European Journal of Clinical Investigation (1979) 9,397404

Lactate elimination in man: effects of lactate concentration and hepatic dysfunction P. J. WOLL & C. 0. RECORD, Gastroenterology Unit, Royal Victoria Infirmary and University of Newcastle upon Tyne Received 23 October 1978 and in revised form 26 February 1979

Abstract. Lactate elimination was studied in twenty-six healthy volunteers during primed constant lactate infusion or multiple lactate injection tests, at blood lactate concentrations of 1-8 mmol-'. Although lactate elimination fitted a single exponential curve over a 30 min period, a significant correlation between the rate removal constant ( K L )and the peak blood lactate concentration (L4)was demonstrated:

log, KL= - 2.43 - 0.132 L4 (P =0.003, r = 0.63, n = 20) This suggests that lactate removal does not follow first order kinetics over a wide concentration range but becomes saturated at relatively low blood lactate concentrations. Estimates of the lactate distribution volume did not differ significantly a t different dosage levels, but remained in the range 270-300 ml kg-I. Skeletal muscle uptake accounted for about 26% of the infused lactate load. Seven patients with well-compensated hepatic cirrhosis were compared with a group of six control subjects during primed constant infusion tests. Fasting and steady state blood lactate concentrations achieved were similar in both groups. A significant prolongation in lactate half-life was demonstrated in the cirrhotics (18.8 k 1.4 min (mean fSEM) compared to 14.7f2.2 min; P < 0.02). Since peripheral uptake of lactate in the forearm was similar in the two groups, this suggests that hepatic lactate uptake was impaired, due either to hepatocyte dysfunction or portal diversion. Key words. Lactate, cirrhosis.

Introduction

Lactate kinetics have not been extensively studied in man. Isotopic techniques have been used in the study of lactate-glucose interconversion [ 11 and lactate turnover [2] but an alternative approach is to examine the response to infused or injected lactate loads. Doar & Correspondence: Dr C. 0. Record, Royal Victoria Infirmary, Newcastle upon Tyne, U.K. 00 14-2972/79/1000-0397$02.00 0 1979 Blackwell Scientific Publications

Cramp [3] described a primed constant infusion test and analysed it in terms of a single compartment model. However, in that study the maximum blood lactate concentrations achieved (about 2 mmol 1-I) were well below those seen in diseased states and during exercise. Hyperlactataemia is a common concomitant of liver disease but is also found in obesity, oral contraceptive users and lactic acidosis. Delayed lactate removal was described in acute liver damage by Hartmann & Senn in 1932[4] and has been suggested in cirrhotics [5], viral hepatitis [6], fulminant hepatic failure [7] and paracetamol-induced liver damage [8]. The present study was designed to study lactate elimination and sites of removal over a wide range of blood concentrations in normal man and in chronic liver disease. Methods

Subjects Twenty normal healthy volunteers (thirteen male and seven female) were studied during primed lactate infusion tests at one, two or three different dosage levels. The mean age was 35.7 years and the age range was 2 0 4 3 years. Six normal healthy volunteers (three male and three female) of mean age 23.5 years and age range 21-34 years, undertook multiple lactate injection tests at rising, constant or falling peak lactate concentrations. Seven patients with hepatic cirrhosis were studied during primed lactate infusion tests at two dosage levels. The cirrhotics (five alcoholic, one primary biliary cirrhosis, one cryptogenic) were stable outpatients with mildly abnormal liver function tests and clinical evidence of portal hypertension. Their results were compared with those of a group of six control subjects who were age, sex and weight matched. Each subject volunteered for the study after the nature, purpose and risks of the procedure had been explained. No subject was taking any drug known to affect carbohydrate metabolism: oral contraceptive users were specifically excluded. All subjects were 397

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within 20% of the mean weight for their height and age (Scientifica Geigy Tables, 1975) and no control subject had any history of liver disease or diabetes mellitus. Primed constant infusion tests Subjects were studied at rest, after a 12 h fast. Samples of arterialized venous (AV) blood [9] were obtained from an indwelling needle in a superficial vein on the dorsum of the left hand which was heated to 5540°C between two electric heating pads. Mixed venous (MV) blood was obtained from an indwelling needle in an antecubital vein arising from deep structures of the right arm. Basal samples were withdrawn at 10 and 5 min before starting the test and at 5 rnin (AV blood) and 10 min (MV blood) intervals throughout the test. A neutral solution of 1.79 mol 1-' sodium lactate (Koch-Light) was used, and enzymatic analysis showed that it contained 80% of the L( +)-isomer. It was administered in a loading dose of 466 pmol kg-' body weight over 30 s, followed by an infusion of 3 1.7 pmol kg-' min-' for 20 min. This regime was designed to raise the blood lactate concentration by 1.75 mmol I-' and maintain it at this level. By the administration of further loading doses at the end of the infusion periods and the use of proportionately increased infusion rates, blood lactate concentrations were raised by further 1.75 mmol 1-' increments. In this way subjects were infused with one, two or three different levels sequentially. Sampling was continued for 30 rnin after cessation of the last infusion (Fig. I). Forearm utilization of metabolites was estimated at 10 rnin intervals from AV-MV differences and forearm blood flow [ 101. The latter was determined, after exclusion of the hand with a wrist cuff, with a mercury-inrubber strain gauge plethysmograph (Devices Ltd) [I 11.

constant infusions [3]. Values are expressed as mean +SEM. Standard statistical methods were used [14], and calculations were performed on an IBM-370 computer. t-tests or paired t-tests were used where no other test is indicated. NS implies 'not significant' throughout.

Results Basal observations Resting blood concentrations of lactate and pyruvate were measured in healthy volunteers. The mean AV lactate concentration was 0.68 & 0.03 mmol 1-' (N=23) and the AV pyruvate was 0.062 k 0-004 mmol I-' ( N = 17). There was no significant difference in basal lactate and pyruvate concentrations between male and female or young and old subjects. Effects of lactate concentration on elimination A semi-logarithmic plot of the decay in incremental blood lactate concentration following primed constant infusions was linear (Fig. l), so results were analysed in terms of a single compartment model [3]. The absolute lactate concentration at the instant of cessation of the infusion (L4) was estimated from the computer fitted decay curve. A wide range of values for L4 was obtained by studying decays from the first, second or third dosage level. It was observed that the half-life (Ti) for blood lactate decay increased with Lo, from about 10 rnin at 2 mmol 1-' to 20 rnin at 8 mmol I - ' . The fractional rate removal constant (KL)is given by KL=lOge 0.5/Ti A significant correlation was found between the fractional rate removal constant (KL)and the peak lactate

Multiple injection tests Dosage regime

The conditions were similar to those of the primed infusion test, except that no infusions were used and AV blood only was sampled. The lactate solution was administered intravenously over 30 s at 30 rnin intervals and blood samples were taken at 3,6,10,15,20,25 and 30 min. Subjects were given six injections, to achieve sequential increases in peak lactate levels (Fig. 3), constant peak levels or sequential decreases in peak level during the test. Analysis Blood samples were assayed for L( +) lactate and pyruvate by standard spectrophotometric methods [12]. Methods of sampling, storage and assay were critically assessed [13]. The half life and fractional rate removal constant for lactate were computed by log regression analysis of the blood lactate decay curves, using a single compartment model and the lactate distribution volume was calculated from the primed

8

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I 20

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I 60

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Figure 1. The response of eight normal subjects to primed constant infusions of lactate at three dosage levels (mean 1 S E M ) . The solid line during the decay period was obtained by log regression analysis.

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concentration (L4) (Fig. 2) such that the best estimate of K L is given by log, K L = -2.43 -0432 x Lo (P=0.003, r=0.63, N = 2 0 ) . 95% confidence limits for the coefficient are -0-21 3 and - 0.05 1. No significant differences in lactate elimination between male and female or young and old subjects were found.

tions attained (L+)showed no linear trend, and were not correlated to the fractional rate removal constant (KL).Two subjects (C.R. and D.S.) received increasing doses (Fig. 3 ) and two others (K.J. and N.D.) decreasing doses of lactate. Each demonstrated a significant correlation between L+ and K L (Table 1).

Multiple injection test

Volume of lactate distribution

In two subjects given repeated injections of the same volume of lactate, the peak blood lactate concentra-

During primed constant infusion tests the blood lactate concentration rose rapidly after loading to achieve the steady state level, and remained reasonably constant during the infusions, except at the third dosage level (Fig. 1). The rising mean concentration at this level was taken into account in making an estimate of the distribution volume (see Appendix). The fractional rate removal constant was estimated for each steady state level from the relationship betweeh L+and K L described above. In eight subjects studied a t three dosage levels the distribution volume for lactate is shown in Table 2. The differences between dosage levels were not statistically significant.

r 0.08

-

-

0.06

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.........:. .*'.

-

E

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Y 0.04

Lactate metabolism by skeletal muscle Forearm muscle blood flow was estimated from the total forearm blood flow by the method of Cooper et al. [15]. Results are shown in Table 3. The forearm muscle uptake of lactate was calculated from steady state values as Q = (AV - MV lactate) x muscle blood flow (as pmol lactate per 100 ml forearm per minute). Forearm lactate uptake at rest did not differ significantly from zero. Cooper et al. [15] dissected out the tissues from the forearm of five cadavers and the muscle density can be calculated from their data as 1.016?0.006 kg 1-I. Muscle constituted 60% of the

0.03 -

0.025L 2

6

4

8

L+ (mmo11-1)

Figure 2. Regression of loge rate removal constant ( K L min-I) against absolute lactate concentration at time of cessation of the infusion (156 mmol I - I ) in twenty normal subjects undergoing primed constant lactate infusion tests, showing 95% confidence limitsfor theslope. log,KL= -2.43-0.132. Lg(P=0403, r=0.63, SE of slope=0.039).

AV blood lactate (mmo11-1)

5F

4

a

t

2

1 I 73

(rnins) =

0

11.6

ll.O

I 0

30

13,l

17.0

13.5

19.5

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I

I

I

I

60

90

120

150

180

210

Time (min)

Figure 3. The response of one subject (D.S.) to multiple injections of lactate. Peak lactate concentration (Lb mmol I-') and fractional rate removal constants ( K L min-I) were related as log, K L = - 2.36-0.205 Lb (P=0,002, r=0.96; SE of slope=0.047).

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P. J . WOLL & C . 0.RECORD

forearm mass. Thus forearm muscle uptake of lactate can be expressed as Q' =

Q

x

100 6o pmol per 100 g muscle per minute.

Assuming that all skeletal muscle behaves like that in the forearm an estimate can be made of the lactate removed by the 30 kg of skeletal muscle in a 70 kg man as lactate removed by skeletal muscle equals 100

300

60

1.016

Eflects of hepatic dysfunction on lactate elimination The basal blood concentrations of lactate and pyruvate and the concentrations achieved during primed constant lactate infusion tests at two dosage levels were not significantly different in cirrhotic and control groups (Fig. 4). There was no significant difference between the two groups in distribution volume or forearm muscle uptake of lactate. The fractional rate of removal for lactate was significantly lower in the cirrhotic than the control group, leading to a prolongation of lactate half-life in the cirrhotics (Table 4).

x Q pmol min-'

Skeletal muscle lactate uptake during the three infusion periods is shown in Table 3. The mean infusion rate was used to estimate the proportion of the infused lactate load removed by skeletal muscle. Table 1. Correlation between fractional rate removal constant ( K L ) and peak lactate concentration (Ld) in multiple lactate injection tests C.R. loge KL= -2.29-0.109 D.S. loge K L = -2.36-0'154

Ld P=0.014 r=0.95 N = 5 4 P=0.002 r=0.96 N = 6

K.J. logeKL= -2.03-0.205 154 P=0.015 r=0.90 N = 6 N.D. log, K L = -2.56-0.182 L4 P=0.038 r=0,84 N = 6

Discussion Measuring lactate kinetics Primed infusion and multiple injection techniques were used in this study and the limitations of these methods should be taken into account when considering the results [3], e.g. the assumption is made that after lactate injection mixing will occur in one circulation time but it should be complete in any case before sampling commenced at 3 min. Because the lactate decay curves, after injection or cessation of infusion, were log linear, lactate kinetics were determined using a single compartment model. It is most unlikely that this should correspond to a single anatomical compartment but if interconversions between compart-

Table 2. Some indices of lactate metabolism in eight normal subjects infused with lactate at three dosage levels (mean If: SEM) Mean AV (lactate) Calculated KL* Distribution volume Dosage level (mmol I-') (min-') (ml kg-') 1

2 3

2.00 f0.1 3 3.84 f0-27 6.687

0 ~ 0 6 7 7 ~ 0 ~ 0 0272.1 1 1 f 10.3 0.0532 f0.0019 293.5 f 9 . 0 0.0365 280.9

* The K L corresponding to the mean lactate concentration observed during the infusion periods was calculated from the relationship shown in Fig. 2. t Peak lactate concentration (Ld).This value was obtained from regression analysis of the means of the observed lactate concentrations during the third infusion period.

Table 3. Lactate removal (mean f SEM) by skeletal muscle in eight subjects during constant lactate infusion tests Dosage level ~~~

Basal 3.17k0.29 Mean flow (m1/100 ml muscle/min) -0.09 f0.09 Forearm lactate uptake (pmo1/100 ml forearm/min NS Significance of difference from zero (Pvalue) Skeletal muscle lactate uptake in a 70 kg man (mmol min-I) Percentage of infused lactate removed by skeletal muscle

(I)

(2)

3.43k0.39 0.91 f0.22 0.0009 0.45 fO.11 23.2%

3.56k0.46 4.74k0.53 2.27 f0.40 3.00 0.64 0.0001 0.0004 1.12 f 0.20 1.48k0.32 28.9% 25.6%

(3)

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AV blood lactate (rnrnol I-')

1

1

1

1

0

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1

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20

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1

1

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40

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Figure 4. The response of cirrhotic patients (N=7) and control subjects (N=6) to primed constant infusions of lactate at two dosage levels, showing log regression lines during decay period ( 0 , controls; 0,cirrhotics; mean fSEM). Mean Ti: cirrhotic 18.8 rnin; control 14.7 rnin.

Table 4. Responses of cirrhotics and control subjects during lactate infusion tests (mean & SEM)

Fasting AV lactate L# (prnol I-') (rnrnol I - I ) ~~

Controls 0.70 f0.05 Cirrhotics 0.61 k0.08 NS

KL (rnin-I)

TI (rnin)

VL

(rnl kg-I)

Forearm lactate uptake (prnol IOO rnl-' rnin-') at dosage level 2

~~

4.1 1 f0.29 0.052 f0.007 14.7 2.2 242 f 1 1 3.76k0.25 0.037k0.003 18.8k 1.4 231 + 6 NS P