Acta mttd. scand. Vol. 185, pp. 351-356, 1969

PLASMA FREE FATTY ACID TURNOVER RATE IN OBESITY

Per Bjorntorp, Halvar Bergman and Edvardas Varnauskas

From the First Medical Service, Sahlgrenska Sjukhuset, University of Goteborg, Goteborg, Sweden

Abstract. Free fatty acid turnover rate was measured by constant infusion of 1-"C palmitic acid complexed to human albumin in eight extremely obese patients and in seven controls after a 12-hour fast. In some of these patients these measurements were performed also during work, in a few of the obese patients before and after physical training. The results were expressed in relation to different body compartments. It was found that free fatty acid turnover rate was higher a t rest in the obese than in controls. This difference disappeared when free fatty acid turnover rate was calculated per kg body weight or per kg body fat. When calculated per kg lean body mass. however, the obese patients again had higher values of free fatty acid turnover rate than the controls. During a standard work load the obese did not show lower free fatty acid turnover rates during work than the controls, even if the increase in two of the obese patients, who had a high turnover rate at rest, was small during work. The results thus give no evidence of a decreased fatty acid turnover rate in obesity. On the contrary, after fast- ing for 12 hours it seems to be higher than normal.

The metabolism of th:: e:ilarged adipose tissue in obesity has attracted much interest, not least concerning the mobilization of fat. During fasting the free fatty acids (FFA) of plasma originate mainly from adipose tissue, and consequently the plasma FFA have been studied repeatedly in obesity.

Dole (10) found fasting venous levels of FFA in obese patients apparently proportional to the degree of obesity. Gordon (15) later confirmed the high FFA levels in obesity. Klein et al. (20) on the other hand found an inverse correlation be- tween FFA in plasma and body size in a material which included no extremely obese patients. Gordon (15) reported a delay in FFA increase during prolonged fasting. This was later confirmed by Opie and Walfish (25) and was interpreted as a deficient FFA mobilization in obesity.

Measurements of FFA after different stimuli

for their mobilization, other than fasting, have also been repeatedly made in obesity. Epinephrine injections have been tried (26), as well as exposure to cold (13), and in a few investigations the effect of exercise on FFA has been studied in obesity as a more physiological stimulus to adipose tissue mobilization. Opie and Walfish (25) found a diminished response of FFA in plasma after a short period of exercise. Klein et al. (20) observed a damped FFA curve in obese patients during exercise, similar to that of patients given glucose. Issekutz et al. (1 8), however, recently found no evidence of a decreased increment of FFA con- centration in obese patients during work.

Several factors complicate the interpretation of adipose tissue lipid mobilization from the FFA concentration in plasma. First, this level is dependent not only on the production of FFA from depots, but also on the outflow of FFA to consuming tissues. Second, the FFA production from adipose tissue is the resultant of lipolysis and reesterification, and these two processes are regulated by different mechanisms which to a large extent are independent of each other. Third, interpretations of hormonal and substrate controls of adipose tissue metabolism are easier when the amount of active tissue taking part in lipid mobilization is known, viz. the size of adipose tissue depot and its cellularity.

Attempts have been made to circumvene these difficulties by studies of adipose tissue in vitro. Such studies have shown that lipid mobilization is decreased in obesity per unit of adipose tissue weight, while fatty acid outflow and lipolysis per adipose tissue cell are not abnormal (6). If one assumes an increased number of fat cells in the obese patients studied, and the in vitro results are extrapolated to the situation in vivo, this would

Acta med. scand. 185

352 P . Bjorntorp e tal .

Table I. Clinical data of controls and obese patients

Figures within brackets: determinations according to (21,22). __-

Leanb body

Age Height Weight Weight Body fatb mass Pat. Sex (y.) (cm) (kg) indexa (kg) (kg) Comments

Controls F. L. 6 J . A . 6

K. 0. 6 R.A. 6 A. J. 6 F. R. 6

W. B.-B. 6

MeanfS.E.M:

Obese patients B. B. 6 I .G . 9 M.W. ?

F. I<. 6 R . G . p

L. M. <?

K . W . 3

H. J .

Mean i s.F.M.:

45 27 32 50 41 32 61

29 19 46

45 60

47

71

31

182 180 171 I83 I77 173 171

183 170 155

182 165

173

162

I70

74 1.01 71 1.04 65 1.15 75 1.01 68 1.01 80 1.21 80 1.23

7 3 k 2 1.09+0.04

17 16 17 17 (15) 16 25 26

19+26

130 1.76 47 (49) 134 2.23 60 76 1.52 34

107 1.46 35 103 1.84 45

100 1.64 37

113 2.10 54 (54)

1 1 1 1.85 40 (38)

109+6 1.80f0.09 4 5 2 3

57 55 48 58 52 55 54

5 4 i 1

83 74 42

72 58

63

59

65

65+4

-

Athlete in good physical condition

Ischemic heart disease Paroxysmal atrial fibrillation Slight hypertension? Ischemic heart disease

-

Obese since childhood. Heredity for obesity Obese since childhood. No heredity Slow weight increase during last 15 years.

Obese during last 10-15 years. No heredity Obese since 30 years. Sharp weight increase during last 3 years because of immobilization. Heredity for obesity

No heredity

Slight hypertension.

No heredity

No heredity

Successive increase during last 20 years.

Obese since childhood. Heredity of obesity.

Obesity after pregnancy 10 years ago.

a Actual weightiideal weight (23). Calculated from weight and height according to ( I I ) .

mean a high FFA concentration and turnover rate.

It is necessary to know in detail the nature of lipid mobilization on the cellular level in order to be able to interpret measurements of plasma me- tabolites originating from this process in adipose tissue. This is particularly the case in studies in man, whose adipose tissue cell lipid mobilization is quantitatively and qualitatively different from that of the rat epididymal fat pad (3 , 5, 8). Studies in vitro are, however, subject to obvious limita- tions for interpretations of the conditions in vivo because of e.g., the absence of regulation of adipose tissue blood perfusion and of circulating homeostatic factors.

In the present work FFA turnover rate has been determined during fasting in obese patients at rest and in a few patients during work. The results have been expressed in relation to different

Acio med. scand. 185

body compartments. A preliminary report on this study has been given previously (2).

MATERIAL

Eight patients with an extreme degree of obesity were selected for study. Their clinical data are listed in Table 1. Two were men and six women, age 29-71 (mean 44) years. Their body weight surmounted that considered ideal (23) by at least 46 per cent. Their body fat, calculated from weight and height according to Edwards and Whyte ( I l ) , was more than twice that of the controls. Their estimated lean body mass was also significantly higher than that of the controls (P < 0.05). One of these patients also had a slight hypertension. None was clinically diabetic and thus showed no glucosuria or fasting blood glucose below 80 mg per 100 ml. All had an intravenous glucose tolerance test with a K-value (14) above 0.81. It is also evident from Table I that patients both with a rather late onset of obesity during life and an obesity from early childhood are included.

Seven control patients comprised a material for com-

Plasma free fat ty acid turnover rate in obesity 353

Table 11. FFA concentration and turnover rate at rest and during work in obese patients and controls Figures within brackets denote conditions after physical training

Increase of Lactate Oxygen FFA turnover FFA turcover FFA turnover during consumption

FFA at rest rate at rest rate during work rate by work work during work Pat. (,uEq/l) (IcEqimin) (pEq/min) ( % of rest) (mg %) (mlimin)

Controls

F. L. J . A.

K. 0. R. A. A. J . F. R .

Mean i s.E.M.:

Obese patients

B. B.

I . G.

M. W.

F. K . R. G. L. M . K . W. H . J.

M e a n f s . ~ . ~ . :

W. E.-B.

300 280 800 550 594 889 602

573 -k 86

560

930

890

905 1154 954 950

1060

(690)

(622)

(963)

925 61a

341 282 676 470 541 850 376

505 C 76

876 (776) 1223 (953) 617

(870) 895

1305 1423 710 847

9 9 4 t l O l a

I240 622 968

1040 - - -

1063 (735) 1460 (960) 1010

( 1440) - - - - -

1500 1664 1669 I392 - - -

I738 (1601) 1755

(1324) 1094

(1 032) - - - - -

(’ P 0.01, Comparison with controls.

parison. These were all men, age 27-61 (mean 41) years. All had a body weight index not exceeding 1.23. Two patients had signs of ischemic heart disease, two others were submitted for minor illnesses of presumably no importance for the present study. The remaining three controls were volunteers not admitted to the hospital.

METHODS All patients except the obese M. W., K. W. and H. J. and the controls F. L., J. A. and W. B.-B. were admitted to the hospital and instructed to eat a 2500-3000 cal.,’day or- dinary diet with a caloric composition of 20% protein, 30- 35% fat and 40-50% carbohydrate. The patients in- vestigated under outpatient conditions ate an ordinary diet with presumably similar calory composition (cf. 9) without restrictions and were in caloric balance as judged from weight histories.

After a 12-hour fast one polythene catheter was in- troduced centrally into a brachial vein and one short catheter into one brachial artery with the patient in lying position. These catheters, free from heparin or other anticoagulant, were then kept open by frequent flushing with normal saline. ECG and intraarterial blood pressure were continuously monitored and recorded at 2 min intervals. Patients who were exercising were also sub- jected to measurements of oxygen consumption as de- kcrihed previously (27).

23 (iD”93

When all catheters were in place, and with the patients sitting in a chair, a constant infllsion of radioactive palmitate, complexed to human albumin, was started through the venous catheter. The rate of infusion was approximately 0.05 ,uC per min, determined exactIy in each patient, with an initial dose of 0.5 PC, given during approximately three min. The radioactive palmitate solu- tion was prepared under sterile conditions in the followin2 way. The solvent in the ampoule with 0.1 mC 1-”C palmitate (CFA 23, The Radiochemical Centre, Amersham, England) was evaporated under nitrogen. The contents were then dissolved in 1-2 ml absolute ethanol and about 0.5 ml 0.02 N NaOH. This was then evaporated on a boiling water bath just to dryness. Ten ml of 20% human serum albumin (Kabi, Stockholm, Sweden) were then added and the contents thoroughly mixed. One ml of this solution was then diluted in 100 ml normal saline just before the experiment.

At least 30 min after insertion of catheters, three blood samples were taken from the arterial catheter into hep- arinined tubes with an interval of 10 min between each. Part of this blood was immediately taken for blood lactate determination (1) and the rest then directly cooled and centrifuged for determination of FFA (12) and separation of FFA (16) for determination of radioactivity in this fraction.

After these initial procedures the exercising patients performed a work of 600 kpm/min (men) or 400 kpm/

Acta med. srand. 185

354 P . Bjorntorp e ta l .

Table 111. FFA turnover rutes in relation to diyerent body coniparttnents in controls and obese pateitits

FFA turnover FFA turnover FFA turnover FFA turnover rate rateikg body weight rateikg fat rateikg lean body mass (pEq/inin) (pEq/min) (trEq/min) (flEq/min)

Controls 505 2 76 6.9f 1.0 26.7k3.6 9.5+ 1.5 Obese pa!ients 994L 101 9.2f1.0 22.9 2.8 15.75 1.6

P . 0.01 Not significant Not significant P. 0.02

min (women) during 30 min sitting on an ergometer bi- cycle. Blood samples were taken at the 5th, loth, 20th and 30th min of work and then at 5 , 10, 20 and 30 min after work with the patient a:ain sitting in a chair.

FFA turnover rate was calculated as described by Have1 et al. (16). Three of the obese patients (B. B., 1. G. , M. W.) were subjected to physical training by a procedure described previously (27) and were thereafter reexamined in a similar way.

Body fat and lean body mass were calculated from weight ( W ) and height ( H ) utilizing the regression equation (0.18 ( W / H ' x 10') - 23.2) obtained by Edwards and Whyte (11) by comparison between W / H 2 and body compartment determinations with antipyrin space. In some instances determinations of body compartments were also performed with the aid of total exchangeable potassium and total body water according to the techniques and calculations utilized by Moore et al. (24) as modified by Lindholm (21, 22).

RESULTS Table I1 presents the results of FFA turno;ler as a mean of the three samples at rest and the mean of the two last samples during work. FFA con- centration as well as turnover rate of FFA at rest was significantly higher in the obese patients thnn in controls. The oxygen uptake during work did not show much difference between the obese and the controls. As a matter of fact the averages are very similar: 1556 and 1529. During this work load the FFA turnover was apparently not lower in the obese patients than in the controls. The increase from resting values was limited in the obese patients, who had a high FFA turnover rate at rest (B. B. and I. G.). Physical training in thesz two patients lowered the lactate concentration during work, but did not increase FFA turnover rate during work. Patient no. 3 (M. W.) showed no decrease in lactate after training.

Table 111 gives the results of resting FFA turn- over rate determinations in relation to different body compartments. It is seen that even if the total turnover rate of FFA is increased in the

Aria med. scand. 185

obese patients, the turnover rate of FFA per kg body weight is not increased. Nor is it increased when calculated per kg body fat. Per kg lean body mass, however, the obese patients showed a sig- nificant increase in FFA turnover rate.

DISCUSSION

It hzis been, shown both in the dog and in non- obese man (17) that the plasma FFA concentr'i- tion correlates well with FFA turnover rate. Plasma FFA concentration is the result of an FFA inflow rate from adipose tissue and an outflow rate to fatty acid consuming tissues. Wide in- dividual variations in the quantitative relation- ship between these two types of tissues may be suspected to influence the correlation between FFA concentration and FFA turnover rate. Thi\ has also been demonstrated by Issekutz el al. ( 1 7) who have shown that, at the same plasma FFA concentration, obese patients had a higher turnover rate than normal subjects, and the latter higher than dogs presumably with less adipose tissue than humans. Therefore, it is not directly possible to interpret plasma FFA concentration in obesity a$ a measure of lipid mobilization in comparisons with non-obese controls.

The material of obese patients consisted mainly of women, while the controls were exclusively men. In vitro adipose tissue from both sexes does not show any differences in lipid mobilization (8). I t seems unlikely that this difference in composition of the two materials should be of any significance.

The present work thus shows that FFA turn- over rate at rest is increased in obesity. This has recently also been found by Issekutz et al. (17). When expressed per kg body weight, however, there was no difference between the plasma FFA turnover rate of obese and controls.

Calculations of body compartment weights ac-

Plasma free fat ty acid turnover rate in obesity 355

cording to the regression equations of Edwards and Whyte (11) are subject to uncertainties, as pointed out by these authors. The results of these calculations were checked in some patients in the present work by determinations of total body fat with the aid of total body water and exchange- able potassium (21, 22, 24), and were in these cases found to agree fairly well. Until more reliable determinations are available, these results have to he interpreted as preliminary. They appear to show that the FFA turnover rate is the same per kg adipose tissue weight in obese patients and in controls. Per kg lean body mass, however, the turnover rate of FFA seems to be increased in the obese cases.

These results then suggest that lipid mobiliza- tion in obesity is not decreased during fasting. On the contrary it is higher than in non-obese humans. The FFA consuming tissues, presumably comprising the main part of the lean body mass, are thus furnished with a surplus of FFA. The present study also suggests that FFA turnover rate per kg adipose tissue is similar in obesity and in controls. Obese patients usually have fewer fat cells per unit weight of adipose tissue than con- trols (7). Taken together, this indicates that when FFA turnover rate is calculated per fat cell there does not seem to be a deficient lipid mobilization i n obesity either. This is in general agreement with findings in vitro (6), but this question needs further penetration before more quantitative conclusions can be drawn.

When measurements were performed during work the patients were in circulatory stexdy state. FFA fluxes were also reasonably stable but the lactate concentration was usiially in a decreasing phase.

Previous studies of FFA mobilization in obesity during work have been performed on the basis of FFA concentrations and not with measurements of FFA turnover rate (18, 20, 25). The difference in correlation between FFA concentration and turn- over rate between obese and controls has been discussed above. Furthermore, during work frac- tional turnover rate of FFA increases abruptly (9), producing a decrease in FFA concentration. The FFA concentration may therefore be misleading a s an index of FFA mobilization during work, and comparisons between obese patients and controls may be difficult.

The present investigations during exercise are

few and allow only limited conclusions. These ex- periments do not indicate a decreased lipid mobilization in the obese patients during exercise since the FFA turnover rates were apparently not lower in the obese during a standard work load.

The increment of FFA turnover rate during work was small in two obese patients (B. B. and I. G.), who showed high resting FFA turnover rate values. Inhibition by lactate of FFA turnover rate increase during work might be discussed, since both lactate infusions (19) and lactate in in vitro systems (4) inhibit lipid mobilization. This explanation is not likely, however, since these two patients did not increase their F F A turnover rate during the same work load after physical training, when the lactate increase was smaller.

In conclusion, this work has given no evidence to indicate a decreased lipid mobilization in obesity at rest or during work. On the contrary, at rest, lipid mobilization seems to be increased, perhaps also when expressed per unit lean body mass. FFA turnover rate per kilogram body weight or adipose tissue did not seem different in obese patients and controls. The conclusions, including measurements of body compartments, must so far be considered as only preliminary. Whether the increase in FFA turnover rate in obese patients is due to an increased lipolysis or a deficient FFA reesterification in adipose tissue is the subject for current studies.

ACKNOWLEDGEMENT

Supported by a grant from the Swedish National AFsocia- tion Against Heart and Chest Diseases.

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