The Clearing Factor Lipase and Its Action in the Transport of Fatty Acids between the Blood and the Tissues

129

A B S T R A C T Plasma transport of free fatty acids (FFA) and triglyceride fatty acids (TGFA) was studied in seven subjects with normal lipid metabolism, one case of total lipodystrophy, and one case of familial hyperlipemia (Type V). Studies were carried out after intravenous injection of radioactive FFA, of lipoproteins previously labeled in vitro in the triglyceride moiety, or both.Computer techniques were used to evaluate a series of multicompartmental models, and a general model is proposed that yields optimum fitting of experimental data for both FFA and TGFA. The results show that as much as 20-30% of FFA leaving the plasma compartment in normal subjects is transported to an exchanging extravascular pool and quickly reenters the plasma pool as FFA. The rate of irreversible delivery of FFA from plasma to tissues averaged 358 AEq/min in normals. The lipodystrophy patient, despite the virtual absence of adipose tissue (confirmed at autopsy), had a plasma FFA concentration and a total FFA transport, both more than twice normal. Total TGFA transport ranged from 25 to 81 MLEq/min in four normal controls.The rate constant for TGFA turnover in the patient with Type V hyperlipemia was so small that total transport could not be quantified from the data available; the TGFA half-life was over 500 min.In two normal subjects given injections of autologous lipoproteins labeled in vitro with triolein-"C and simultaneously given oleic acid-8H, it was shown that the time course for the disappearance of the TGFA in the in vitro labeled samples conformed almost exactly to that of the physiologically labeled lipoprotein TGFA synDr. Eaton's present address is

Section: Plasma Free Fatty Acid and Triglyceride In Man Discussionmentioning

confidence: 99%

Kinetic studies of plasma free fatty acid and triglyceride metabolism in man

Eaton¹,

Berman²,

Steinberg³

1969

129

“…It has long been known that several lipid-binding proteins, such as lipoprotein lipase (LpL) (14), apo E (15,16), and hepatic lipase (17,18), avidly adhere to heparin and to HSPGs. Early studies indicated that LpL can bridge between lipid-rich chylomicrons and endothelial HSPGs, thereby mediating cell-surface attachment of the lipoproteins (19). Subsequently, it was suggested that LpL might be the ligand responsible for hepatic clearance of chylomicrons, though no information was presented about the nature of the putative cellular recognition site (20).…”

Section: Introductionmentioning

confidence: 99%

The syndecan family of proteoglycans. Novel receptors mediating internalization of atherogenic lipoproteins in vitro.

Fuki¹,

Kuhn²,

Lomazov³

et al. 1997

222

215

“…Lipoprotein lipase (LPL) ,' present mainly in adipose tissue and to some extent in other tissues (1)(2)(3), is the rate-limiting enzyme for tissue uptake of plasma triglycerides (TG) (4)(5)(6)(7). In a number of animal studies, adipose tissue LPL has been shown to be sensitive to caloric and hormonal balance (8)(9)(10)(11) and particularly dependent on availability of glucose and insulin (11)(12)(13).…”

Section: Introductionmentioning

confidence: 99%

Determinants of human adipose tissue lipoprotein lipase. Effect of diabetes and obesity on basal- and diet-induced activity.

Pykälistö¹,

Smith²,

Brunzell³

1975

280

106

A B S T R A C T The role of insulin in the regulation of human adipose tissue lipoprotein lipase was evaluated. Adipose tissue heparin-releasable lipoprotein lipase (thought to be related to peripheral clearance of plasma triglycerides) was low in insulin-deficient, untreated hyperglycemic diabetic subjects (P <0.001) and treatment of hyperglycemia returned the activity to normal. In chronic hyperinsulinism, represented by obesity, heparin-releasable activity among control subjects was correlated to percent of ideal body weight (r = 0.53, P < 0.05) and to fat cell size (r = 0.61, P < 0.02).Acetone-ether powder lipoprotein lipase activity (presumed to reflect total tissue enzyme) was also related to percent of ideal body weight (r = 0.76, P < 0.001 for controls; r = 0.67, P <0.05 for diabetics) and to fat cell size (r = 0.71, P <0.01 for controls; r = 0.85, P <0.01 for diabetics. Postprandial-stimulated insulin secretion was related to diet-induced changes in lipoprotein lipase in control subjects; both were dependent upon the amount of dietary carbohydrate. In contrast, the diabetic patients with low insulin responses, failed to increase lipoprotein lipase activity with feeding. The changes in heparin-releasable (r = 0.66, P <0.01) and acetone-ether powder (r = 0.69, P <0.01) activity during feeding were related to the percent increase in plasma insulin.Thus, insulin appears to be important in the regulation of human adipose tissue lipoprotein lipase activity. Elevated insulin levels in obesity and increased insulin secretion after eating were associated with increased lipoprotein lipase activity. Defects in insulin secretion, both in postabsorptive and postprandial states, are asThis study represents a part of the clinical investigation by the late Dr. Olavi J. Pykdlist6 during a fellowship at the Veterans Administration Hospital in Seattle, Wash.