepatocytes, which indicated rat hepatocytes may oxidize fatty acid more completely. Differences in metabolic rate, based on oxygen consumption, between isolated goat and rat hepatocytes were minor and could not account for marked differences in very low density lipoprotein secretion. Goat hepatocytes did not incorporate detectable quantities of labeled fatty acid into low or high density lipoproteins. Ruminants may be susceptible to fatty liver when the liver takes up large amount of nonesterified fatty acid due to an inability to efficiently export fatty acid as very low density lipoprotein triglyceride.

Animals↗
PubMed1992

Effect of prepartum dry matter intake on liver triglyceride concentration and early lactation.

Depression in feed intake during the final week before calving was hypothesized to be a major factor in the etiology of fatty liver development near parturition. Eleven cows were allowed to eat for ad libitum intake prior to calving (control), and 11 cows were maintained at the same level of DMI recorded during d 21 to 17 prior to calving by force feeding the feed refusals via rumen cannulas. Feed intake by control cows decreased 28% during the final 17 d prior to calving. Lipid triglyceride increased 227 and 75% for control and force-fed cows between d 17 prior to parturition and d 1 following calving. Dry matter intake prior to calving was correlated negatively with liver triglyceride immediately after calving (r = -.80). Plasma glucose concentrations for control and force-fed cows were 63 and 76 mg/dl 2 d prior to calving and also were related closely to liver triglyceride immediately after calving (r = -.50). By d 28 after calving, there were no differences in liver triglyceride between treatments. Cows that were force-fed prior to calving tended to yield milk with greater fat percentage (4.22 vs. 3.88%) and to yield more 3.5% FCM (46.1 vs. 41.7 kg/d) during the first 28 d postpartum.

3-Hydroxybutyric Acid↗
PubMed1994

Peripartum liver triglyceride and plasma metabolites in dairy cows.

Nine pregnant, nonlactating cows were used to monitor liver triglycerides before and after parturition. Estimates were made of the contribution of depressed feed intake and parturition to plasma NEFA concentrations and development of fatty liver. Liver biopsies and plasma samples were obtained on d 19, 10, 5, 3, and 1 prior to calving and on d 1, 7, 14, and 21 after calving. Depression of DMI started on d 2 prior to calving and was 40% of DMI on d 3 prior to depression of feed intake. Elevation of plasma NEFA concentrations started prior to DMI depression, on d 5 before parturition. Liver triglyceride infiltration did not occur until the concentration of plasma NEFA was maximized on d 1 after calving. This result implicated the acute rise in NEFA at calving as a contributing factor to triglyceride accumulation in the liver. The increasing plasma glucose and decreasing plasma BHBA prior to calving may have reflected metabolic changes toward gluconeogenesis. Liver glycogen decreased 70% during the final 19 d prior to calving. Hepatic triglyceride infiltration (7.7% DM basis) on d 1 post-partum and duration of DMI depression prepartum were less severe than those observed in previous studies. Frequent liver biopsies did not affect DMI.

3-Hydroxybutyric Acid↗
PubMed1992

A simple enzymatic quantitative analysis of triglycerides in tissues.

We determined a method to measure the triglyceride levels in tissues by using a modified enzymatic kit. This enzymatic kit was originally designed to be used to measure the triglyceride levels in plasma. Our method of triglyceride level determination includes dissolving the tissue lipid extracts in an alcohol. Before using the enzymatic kit directly, the lipids were dissolved in tert-butyl alcohol, then a Triton X-100/methyl alcohol mixture was added (1/1 by volume). The presence of organic surfactants such as tert-butyl alcohol and methyl alcohol, and of a surfactant such as Triton X-100, did not interfere with the enzymatic activity. This method enabled us to determine triglyceride levels between 10 and 90 nmol, by using a spectrophotometer to measure the absorbances.

Animals↗
PubMed1975

Effects of synthetic androgen fluoxymesterone on triglyceride secretion rates in the rat.

Fluoxymesterone, a C-17 methylated derivative of testosterone employed in the treatment of renal-failure patients with refractory anemia, was administered to Sprague-Dawley rats and the effects on plasma triglyceride (TG) and immunoreactive insulin (IRI) levels and the rate of hepatic triglyceride secretion (TGSR) into plasma determined (Triton). Animals treated with fluoxymesterone demonstrated significantly lower TG (less than 0.05) and no alteration in TGSR. These findings are consistent with other observations which suggest that the triglyceride-lowering effect of androgens results from an accelerated rate of removal of triglyceride-rich lipoproteins from plasma.

Animals↗
PubMed1986

Heritability of plasma cholesterol and triglyceride concentrations in swine.

Three-hundred and eighteen female swine representing contemporary commercial swine breeds (34 Chester White, 43 Large White, 42 Landrace, 40 Yorkshire, and 159 four-breed crossbreeds) were used to evaluate genetic variation between and within breeds for levels of plasma cholesterol and plasma triglycerides. Blood was sampled from all pigs after a 16-hr fast at 154 days of age. Plasma cholesterol was measured in all pigs and triglycerides were measured in 232 pigs. Paternal half-sib heritabilities (h2) for plasma cholesterol and plasma triglycerides were 0.45 +/- 0.23 and 1.04 +/- 0.32, respectively. Breed differences were not apparent for either trait. Phenotypic and paternal half-sib genetic correlations between the two traits were 0.16 and 0.66, respectively. Neither body weight nor backfat depth were important in affecting the estimate of h2 for either trait. The relatively high h2 of total plasma cholesterol and of total triglycerides offers the possibility of developing, through selection, populations of hypercholesterolemic or hypertriglyceridemic swine useful as models for studies directed toward further understanding of human cardiovascular disease.

Animals↗
PubMed1993

Age-related response to dietary fructose in the rat: discrepancy in triglyceride and apolipoprotein B synthesis as a possible mechanism for fatty liver induction in adult rats.

The effects of fructose feeding on plasma and liver lipids, triglyceride secretion, and plasma apolipoprotein B and their liver mRNA level were studied in young and adult rats. We have shown that the responsiveness of adult rats to dietary fructose differs from that of young rats with regard to body parameters as well biochemical analyses. In young rats, fructose diet causes a coupled induction of liver triglyceride and apolipoprotein B synthesis via increased mRNA level. In adult rats it appears that triglyceride secretion is lower and less inducible by dietary fructose than in young rats. This insufficient export of the excess of synthesized triglycerides may cause fatty liver in adult animals. Reduced adaptation of liver lipoprotein secretion to dietary carbohydrates in adult animals may be explained by the failure to stimulate apolipoprotein B synthesis at the mRNA level in these rats.

Age Factors↗
PubMed1996

Copper intestinal absorption in the rat: effect of free fatty acids and triglycerides.

The absorption of some minerals has been shown to be affected by the presence of unhydrolyzed dietary triglycerides and free fatty acids generated from their partial hydrolysis. Since copper (Cu) can form poorly soluble soaps with long-chain fatty acids, we examined whether the uptake of Cu from the intestinal lumen is altered by the presence of fatty acids and triglycerides using an in vivo jejunal perfusion procedure. Long-chain fatty acids palmitate and stearate at 1.0 mM reduced Cu absorption rates compared with infusates without either fatty acid or triglycerides (means +/- SEM, controls: 104.4 +/- 8.8 pmole/min x cm vs palmitate: 12.5 +/- 17.6, P < 0.01; stearate:37.2 +/- 25.6, P < 0.05). Medium chain free fatty acids had no effect on Cu absorption (caprylate: 90.6 +/- 14.9, not significant; caproate: 69.5 +/- 14.2, not significant). Similarly, neither an emulsion of medium chain nor long-chain triglycerides at a total 1.0 or 2.5 mM concentration altered Cu absorption. The inhibitory effect of palmitate and stearate on Cu absorption was accompanied by a reduction in lumen-to-mucosa water influx (controls: 5.33 +/- 0.26 microl/min x cm vs palmitate: 3.20 +/- 0.70, P < 0.01; stearate: 3.36 +/- 0.52, P < 0.01). The data are consistent with a potential impairment of Cu intestinal absorption by long-chain free fatty acids which may accumulate in the jejunum following excessive fat intake and/or lipid malabsorption.

Animals↗