Acta physiol. scand. 1971. 81. 455-458 From the Department of Physiology, Gymnastik- och idrottshogskolan, Stockholm, Sweden

Pyruvate and Lactate Ratios in Muscle Tissue and Blood during Exercise in Man

BY JAN KARLSSON

Received 23 September 1970

Abstract

KARLSSON, J. Pyruuate and lactate ratios in muscle tissue and blood during exercise in man. Acta physiol. scand. 1971. 81. 4 5 5 4 5 8 .

To study the changes by exercise in the relationships betwen pyruvate (Py) and lactate (La) in muscle tissue and blood of man, Py and La were determined in muscle biopsy specimens (M..quadriceps fernoris) and in blood in 8 subjects a t rest (I) and after submaximal (11) and maximal (111) bicycle exercise. In the resting muscle Py was 0.06 mmoles x kg-’ wet muscle and increased with exercise to 0.14 (11) and 0.13 (111) mmolesxkg-l whereas La increased from 2.3 (I) to 10.4 (11) and 17.1 (111) mmoles ~ k g - ’ wet muscle. In the blood the cor- responding values for Py were 0.11 (I), 0.24 (11), and 0.39 (111) mmolesxl-I and for La 1.6 (I), 7.7 (11), and 10.0 (111) r n m o l e s ~ l - ~ . Thus the LalPy ratio increased from 38 (I) to 74 (11) and 131 (111) in the muscle and from 15 (I) to 32 (11) and 26 (111) in the blood. The increase in the muscle Py concentration during exercise could not account for more than 3 very minor part of the muscle La concentration which means that the excess lactate (XL) is of very minor physiological importance.

Pyruvate and lactate are interconvertible in the presence of the enzyme lactate- dehydrogenase (LDH) and excess of nicotinamide-adenine dinucleotide (NAD) in its reduced or oxidized form. In general the equilibrium is supposed to be defined by the mass action law, the pH, the properties of the enzyme, and to what extent extramito- chondrial NADH is present. According to the concept of the mass action law, lactate might be expected to be formed due to an accumulation of pyruvate in the cell. On this basis the term “excess lactate” (XL) was introduced by Huckabee in 1958, calculated from simultaneous lactate and pyruvate determinations in blood. Accord- ing to the concept, XL would better correlate to the oxygen deficit and the degree of anaerobiosis than the lactate concentration per se.

The present study was then performed to simultaneously determine pyruvate and lactate concentrations at rest and during exercise in blood and the exercising muscle and to evaluate whether a pyruvate accumulation was present in the muscle as earlier described for lactate (Diamant, Karlsson and Saltin 1968).

455

456 JAN KARLSSON

Subjects 8 healthy physical education students with a mean age of 23 (range 21-24) years participated in the study. Their mean height was 178 cm and mean weight was 70 kg. Maximal oxygen uptake averaged 56 (range 51-66) ml x kg-l x min-l.

Methods and procedure Concentrations of lactate and pyruvate were determined enzymatically in blood (Scholz el al. 1959) and muscle tissue (Lowry et al. 1964, and Karlsson, Diamant and Saltin 1970).

In order to obtain accurate readings of the muscle pyruvate concentrations, which was dif- ficult with the native decrease of fluorescence of the sample, the procedure using strong alkali according to Lowry, Roberts and Kapphahn 1957 was applied. Thus accurate readings for con- centrations higher than 0.05 mmoles x kg-l wet muscle were obtained.

The needle biopsy technique (Bergstrom 1962) was used to obtain muscle tissue specimens. The subjects were studied at rest, after submaximal bicycle exercise lasting for 10 min, and

after maximal exercise (exhaustion time 3-5 min). The biopsies were taken in the lateral portion of the thigh (M. quadriceps femoris) a t rest with the subject in supine position and immediately after exercise sitting on the bicycle. All samples were frozen within 3 - 4 sec after cessation of work. Simultaneously, blood samples were drawn from a prewarmed finger tip to determine blood lactate and pyruvate concentrations.

Results Mean values are given in Table I. All individual values for muscle pyruvate and lactate concentrations are shown in Fig. 1.

At rest the mean muscle pyruvate (Py) concentration was 0.06 mmoles x kg-l and increased during submaximal and maximal exercise to 0.14 and 0.13 mmoles x kg", respectively. I n the corresponding situations muscle lactate concentration (La) was 2.3, 10.4, and 17.1 mmolesxkg''. Thus the La/Py in the muscle tissue being 38 at rest was increased to 74 during submaximal and to 131 during maximal exercise. In the blood the La/Py ratio was 15 at rest. Lactate concentration was 1.6 and pyruvate concentration 0.1 1 mmoles x 1-la The corresponding ratios at submaximal exercise and at maximal exercise were 32 and 26, respectively; lactate concentration being 7.7 and 10.0 and pyruvate concentration 0.24 and 0.39 mmolesxl-'.

TABLE I. Mean values and range are given for the work loads and oxygen uptakes. Muscle and blood concentrations of pyruvate and lactate, respectively, are presented as means &SE and SD.

Work load Oxygen Pyruvate Lactate

kpm x min-1 1 x min-1 muscle* blood** muscle* blood** uptake

Rest - - 0.06&0.01 0.11&0.02 2.3k0.2 1.6k0.1 n = 8 0.03 0.7 0.7 0.3 Submaximal work 1290 3.1 0.14&0.02 0.24&0.03 10.4*0.6 7.7k0.5 n = 5 (1200-1350) (2.8-3.2) 0.04 0.06 1.3 1.1 Maximal work 2040 3.9 0.13k0.03 0.39 k0.05 17.1 f 1.6 10.0 f 1.1 n = 5 (1950-2100) (3.8-4.1) 0.07 0.1 1 3.5 2.4

* mmoles x kg-' wet muscle. ** mmoles x 1-1 blood.

PYRUVATE AND LACTATE IN MUSCLE 457

o rest 0 submaximal T maximal

}exercise 1 i

Fig. 1 . Muscle lactate concentrations are presented in relation to muscle pyruvate concentrations at rest and

load. immediately after a submaximal and maximal work 0.5 1.0 1.E

PYRUVATE, rnmoles x kg-' wet muscle

Discussion The resting pyruvate concentration in the blood was higher than that in the muscle tissue which is also true if the comparison is made on per liter of water basis. The water content has been found to range 76-79 per cent of the wet weight in a ma- terial of biopsy specimens obtained and treated similarly to the present (unpublished results). This discrepancy in pyruvate concentration between muscle and blood tended to be enhanced during exercise. I t seems therefore reasonable to assume a concentration gradient of pyruvate from the extracellular to the intracellular space. Since the gradient is small and the pH of the extra- and intracellular spaces may favour the observed distribution an uptake of pyruvate by the muscle may not be present (Siesjo, Granholm and Kjallquist 1968).

At rest in a canine gracilis muscle a negative a-v difference for pyruvate has been observed (Karlsson, Rose11 and Saltin 1971). During stimulation that caused the muscle lactate concentration to increase to approximately 17 mmolesx kg-l wet muscle and lactate to be released to the venous blood in the order of 0.2-0.3 mmoles x kg-l x min'l a positive a-v difference for pyruvate was observed. This can be explained either by an uptake of pyruvate by the muscle or a reduction of extra- cellular pyruvate by membrane located LDH fractions. The latter possibility has been suggested by Siesjii, Granholm and Kjallquist (1968) to be valid for brain tissue.

The present data do not confirm Huckabee's basic assumption that blood lactate and pyruvate concentrations reflected intramuscular concentrations. On the other hand there was an increased pyruvate concentration in the muscle during exercise as postulated by Huckabee, but its quantitative role for the observed lactate accumu-

458 JAN KARLSSON

lation must be minimal (c f . Fig. 1 ) . Recent studies indicate that at least during very heavy exercise the accumulation of lactate is directly related to the oxygen deficit (Karlsson and Saltin 1970) in the exercising muscles.

This study was supported by grants from the Swedish Medical Research Council (project B70-14X-2203-04B).

No.

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