Acta Medica Scandinavica. Vol. 178, fasc. 2, 1965

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

The Effect of Lactic Acid on Adipose Tissue Metabolism in Vitro

BY

PER BJORNTORP

Norepinephrine and other catecholami- nes cause an increase of plasma free fatty acids (FFA) (8) , by an increased lipid mobilization from adipose tissue depots. This corresponds in vitro to an increased outflow of both FFA and gly- cerol from surviving adipose tissue (6). The trigger mechanism for these lipolytic agents seems to be a lipase, possible to activate in vitro (9, 3, 10, 1).

When screening different agents as far as their effects on the lipase activation by norepinephrine it was found, that lactic acid caused an inhibition of this activa- tion. Because of the possible importance of this finding for the present concept of regulation of lipid mobilization, it was considered advisable to report these findings separately.

Materials and methods

Male, 200-300 g rats of a Sprague-Dawley strain (Anticimex) were killed by a blow on the head and decapitation. The epididymal fat pads were immediately removed, placed in 0.15 M KCI at room temperature and the Submitted for publication March 10, 1965.

distal end dissected into two approximately equal halves. These were then incubated in 4 % albumin (Armour, Fraction V) and 10 mM glucose in Krebs-Ringer bicarbonate solution, pH 7.4, at 37" C during 90 minutes. Glycerol (4) and FFA (5,2) of the incubation medium was determined at 0 and 90 minutes. Lactate was added from beginning of incuba- tion to a final concentration of 30 or 3 mM in the form of the lithium salt (British Drug House). Norepinephrine (0.1 pg/ml) was added 10 minutes before ending incubation.

The tissues were then removed from the incubation media, rinsed in 0.15 M KC1, homogenized and assayed for lipase activity as described by Vaughan et al. (10).

Results

Tables I and I1 give the results for lactate in the concentration of 3 and respectively 30 mM. Norepinephrine increased glycerol and FFA concentra- tions in the incubation medium and also lipase activity (< 0.01). Lactate at 3 m M concentration inhibited the norepine- phrine stimulated outflow of glycerol and FFA to the medium as well as lipase activity (table I, p < 0.05) and at 30

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254 PER BJORNTORP

TABLE I. The effect of 3 mM lactate on norepinephrine stimulated glycerol and free fatty acid out- flow and lipase activity in rat epididymal fat pads in vitro. Means f S.D. for 7 experiments

~~ ~~ ~

Lipase activity (pEq FFA/g/h)

Glycerol FFA 0 lactate Lactate (pEqlgl90) (~Eq/g/90) in assay in assay

0 0.44+0.12 0.6It 0.2 12.643.0 12.0 k 3.1 Norepinephrine 0.9010.13 2.410.7 21.4k3.3 22.1 k4 .9 Norepinephrine + Li lactate 0.71It0.12 1.7k0.3 17.4k2.6 18253.7 Norepinephrine + Li C1 0.94+0.10 2.340.6 21.0&5.1 24.2 5.1

TABLE 11. The effect of 30 mM lactate on nore- pinephrine stimulated glycerol outflow and lipase activity in rat epididymal fat pads in vitro. Means 4 S.D. of 9 experiments

0 0.4840.11 11.1 It 3.0 Norepinephrine 0.95&0.20 24.91 5.1 Norepinephrine+ 0.7240.14 18.0 44.5 Li lactate Norepinephrine+ l.OOkO.12 25.2It4.5 Li C1

mM concentration glycerol outflow and lipase activity (table 11, p < 0.02). Lithium chloride had no effect on the norepinephrine stimulated activity, showing that lactate was responsible for the inhibition. Lactate in the assay sys- tem had no effect as seen in table I.

Discussion

I t was thus shown, that lactate inhibits the norepinephrine increase of FFA and

glycerol outflow from adipose tissue and also the lipase activity, sensitive for hormone stimulation. There was no effect on preformed lipase activity, de- monstrating, that its effect is probably exerted on the lipase activation mecha- nism. In this regard it has a similar effect to nicotinic acid as described recently (2).

Issekutz has shown, that infusion of lactate to the dog decreases plasma FFA and increases specific activity of plasma FFA during constant infusion of labelled FFA (7). This indicates a decrease of outflow of FFA from fat depots. Such a decrease caused by lactic acid has also been suggested to occur during work (7).

The lactate concentrations shown to inhibit adipose tissue lipolysis are within the physiological concentration range in plasma, occurring for example during work. It therefore seems quite possible, that the findings in vitro should corre- spond in vivo. Theoretically it seems suitable with a messenger such as lactic acid, indicating a relative oxygen defi- ciency in working muscles and inhibiting adipose tissue outflow 'of fatty acids, which are broken down exclusively aero- bicall y.

EFFECT OF LACTIC ACID ON ADIPOSE TISSUE METABOLISM 255

The possibility of lactate inhibition of adipose tissue lipolysis seems to be of interest in conditions, where pulmonary or circulatory insufficiency causes accu- mulation of lactic acid in plasma. Of particular interest in this regard are questions related to obesity and physical training.

Summary

Lactic acid in concentrations occuring in plasma in vivo inhibited norepinephrine increase of fatty acid and glycerol out- flow as well as lipase activity in rat epididymal fat pads in vitro.

References 1.

2.

BJORNTORP, P.: The fatty acid release and lipolysis of human adipose tissue in vitro. Metabolism 13: 1318, 1964. BJORNTORP, P. : The effect of nicotinic acid on adipose tissue metabolism in vitro. Metab-

3. BJORNTORP, P. & FURMAN, R. H.: Lipolytic activity in rat epididymal fat pads. Amer. J. Physiol. 203: 316, 1962.

4. CARLSON, L. A.: Determination of serum glycerides. Acta SOC. Med. Upsalien. 64: 208, 1959.

5. DUNCOMBE, W. G.: The colorimetric micro- determination of non-esterified fatty acids in plasma. Clin. Chim. Acta 9: 122, 1964.

6. GORDON, R. S. Jr. & CHERKES,A.: Production of unesterified fatty acids from isolated rat adi- pose tissue incubated in vitro. Proc. SOC. exp. Biol. 97: 150, 1958.

7. ISSEKUTZ, B. JR.: Effect of exercise on the metabolism of plasma free fatty acids, in “Fat as a tissue”, Rodahl, K. & Issekutz, B. Jr. ed. Mc Graw-Hill, New York 1964, p. 228.

8. MUELLER, P. S. & HORWITZ, D. : Plasma free fatty acids and blood glucose responses to analogues of norepinephrine in man. J. Lipid Res. 3: 251, 1962. RIZACK, M. : An epinephrine-sensitive lipolyt- ic activity in adipose tissue. J. Biol. Chem. 236: 657, 1961.

10. VAUGHAN, M., BERGER, J. E. & STEINBERG, D.: Hormone-sensitive lipase and monoglycer- ide lipase activities in adipose tissue. J. Biol.

9.

olism. In print. Chem. 239: 401, 1964.