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Biomedical subjects

R H Eckel

Publications and source records attributed to R H Eckel.

At least 109 records · Page 6Linked to original sources
PubMed1988

Plasma lipolytic activity. Relationship to postheparin lipolytic activity and evidence for metabolic regulation.

Lipolytic activity was measured in human plasma without prior administration of intravenous heparin. Eluted from heparin-Sepharose in a barbital buffer containing 6 mg/ml heparin, plasma lipolytic activities in 20 subjects were distributed between hepatic triglyceride lipase (HTGL, mean +/- SE 60.6 +/- 4.6%) and extrahepatic lipoprotein lipase (LPL, 39.4 +/- 4.6%). Confirmation of the identities of HTGL and LPL was provided by inhibitory antisera. Preheparin LPL activity was absent in plasma from a patient with type I hyperlipoproteinemia. Both preheparin HTGL and LPL activities correlated with the respective activities measured in plasma obtained 15 min after intravenous injection of heparin (rs = + .774 and + .685, respectively; n = 12). Evidence for the metabolic regulation of preheparin lipases was provided by measurement of significant increases in LPL and HTGL activities after oral glucose ingestion. Overall, preheparin plasma HTGL and LPL activities may reflect ongoing lipoprotein lipolytic activity in tissue beds, and because these measurements do not require the administration of intravenous heparin, they should prove useful for additional studies of short-term regulation of the lipases.

Adult↗
PubMed1988

Deficiency of the insulin, glucose-mediated decrease in serum triglycerides in normolipidemic obese subjects.

The effects of a 6-h insulin, glucose infusion on lipid metabolism were compared in 29 normolipidemic obese and 20 control subjects. Alterations in serum triglycerides (TG), cholesterol, and high-density lipoprotein (HDL) cholesterol were similar within groups when either 40 or 120 mU/m2 per min of regular insulin were infused. Although changes in the HDL cholesterol responses to the insulin, glucose infusions were also similar in obese and control subjects, TG fell more in insulin, glucose-infused controls (35 +/- 4 mg/dl, means +/- s.e.m.) than obese subjects (23 +/- 3) (P less than 0.001). The rate and magnitude of the insulin, glucose-mediated fall in free fatty acids, however, were not different between the two groups. This diminished responsiveness of TG to an insulin, glucose infusion in normotriglyceridemic obese subjects is another manifestation of the insulin resistance of obesity.

Adult↗
PubMed1987

The effect of short-term alpha-glucosidase inhibition on carbohydrate and lipid metabolism in type II (noninsulin-dependent) diabetics.

With use of the alpha-glucosidase inhibitor bay g 5421 (acarbose), it is possible to improve glycemic profiles in diabetics without a concomitant increase in insulin levels or weight reduction. We have taken advantage of this feature to test whether an improvement in glycemic control alone can ameliorate some of the known abnormalities of type II diabetes (ie, impaired insulin secretion, elevated rate of basal hepatic glucose output, peripheral insulin resistance). We have studied eight type II diabetics (mean +/- SE fasting serum glucose 193 +/- 25 mg/dL) before and after 2 weeks of acarbose therapy (100 mg with each meal). Assessment of endogenous insulin secretion, peripheral and hepatic insulin sensitivity, and adipose tissue lipoprotein lipase (ATLPL) activity were performed. Results showed significant lowering of postprandial glucose excursions above basal but no change in basal serum glucose levels, marked reduction in fasting and day-long triglyceride levels and in spite of a reduction in ATLPL activity, an increase in hepatic sensitivity to insulin's ability to suppress hepatic glucose output, and no effect on peripheral insulin sensitivity. In conclusion, inhibition of carbohydrate digestion with alpha-glucosidase inhibitors ameliorates many of the metabolic abnormalities in type II (noninsulin-dependent diabetics), suggesting that agents of this type can be of therapeutic value.

Acarbose↗
PubMed1987

Weight reduction increases adipose tissue lipoprotein lipase responsiveness in obese women.

Lipoprotein lipase was measured in gluteal adipose tissue from nine obese (90.6 +/- 2.7 kg) women fasting and after the intravenous infusion of insulin and glucose before, immediately after, and 3 mo subsequent to a 14.0 +/- 1.8% (mean +/- SEM) weight reduction. Fasting adipose tissue lipoprotein lipase activity (ATLPL) decreased from 5.3 to 2.3 nEq FFA/10(6) cells per min (P less than 0.02) immediately after weight reduction, yet after weight maintenance, higher levels were again found (6.1 nEq FFA/10(6) cells per min). Although responsiveness of ATLPL to 40 mU/m2 per min of insulin infusion over 6 h was absent before weight loss, increases were seen immediately after weight loss (delta 0.8, P = 0.05) and more so (delta 7.7, P less than 0.01) after 3 mo. Moreover, whereas before weight loss the ATLPL response to ingested mixed meals (delta 0.9) was minimal, in the maintained reduced-obese state a marked increase was seen (delta 12.6, P = 0.02). Thus, because ATLPL is important to lipid filling in adipose tissue, the maintenance of high levels of fasting ATLPL and the increase in enzyme responsiveness in the reduced-obese state could play an important role in the resumption of the obese state, which so commonly follows weight reduction.

Adipose Tissue↗
PubMed1987

Regulation of lipoprotein lipase by glucose in primary cultures of isolated human adipocytes. Relevance to hypertriglyceridemia of diabetes.

Human adipose tissue lipoprotein lipase (LPL) is stimulated in vivo by an insulin-glucose infusion. However, previous work by us showed no effect of physiologic insulin concentrations on LPL in isolated human adipocytes. To pursue further the regulation of LPL in vitro, primary cultures of isolated human adipocytes were prepared and exposed to glucose concentrations of 0-4.5 mg/ml. LPL activity was measured as activity secreted into the culture medium (CM), released from cells by heparin (HR), and extracted from cell digests (EXT). After 5 h in culture, a stimulatory effect of glucose on HR was observed. After 24 h there was a gradual increase in CM, HR, and EXT in parallel with increasing glucose concentrations of 0-1.0 mg/ml. At glucose concentrations greater than 1.0 mg/ml, however, there was a decrease in CM. At a glucose concentration of 4.5 mg/ml, CM was only 51 +/- 14% (P less than .02) of its value at glucose concentrations of 1.0 mg/ml. Cellular LPL (HR and EXT) was not affected by high glucose concentrations. Response of cellular LPL to the hormonal regulator insulin-like growth factor I (IGF-I) was modulated by medium glucose. HR in cultures treated with 50 ng/ml IGF-I was 166 +/- 40 and 147 +/- 23% of HR in control cultures at glucose concentrations of 1.0 and 2.5 mg/ml, respectively (P less than or equal to .05). However, IGF-I failed to stimulate HR at glucose concentrations greater than 2.5 mg/ml or less than 1.0 mg/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1986

Contraceptive steroids increase hepatic uptake of chylomicron remnants in healthy young women.

In an investigation of alterations in cholesterol metabolism during contraceptive steroid use, we studied plasma clearance of chylomicron remnants. Six healthy women were studied on and off contraceptive steroid therapy. Remnant clearance was measured from the disappearance of retinyl palmitate administered intravenously in plasma endogenously labeled with retinyl palmitate. We also measured cholesterol in HDL and its subfractions and postheparin lipoprotein lipase and hepatic triglyceride lipase activities. Plasma decay of retinyl palmitate was biexponential. The rapid component, reflecting chylomicron remnant removal, accounted for about 90% of the total clearance in all studies. During contraceptive steroid intake, both rapid and slow decay constants and the calculated plasma clearance rates were significantly increased (mean values: rapid decay constant, control 0.048 versus treated 0.101 min-1, P less than 0.05; slow decay constant, 0.004 versus 0.014 min-1, P less than 0.01; plasma clearance 74 versus 115 ml/min, P less than 0.025) indicating enhanced hepatic uptake of chylomicron remnants and probably an increased hepatic uptake of higher density lipoproteins (d greater than 1.006 g/ml). Total postheparin lipolytic activity and lipoprotein lipase activity were depressed in all six women (P less than 0.05) and hepatic triglyceride lipase activity was increased in four of five subjects. Contraceptive steroids also caused a decrease in the HDL2/HDL3 cholesterol ratio (P less than 0.05), implying impaired peripheral lipoprotein triglyceride hydrolysis and/or increased HDL2 clearance by hepatic triglyceride lipase. In conclusion, during intake of contraceptive steroids, the plasma clearance of chylomicron remnants and higher density lipoproteins was increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Regulation of lipoprotein lipase in primary cultures of isolated human adipocytes.

To study the regulation of adipose tissue lipoprotein lipase (LPL) in human adipocytes, omental adipose tissue was obtained from healthy subjects and digested in collagenase. The isolated adipocytes thus obtained were suspended in Medium 199 and cultured at 37 degrees C. Cell viability was demonstrated in adipocytes cultured for up to 72 h by constancy of cell number, cell size, trypan-blue exclusion, and specific 125I-insulin binding. In addition, chloroquine induced an increase in cell-associated 125I-insulin at 24, 48, and 72 h after preparation. Thus, isolated adipocytes retained their ability to bind, internalize, and degrade insulin. LPL was measured as activity secreted into the culture medium (CM), released from cells by heparin (HR), and extracted from cell digests. A broad range of heparin concentrations produced a prompt release of LPL from a rapidly replenishable pool of cellular activity. When cells were cultured in medium containing 10% fetal bovine serum, there was a marked stimulation of CM and HR. The secretory response to serum (CM) correlated strongly with HR 24 h after preparation (rs = 0.731, P less than 0.001). In addition, HR was found to correlate logarithmically and inversely with body mass index (r = -0.731, P less than 0.001). Insulin, at 400 ng/ml only, increased HR by 36 +/- 10%, an effect simulated by lower concentrations of insulin-like growth factor-1 (IGF1). Thus, LPL is produced and regulated in isolated human adipocytes. The degree of adiposity and serum are important regulators of HR activity, whereas insulin is stimulatory only at a pharmacologic concentration. This effect of insulin may be mediated through the IGF1 receptor. Isolated human adipocytes represent a novel and useful system for the study of LPL and lipid metabolism as well as for other aspects of adipocyte biology.

Adipose Tissue↗
PubMed1984

Fat feeding decreases insulin responsiveness of adipose tissue lipoprotein lipase.

The acute effect of fat feeding on the insulin-mediated stimulatory response of adipose tissue lipoprotein lipase (ATLPL) was examined in normal-weight subjects. After two days of isocaloric-formula feeding, subjects were divided into the following four groups: intravenous (IV) saline alone (sal) (n = 5), IV saline and 67 g of oral corn oil ingested at the outset of the infusion (sal/fat) (n = 5), IV insulin (40 mU/m2/min) and glucose to maintain euglycemia (ins/glu) (n = 9), and IV insulin and glucose and oral corn oil (ins/glu/fat) (n = 8). Triglycerides fell less in the ins/glu/fat group than in the ins/glu group (0 +/- 8% v 35 +/- 5%, means +/- SEM, at three hours, P less than 0.01; 15 +/- 8% v 43 +/- 6% at six hours, P less than 0.02). ATLPL in the sal and sal/fat groups did not change during the six-hour period. When the responsiveness of ATLPL was compared between ins/glu/fat subjects and ins/glu subjects, decreases were seen at both three and six hours (-0.3 +/- 3.0 v 15.1 +/- 5.4 nEq/g/min, P less than 0.05; 6.7 +/- 2.7 v 27.9 +/- 3.9 nEq/g/min, P less than 0.001). The glucose infusion rates needed to maintain euglycemia were also decreased by fat feeding, 229 +/- 18 v 287 +/- 20 mg/m2/min (P less than 0.05). Thus, fat feeding with insulin and glucose infusions diminishes the insulin responsiveness of ATLPL.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1984

Lipoprotein lipase is produced, regulated, and functional in rat brain.

Lipoprotein lipase (LP lipase, triacylglycero-protein acylhydrolase EC 3.1.1.34) activity was found in four dissimilar brain regions (hypothalamus, cortex, cerebellum, and midbrain) of adult male rats. Progressive accumulation of LP lipase activity in cultured fetal rat hypothalamic cells was also observed, indicating de novo synthesis of the lipase. The brain LP lipase activity was serum-dependent and was inhibited by 1 M NaCl and by protamine sulfate. Kinetic analysis revealed an apparent Km of 0.79 mM very similar to that of rat adipose tissue LP lipase. That the lipase was functioning in the cultured brain cells was indicated by uptake and incorporation of radioactivity from tri[( 1-14C]oleoyl)glycerol into cellular triacylglycerols, and into more polar lipids, such as phosphatidylcholine. Furthermore, brain LP lipase activity in adult rats was decreased in all four regions examined, most significantly in the hypothalamus, after 72 hr of food deprivation. Thus, authentic LP lipase is present in adult rat brain and can be synthesized by isolated brain cells in vitro. LP lipase also mediates the uptake of triacylglycerol fatty acids and their subsequent incorporation into cellular lipids of cultured brain cells. Decreased brain LP lipase activity after fasting suggests that this enzyme may be regulated by metabolic or nutritional factors. Because the largest changes in LP lipase activity in response to food deprivation occurred in the hypothalamus, the enzyme may have a role in hypothalamic control of food intake or in body-weight regulation.

Animals↗
PubMed1984

Insulin regulation of lipoprotein lipase in cultured isolated rat adipocytes.

The cellular regulation of adipose tissue lipoprotein lipase by insulin was investigated using cultured isolated rat adipocytes. Evidence for sustained cell viability over 3 days included stability of specific [125I]insulin binding and adipocyte number. Lipoprotein lipase was measured in three functional compartments: 1) enzyme activity secreted into the culture medium, 2) activity releasable from cell suspensions by heparin, and 3) activity extractable from cells (after maximal heparin release) in deoxycholate and detergent. One day after preparation, these activities stabilized and were 1.3 +/- 0.2, 1.4 +/- 0.2, and 7.7 +/- 0.9 neq/10(6) cells X min, respectively (n = 24, mean +/- SEM). Insulin, added the day after preparation, produced a dose-dependent (1-400 ng/ml) increase in lipoprotein lipase releasable from cells by heparin at 2, 4, and 24 h. Insulin also increased intracellular enzyme measured as deoxycholate-detergent-solubilized activity extracted from previously heparin-released cells. However, insulin-mediated increases in culture medium enzyme only occurred subsequent to cellular effects. All insulin-mediated effects were prevented by cycloheximide (1 microgram/ml). Thus, insulin increased two cellular pools of adipocyte lipoprotein lipase in a dose-dependent manner, but had no direct effect on enzyme secretion. Overall, cultured isolated rat adipocytes appear to be a valuable system for the study of lipoprotein lipase regulation at the level of the adipocyte.

Adipose Tissue↗
PubMed1984

Insulin responsiveness of adipose tissue lipoprotein lipase is delayed but preserved in obesity.

Because increases in adipose tissue lipoprotein lipase (ATLPL) may be important in the pathogenesis of obesity, the response of ATLPL to insulin during maintenance of euglycemia was examined in 22 obese and 8 normal weight subjects. Basal levels of ATLPL per g fat tissue for the obese and control groups were 18.7 +/- 2.0 (+/- SEM) and 9.6 +/- 2.7 neq/g X min, respectively. Insulin and glucose infusion rapidly produced antilipolysis in both groups, as evidenced by large falls in FFA by 20 min. When the responses of ATLPL in absolute change from basal were compared between the obese and control groups, no significant differences were found. However, because of the higher baseline ATLPL values in the obese subjects, the percent change in ATLPL from basal was significantly blunted at the 80 (P = 0.02), 180 (P less than 0.05), and 360 (P = 0.005) min timepoints compared to those in the normal subjects. By 3 h into the infusion, the control group had a significant rise in ATLPL above the basal level (4.2 +/- 1.3 ngq/g X min; P = 0.01), whereas the obese group did not (2.3 +/- 1.9 neq/g X min; P = NS). However, by 6 h, the ATLPL per g response above baseline was significantly increased in both normal (19.2 +/- 6.5 neq/g X min; P = 0.01) and obese subjects (9.8 +/- 2.3; P less than 0.001). Because adipose cell size was greater in obese subjects, data were also expressed per 10(6) cells. Basal ATLPL per 10(6) cells [11.8 +/- 1.7 neq/10(6) cells X min (obese); 3.4 +/- 0.9 neq/10(6) cells X min (normal)] was a function of cell size (rs = 0.713; P less than 0.001), body mass index (rs = 0.565; P less than 0.005), and basal insulin levels (rs = 0.434; P less than 0.05). As with the ATLPL per g response, the increases in ATLPL per 10(6) cells above basal were significant at both the 3 and 6 h marks for the normal subjects, but only at the 6 h timepoint for the obese group. Both steady state insulin levels [342 +/- 24 microU/ml (obese); 251 +/- 27 microU/ml (normal)] and the glucose infusion rates needed to maintain euglycemia [319 +/- 23 mg/m2 X min (obese); 312 +/- 33 mg/m2 X min (normal)] did not correlate with changes in ATLPL. Thus, insulin responsiveness of ATLPL in obese subjects was delayed but preserved. This phenomenon may be important in maintenance of the obese state.

Adipose Tissue↗
PubMed1983

Isolation and culture of microvascular endothelium from human adipose tissue.

The study of human endothelial cells in tissue culture has been previously limited to umbilical vein, a large vessel source, and microvascular endothelium from human foreskin, spleen, and adrenal. Microvascular endothelium cultured from these sources have required matrix-coated culture flasks, tumor-conditioned medium, or 50% human serum for growth and subcultivation. To obtain cultures of microvascular endothelium with less stringent growth requirements, human adipose tissue was digested with collagenase and endothelial cells were separated from other stromal elements by sequential filtration and layering cells onto 5% albumin. Using standard medium containing 10% fetal calf serum, these cells grew readily to confluence and survived serial passages. When the cultures were subconfluent, cytoplasmic extensions and a capillary-like morphology were observed. Confluent cultures displayed the "cobblestone" appearance characteristic of other endothelial preparations. Electron microscopy demonstrated the presence of characteristic tight junctions and pinocytotic vesicles. Immunofluorescent staining for Factor VIII was positive, and cultures contained angiotensin-converting enzyme activity. Thus, cultures of human microvascular endothelium were readily obtained from adipose tissue and required only standard medium with 10% serum for growth and subcultivation. This system can be used to study human endothelial cell biology and may prove useful in the study of pathologic states such as diabetic microvasculopathy and tumor angiogenesis.

Adipose Tissue↗
PubMed1982

Insulin stimulation of adipose tissue lipoprotein lipase. Use of the euglycemic clamp technique.

The role of insulin in the regulation of adipose tissue lipoprotein lipase activity in humans was investigated in 11 normal subjects and compared with the effects of 0.9% saline infusions in five control subjects. After a basal adipose tissue biopsy for lipoprotein lipase activity, insulin was rapidly infused to achieve and maintain serum levels of approximately 70 microunits/ml while plasma glucose was kept at basal concentrations. Free fatty acids in serum fell to 27 +/- 3% of basal by 20 min (t = 5.19, P less than 0.001) and triglycerides decreased to 77 +/- 3% of basal by 80 min (t = 3.76, P less than 0.01). Adipose tissue lipoprotein lipase activity failed to increase significantly above that measured in controls by the first 3 h of the study. By 6 h of the infusion a stimulatory effect of insulin on adipose tissue lipoprotein lipase was found (t = 3.94, P less than 0.01). There was no relationship between the amount of glucose infused and the insulin effect on the enzyme. The increase in adipose tissue lipoprotein lipase activity at 6 h, however, was inversely related to the basal lipase activity (r = -0.690, P less than 0.02). Thus, insulin appears to stimulate adipose tissue lipoprotein lipase activity in humans. This effect of insulin is delayed when compared with antilipolysis and the fall in plasma triglyceride. The inverse relationship between insulin-stimulated adipose tissue lipoprotein lipase activity and basal enzyme activity suggests that adipose tissue itself is the main regulator of the lipase response to insulin.

Adipose Tissue↗
PubMed1981

Insulin-stimulated glucose uptake, leucine incorporation into protein, and uridine incorporation into RNA in skin fibroblast cultures from patients with diabetes mellitus.

Since intrinsic cellular abnormalities have previously have reported in diabetes mellitus, skin fibroblasts from patients with insulin-dependent diabetes and non-insulin-dependent diabetes, and from age-matched young and old controls, were examined for stimulation by insulin (4--4000 ng/ml) of glucose uptake, leucine incorporation into protein, and uridine incorporation into RNA. No differences in insulin-stimulated glucose uptake were seen between donor types. At 40 and 400 ng/ml, insulin did not stimulate as much leucine incorporation into protein in insulin-dependent diabetics as in young controls (p less than 0.05) and at 4000 ng/ml, less insulin-stimulated leucine incorporation was seen in insulin-dependent diabetics than in young controls or non-insulin dependent diabetics (p less than 0.01). Lower insulin-simulated uridine incorporation into RNA in old controls than in other cell lines appeared to be largely secondary to a two-fold increase in basal incorporation in these old controls. These results provide additional evidence for intrinsic cellular abnormalities in diabetes mellitus. Whether the differences in basal or insulin-stimulated response between fibroblasts of different donor types are attributable to alterations in protein or RNA synthesis, metabolite pool size or turnover have yet to be determined.

Adult↗
PubMed1981

High density lipoprotein composition in insulin-dependent diabetes mellitus.

Although atherosclerotic cardiovascular disease (ASCVD) is the leading cause of death in insulin-dependent diabetics, plasma levels of high density lipoprotein (HDL) cholesterol (an independent "negative" risk factor for ASCVD) have been reported to be normal or high. To test whether alterations in HDL composition might increase potential risk of insulin-dependent diabetics to ASCVD, their major constituent apolipoproteins, A-I and A-II, were measured and compared with levels in controls. HDL cholesterol levels were slightly higher (P = NS) in diabetics than in controls. The HDL cholesterol/LDL cholesterol ratio (an inverse index of relative risk of developing ASCVD) was significantly higher in diabetic men than in controls (P less than 0.02). HDL composition differed markedly in diabetics and controls: the apolipoprotein A-I/A-II ratio was significantly higher (P less than 0.001) in both diabetic men and women (diabetic men--4.1 +/- 0.5, mean +/- SD, controls 3.6 +/- 0.4; diabetic women--4.6 +/- 0.4, controls 3.9 +/- 0.5). Subsequent analysis of plasma from four patients by analytic ultracentrifugation demonstrated a high correlation (r = 0.993, P less than 0.01) between the apolipoprotein A-I/A-II ratio and HDL2, the cholesterol-rich lighter subclass of HDL thought to be the group of particles involved in reduced risk of ASCVD. Therefore, the alteration of HDL composition in insulin-dependent diabetics appears similar to that associated with reduced risk in nondiabetics. Thus, whether a genetic or acquired abnormality, the high apolipoprotein A-I/A-II ratio in insulin-dependent diabetics does not appear to counteract their increased risk of developing ASCVD.

Adolescent↗
PubMed1981

Effect of in-vitro lifespan of 3T3-L1 cells on hormonal responsiveness of lipoprotein lipase activity.

The synthesis and secretion of lipoprotein lipase activity is one marker of the adipocyte state in cultured 3T3-L1 cells. Lipoprotein lipase in these cells is responsive to hormones (insulin and GIP); however, this has not been a constant feature. To determine if in-vitro lifespan or passage number contributes to this responsiveness, cells over an in-vitro lifespan of nine to 22 passages were examined for insulin- and GIP-mediated increases in enzyme synthesis and secretion. Differences in GIP responsiveness between the parent line and 3T3-L1 subclones were also tested. Insulin-mediated release of lipase into the culture medium (P less than 0.02) and the stimulation of heparin-releasable activity from cells by insulin (P less than 0.05) were inversely related to passage number. The responsiveness to GIP also decreased with increasing in-vitro lifespan. Differences between the parent cell and subclones were also seen for GIP. The loss of responsiveness in these cells appears to be associated with an increase in confluent density. There was no relationship between basal lipoprotein lipase activity and passage number. Therefore, the effect of insulin and GIP on lipoprotein lipase activity in 3T3-L1 cells is not a stable property and some caution is required before applying data obtained from these cells to the in-vivo situation.

Adipose Tissue↗