Net Uptake Of Free Fatty Acids Research Articles

Evaluation of exercise and training on muscle lipid metabolism.

To evaluate the hypothesis that endurance training increases intramuscular triglyceride (IMTG) oxidation, we studied leg net free fatty acid (FFA) and glycerol exchange during 1 h of cycle ergometry at two intensities before training [45 and 65% of peak rate of oxygen consumption (V(O2) peak)] and after training [65% pretraining V(O2) peak, same absolute workload (ABT), and 65% posttraining V(O2) peak, same relative intensity (RLT)]. Nine male subjects (178.1 +/- 2.5 cm, 81.8 +/- 3.3 kg, 27.4 +/- 2.0 yr) were tested before and after 9 wk of cycle ergometer training, five times per week at 75% V(O2) peak. The power output that elicited 66.1 +/- 1.1% of V(O2) peak before training elicited 54.0 +/- 1.7% after training due to a 14.6 +/- 3.1% increase in V(O2) peak. Training significantly (P < 0.05) decreased pulmonary respiratory exchange ratio (RER) values at ABT (0.96 +/- 0.01 at 65% pre- vs. 0.93 +/- 0.01 posttraining) but not RLT (0.95 +/- 0.01). After training, leg respiratory quotient (RQ) was not significantly different at either ABT (0.98 +/- 0.02 pre- vs. 0.98 +/- 0.03 posttraining) or RLT (1.01 +/- 0.02). Net FFA uptake was increased at RLT but not ABT after training. FFA fractional extraction was not significantly different after training or at any exercise intensity. Net glycerol release, and therefore IMTG lipolysis calculated from three times net glycerol release, did not change from rest to exercise or at ABT but decreased at the same RLT after training. Muscle biopsies revealed minor muscle triglyceride changes during exercise. Simultaneous measurements of leg RQ, net FFA uptake, and glycerol release by working legs indicated no change in leg FFA oxidation, FFA uptake, or IMTG lipolysis during leg cycling exercise that elicits 65% pre- and 54% posttraining V(O2) peak. Training increases working muscle FFA uptake at 65% V(O2) peak, but high RER and RQ values at all work intensities indicate that FFA and IMTG are of secondary importance as fuels in moderate and greater-intensity exercise.

AN EVALUATION OF EXERCISE AND TRAINING ON MUSCLE LIPID METABOLISM

1746 To evaluate the hypothesis that endurance training increases intramuscular triglyceride (IMTG) oxidation, we studied leg net free fatty acid (FFA) and glycerol exchange during one hour of cycle ergometry at two intensities before training (45% and 65% ˙VO2peak) and after training (65% pre-training ˙VO2peak, same absolute workload, and 65% post-training ˙VO2peak, same relative intensity). Nine male subjects were tested before and after 9 weeks of cycle ergometer training, 5x/week at 75% ˙VO2peak. The power output that elicited 66.0±1.1% of ˙VO2peak prior to training elicited 54.0±1.7% after training due to a 14.6±3.1% increase in˙VO2peak. Training significantly (p<0.05) decreased RER values at the same absolute workload (0.96±0.01 at 65% pre- vs. 0.93±0.01 post-training), but not the same relative workload(0.95±0.01 at REL). After training leg RQ was not significantly different at either the same absolute (0.98±0.02 pre- vs. 0.98±0.03 post-training) or relative workload (1.01±0.02 at REL). Net FFA uptake was not significantly different at the same absolute workload after training. At the same relative workload, net FFA uptake was greater for the first 5 minutes of exercise after training, but similar to pre-training for the last 45 minutes of exercise. FFA fractional extraction was not significantly different at any exercise intensity or following training. Likewise, net glycerol release did not change from rest to exercise, or at the same absolute and relative workloads after training. Simultaneous measurements of leg RQ, and net FFA uptake by working legs indicated no change in leg fat oxidation, FFA uptake, or IMTG oxidation during leg cycling exercise that elicits 65% pre-, and 54% post-training ˙VO2peak. The high RER at all work intensities indicate that FFA and intramuscular triglycerides are of secondary importance as fuels in moderate and greater intensity exercise.

Hemodynamics and metabolism of the in vivo vascularly isolated canine pancreas.

Surgical procedures are detailed that have yielded for the first time an in vivo vascularly isolated, autoperfused preparation of the entire pancreas in anesthetized dogs. Previous studies had isolated only part of the pancreas or had resorted to blood-flow techniques not requiring pooled pancreatic venous blood, necessary for metabolic studies of the organ. Pancreatic blood flow (48 ml/min), O2 uptake (180 mumol/min), glucose uptake (51.0 mumol/min), lactate output (6.6 mumol/min), net free fatty acid uptake (2.23 mumol/min), all per 100 g tissue, and various other measured and calculated hemodynamic and metabolic variables were determined on the preparation during control conditions. The stability of the preparation was verified by serial determinations of these parameters and of blood alpha-amylase and beta-glucuronidase levels from 1 to 2.5 h postsurgery. Metabolic rate and glucose uptake were both found to be much higher than in intestinal tissues and approached values characteristic of liver tissue.

Exercise-and post-exercise metabolism of the lower leg in patients with peripheral arterial insufficiency.

Exercise- and post-exercise metabolism were studied in the lower legs of six subjects without known arterial insufficiency and in sixteen claudicants. Lower leg blood flow was measured with a thermodilution catheter in the popliteal vein. The catheter allowed blood sampling from the calf before, during and after an exhaustive, stepwise increasing load exercise on a bicycle ergometer. A higher oxygen extraction and higher lactate release during exercise in claudicants than in normal subjects persisted in the post-exercise period (P less than 0.05). Leg arteriopoplitealvenous differences of free fatty acids (FFA) showed an inverse intergroup relationship to that of glucose. Being higher in claudicants than in normal subjects during exercise (P less than 0.05). However, net uptake of FFA was not significantly different in the groups of legs although it appeared increased relative to glucose in claudicants both during and after the exercise. Thus no statistically significant substrate preference was detected although the results suggests a preference for FFA relative to glucose in legs with arterial insufficiency. The study furthermore demonstrated the lag of exercise metabolism into the post-exercise period in such legs and a close relationship between this metabolic delay and the severity of the disease.

Changes in the metabolism of the shivering hind leg of the young ox during several days of continuous cold exposure.

The effect of 4 days of continuous exposure to a cold environment on blood flow in, and oxygen and energy substrate uptake by the shivering hind leg has been studied in young steers. The animals shivered throughout the period of cold exposure and total oxygen consumption (total VO2) remained 40-50% greater than VO2 during thermoneutrality. Leg blood flow (leg Q) and oxygen uptake (leg VO2) increased two- and four-fold respectively on the first day of cold. Both had declined significantly by the final day, leg Q to a level 37% greater than, and leg VO2 to about double, pre-cold levels. The change in the relationships of leg Q and leg VO2 to total VO2 was examined by linear regression analysis, which suggested that the changing contribution of leg VO2 to total VO2 was entirely due to changes in leg Q, rather than in the arteriovenous difference in blood oxyhaemoglobin saturation across the leg. The net uptakes by the leg of free fatty acids (FFA), acetate, glucose and lactate all increased on the first day of cold. Both glucose and acetate uptakes were greater on day 4 than on day 1 in the cold, in spite of the lower leg VO2, but net uptakes of FFA and lactate were considerably lower. The decrease in net uptake of FFA is attributed mainly to an increase in the rate of lipolysis and release of FFA from fat depots in the leg, because of the associated progressive increase in the release of glycerol and oleic acid from the leg. The molar ratios of net carbohydrate substrate, acetate and FFA uptakes to leg VO2 are compared. The results suggest that tissues other than the leg muscles become increasingly important as sites of heat production, and that there are changes in the utilization of glucose, acetate and FFA by shivering muscle, during prolonged cold exposure.

Effects of Cold Exposure and Feeding on Net Exchange of Plasma Free Fatty Acids and Glycerol across the Hind Leg of the Young Ox

Hind leg blood flow (leg Q) and oxygen uptake (leg VO 2 ) and net exchange of free fatty acids (FFA) and glycerol between the leg and the rest of the body was measured in young steers fed either 3 h or 20 h before exposure to a thermoneutral or a moderately cold environment. Cold exposure caused a 10-fold increase in leg VO 2 in both feeding groups, and a highly significant change from net output to net uptake of FFA by the leg in the 20 h-fed, but not the 3 h-fed animals. Net exchange of glycerol was not significantly affected by cold or feeding.

Utilization of exogenous free fatty acids for the production of very low density lipoprotein triglyceride by livers of carbohydrate-fed rats

High carbohydrate diets enhance the hepatic output of very low density lipoprotein triglycerides. The fatty acids of these triglycerides could come from exogenous sources (i.e., diet or adipose tissue) or from de novo fatty acid synthesis in the liver. The role of exogenous free fatty acids was evaluated in rats fed Purina Chow or diets containing 10% fructose for up to 14 wk. In carbohydrate-fed rats, serum triglycerides were twice normal, and VLDL accounted for about 60% of the increases. Pre-beta-lipoprotein was increased and alpha- and beta-lipoprotein were decreased. Phospholipid and cholesterol levels were unchanged. Livers were perfused with glucose and free fatty acids. Perfusate free fatty acids rose from 180 to 1800 micro eq/liter as the infused acids increased from 0 to 992 micro eq/3 hr; simultaneously, net free fatty acid uptake rose from < 1 to 18 micro eq/g/hr and triglyceride output by the liver doubled. However, rates of secretion of triglyceride became constant, and triglyceride accumulated in liver at uptakes of free fatty acids > 13 micro eq/g/hr. More lauric and myristic acid appeared in the perfusate than was infused, suggesting the hepatic discharge of free fatty acids. Livers of fructose-fed rats secreted twice as much oleate-(14)C-labeled triglyceride as controls at all levels of free fatty acid uptake. The ratios of the specific activities of perfusate triglyceride to free oleate-(14)C were unaffected by diet and were about 0.6 and 1.0 at low and high triglyceride secretion rates, respectively. Thus, carbohydrate feeding did not result in altered uptakes of free fatty acids or preferential secretion of triglycerides containing endogenously synthesized fatty acid. Instead, the increased secretion of triglyceride was accomplished by enhanced formation of VLDL triglyceride from exogenous free fatty acids.