Uptake of individual free fatty acids by skeletal muscle and liver in man

Abstract

A B S T R A C T Arterial-venous concentration differences for individual free fatty acids (FFA) were measured across the deep tissues of the forearm, the splanchnic vascular bed, and the kidney in healthy, postabsorptive subjects. In addition, arterial-portal venous FFA differences were determined in five patients undergoing elective cholecystectomy.The differences in fractional uptake among the individual FFA across the forearm were small and not statistically significant. Splanchnic fractional uptake was high for FFA with short chain lengths and rose with increasing degree of unsaturation. Small, negative arterial-portal venous differences for individual FFA were observed, indicating that arterial-hepatic venous FFA differences mainly reflect hepatic uptake. When the arterial FFA concentration was reduced to approximately 25% of the control values by the administration of nicotinic acid, net uptake of total FFA ceased but there was release of stearic acid and uptake of lauric, myristic, and palmitoleic acid to the splanchnic region. Muscle and liver uptakes of individual FFA were both dependent on their arterial concentrations with the exception of the splanchnic uptake of stearic acid. There was no uptake of free arachidonic acid by either muscle or liver, nor was there significant uptake of any of the free fatty acids by the kidney. It is concluded (a) that there are important quantitative differences between the net exchanges of individual FFA across the splanchnic vascular bed, (b) that tracer studies of FFA metabolism require the determination of individual FFA specific activities, (c) that palmitic and oleic acid appear to be suitable tracers for the entire FFA fraction in most instances.

What Does the Measurement of Whole-Body Fatty Acid Rate of Appearance in Plasma by Using a Fatty Acid Tracer Really Mean?

“…Plasma stearate and myristate clearance rates were lower and higher, respectively, than the clearance rate of other fatty acids, and the use of stearate and myristate tracers underestimated and overestimated, respectively, measured total FFA R a values. Data from earlier studies have shown that the fractional uptake of different fatty acids by forearm tissues was not different, whereas splanchnic myristate uptake was greater and splanchnic stearate uptake was smaller than the uptake of other fatty acids (35,36). In addition, when injected simultaneously into rats, 14 C-stearate disappeared more slowly from plasma than 3 H-palmitate (37).…”

Mechanisms of the Triglyceride- and Cholesterol-Lowering Effect of Fenofibrate in Hyperlipidemic Type 2 Diabetic Patients

“…In addition, plasma FFA levels were decreased by fenofibrate. Because the uptake of fatty acids by the liver is proportional to their concentration in plasma (33), it is probable that the total amount of plasma fatty acids delivered to the liver for oxidation or reesterification was also decreased. Several mechanisms could have contributed to this fall in plasma FFAs.…”

Visceral fat and insulin resistance — causative or correlative?

“…Sampling from the portal vein is not easy in humans, but it has been performed in a small number of metabolic studies. In these studies, concentrations of NEFA or glycerol (another product of lipolysis) in the portal vein have been found to be close to those in arterial plasma (Hagenfeldt et al 1972;Björkman et al 1990;Blackard et al 1993). One example is the study of Blackard et al (1993): during laparotomy in obese women the portal vein was catheterized and samples taken.…”