the problems of acidosis - journal of clinical...

J. clin. Path., 23, Suppl. (Roy. Coll. Path.), 4, 73-83

The problems of acidosis

GABRIEL G. NAHASFrom the Department of Anesthesiology, College ofPhysicians and Surgeons,Columbia University, New York, USA

After trauma the failure ofvarious organ functionstends to disturb acid-base equilibrium and pro-duce acidaemia. Circulatory failure producesstagnation of blood in tissues and pulmonaryfailure, impairment of CO2 elimination and °2uptake. Liver failure impairs the metabolic con-version of acid metabolites such as lactate orketones into oxidizable substances and kidneyfailure impairs the excretion of acid metabolites.It is evident that the degree of acidaemia duringshock will be a function of the severity of theimpairment of organ function, mostly of theheart and lungs.The physiological effects of acidaemia are well

established. It depresses the functional activityof all vital organs. The cardiovascular system isprimarily affected (Clowes, Sabga, Konitaxis,Tomin, Hughes, and Simeone, 1961). Bothcardiac conduction and the contractile force ofthe myocardium are depressed and there is vaso-dilatation in the peripheral circulation andcerebral vessels. By contrast, vasoconstrictiondevelops in the lung vasculature. In the liverenzymatic activity is generally depressed. Acid-aemia has a thromboplastic effect and increasescoagulation, contributing to intravascularclotting,as described by Hardaway (1966).

It is also known that acidosis decreases cate-cholamine activity (Burget and Visscher, 1927).Adrenaline and noradrenaline, at acid pH, in-fluence heart rate and blood pressure less than atnormal pH. It should, however, be rememberedthat acidosis is also a profound stimulus to cate-cholamine production (Nahas, Zagury, Milhaud,Manger, and Pappas, 1967). These two anta-gonistic effects of acidosis result in a new, un-stable condition which will vary from one in-dividual to the next and will depend upon thedegree of sympatho-adrenal stimulation and thedegree of inhibition of catecholamine activityproduced by a given 1t*e1 of acidosis. In the

present paper I will describe primarily the effectsof acidosis on catecholamine activity and somesteps of intermediary metabolism.

I Effects of Acidaemia on Adrenal Function

Fenn and Asano reported in 1956 that hyper-capnia was accompanied by an increase insympatho-adrenal activity in the cat. SubsequentlyTenney (1956) showed that CO2 serves as a potentstimulus to increase the titre of circulating sym-patho-adrenal catecholamines in the cat. In 1960we attempted to quantitate these changes. Hyper-capnic acidosis was produced in dogs by theprocess of 'apnoeic oxygenation' and arterialblood pH was decreased to 7.0 and PaCO2increased to about 100 mm Hg (Nahas, Ligou,and Mehlman, 1960). Under these conditions,plasma concentrations of adrenaline and nor-adrenaline increased, while oxygen uptake didnot, although an increase in catecholamine isusually accompanied by increased oxygen uptake(Steinberg, Nestel, Buskirk, and Thompson,1964). Furthermore, mean blood pressure didnot change much in these animals (Fig. 1).However, when the acidosis was corrected therewas a sudden increase in oxygen uptake andblood pressure. These observations were inter-preted as indicating that correction of acidosisrestored a normal hydrogen-ion concentrationand catecholamines exerted their optimal meta-bolic activity.

Similar observations were made on animalsventilated with 10% CO2 and 30% O2 so thatarterial pH fell to 7.0. There was no increase inoxygen uptake and no increase in non-esterifiedfatty acids (FFA) or glycerol concentrations inplasma. When pH was restored to normal, therewere marked increases in FFA and glycerol con-

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Gabriel G. Nahas

MECH

VENT

+ R-NH2 O. 66 MM kg/m-i

O110 -

QO2 9 _mI/Kg/min

8_

7.4 -

ARTERIALBLOOD 7.2 -

pH

PLASMACATECHOLAMINES

mcg /L

MEANBLOOD

PRESSUREmm Hg

Po CO2

mm Hg

TIME IN MINUTE

Fig. 1 Effects ofa rapid restoration of an acidblood pH to normal on QO2, blood pressure, andplasma catecholamine levels. Mean of three experi-ments. (From Nahas et al, 1960; US Armyphotograph ANWSO.)

centrations and in oxygen uptake (Poyart andNahas, 1966). These experiments indicate furtherthat catecholamines endogenously released byhypercapnic acidosis will resume their metabolicactivity when pH is restored to normal (Fig. 2).

It was shown that the rise in circulating plasmacatecholamines during acidosis could be attri-buted to an increased release from peripheralnerve endings (Euler and Lishajko, 1963) andalso from the adrenal gland (Nahas et al, 1967).The isolated adrenal gland of the dog was per-

fused at constant flow at 37°C with dilutedhomologous blood at normal and acid pH(Fig. 3). It was shown that this medium preservedthe integrity of the fine structure of the adrenalgland (Fig. 4). The perfusion medium was madeacid by equilibration with hypercapnic mixturesor addition of lactic acid. Noradrenaline andadrenaline concentrations were measured in thediluted blood after perfusion and adrenal cate-cholamine output was calculated. At normal pH,

74it averaged 70 ng/gland/min. Adrenal catechol-amine output was increased by 100% followingperfusion with hypercapnic mixtures at a pH of6.96 to 7.10 (PaCO2 70-118 mm Hg) and 660%with a mixture at a pH of 6.79 to 6-92 (PaCO2125-210 mm Hg). This increase was primarily dueto a rise in adrenaline concentration. Similarresults were obtained following perfusion withmedia made acid by the addition of lactic acid.These results indicate that increases in [H+]directly stimulate adrenal medullary secretion.

It was also observed (Mittelman, Dos, Barker,and Nahas, 1962) that hypercapnic acidosis in thedog significantly increased cortisol output. Thephysiological importance of catecholamine re-lease during hypercapnia was demonstrated byobservations (Nahas and Cavert, 1957) whichshowed that giving adrenaline or noradrenalinereversed or prevented the acute myocardialfailure produced by respiratory acidosis whichwas first observed by Jerusalem and Starling(1910) in the heart-lung preparation (Fig. 5).The increased catecholamine output of acid-

aemia was related to an augmentation of cate-cholamine synthesis in rats (Nahas and Steins-land, 1968). It was first observed that exposure tohypercapnia was not accompanied by significantdepletion of catecholamine stores: in a group ofrats exposed to 20% CO2, 25% 02, balance N2,for periods of up to five hours, there were nosignificant changes in the noradrenaline contentof the heart, salivary glands and brain and thecatecholamine content of the adrenal gland com-pared with a control group breathing air. Anothergroup of rats was given intraperitoneally 300mg/kg of L-x-methyl-p-tyrosine in three divideddoses before a similar period of hypercapnia.They presented a 3717% decrease in the noradren-aline content of the heart and a 34.3% decreasein the catecholamine content of the adrenals(Fig. 6). Rats treated with L-a-methyl-p-tyrosineand breathing room air did not present significantchanges in the catecholamine content of heart oradrenal gland. Forty hours after the administra-tion of dopa-3H, exposure to hypercapnia signifi-cantly decreased specific activity ofcatecholaminesin the adrenal gland. Conversion of tyrosine-3Hto labelled catecholamines was also increased inrats during hypercapnia. These results indicatethat the rate of catecholamine synthesis isincreased during hypercapnia and enables theanimal to sustain the elevated catecholaminerelease required to maintain vital physiologicalfunctions.

Lotspeich (1967) has reported that metabolicacidosis produces in the rat an increase in gluta-minase enzymes and in the hexose monophos-phate shunt enzymes. Kidney hypertrophy is alsopresent and can be explained by an incorporationof the glutamine carbon skeleton into renal tissuecomponents. When protein synthesis was blockedby actinomycin D, the hypertrophy of metabolicacidosis did not occur. This led Lotspeich topostulate that the increased [H+] of NH4C1



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pH7.41 702 70 736 738

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CO2 AIRr-

F.F.A

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L,YC---

GLYCEROL

AIRF.F.A.

GLUCOSF(meq/I) (mg%)

1.00 140

.60 120 _

.20 C1O - K

C02 AIRab

A lA

V02(% increase)

30

10

0 60 120 180

B.P PULSE RATE(mm Hw) (mi.)

PULSE RATE180 11801401 140

10060 1. ]100

0 60 120 180

TIME (MINUTES)

Fig. 2 Changes in oxygen consumption (VO2) and plasma free fatty acids, glycerol, glucose, mean bloodpressure, and pulse rate in six dogs during and after a 60-min period of hypercapnic acidosis induced byventilation (10% CO2, 25% 02, balance N.). (From Poyart and Nahas, 1966.)

Fig. 3 Diagram illustrating the apparatus usedfor the perfusion of the isolated adrenal gland. Perfusingmedium is kept under pressure in two flasks by means ofa gas mixture. Pressure is recorded by means ofaHg manometer. Perfusing medium is made to pass through a water bath which is maintained at therequired temperature before reaching the gland. (From Nahas et al, 1967.)

AIR

GLYCEROL

(p mol/l)250 _

150 _

50 _ F



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Gabriel G. Nahas

Fig. 4 (Left) Electron micrograph of a section of the adrenal medulla. The adrenal was fixed in vivo withbuffered glutaraldehyde. Cells are seen between a venule (V) and a sinusoid (S). (Right) Electron micrographprepared from an adrenal gland which was perfused in vitro with diluted blood for two hours. Portionsof two chromaffin cells are seen around a sinusoid (S). (From Nahas et al, 1967.)

Fig. 5 Selected records taken from a Starling heart-lung preparation. Reversal of acidotic heartfailure is obtained by administration of 4 ,ug/min of adrenaline. (From Nahas and Cavert, 1957.)

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acidosis might derepress a gene site in kidney--------------------------------- 1 IHYPERCAPNIA cells responsible for protein and enzyme synthesis.

---------- -II>-M-T In our experiments, the adrenals of hypercapnicROOM AIR rats were not weighed; however, it was previously

reported (Schaefer, King, Mego, and Williams,

Room Air

1955) that, after one hour of exposure to 30%0Room Air C02, the weight of the adrenal gland in guinea20%Cc2 \ pigs was significantly increased, indicating that

HYPERCAPNIA hypercapnia might also produce a hypertrophy________________________,__________ of the adrenals. However, further investigations

04 8 12 16 20 are required to ascertain if the increased rate ofTIME(HOURS) synthesis of adrenal catecholamine is also accom-

panied by an increased synthesis of the enzymeswhich convert tyrosine into dopa and dopamine.

-------- HYPERCAPRIA Acidosis profoundly alters sympatho-adrenalregulation, producing an increase in catechol-amine synthesis and release, and at the same timedecreasing the metabolic activity of these amines.

i--4 a-M-T

ROOM AIR

\Hx-M-T +HYPERCAPNIA

2 % C------- RoorrAir

II Effects of Acidaemia on the Metabolic Activityof the Catecholamines

0 4 2 16 20

TIME (HOURS)

Fig. 6 (Top) Adrenal catecholamine (CA) content(,ug/kg BW) of rats breathing room air or exposedto acute hypercapnia. The rats received 100 mg/kgbody weight ofL-a-methyl-p-tyrosine at the 0, sixth,and 12th hours. (Bottom) Heart noradrenaline content(ug/g tissue) of rats breathing room air or exposedto acute hypercapnia. The rats received 100 mg/kgbody weight ofL-a-methyl- p-tyrosine at the 0, sixth,and 12th hours. (From Nahas an

AIR

NE

V02(% increase)

0 60 120

TIME( MINUTES)

Fig. 7 Changes in oxygen cons,plasma free fatty acids in six doAinfusion at normal pH and durin,induced by ventilation with a gas

C02, 25% 02, balance N2. Barsthe mean. (From Poyart and Nal

During hypercapnia, the increase in enzymeactivity which controls catecholamine synthesiscontrasts with the inhibitory effect of [H+] onenzymes which regulate intermediary metabolism,and which are activated by these catecholamines.This inhibition was observed in vivo as well as

in vitro.

id Steinsland, 1968.) EXPERIMENTS IN VIVO

For the experiments in vivo, pedigree beagleswere used because they have constant andreliable substrate and acid-base levels (Poyartand Nahas, 1966). They were given a standarddose of noradrenaline or adrenaline (1.5 ,ug/kg/min for 30 min) while being mechanically ven-

AIR C02 AIR tilated with room air. (Arterial pH was 7.42 and

NE pC02 30 mm Hg.) A week later, the animalsreceived the same dose of catecholamine, but this

time were ventilated with a mixture of 10% CO2X X and 25% 02 in N2 so that their average pHa was

-.< g 7.0 and average PaCO2 was 100 mm Hg. Theseresults are summarized in Figure 7. Noradrenaline'infusion, when ventilation was with room air,

produced 25-30% increments in °2 uptake which:".. persisted for at least an hour after the end of the

30-minute infusion. By contrast, when the same

animals were made hypercapnic, a week later,

oxygen uptake was not significantly different

from the control uptake. Changes in free fatty

0 120 180 acid levels with noradrenaline infusion are alsoshown in Figure 7. There was a marked increasein free fatty acids when pH was maintained atnormal. At pH 7.0 the lipolytic activity of nor-

umption(nd2) and adrenaline was depressed by 70%. Similar altera-

g's with noradrenailineIg hypercapnic acidosis lions in free fatty acids, glucose, and lactic acid

mixture of 10° blood concentrations with adrenaline infusion

indicate + 1 SE of are shown in Figure 8. At normal pH, there was

has, 1966.) a marked increase in free fatty acid and glycerol

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77The problems of acidosis

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78Gabriel G. Nahas

AIR0

F.F.A(meq/l)

GLUCOSE(mg %)

V02(% increase)

0 60 120

AIR 10% Co AIR

0 60 120 180

_ 150GLYCEROL(Mm/I)

50

300

] 2.00 L.A

1.00 (mM/I B.W)

TIME (MINUTES)Fig. 8.

739 734 739732 736 pH0

707 706 705702 705r

33 36 40 35 33

NE

I' B

Pa C02 28 32.2 32.4 288 29

(mm H9) NE

NE

120 180 0 60

TIME (MINUTES)Fig. 9.

GL YCEROL(, M)0--0_300

Fig. 8 Changes in oxygen consumption (V02) andplasma FFA, glycerol, glucose, and lactic acid (LA)concentrations in dogs receiving adrenaline (E)(1-5 ,g/kg/min) and breathing room air and a hyper-capnic mixture (10% CO2, 25% 02, balance N,.Bars represent + 1 SE of the mean. (From Poyartand Nahas, 1966.)

200Fig. 9 Comparative changes in oxygen consumption(V02), FFA, and glycerol plasma concentrationsproduced by noradrenaline (NE) infusion in two

100 groups of dogs: one with normal pHa, the other withacid pHa produced by NH,Cl administration.Vertical bars indicate + 1 SE of the means. Stars

0 indicate that the values are significantly different(p < 0.05) from initial control measurements. (FromNahas and Poyart, 1967.)

NE

120 180

FfA(ueq/1)

2100 P

1500

900 L

300

V02(0/0 inc

30

20

10

ease)

o0,-0 60



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concentrations; during acidosis, thesdid not increase significantly. Undeof normal pH, glucose concentratior100 to 300 mg% and lactic acid leveDuring hypercapnic acidosis, theresignificant increase in glucose, but nlactic acid. This would indicate thatgenolysis does proceed during acid(utilization might be impaired.

In an additional group of dogacidosis was induced by the intraverstration of ammonium chloride (0 ]to 60 hours until pHa was decreasec7.05 and 7.15 (Nahas and Poyart, 1the experiment, ventilation wasmaintain pHa and PaCO2 at this leadrenaline was then infused forBefore the noradrenaline infusion,centrations of free fatty acids, glyceand lactic acid were the same as atwhile V02 was slightly higher. Nincreases in V02 and free fatty aci

\\-* .

"i-

oh 0

32 18 20

755

7.39 7.48

400GLYCEROL(,uM/I)

300

200

100

0

*1

4.

.

NE

_

aWlM_NE

79

e substances following noradrenaline infusion, and the increaser conditions in glycerol, although significant, was small andas rose from comparable to the change in free fatty acids. As-ls also rose. compared with controls, the increase of VO2was still a induced by noradrenaline during acidosis was

io change in inhibited by 60%, free fatty acids by 68%, andwhile glyco- glycerol by 80% (Fig. 9). There were no signifi-osis, glucose cant changes in blood glucose or lactic acid con-

centrations.,s metabolic Similar experiments were performed to studyious admini- the effect of respiratory and metabolic alkalosis15M) for 48 on noradrenaline-induced calorigenesis and lipo-A to between lysis (Nahas and Poyart, 1967). Three groups of967). During dogs were either hyperventilated mechanicallyadjusted to or alkalosis was induced by the infusion ofTHAMvel and nor- (0.3M) or sodium bicarbonate (0.3M). Neither30 minutes. metabolic nor respiratory alkalosis significantlyblood con- altered control values. When noradrenaline was

rol, glucose, simultaneously infused with alkali, there was anormal pH slight but not significant enhancement of lipolysis.

o significant There were no significant differences in changes inids occurred blood glucose and lactic acid except for a marked

hypoglycaemia while THAM was being infused.When noradrenaline was infused during hyper-

18 16 17 ventilation, the increase in V02 was significantly753'75 higher than the increase produced by noradren-

' 754 ' aline at normal pHa. At the end of noradrenalineinfusion during hyperventilation, plasma freeacid concentrations were also significantlyhigher than at normal pHa but there was only aslight change in glycerol (Fig. 10).

Alterations of the metabolic effects of nor-adrenaline are, therefore, related to changes in[H+]rather than to changes in PaCO2or [HCO3-].Acid pH, produced either by hypercapnia or byinfusion of NH4C1, inhibits to the same extentnoradrenaline-induced lipolysis and calorigenesis.On the other hand, a decrease in [H+], either bymeans of hyperventilation or by administrationof base, results in higher V02 and slightly higherrelease of free fatty acids. Figure 11 shows the

. , . correlation between the increase in V02 and theplasma concentration of free fatty acids, the latterbeing determined by the [H+] of the blood at the

* * * end of the noradrenaline infusion.

0 30 90 150 210

TIME (MINUTES)

Fig. 10 Changes in oxygen consumption (V02) andFFA and glycerol plasma concentrations produced bynoradrenaline (NE) in four dogs at normal pHa(hyperventilation). Each dog was studied twice at a

week's interval. (From Nahas and Poyart, 1967.)

EXPERIMENTS IN VITRO

This inhibition of activated lipolysis by acid pHwas also observed in vitro. Rat epididymaladipose tissue was incubated in Krebs-Ringerphosphate medium with 5% albumin withoutglucose and with glucagon, ACTH, noradrenalineor cyclic 3',5'-AMP dibutyrate; the pH of themedium was varied from 7-4 to 6.6. Glycerolrelease was measured and taken as the index oflipolytic activity. In a first series of experimentsat pH 7.4, noradrenaline, ACTH, and glucagon-activated lipolysis was potentiated by increasingdoses of theophylline. In a second series, with thepH of the medium at 6-6, the lipolytic effects ofthese three hormones were significantly inhibited.When theophylline (10-2M) was added in com-

pC02(mmHg) 31 34 34 35 33

pH ' 731 735

741 7.36 7.36NE

2700EF.A(,ueq/1)0-@

2100

1500

900

300

0 3 90 150



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Gabriel G. Nahas

bination with optimal doses of the hormones, therate of glycerol release was similar at normal andacid pH (Fig. 12). These results were interpretedas indicating that H+ might exert its inhibitoryeffect on a common mechanism which results incyclic 3',5'-AMP formation (Triner and Nahas,1965). This hypothesis was confirmed: whencyclic 3',5'-AMP dibutyrate (10-3M) was addedto the medium, the same glycerol release was

AV02(mI/kg/min)

3.5_

2.5p

@0/./02.0L

1.5

1.0

1 /

~

5 [

0 05 1.0 15A F.F.A (me

Fig. 11 Relationship betwee,consumption (V02) and FFAinfusion (1PS pg/kg/min for 3lwhich had normal, acid, or alNahas and Poyart, 1967.)

80

found atpH 7-4 and 6.6 (Poyart and Nahas, 1968).When combined with noradrenaline, cyclic 3',5'-AMP dibutyrate also reversed the inhibitoryeffects of acidosis (Fig. 13). These results, whenanalysed according to the drug-receptor theory,would indicate that acidosis might inhibit, atleast in part, the different lipolytic drugs used inthis study by hindering the formation of thedrug-receptor complexes which activate lipolysis.

III Effects of Acidosis on Glucose Metabolism

The effects of variations in extracellular pH onglucose metabolism have been studied in differenttissues. In rat liver slices, epididymal fat pad, anddiaphragm muscle, a direct relationship wasfound between the rate of lactate production and

. ,, / the pH of the incubation medium (Gevers andDowdle, 1963). During acidosis, glucose uptakein human red blood cells was inhibited andlactate production decreased. It was suggestedthat this inhibiting effect of acidosis was exerted

. ,/ between the hexose phosphate and the triose*-p 728 733 phosphate stages (Murphy, 1960). Conversely,0-pH: 746 -.53 during alkalosis, accelerated glycolysis and ao-PH 99 7,06

higher glucose uptake and production of lactate\'rc,',,,'0 2 were observed in erythrocytes (Triner, Kypson,0,49U+ 01313(F.F.m, Mraz, and Zicha, 1964). In the perfused rat heartr-+C803,p<(C''vrlDelcher and Shipp (1966) observed increased

glucose uptake, lactate production, and glycogenbreakdown. The activities of several enzymes are

2.0 25 30 sensitive to changes of pH: Reynolds andq/1) Haugaard (1967) observed decreased phosphory-

lase activity in diaphragm muscle and Trivedin changes In oxygen and Danforth (1966) demonstrated a significant

0 min) in 30 beagles fall in the activity of phosphofructokinase from'kalinp nma (Frnm frog skeletal muscle at low pH. The purpose of

Th 33.IC3+ NE Ix.Os pH 74

Th 33.10-3 pH 7.4

Th 33 103+NE I.IO5 pH 66

Th 33.103apH 66

Fig. 12 Glycerol.formation (gcmol/ml cells) in fatcells from rat epididymal pad incubated withtheophylline (Th) (3.3 x 10-3M) and noradrenaline(NE) (1 x 10-5M) at pH 7-4 and pH 6-6. (FromTriner and Nahas, 1965.)

GLYCEROL(,mmol/g)

70r

60

50

40

30

20

0-

NE I0TMNE 10-5M 3'5'Amp 103 35Amp IO'M

66 74 66 74 66 74

(pH)

Fig. 13 Effect of noradrenaline, cyclic 3',5'-AMPdibutyrate, and the combination of these compoundson net glycerol release of rat epididymal adiposetissue incubated at normal and acid pH. (FromPoyart and Nahas, 1968.)

14.0r

120L

10.0 LGLYCEROL(,uMoI/mI cells)

80[

60p

40

20

010

CONTROL: pH 7.4 0pH 6.0

15 30 45 60 75TI ME (MINUTES)

woF

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Aullfic F11(4. ki-turit

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the study performed on the rat diaphragm was toinvestigate further the effect of acid pH on theconcentration of some intermediates in the glyco-lytic pathway in skeletal muscle. At pH 6.8,glucose uptake was significantly decreased (by34 %), while glycogen content was significantly in-creased over control (+22 %) at pH 7.4 (Table I).Both lactate and pyruvate production weresignificantly decreased (-38% and -20%, res-pectively). In the muscle there was a significantincrease in glucose-6-phosphate (G-6-P, +22%)but not in glucose-l-phosphate (G-l-P, + 12%)or fructose-6-phosphate (F-6-P, + 11 %) con-centrations while fructose-l, 6-diphosphate (F-I,6-P) concentration was significantly lower(-29 %)(Table II). These changes indicate that acid pHinhibits in mammalian skeletal muscle phos-phofructokinase activity, the rate-limiting stepin the glycolytic pathway. There were no signi-ficant changes in 02 consumption or citrate con-centration in the muscle with acidpH (Table III),indicating that the Krebs cycle and electrontransfer through the respiratory chain are notinhibited by this degree of acidosis. Similarly,there was no change in 02 uptake in vivo duringhypercapnic or metabolic acidosis.

Medium krebs-Ringer Phosphate

pH 7-4 pH6-8

Glycogen 7-15 + 0.56 8-76 062'(tsmol glucose/g wet tissue) (11) (11)Glucose uptake 15-36 + 1-39 10-24 1-62'(jsmol glucose/g wet tissuie) (14) (13)Lactate 31-58 ± 1-26 19-74 1-06(,umol lactate/g wet tissue) (16) (15)Pyruvate 1*41 0.00 1-13 0.00'(umol pyruvate/g wet tissue) (15) (15)

Table I The effect of acid pH on glycogen contentin muscle and on lactate and pyruvate concentrationsin medium''Values are means + SE. Figures in parentheses represent numberofexperiments.2Significantly different (p< 0.05) from control values(pH 7.4).

Medium Krebs -Ringer Phosphate

pH 7-4 pH 6-8

Glucose-l-phosphate 4.0 ± 0.7 4-5 + 1.3(14) (13)

Glucose-6-phosphate 16-1 0-8 19-6 i 1.1'(17) (15)

Fructose-6-phosphate 4-3 0.3 4-8 0.5(13) (13)

Fructose-1, 6-diphosphate 7.5 ± 0.5 5 3 + 0.5'(13) (10)

Table II The effect of-acid pH on the concentrationof hexose phosphates in muscle (pumol/100 g wettissue)''Values are means + SE. Figures in parentheses represent numberof experiments.'Significantly different (p <0-05) from control values (pH 7.4).

81

Medium

Oxygen consumption(4l O/mg dry tissue/hour)Citrate concentration(jsg/g wet tissue)

Krebs-Ringer Phosphate

pH 7-4 pH 6-83.35 + 0-14 3-14 ± 0.15

(15) (16)220 + 22 204 ± 31

(13) (13)

Table III The effect of acid pH on oxygen consump-tion and citrate concentration of rat diaphragm''Values are means ± SE. Figures in parentheses represent numberofexperiments.'Significantly different (P<0-05) from control values (pH 7.4).

Metabolic changes occurring in K+-freemedium are similar to those at acid pH. WhenK+ is not present in the medium, there is a shiftof K+ and other ions from the intra- to theextracellular compartment and it is known thatsimilar shifts of K+ occur at low pH (Fenn andCobb, 1934). The importance of ions, such as K+,in the activation of certain enzymes of the glyco-lytic pathway has often been demonstrated andrecently reviewed by Bygrave (1967). An elevatedK+ concentration in the incubation mediumincreases glucose metabolism in liver slices(Ashmore, Cahill, Hastings, and Zottu, 1957)and glycogen breakdown in heart muscle (Stadie,Haugaard, and Perlmutter, 1947).Changes in intermediates of the glycolytic

pathway at lowpH suggest that the activity of theenzymes, phosphorylase and phosphofructo-kinase, which require phosphate ions for theiractions, are inhibited. These enzymes are alsovery sensitive to changes in concentration ofcyclic3',5'-AMP. The results of this study do not showwhether or not metabolic changes due to acidpHand ouabain are caused by an inhibition of theadenyl cyclase system. However, since the effectof cyclic 3',5'-AMP on phosphorylase activity ofskeletal muscle is not pH dependent (Reynoldsand Haugaard, 1967), at lowpH there might be adecreased formation of cyclic 3',5'-AMP.One can ask, what is the relevance of these

studies to actual injury? A series of experimentswas designed to examine this problem (Nahas,Triner, Small, Manger, and Habif, 1966). Oxygenuptake, free fatty acid, and glucose plasma con-centrations were measured in mechanically ven-tilated animals following moderate haemorrhage.The haemorrhage was graded so that, althoughoxygen-carrying capacity was decreased, normalperipheral oxygenation was still maintained. Theanimals, after a control period, were bled 25ml/kg of body weight, over 30 minutes. Theyremained hypovolaemic for one hour, were re-transfused, and then observed for another hour.When they were mechanically ventilated so thatpH remained within 0-1 unit of 7.4, we observedan increase in oxygen uptake of about 12 %. Thehypovolaemic period was also characterized byan initial increase,in blood glucose which, how-ever, tended to decrease as the hypovolaemiaprogressed. Free fatty acid levels were alsoelevated during the period of hypovolaemia.



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Gabriel G. Nahas 82

CONT- HAEMOR-16-ROL RHAGE HYPOVOLAEMIA

p 736-733

8

(% CHANGE)4

0

--pH 7.28IS

-4 _---TT1 I-

0 30 60 90

TIME (MINUTES)

Fig. 14 02 uptake (V02) in two groups of animnalsfollowing haemorrhage (2S mi/kg body weight). (FromNahas et al, 1966.)

Another group of animals was treated in thesame way but, at the end of bleeding, were hypo-ventilated, so that the pH fell to an average of7T2. In these dogs, there was no increase in oxygenuptake, but stimulation of the sympatheticnervous system seemed to be as vigorous as beforeor even more so. Blood pressure was increasedabove control, and there was a marked and sus-tained increase in glucose levels. Under theseconditions, free fatty acid levels did not change(Fig. 14).

In conclusion,, the ability of the body tomobilize and utilize its fuel stores and to increasemetabolism above basal levels is significantlyinhibited by acid pH. These fuel stores are thosewhich are normally mobilized in all conditions ofstress. If the trauma is not too severe, the body isable to compensate and the traumatized individualwho is conscious tends to maintain his pH atnormal by hyperventilation. However, in casesof severe trauma, these compensatory mechanismsare not always operative and alterations of themetabolic effects of the catecholamines as afunction of [He] might be one of the factorswhich will alter fuel mobilization and utilization.These alterations must be be-tter known in orderto devise more efficient forms of therapy. Twotherapeutic implications may be derived fromour observation: the use of pressor amines intrauma should be carefully controlled, sincethere is such a marked endogenous production ofcatecholamines and, furthermore, correction ofacidaem-ia should precede administration ofpressor amines so that they may exert their fullactivity.

This work was supported in part, by a NationalInstitutes of Health grant GM-09069-06 and 07-,

army contract DADA-17-67-C-7126, the RobertSterling Clark Foundation Inc, and the Doloresand Bob Hope gift for the study of shock.

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