Effect of exercise on splanchnic exchange of free fatty acids

Effect of Exercise on Splanchnic Exchange of Free Fatty Acids By Lars Hagenfeldt Splanchnic

exchange

of free

fatty

The A-HV significantly

acids

(FFA) was studied in seven healthy male subjects at rest and during bicycle exercise at 700-900 kg-m/min following arterial and hepatic venous catheterization. The arterial-hepatic ence correlated

differed creased hepatic

correlated level. A

FFA difference did not differ from zero during exercise and negatively to the arterial lactate net release of FFA from the

splanchnic area was observed under extreme exercise condition with low FFA

venous

(A-HV) FFA differsignificantly with arterial

FFA both at rest and during regression lines for rest

and John Wahren

levels and arterial lactate liter. It is concluded that

exercise. The and exercise

above 5 mmole/ the net splanch-

nit FFA uptake is reduced permitting a redistribution

significantly, indicating an inrelease of FFA from the extrasplanchnic area during exercise.

FFA turnover tion

by

towards

during exercise of the body’s

greater

FFA utiliza-

muscle.

free fatty acids T IVER AND MUSCLE are the two main tissues utilizing k (FFA) in the postabsorptive state in man. During exercise the uptake and oxidation of FFA by muscle are known to be markedly augmented.6~8~” Studies in rats have shown that the uptake of FFA by the liver is lower during exercise,13 but little information is available on the FFA metabolism of the splanchnic area during exercise in man. l4 The arterial-hepatic venous (A-HV) FFA difference is determined both by the uptake of FFA in the liver and by the exchange of FFA in the extrahepatic spianchnic region.’ The latter comprises a considerable amount of adipose tissue, which is known to be invoIved in the regulation of FFA metabolism during exercise.3 Furthermore, the reduction of splanchnic blood flow during physical exertion may influence FFA exchange in the splanchnic region. With this background, arterial-hepatic venous differences in FFA and hepatic blood flow were examined in a group of healthy subjects at rest and during exercise. Since lactate has been claimed to influence FFA mobilization from adipose tissue during exercise,12 the results were compared with the simultaneous changes in arterial lactate levels. MATERIALS

AND METHODS

Seven healthy, male volunteers (mean age 28 yr, range 23-32 yr; length 178 cm, range 176-185 cm; weight 74 kg, range 71-78 kg) were studied in the morning after an overnight From the Departments rettet, Stockholm, Sweden. Received

for publication

Supported

by Swedish

of Clirrical Chemistry November Medical

and Clinical

Physiology,

Serafimerlasa-

I, 1972.

Research

Council

Grant

79x-722.

Professor, Karolinska Institute, Department of Clinical Chemistry, Serafimerlasareftet, Stockholm, Sweden. John Wahren, M.D.: Assistant Professor, Karolinska Institute, Department of Clinical Physiology, Serafimerlasarettet, Stockholm, Sweden. Reprint requests should be addressed to Lars Hagenfeldt, M.D., Department of Clinical Chemistry, Karolinska Hospital, S-104 07 StockhoIm, Sweden. @ 1973 by Grune & Stratton, Ins.

Lars Hagenfeldt,

Metabolism,

M.D.: Assistant

Vol. 22, No. 6 (June), 1973

815

818

HAGENFELDT

AND WAHREN

fast of 12-14 hr. Catheters were inserted precutaneously into a brachial artery and-under fluoroscopic control-into a right-sided hepatic vein. Hepatic blood flow was estimated using the continuous infusion technique and indocyanine green dye, as described elsewhere.17 Blood samples were drawn simultaneously from the arterial and the hepatic venous catheter in the supine position at rest for analysis of FFA, lactate, and indocyanine dye. Exercise was performed in the sitting position on a bicycle ergometer at work loads of 700-900 kg-m/min. Blood samples were collected after 12-18 min exercise. In six subjects, the exercise procedure was repeated after a rest interval of 30-45 min giving a total of 13 observations during exercise. FFA was measured by gas chromatography,’ and lactate was analyzed using a enzymatic procedure.16 Indocyanine green dye was measured spectrophotometrically in plasma at 805 nm. Statistical comparisons between rest and exercise were done using Student’s t test. Values in the text are mean & SE.

RESULTS The results are summarized in Table 1. At rest there was a positive correlation between arterial FFA and the arterial-hepatic venous (A-HV) FFA difference (r = 0.89, p < 0.01, Fig. 1). Neither the estimated hepatic blood flow (EHBF) nor the arterial lactate correlated to the A-HV FFA difference at rest. During exercise, a sevenfold rise in arterial lactate (~7 < 0.001) was accompanied by a fall of ERBF to about half the resting level (p < 0.001). Arterial FFA was lowered during exercise (p < 0.001) and the mean A-HV FFA difference did not differ significantly from zero. The rate of splanchnic FFA uptake amounted to 152 * 22 pmoles/min at rest and fell to 53 -C 24 pmoles/min during exercise. The relationship at rest between the A-HV FFA difference and arterial FFA was maintained during exercise but the regression line was different, with a higher regression coefficient (p < 0.01) and a

Table 1. Estimated

Hepatic Blood Flow (EHBF,

and Arterial-Hepatic Venous Differences (FFA, ~molelliter) and Lactate (mmole/liter)

ml/min),

Arterial

Concentrations

(A),

(A-HV) for Free Fatty Acids at Rest and During Exercises

in Seven Healthy Subjects Exercise

Rest FFAA

FFAA-HV

EHBF

LactateA

FFAA

FFAA-HV

0.81 0.87

822 308

221 103

818 607

738

498 -27 5

1470

0.63

495

175

4

1152

0.82

427

116

5

1531

0.55

775

213

6

1447

1.23

762

180

7

1142

0.78

684

310

Mean SEM

1381 69

0.73 0.09

639 85

188 26

2.05 5.51 4.65 2.74 2.28 4.42 6.42 2.65 8.07 5.71 4.86 7.41 10.17 5.00 0.64

Exp.

EHBF

1 2

1811 1314

3

Lactate*

615 1042 1019 635 496 1088 594 433 368 403 363 654 72

105 142 497 566 469 141 700 242 326 340 204 216 360 60

197 360 105 7 216 33 -57 36 -74 -102 92 50

EFFECT OF EXERCISE

1. Regression

Fig.

ON SPLANCHNIC

EXCHANGE

817

OF FFA

of the arterial-hepatic

venous (A-HV) FFA difference on arterial FFA at rest (open circles) and during exercise (solid circles). for rest, Y = 0.276X

Regression equations: + 12 (n = 7, r = 0.89,

p < 0.01) for exercise, (n

=

Y = 0.725X

-

169

13, r = 0.87, p < 0.001).

significant intercept of 234 pmole/liter on the X axis (p < 0.01, fig. 1). Furthermore, arterial FFA and the A-HV difference both correlated negatively to arterial lactate and positively to the EHBF during exercise (Table 2). The multiple regression equation of the A-HV FFA difference on arterial FFA and arterial lactate was FFAA-HV = 0.45 FFAA - 33.7 LaA + 97.8 (R = 0.91), both regression coefficients differing significantly from zero (p < 0.02 for FFAA and p < 0.05 for LaA). The inclusion of EHBF as a third independent variable had little influence on the mean square of the deviations. Data for the individual FFA during exercise are presented in Table 3. A significant A-HV difference was noted for Iauric, myristic, and palmitoleic acids. The regressions of the A-HV differences on the arterial concentrations were significant for all of the individual FFA.

DISCUSSION

The present results demonstrate that the splanchnic uptake of FFA during exercise, as reflected by A-HV FFA differences, is correlated not only with the arterial level of FFA, as at rest, but also with arterial lactate and the EHBF. The high degree of intercorrelation between these four variables (Table 2) complicates an interpretation of the results. The negative correlation

Table

2. Correlation

Coefficients

(r) Between

the Arterial

Concentrations

(A) of Lactate

and FFA, the Arterial-Hepatic Venous (A-HV) Difference of FFA, and the Estimated Hepatic Blood Flow (EHBF) During Exercise (p < 0.01 for all r) EHBF

EHBF LactateA FFAA FFAA-xv

(1) -0.83 0.74 0.78

LactateA

FFAA

(1) -0.76 -0.84

(1) 0.87

FF*A-HV

(1)

818

Table

HAGENFELDT 3. Arterial

Concentrations,

Regression Coefficients Arterial Concentrations

FFA

Arterial Concentration (pmole/liter)

12:o

6-c

14:o 16:O

2

13k 3 109 -c’l5

16:l

202

5

18:O 18:l

33-c 3 134 k 25

18:2 Total FFA

45k 5 360 k 60

Arterial-Hepatic

Venous

(A-HV)

AND WAHREN

Differences,

and

the

(b) for the Regressions of (A-HV) Differences on for Individual Free Fatty Acids During Exercise* A-HV (pmole/liter)

4.6 ?I 9.2 k

1.4 2.5

P

b

P

< 0.01

1.04 1 .oo

< 0.001

0.73

< 0.001

0.86

< 0.001

0.43 0.63

< 0.05 < 0.001 < 0.01

< 0.01

28.3 -c 15.0 12.9 ?I

4.3

< 0.02

-1.9 ? 2.3 29.4 2 18.7 9.4 -c 6.7

0.88 0.73

91.9 2 49.6

< 0.001

< 0.001

*Data are given as mean 2 SE (n = from zero for the (A-HV) differences

13). P indicates the probability that the deviations and the regression coefficients are caused by

random

acids

double

factors.

The

individual

fatty

are

denoted

by

chain

length:

number

of

bonds.

between arterial lactate and EHBF should not be taken to imply a causative relationship between these two variables as it is likely to be due to their mutual dependence on the relative work intensity. The same reservation may also apply to the negative correlation between the arterial levels of lactate and FFA. A similar correlation has been reported for exercising dogs of lactic acid elicited by Issekutz and Miller,‘” who also found that infusion a decrease in circulating FFA. They concluded that the fall in plasma FFA during exercise was caused by the rise in blood lactate. Subsequent in vitro experiments have demonstrated that lactate may inhibit the release of FFA has also been reported for exercising man from adipose tissue. 2,5 A correlation between the fall in FFA in the first minutes of exercise and the simultaneous “excess lactate.“4 However, the turnover of FFA is increased even during the initial phase of exercise, when lactate production is high,6 and both these variables are probably related to work intensity. Thus the relative importance of elevated lactate levels and augmented FFA utilization by muscle as determinants of the plasma FFA concentration in man during the initial phase of exercise remains to be etablished. Similar arguments apply to the negative correlation observed in the present study between arterial lactate and A-HV FFA differences during exercise. Multiple regression analysis showed, however, that arterial lactate still influenced the A-HV FFA difference even when allowance was made for the effect on this correlation of arterial FFA. The relative importance of arterial lactate and FFA as determinants of the A-HV FFA difference was evaluated from estimate the their standard partial regression coefficients. l5 These coefficients change in the dependent variable-as a fraction of its variance-produced by l-SD change of the independent variable. The coefficient for arterial FFA was 0.54 and for arterial lactate 0.43, indicating a somewhat greater influence from arterial FFA than for lactate on the A-HV difference of FFA during exercise.

EFFECT OF EXERCISE

ON SPLANCHNIC

EXCHANGE

OF FFA

819

It is also noteworthy that these two variables together account for almost the entire variability in splanchnic FFA uptake during exercise. The question remains whether the dependence of A-HV FFA differences on lactate levels is a direct effect of the lactate or whether it reflects some mutual relationship with other variable(s) not included in the present study. This problem is further complicated by the fact that the splanchnic area is inhomogeneous with regard to its FFA metabolism, the hepatic uptake of FFA being accompanied by an exchange of FFA in the extrahepatic splanchnic tissues.’ At rest, the A-HV FFA difference mainly reflects hepatic uptake,“’ but this does not appear to be the case during exercise, since a net release of FFA from the splanchnic region was observed in some subjects. By analogy with changes in the uptake of FFA by skeletal muscle during exercise,“.” it may be argued that the decreases in arterial FFA and EHBF elicited by exercise could have increased the fractional uptake of FFA (the A-HV difference of an FFA tracer divided by its arterial concentration). Support for this interpretation is obtained from the regression lines in Fig. 1, the higher regression coefficient during exercise possibly reflecting an increased fractional uptake. The positive intercept on the X axis of the exercise regression line implies an increased release of FFA from the splanchnic area, probably from extrahepatic tissues. It is reasonable to assume that this augmented release of FFA is dependent on the relative work intensity, mediated by sympathic nervous activity and/or circulating catecholamines. This would mean that the negative correlation observed between arterial lactate and the A-HV FFA difference could be explained on the basis of their mutual dependence on work intensity. High lactate levels were thus associated with augmented release of FFA from the extrahepatic splanchnic region. This finding further underscores the uncertainty inherent in interpreting the negative correlation between the arterial levels of lactate and FFA as being due to an inhibition of the release of FFA by lactate, as discussed above. As a result of the simultaneous decrease of the A-HV FFA difference and the EHBF during exercise, the rate of net splanchnic FFA uptake fell to about one-third of the resting value, thereby permitting a redistribution of the total body FFA turnover towards preferential utilization by the exercising muscle. For the entire group the A-HV FFA difference during exercise did not differ significantly from zero. Under extreme exercise conditions with low arterial FFA and lactate levels above 5 mmole/liter there was a net release of FFA from the splanchnic region. Further studies are, however, required to evaluate the quantitative importance of the interrelationship between these variables in determining the turnover and distribution of FFA mobilization during exercise. At rest there are considerable differences in the uptake of individual FFA in the splanchnic area. lo The fractional uptake has been shown to decrease as the chain length increases and to be higher for unsaturated fatty acids than for saturated acids of the same chain length. Similar differences in splanchnic uptake among the individual FFA were also observed during exercise. The

820

HAGENFELDT

AND WAHREN

coefficients for the regression of A-HV differences on arterial concentrations were greater for all the individual FFA than the corresponding values reported earlier for the resting statelo and showed a similar dependence on chain length and degree of unsaturation. REFERENCES 1. Basso LV, Have1 RJ: Hepatic metabolism of free fatty acids in normal and diabetic dogs. J Clin Invest 49 :537, 1970 2. Bjiirntorp P: The effect of lactic acid on adipose tissue metabolism in vitro. Acta Med Stand 178~253, 1965 3. Carlson LA, Boberg J, Hijgstedt B: Some physiological and clinical implications of lipid mobilization from adipose tissue, in Renold AE, Cahill GF, Jr (eds): Handbook of Physiology, Adipose Tissue, sec. 5. Washington, DC, American Physiological Society, 1965 4. Cobb LA, Johnson WI’: Hemodynamic relationships of anaerobic metabolism and plasma free fatty acids during prolonged, strenuous exercise in trained and untrained subjects. J Clin Invest 42:800, 1964 5. Fredholm BB: The effect of lactate in canine subcutaneous adipose tissue in situ. Acta Physiol Stand 81 :llO, 1971 6. Friedberg SJ, Harlan WR, Jr, Trout DL, et al: The effect of exercise on the concentration and turnover of plasma nonesterified fatty acids. J Clin Invest 39:215, 1960 7. Hagenfeldt L: A gas chromatographic method for the determination of individual free fatty acids in plasma. Clin Chim Acta 13:266,1966 8. Hagenfeldt

L, Wahren J: Human forearm muscle metabolism during exercise. II. Uptake, release and oxidation of individual FFA and glycerol. Stand J Clin Lab Invest 21:263,1968

9. Hagenfeldt L, Wahren J: Metabolism of free fatty acids and ketone bodies in skeletal muscle, in Pernow B, Saltin B (eds) : Muscle Metabolism during Exercise, New York, Plenum Press, 1971 10. Hagenfeldt L, Wahren J, Pernow B, et al: Uptake of individual free fatty acids by skeletal muscle and liver in man. J Clin Invest 51:2324, 1972 11. Have1 J, Pernow B, Jones NL: Uptake and release of free fatty acids and other metabolites in the legs of exercising men. J Appl Physiol 2390, 1967 12. Issekutz B, Jr, Miller H: Plasma free fatty acids during exercise and the effect of lactic acid. Proc Sot Exp Biol Med 110:237, 1962 13. Jones NL, Have1 RJ: Metabolism of free fatty acids and chylomicron triglycerides during exercise in rats. Am J Physiol 213~824‘1967 14. Rowe11 LB, Masoro EJ, Spencer MJ: Splanchnic metabolism in exercising man. J Appl Physiol 20:1032, 1965 1.5.Snedecor GW, Cochran WG: Statistical Methods (ed 6). Ames, Iowa, The Iowa State University Press, 1967 16. Wahren J: Quantitative aspects of blood flow and oxygen uptake in the human forearm during exercise. Acta Physiol Stand Suppl 67:296, 1966 17. Wahren J, Felig P, Ahlborg G, et al: Glucose metabolism during leg exercise in man. J Clin Invest 50:2715, 1971