Correction of Metabolic Alkalosis by the Kidney

after Isometric Expansion of Extracellular Fluid

JORDANJ. COHENwith the technical assistance of JOHNH. ELLISFrom the Division of Biological and Medical Sciences, Brown University, andthe Renal Division, Rhode Island Hospital, Providence, Rhode Island 02903

AB ST RA C T Metabolic alkalosis was induced indogs by administering ethacrynic acid and sus-tained by feeding a chloride-deficient diet. At theheight of the alkalosis extracellular fluid was ex-panded "isometrically," i.e., with an infusion thatduplicated plasma sodium, chloride, and bicarbon-ate concentrations. Correction of metabolic alka-losis promptly followed such expansion and wasattributed to the selective retention by the kidneysof chloride from the administered solution. Sinceplasma chloride concentration was not increased asan immediate consequence of the infusion, it isconcluded that the change in renal tubular functionthat led to the selective retention of chloride musthave been mediated by factors independent of fil-trate chloride concentration.

A decrease in circulating mineralocorticoid level,as a consequence of volume expansion, does notseem to account for this change in tubular func-tion since identical studies in dogs receiving ex-cessive amounts of 11-deoxycorticosterone acetateduring the day of infusion yielded similar findings.Moreover, no other consequence of volume expan-sion appears to be sufficient to cause this changein tubular function in the absence of metabolicalkalosis; when the alkalosis was corrected withhydrochloric acid before infusion, isometric expan-sion of extracellular volume did not induce selec-tive chloride retention.

We suggest that isometric expansion duringmetabolic alkalosis causes a decrease in proximalsodium reabsorption that relinquishes filtrate toa more distal site in the nephron and that this site

Received for publication 9 October 1967 and in revisedform 4 January 1968.

may retain chloride preferentially when hypo-chloremia or chloride deficiency is present.

INTRODUCTION

Correction of metabolic alkalosis requires thatplasma bicarbonate concentration and renal bicar-bonate threshold be reduced to normal levels. Al-though recent studies in a variety of clinical andexperimental situations have demonstrated clearlythat such correction is critically dependent on theprovision of adequate chloride (1-8), the precisemechanism whereby the provision of chloride per-mits restoration of normal acid-base equilibriumhas not been elucidated.

It has been suggested that, before the adminis-tration of chloride, the low plasma concentrationof this anion may be directly responsible for per-petuating the- alkalosis. Since chloride is uniqueamong physiologically prevalent anions in beingreadily reabsorbable by the kidney, it has beenreasoned that sustained. hypochloremia limits theavailability of reabsorbable anion in the glomerularfiltrate (6). Conservation of sodium filtered withinadequate reabsorbable anion would enhance thetranstubular potential difference and acceleratesodium-cation exchange. To the extent that thissequence of events accelerates the rate of sodium-hydrogen exchange, a high rate of bicarbonatereabsorption by the kidney and an elevated plasmabicarbonate concentration would be maintained.

It is theoretically possible, therefore, that anincrease in plasma chloride concentration towardsnormal might be a necessary first step in theprocess of correcting metabolic alkalosis. If the

The Journal of Clinical Investigation Volume 47 1968 1 181

acceleration of renal sodium-hydrogen exchangethat maintains metabolic alkalosis is the directconsequence of a low filtrate chloride concentra-tion, the deceleration of sodium-hydrogen ex-change that permits a fall in plasma bicarbonateconcentration might require some previous increasein filtrate chloride concentration.

The present study explores this possibility indogs rendered alkalotic by the administration ofethacrynic acid and a chloride-deficient diet. Inorder to provide adequate chloride without directlyincreasing glomerular filtrate chloride concentra-tion, we expanded extracellular fluid volume iso-metrically, i.e., with a solution comparable in com-position to plasma with respect to major electro-lytes. Despite this restriction, the kidneys wereable to retain administered chloride and rejectexcess bicarbonate selectively with prompt cor-rection of the alkalosis.

It is concluded that the provision of chloridemay alter over-all tubular function during thecorrection of metabolic alkalosis by mechanismsindependent of filtrate chloride concentration. Theassociated expansion of extracellular fluid volumemay be involved in mediating this effect of ad-ministered chloride.

METHODS19 studies, including 11 with detailed balance observations,were carried out on 16 female mongrel dogs ranging inweight from 12 to 22 kg. The animals were fed a syn-thetic diet consisting, by weight, of 10 parts dextrin, 10parts casein, 6 parts hydrogenated vegetable oils (Crisco),5.5 parts dextrose, USP, 1.2 parts purified agar, and 40parts distilled water. Multivitamins (ABDEC Drops)and iron (Fer-in-sol) were added in liberal amounts.When properly prepared and refrigerated this mixtureforms an easily handled, solid diet containing, by analy-sis, no more than 1 mEqof sodium, 0.1 mEqof potassium,and 0.5 mEq of chloride per 100 g. A daily allowance ofthis diet, 30 g/kg, was homogenized with 500-1000 ml ofhot distilled water shortly before feeding the dogs. Addi-tional water was offered ad lib. The diet was supplementedwith 3 mEq of sodium per kg and 2 mEq of potassiumper kg per day, both as neutral phosphate (4 partsHP04: 1 part H2PO4-). Most animals ate their totaldaily allowance throughout the study; some required tubefeeding after the induction of metabolic alkalosis (seebelow). Fasting blood samples were obtained by percu-taneous femoral artery puncture at 24-72-hr intervalsthroughout the course of the study.

Experimental design. The chloride-deficient diet wasfed for 3-5 days before beginning each study. Ensuingcontrol periods were of 4-7 day's duration for the 11

studies involving detailed balance observations and of 2-3day's duration for the remaining 8 studies.

Immediately after the control period, metabolic alka-losis was induced in all animals by the intravenous ad-ministration of ethacrynic acid,' 1 mg/kg of body weightper day, for 4 or 5 consecutive days. The injections weregiven at least 3 hr after the daily diet had been consumedand did not induce vomiting.

A few days after the last dose of ethacrynic acid, at theheight of the metabolic alkalosis, one of four experimentalprotocols was introduced. In each' instance the experi-mental protocol involved a 24-hr period initiated by therapid infusion of an individually tailored solution formu-lated as described below. The infusion day constitutedthe only experimental period except in protocol IVwhere an additional brief period preceded the infusionday.

Protocol I, standard infusion (eight animals, six bal-ance studies). The objective of this protocol was to ad-minister ample chloride to these chloride-depleted, alka-lotic animals without altering the plasma concentration ofmajor electrolytes. Accordingly, plasma sodium, chloride,and bicarbonate concentrations, determined in each studyon the morning of the proposed infusion, were used toprepare the infusate. The concentration of undeterminedanions, defined as sodium concentration minus the sumof chloride and bicarbonate concentrations, was accountedfor by the addition of neutral phosphate to the infusionsolution. The solution contained no potassium.

Animals were anesthetized with intravenous pentobarbi-tal sodium and indwelling catheters were placed in abrachial vein, femoral artery, and the urinary bladder.After a preinfusion control period of 1-2 hr duration,"isometric" expansion was accomplished by administeringthe infusion solution at a rate of 50 ml/kg per hr for 3 hrwith a constant infusion pump. This rate of infusion waschosen in order to present each animal with approximately50% more chloride during the 3 hr infusion period thanhad been lost during the ethacrynic acid period (seeResults).

Frequent arterial blood samples and consecutive urineperiods were obtained before, during, and for 3 hr afterthe infusion. Thereafter, the animals were returned tometabolic cages and offered 500 ml of water in a pan.Urine voided during the night drained into collectionbottles (see below). On the following morning, 24 hrafter beginning the infusion, a final arterial blood samplewas obtained and the bladder was emptied by catheteriza-tion. No food was given during the 24 hr infusion-dayperiod.

Protocol II, low chloride infusion (three animals). Theobjective of this protocol was to administer an amountof chloride similar to that provided in protocol I but at aconcentration substantially lower than that of the coex-isting plasma. Accordingly, whereas the sodium and neu-tral phosphate concentrations of the infusion solutionwere determined as in protocol I, the concentration of

1 Merck Sharp and Dohme Research Laboratories,West Point, Pa.

1182 1. J. Cohen

chloride in the infusion solution was reduced to a valueequal to one-half the concentration of chloride in theplasma. Additional bicarbonate made up the remaininganion equivalents producing a concentration of bicarbo-nate in the infusion solution that greatly exceeded theconcentration of bicarbonate in the plasma. This solu-tion was administered at a rate of 50 ml/kg per hrfor 6 rather than 3 hr in order to provide a total amountof chloride comparable to that provided in protocol I,In all other respects protocol II followed the pattern setby protocol I.

Protocol III, standard infusion plus 11-deoxycorticos-terone acetate (DOCA) (three animals). This protocolwas identical with protocol I with the exception that 10mg of DOCAin oil was administered intramuscularly12 and 2 hr preceding the infusion and an additional 2.5mg of an aqueous suspension of DOCAwas added to eachliter of infusate.

Protocol IV, standard infusion after correction of meta-bolic alkalosis with hydrochloric acid (five animals, fivebalance studies). The objective of this protocol was torepair the plasma chloride and bicarbonate concentrationsbefore infusion without repairing the sodium or potas-sium deficits. Accordingly, after the induction of meta-bolic alkalosis, an additional experimental period of 2-6days preceded the infusion day. Supplemental sodium andpotassium were eliminated from the diet throughout thisperiod and hydrochloric acid was added to the diet (tubefed in all cases) on each of the initial 2 days of this pe-riod; the amount of hydrochloric acid added (25-100mmoles/day) was adjusted for each dog in an effort toreduce plasma bicarbonate concentration to as close tocontrol levels as possible.

An infusion day protocol identical with protocol I wasthen employed; as in the preceding studies, the compo-sition of the infusion solution approximated the plasmasodium, chloride, and bicarbonate values obtained im-mediately before infusion. In contrast to the previousstudies, however, these animals were not hypochloremicimmediately before infusion and, hence, received a rela-tively larger amount of chloride from the infusion (seeResults).

Balance technique. Animals were kept in metaboliccages throughout the control and alkalosis periods.Urine was voided over siliconized metal surfaces intobottles containing mineral oil and thymol chloroform.When tested with water, this system yielded greaterthan 98%o recovery. Collection bottles were changed at9 a.m. daily. Feces were pooled during both the controland alkalosis periods; collections were started and termi-nated 24 hr later than the corresponding periods. Dailybalances were calculated as the difference between the netintake and the combined outputs in urine, stool, and bloodsamples. The change in net external balance during thealkalosis period was calculated as the difference betweenthe average daily balance during the control period andthe daily balance during the alkalosis period. The externalbalance on the day of infusion was calculated as the dif-ference between the amount infused and the combinedoutputs in urine and blood samples.

Quantitative urine collections were also obtained duringthe six nonbalance studies comprising protocols II andIII in order to permit estimates of the chloride deficitsinduced by the administration of ethacrynic acid to theseanimals.

Analytical procedures. Blood and urine pH were de-termined anaerobically at 380C with Metrohm Ltd., Heri-san, Switzerland water-jacketed, capillary glass electrodeand Radiometer, expanded-scale pH meter. Total carbondioxide content of plasma and urine were determined bythe manometric method of Van Slyke and Neill. Carbondioxide tension and bicarbonate concentration were calcu-lated from the Henderson-Hasselbalch equation using apK' of 6.10 and solubility coefficients of 0.0301 and 0.0309for plasma and urine, respectively. Sodium and potassiumconcentration were determined by flame photometry withlithium internal standard. Chloride concentration was de-termined by the method of Cotlove and Nishi (9). Elec-trolyte contents of feces and diet were determined onnitric acid extracts. The Technicon AutoAnalyzer wasused to measure blood and urine phosphate by the methodof Fiske and Subbarow (10) and urinary ammonia bythe method of Logsdon (11). Titratable acidity was cal-culated from urinary phosphate excretion with a pK of6.8. Net acid excretion was estimated as the sum of uri-nary ammonia and titratable acidity minus urinary bi-carbonate. Changes in extracellular fluid volume wereestimated from "chloride space" calculations assumingan initial value of 20% of body weight.

RESULTS

Protocol I

Pertinent plasma values and balance observa-tions are depicted in Fig. 1 for one representativestudy (dog 7).

PLASMAVALUES

Table I contains sodium, chloride, bicarbonate,and undetermined anion concentrations for alleight animals undergoing the standard protocol.Control values represent the average of the two tofive observations obtained before the administra-tion of ethacrynic acid. "Alkalosis" values repre-sent the average of the three to four observationsobtained in the 1st or 2nd hr immediately beforethe infusion and correspond to the height of themetabolic alkalosis. The "after infusion day" val-ues were obtained 24 hr after beginning the infu-sion. The solid line in Fig. 2 depicts the averagesodium, chloride, and bicarbonate concentrationsat each of these times for all animals in thisprotocol.

Sodium concentration fell from an averagecontrol value of 151-144 mEq/liter (P < 0.01)

Correction of Metabolic Alkalost's after Isometric Expansion of ECF 1183

CONTROL

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INFUSION4rI

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-120

-110 Cl0-o

-100

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FIGURE 1 Plasma concentrations of bicarbonateand chloride and cumulative (CUM) delta balancesof chloride, sodium, and potassium during the timecourse of one representative study from protocol I.

(Dog 7). Note that the metabolic alkalosis andsodium and chloride deficits were repaired by theday after "isometric" expansion with the individu-ally tailored infusion. ECA, ethacrynic acid.

12

DAYS

in response to ethacrynic acid and returned to

150 mEq/liter after the infusion. Chloride con-

centration followed a similar but much more

striking pattern, falling from an average controlvalue of 109 to 86 mEq/liter (P < 0.01) and re-

turning to 106 mEq/liter by the morning afterinfusion. Bicarbonate concentration mirrored thechange in chloride concentration; the control valuerose from an average of 21.8 to 31.4 mEq/literafter ethacrynic acid (P < 0.01) and fell to an

average of 24.1 mEq/liter by the morning afterthe infusion. Undetermined anion concentrationaveraged 20 mEq/liter during the control period,rose to 28 mEq/liter before the infusion (P <0.01), and fell to 20 mEq/liter after the infusion.There were no statistically significant differencesbetween the control and "after infusion day" con-

centrations of sodium, chloride, bicarbonate, or

undetermined anions.In six of these eight animals blood samples were

also obtained 48 hr after beginning the infusion.In these animals average chloride concentrationhad increased by an additional 4 mEq/liter andaverage bicarbonate concentration had decreasedby an additional 1.9 mEq/liter beyond their re-

spective values 24 hr after infusion.Mean potassium concentration was 3.4 mEq/

liter during the control period, fell to 2.0 mEq/

liter before the infusion (P < 0.01), and rose to

2.3 mEq/liter after the potassium-free infusion(P < 0.01).

Arterial hydrogen ion concentration averaged36.9 nEq/liter (pH 7.43) during the controlperiod, fell to 31.0 nEq/liter (pH 7.51) in re-

sponse to ethacrynic acid, and rose to 32.9 nEq/liter (pH 7.48) after the infusion. Mean arterialcarbon dioxide tension rose from a control levelof 33.4 to 41.3 mmHg by the infusion day (beforeanesthesia), and fell to 33.2 mm Hg by themorning after the infusion.2

BALANCEOBSERVATIONS

Sodium, chloride, and potassium balance dataare presented in Table II for the six balance stud-ies included in protocol I.

Alkalosis period. The administration of etha-crynic acid resulted in mean accumulated deltabalances of -80 mEq for sodium, -134 mEq forchloride, and -99 mEq for potassium.

2 The animals were allowed to ventilate spontaneouslyduring the light anesthesia required on the infusion day.In no instance did carbon dioxide tension appear to beinfluenced by the anesthesia itself; mean carbon dioxidetension was 40.3 mmHg after anesthesia but before theinfusion, and 35.2 mm Hg after infusion but beforeterminating anesthesia.

1184 J. J. Cohen

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CONTROL ALKALOSIS DAYAFTER

INFUSION

FIGURE 2 Average plasma concentrations of sodium, chloride, and bicarbonateduring the control period, at the height of metabolic alkalosis, and on the morn-ing after the infusion. Note that comparable degrees of hypochloremia andmetabolic alkalosis were achieved in each protocol before infusion and thatcomparable degrees of repair were achieved after expansion with the standardinfusion (protocol I), low chloride infusion (protocol II), and standard infu-sion plus deoxycortiosterone acetate (protocol III).

TABLE IPlasma Electrolyte Concentrations for Protocol I, Standard Infusion

Sodium Chloride Bicarbonate Undetermined anions

After After After AfterAlka- infusion Alka- infusion Alka- infusion Alka- infusion

Dog No. Control losis day Control losis day Control losis day Control losis day

mEqlliter mEqliter mEqlliter mEq/liter1 154 146 151 110 88 107 22.7 33.3 21.4 21 25 233 151 140 147 107 87 99 20.8 28.2 26.7 23 25 214 149 147 152 107 83 109 22.8 32.8 28.6 19 31 145 150 151 154 110 88 106 21.3 32.5 23.7 19 31 246 150 141 146 108 86 102 20.5 27.6 22.5 22 27 227 152 149 153 111 93 112 21.6 32.3 21.1 19 24 208 152 138 140 113 80 95 19.3 29.9 23.3 20 28 22

18 149 142 159 109 79 119 25.1 34.3 25.8 15 29 14

Average 151 144 150 109 86 106 21.8 31.4 24.1 20 28 20SD 1.6 4.4 5.4 1.9 4.3 7.1 1.7 2.3 2.5 2.3 2.5 3.6

Correction of Metabolic Alkalosis after Isometric Expansion of ECF 1185

Balance Data forTABLE I IProtocol I, Standard Infusion

Sodium balance Chloride balance Potassium balance

Alkalosis Infusion Alkalosis Infusion Alkalosis InfusionDog No. period* day: Over-all period day Over-all period day Over-all

mEq mEq mEq1 - 75 + 99 +24 -117 +171 +54 -109 -24 -1333 -107 + 83 -24 - 78 + 71 - 7 - 46 -27 - 735 -172 +120 -52 -192 +164 -28 -226 -28 -2547 - 56 + 77 +21 -119 +148 +29 - 56 -19 - 758 - 18 + 83 +65 -115 + 98 -17 - 96 -12 -108

18 -52 +137 +85 -180 +164 -16 - 61 -28 - 89

Average - 80 +100 +20 -134 +136 + 2 - 99 -23 -122

* Accumulated change in net external balance before infusion.t External balance on this day only.

Consistent weight loss was observed during thealkalosis period and averaged 0.8 kg (range 0.4-1.3 kg). "Chloride space" calculations for the sixanimals on whombalance observations were avail-able indicated a mean change in extracellular fluidvolume of -0.5 liter (range -0.3 to -1.0 liter).

Infusion day period. The total amount of

sodium, chloride, and bicarbonate administered onthe infusion day and the accumulated urinary ex-cretions of sodium, chloride, and net alkali areshown in the upper portion of Table III for alleight animals undergoing protocol I. An averageof 319 mEq of sodium was infused and 218 mEqexcreted. For chloride an average of 190 mEqwas

TABLE I I IA Comparison of Infusion Day Data from Protocols I and IV

Sodium Chloride Bicarbonate

Ex- Re- Ex- Re- Ex-Dog No. Infused creted tained Infused creted tained Infused creted*

mEq mEq mEqProtocol I

1 346 247 99 220 49 171 82 983 260 177 83 148 77 71 59 114 269 147 122 153 18 135 69 345 418 298 120 248 84 164 88 756 289 201 88 181 49 132 67 657 320 243 77 196 48 148 67 848 243 160 83 139 41 98 57 23

18 407 270 137 236 72 164 110 73

Average 319 218 101 190 55 135 75 58

Protocol IV11 369 326 43 278 226 52 48 11

1 B 359 262 97 260 151 109 59 295 B 472 337 135 366 226 140 60 9

20 423 269 154 276 120 156 52 3624 306 198 108 215 120 95 44 3

Average 385 278 107 279 169 110 53 18

* Values shown are for net alkali excretion (urinary bicarbonate-urinary ammonium-titratable acidity).

1186 J. J. Cohen

STANDARD INFUSION(PROTOCOL I)

STANDARD INFUSIONAFTER HCl(PROTOCOL N) FIGURE 3 Chloride retention in excess of so-

dium retention on the infusion day for each ani-mal in protocol I and protocol IV. Each barrepresents the difference between the infusionday chloride balance and the infusion day so-dium balance. Chloride was retained in signifi-cant excess of sodium in response to isometricexpansion in protocol I when metabolic alkalo-sis was present but not in response to compar-able expansion in protocol IV after metabolicalkalosis had been corrected with hydrochloricacid.

infused but only 55 mEq excreted. As a result,previously accumulated sodium and chloride defi-cits, determined in the six balance studies (TableII), were repaid; on the morning after infusionover-all accumulated balance averaged + 20 mEqfor sodium and + 2 mEq for chloride. The differ-ences between the infusion day balances for chlo-ride and those for sodium for all eight animalsundergoing protocol I are illustrated in the left-hand panel of Fig. 3; an average of 34 mEq ofchloride was retained in excess of sodium forthis group (P < 0.02).

Table III also relates the amount of bicarbonateinfused to the accumulated net alkali excreted forthe 24 hr period after the infusion. An average

CONTROL

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of 75 mEqof bicarbonate was infused and 58 mEqof net alkali was excreted.3

Infusion of the potassium-free solution was fol-lowed by additional losses of potassium on theinfusion day which averaged 23 mEq and whichresulted in a mean accumulated deficit over theentire study of -122 mEq.

Mean body weight at the end of the infusion'daywas not significantly different from that just before

3 Daily net acid excretion during the initial control pe-riod averaged 65 mEq for the six balance animals. Thisfigure, however, cannot be used with confidence as abase line to assess the net suppression of acid excretionon the infusion day since endogenous acid production wasprobably altered during this day by such events as anes-thesia and fasting.

CI

FIGURE 4 Plasma concentration of bicarbonate andchloride and cumulative (GUM.) urinary balance(BAL.) of chloride during the time course of onerepresentative study from protocol IL. (dog 14).Note that plasma chloride concentration rose andchloride deficits were largely repaid in response tothe hypochloric infusion.

1t 2?

Correction of Metabolic Alkalosis after isometric Expansion of ECF

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infusion. Extracellular fluid volume, oln the otherhand, as estimated from "chloride space" calcula-tiolls, exhibited a consistent increase which aver-aged 0.6 liter. Shifts of sodium and potassiumbetween intra- and extracellular compartmentswere computed from "chloride space" estimatesand plasma concentrations. Whereas sodium didnot appear to shift consistently in either direction,potassium did appear to shift out of cells in allstudies, the mean shift of potassium amounting to25 mEq. As a consequence, an average of 27 mEqof hydrogen iolls appeared to shift into cells duringthe infusion day.

Protocols II and III

Pertinent plasma values and urinary chlorideblclances are depicted in Fig. 4 for one representa-tive study (dog 14) from protocol II.

Fig. 2 illustrates the average plasma sodium,chloride, and bicarbonate concentrations for thethree animals undergoing protocol II (dashedline) and for the three animals undergoing proto-col III (dotted line) for each of the experimentalperiods. In each of these protocols the changes

observed in the plasma concentration of majorelectrolytes were comparable to those observed inprotocol I; chloride concentration rose and bi-carbonate concentration fell towards control levelsin response to the individually tailored infusiondespite the administration of a solution with onlyone-half the chloride concentration of the animal'splasma (protocol II) or the presence of excessivemiineralocorticoid (protocol III).

Accumulated urinary chloride losses in responseto ethacryn ic acid adcninistration averaged 136mEq (range 124-149 mEq) for protocol II and143 mEq (range 113-198 mEq) for protocol III.These chloride deficits were similar to those ob-served in protocol I (Table II) and were equallywell re)aicl on the infusion dayu; chloride retentionfrom the individually tailored solutions averaged112 mEq (range 107-119 mEq) for protocol IIand 156 mEq (range 126-196 mEq) for proto-col III).

Protocol IV

Pertinent observations for one representativestd(ly (dog 5 B) are shown in Fig. 5.

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-200-0

Na -10o

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K -50'

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2 4 6 8

DAYS

*120

'110 CI

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90

FIGURE 5 Plasma concentrations of bicarbo-nate and chloride and cumulative delta bal-ances of chloride, sodium, and potassium dur-ing the time course of one representativestudy from protocol IN,. (dog 5 B). Note

that metabolic alkalosis and much of the

chloride deficit had been repaired by hydro-chloric acid before isometric expansion with

the individually tailored infusion. The infu-

sion resulted in complete repair of sodium

deficits without appreciable further alterationin plasma anion concentrations.

10 12 14

1188 J. J. Cohen

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PLASMAVALUES

Table IV contains the values for all five animalsundergoing protocol IV. Control values representthe mean of the three to four observations obtainedbefore the administration of ethacrynic acid. "Al-kalosis" values were obtained immediately beforegiving the first dose of hydrochloric acid and rep-resent the extreme of metabolic alkalosis in eachanimal. Values labeled "after HCl" represent theaverage of the two to four observations obtainedin the 1st or 2nd hr immediately before the infu-sion; values labeled "after infusion day" wereobtained 24 hr later.

As can be seen from a comparison of Tables Iand IV, mean plasma electrolyte concentrationsduring the control period and after the administra-tion of ethacrynic acid were quite similar for thegroups of animals undergoing protocols I and IV.In protocol IV, however, the plasma anion con-centrations characteristic of the alkalosis periodwere returned virtually to normal by the adminis-

tration of hydrochloric acid and, despite the sub-sequent infusion, did not change appreciably there-after.

BALANCEOBSERVATIONS

Alkalosis period. The changes in net externalbalance, accumulated before the infusion day, aver-aged -101 mEq for sodium (range -63 to -171mEq) and -88 mEqfor potassium (range -76 to-118 mEq). The change in net chloride balance,accumulated during the development of metabolicalkalosis and before the administration of hydro-chloric acid, averaged -145 mEq (range -104 to-200 mEq). Each of these mean values is com-parable to that observed during the alkalosis periodin protocol I (Table II). Administration of hydro-chloric acid reduced the mean accumulated netchloride deficits to -56 mEq (range -18 to -79mEq) before the infusion day.

Infusion day period. The total amount of so-dium, chloride, and bicarbonate administered on

TABLE IVPlasma Electrolyte Concentrations for Protocol IV, Standard Infusion after Correction of

Metabolic Alkalosis with HCO

Sodium Chloride

After AfterAfter infusion After infusion

Dog No. Control Alkalosis HOC day Control Alkalosis HCl day

mEqiliter mEq/lifer1 B 160 154 154 154 112 92 104 1135 B 158 156 154 158 113 93 110 115

11 150 151 147 150 114 101 111 11620 149 151 149 155 110 91 104 11224 156 146 143 145 104 77 104 114

Average 155 152 149 152 111 91 107 114SD 4.4 3.4 4.2 4.5 3.6 7.8 3.2 1.4

Bicarbonate Undetermined anions

After AfterAfter infusion After infusion

Control Alkalosis HC1 day Control Alkalosis HCl day

mEq/liter mEq/liler23.4 32.8 23.0 22.4 25 29 27 1921.0 30.4 17.8 17.9 24 33 26 2522.1 31.0 16.8 17.8 14 19 19 1620.3 32.3 18.5 15.8 19 28 27 2719.5 30.8 20.3 19.3 33 38 19 12

21.3 31.5 19.1 18.6 23 29 24 201.4 0.9 2.2 2.2 6.4 6.3 3.8 5.6

Correction of Metabolic Alkalosis after Isometric Expansion of ECF 1189

the infusion day and the accumulated urinary ex-cretion of sodium, chloride, and net alkali areshown in the lower portion of Table III for eachof the five animals undergoing protocol IV. Forsodium, an average of 385 mEq was infused and278 mEqexcreted; 107 mEqwas retained, a valueremarkably similar to that observed in protocol I.For chloride, however, an average of 279 mEqwas infused and 169 mEqexcreted; only 110 mEqwas retained. As seen in the right-hand panel ofFig. 3, chloride was not retained in significantexcess of simultaneous sodium retention, as wasthe case in protocol I, even though relatively morechloride was administered than in protocol I.From the standpoint of urinary composition, chlo-ride excretion averaged 60%o of sodium excretionon the infusion day of protocol IV whereas chlo-ride excretion averaged only 25 % of sodium ex-cretion on the infusion day of protocol I.

DISCUSSION

The relationship between metabolic alkalosis andthe metabolism of chloride has been the subject ofconsiderable investigation in recent years (1-8).It has been well established by these studies thatselective depletion of body chloride stores resultsin metabolic alkalosis, restricted access to dietarychloride permits metabolic alkalosis to perpetuateitself and provision of chloride is a prerequisite tothe repair of metabolic alkalosis.

The self perpetuation of metabolic alkalosis dur-ing the period of chloride deficiency has beententatively attributed to an alteration in renaltubular function necessitated by the accompanyinghypochloremia (6). Since chloride is virtually theonly physiologically prevalent anion that can read-ily penetrate the tubular epithelium, it has beenreasoned that a low concentration of chloride inthe glomerular filtrate places a limit on theamount of anion available for reabsorption withsodium. As a result of this limitation, conservationof filtered sodium would require an accelerationof sodium-cation exchange (12). To the extentthat sodium-hydrogen exchange were thus accel-erated, a sustained increase in bicarbonate reab-sorption would result and metabolic alkalosiswould be perpetuated.

If hypochloremia necessitates an acceleratedsodium-hydrogen exchange during selective chlo-

ride depletion, an increase in chloride concentrationtowards normal might be the necessary first stepthat permits a decelerated sodium-hydrogen ex-change during chloride repletion.

The present study explores this thesis by iso-lating filtrate chloride concentration as a variableduring the replacement of chloride deficits inmetabolic alkalosis and by observing the kidney'sability to return plasma composition to normal.Dogs were rendered chloride depleted, hypochlo-remic, and alkalotic by the administration of etha-crynic acid and a chloride-deficient diet. At theheight of the metabolic alkalosis the dogs receivedan infusion designed to provide abundant chlorideisometrically, i.e., without altering the plasmaconcentration of major electrolytes (protocol I).Consequently, the composition of glomerular fil-trate, and the profile of potentially reabsorbablesubstrate presented to the tubule were unchangedby the infusion itself. If the concentration ofchloride in the filtrate were a critical determinantof the rate of cation exchange, deceleration ofsodium-hydrogen exchange and a fall in bicar-bonate threshold might not have been expected tooccur under these conditions.

The results of protocol I indicate, however, thatthe renal tubules were able to effect appropriateadjustments of extracellular composition in re-sponse to such infusions; the bulk of the infusedsodium was rejected while the infused chloridewas selectively retained, net acid excretion waspromptly suppressed and, consequently, over theensuing 24 hr, plasma chloride and bicarbonateconcentrations were returned essentially to normallevels. Moreover, the results of protocol II demon-strate that, even when a low filtrate chloride con-centration is reduced further by the direct effectsof infusing a solution with a substantially lowerchloride concentration, the kidneys are still ableto retain requisite chloride selectively and re-adjust plasma composition towards normal. It isevident, therefore, that a low filtrate chloride con-centration does not necessitate an accelerated rateof bicarbonae reabsorption under all circumstances.

While clearly not invalidating the notion that,before administering exogenous chloride, hypo-chloremia may be a crucial factor in the mecha-nisms perpetuating alkalosis, the present observa-tions do suggest that mechanisms independent offiltrate chloride concentration may operate to cor-

1190 J. J. Cohen

rect metabolic alkalosis once provision of neededchloride has occurred.

The theoretical mechanisms enumerated below,each initiated by acute expansion of extracellularfluid volume, could account for the observed cor-rection of metabolic alkalosis since each wouldpermit infused sodium to be excreted without aproportionate excretion of chloride.

(a) An increase in glomerular filtration rate, inresponse to volume expansion could have resultedin the observed alkali diuresis and selective reten-tion of chloride even if sodium-hydrogen exchangecontinued at an undiminished rate. This possi-bility would require that such infusions promotesustained increases in the rate of both glomerularfiltration and over-all sodium reabsorption so thatonly the relative rate of sodium-hydrogen exchangewas reduced. Direct evidence bearing on this pointis not available from the present study since filtra-tion rates were not measured. There would appearto be no reason to doubt, however, that such briskinfusions produced at least transient increases inthe rate of glomerular filtration in these previouslysodium depleted animals. Further study will berequired to clarify this important point.

(b) Volume expansion could have resulted in aselective suppression of sodium-hydrogen exchangeby inhibiting endogenous mineralocorticoid pro-duction. Since aldosterone is thought to promotesodium-cation exchange, diminished aldosteroneactivity as a consequence of volume expansioncould have dampened this exchange and resultedin what appeared to be "selective" chloride reten-tion. The results of protocol III, however, do notsupport this contention since pharmacologicalamounts of the mineralocorticoid, DOCA, did notprevent the alkali diuresis, the preferential reten-tion of chloride, and the restoration of plasmacomposition towards normal.

(c) Expansion of extracellular fluid volumecould have resulted in selective inhibition ofsodium-hydrogen exchange by the renal tubulethrough some mechanism other than suppressedmineralocorticoid production. It is well recognizedthat volume expansion may inhibit sodium reab-sorption independent of changes in mineralocorti-coid levels (13-15). It is conceivable that suchinhibition of sodium reabsorption involves inhibi-tion of sodium-bicarbonate reabsorption to a pro-portionately greater extent than it does sodium-

chloride reabsorption. However, it seems clearfrom the results of protocol IV that mere expan-sion of volume, at least with solutions such asthose employed here, does not invariably producea disproportionate inhibition of bicarbonate re-absorption. In these studies, similarly volume-depleted animals were acutely expanded with com-parable solutions after previous restoration ofnearly normal plasma anion concentrations. Thesaluresis observed after volume repair which oc-curred under these circumstances was accompaniedby a proportionate chloruresis; by contrast, inprotocol I a similar saluresis was accompanied byvery little chloruresis. Viewed conversely, despitethe retention of similar amounts of sodium, excesschloride was retained only in protocol I whenappreciable chloride deficits were present and notin protocol IV when chloride deficits had beenlargely repaid. It seems clear from these observa-tions that the anion composition of extracellularfluid must be an important determinant of theurinary composition that results from isometricexpansion of extracellular volume. The mechanismenabling the renal tubule to make the appropriateadjustments in urinary composition under theseconditions is still unclear.

(d) A fourth consequence of volume expansionwould appear to offer the most plausible explana-tion for these results. It is not unreasonable topostulate that, before volume expansion, the rateof sodium reabsorption in the proximal tubule wasincreased in response to the previously accumu-lated sodium deficits and that the delivery of fil-trate to the distal nephron was decreased accord-ingly. Once the infusion solution was administeredand extracellular fluid volume restored, the rateof sodium reabsorption in the proximal tubule wasprobably diminished (16). As a direct consequenceof this decrease in proximal sodium reabsorption,filtered chloride as well as sodium might have beenshunted to more distal sites in the nephron provid-ing these sites with a greatly increased opportunityto modify the tubular urine. If such distal sitespossessed a mechanism for selective or preferentialchloride reabsorption under conditions of chloridedepletion or hypochloremia, the results of thepresent study would be explained.

Despite the emphasis in the foregoing discussionon the role played by volume expansion in ac-counting for the present results, it should not be

Correction of Metabolic Alkalosis after Isometric Expansion of ECF 1 191

assumed that volume expansion without chloridemight have produced the same results. The admin-istration of sodium without the provision of ex-ogenous chloride (or equivalent reabsorbableanion) could not have resulted in correction ofmetabolic alkalosis since, in the absence of a de-crease in plasma sodium concentration or an in-crease in undetermined anion concentration, a fallin plasma bicarbonate concentration necessitates atleast a reciprocal increase in chloride concentrationas a direct consequence of the constraints ofelectroneutrality. Furthermore, the present studystrongly suggests not only that the repair of meta-bolic alkalosis is dependent on the provision ofchloride but also that the repair of volume deficitsby the retention of administered sodium is alsodependent on the availability of this anion. Duringthe several days between the last dose of ethacrynicacid and the infusion day, ample sodium, 3 mEq/kg per day, was present in the chloride-deficientdiet of these animals but sodium deficits were notrepaid. It was not until the infusion day whenchloride was also made available that sodiumretention occurred and normovolemia restored.

It would appear that the repair of metabolicalkalosis by the kidneys under the conditions ofthe present study is the result of a process in whichthe repair of volume deficits and the provision ofchloride are inseparable and interdependentfeatures.

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1192 J. J. Cohen