Renal excretion of uric acid during prolonged fasting

Renal Excretion of Uric Acid During Prolonged Fasting Irving H. Fox, Mitchell

L. Halperin,

Marc B. Goldstein,

Serum and urine uric acid were evaluated during prolonged therapeutic fasting in 15 obese patients. With increasing ketonemia the serum uric acid rose from a control value of 5.9 f 0.4 to 12.5 f 1.O mg/lOO ml at 7 days and then decreased progressively to 7.7 f 1.3 mg/lOO ml by 28 days despite sustained ketonemia. The uric acid clearances were 5.5 & 0.9, 1.8 f 0.2, and 4.4 f 1.5 ml/min at days 0, 7, and 28 of fasting. At the same times the creatinine clearances were 114 * 11, 80 f 6, and 64 * 6.3 ml/min. There was no evidence of a renal tubular abnormal-

and Errol

B. Mark

ity as assessed by glycosuria, bicarbonaturia, or increased phosphaturia. Urate binding to plasma proteins remained unchanged. Acute studies of the renal handling of uric acid revealed a uricosuric response to the administration of sodium lactate or sodium bicarbonate by intravenous infusion and low-dose acetylsalicylic acid orally. This renal tubular response departs significantly from that observed during the overnight fasted state and could not be accounted for by extracellular fluid volume expansion or the induced acid-base changes.

P

ROLONGED TOTAL CALORIC DEPRIVATION is a recognized mode of therapy for gross obesity’** and has provided a model for the elucidation of control mechanisms of metabolic regulation during steady-state ketosis. It is recognized as a state in which the organism subsists primarily on fatty acids and ketone bodies as energy substrates and in which progressive curtailment of protein catabolism occurs. Extracellular fluid volume depletion and mild, compensated metabolic acidosis are regularly observed. Hyperuricemia occurs and may even be accompanied by acute attacks of gouty arthritis in susceptible individuals.2-4 The elevation of the serum uric acid has been related to a decrease in the renal clearance of uric acid secondary to the ketonemia.2-6 In the present study, hyperuricemia and ketonemia were observed during the first week of a therapeutic fast. However, after the first week the serum uric acid concentration regularly decreased. During this time the renal clearance of uric acid increased despite persistent steady-state ketonemia. This observation prompted more detailed study of uric acid excretion after the first week of fasting. The administration of sodium lactate and acetylsalicylic acid resulted in a further increase in the uric acid clearance, a response different from that observed in the overnight fasted state.7-9

From the Divisions of Rheumatology. Nephrology. and Endocrinologv. University of Toronto, Ontario, Canada. Received for publication August I I, 1975.

Department of Medicine,

Supported hy grants from the Canadian Arthritis and Rheumatism Society, the Medical Research Council of Canada (MA5623, MA4782), the Banting Research Foundation, rhe Toronto General Hospital Foundation. and the Herbert W. Follows Memorial Fund of the SI. Michael’s Hospital Research Society. Dr. Fox is a Research Associate of the Canadian Arthritis and Rheumatism Society. Reprinl requests should be addressed to Dr. I.H. Fox. University of Toronto Rheumatic Disease Unit. The Welleslqv Hospital. 160 Wellesley St. East. Toronto, Ontario. Canada. o 1976 by Prune & Siratton. Inc. Mefaboiism, Vol. 25, No. 5 (May), 1976

551

552

FOX

MATERIALS

AND

ET AL

METHODS

Eleven females and four males with obesity were admitted to hospital for prolonged therapeutic fasting (Table 1). None had diabetes mellitus, gout, or significant renal. hepatic, or cardiovascular disorders. They were advised of the purpose, nature, and possible consequences of fasting and the associated studies. After an initial period on a controlled isocaloric diet of 40”” carbohydrate, 40% fat, and 20% protein, the patients began a total fast of 4-6 wk duration. During this time the daily oral intake was a minimum of 1500 ml of water, 16 mEq potassium chloride, and a multiple vitamin preparation. On day 0, 3, 5, 7, 14, 21, and 28 a blood sample and a 24-hr urine were collected. Measurement of the serum electrolytes, liver and renal function tests, hemoglobin, hematocrit, and an electrocardiogram were performed each week. Ketoacidosis occurred as documented previously for such subjects.” There were no adverse effects except for mild postural hypotension. After a minimum of 3 wk of fasting, one or more of the following tests were performed: the infusion of sodium lactate, sodium bicarbonate, or sodium chloride, or the oral administration of acetylsalicylic acid. Where more than one test was performed in the same subject, tests were spaced at intervals of at least 5 days. For the 6-hr infusion procedures a catheter was inserted into an anticubital vein at 0800 hr. Infusion rates were controlled using a BuretrolR (Travenol Laboratories, Deerfield, Ill.) with refilling of the cylinder at timed I5 min intervals. Blood samples were obtained from the contralateral arm by means of a similar catheter. Blood was collected at the midpoint of each hour and urine was collected by voluntary voiding every hour. During a 2-hr control period 500 ml containing 78 mEq of sodium chloride and 20 mEq of potassium chloride were administered. This was followed by a 2-hr test period. One thousand milliliters were infused and contained either I55 mEq of sodium chloride, 167 mEq sodium lactate (Baxter Laboratories, Malton, Ontario, Canada) with 40 mEq potassium chloride, or 150 mEq of bicarbonate, 96 mEq chloride, 40 mEq potassium and 206 mEq sodium. This test period was followed by an additional 2-hr period during which a further 500 ml containing 75 mEq sodium chloride and 20 mEq potassium chloride were infused. At the termination of the procedure an electrocardiogram was performed to detect abnormal T waves due to alkalinization and subsequent

hypokalemia and none were observed. sodium as sodium chloride was ingested the extracellular fluid volume depletion

In two subjects receiving lactate infusions, 40 mEq of daily for 3 days prior to the test in an attempt to minimize of fasting. The results were not affected by this pretreat-

Table 1. Clinical Summary

Subject

NormalMean

Age

Sex

f SD

Serum

24.Hr Urine

Uric Acid

Uric Acid

(mg/lOOmi)

5.2 -f 1.5*

426*

CCr (ml/min)

(me)

811

Cur/Ccr 100

Admission

Height

Weight (kg)

(cm)

5.4 f 2.17

HB

26

F

5.7

290

133

2.7

85.6

162

LB

17

M

5.3

440

133

4.3

81.8

178

cc

34

F

6.1

370

119

3.5

86.5

157

HL

46

M

7.4

670

75

a.4

151.9

188

FM

27

F

5.5

340

119

3.6

80.2

165

RM

37

F

7.1

140

73

1.9

133.3

157

JN

37

F

a.8

600

108

8.1

143.2

170

SP

28

F

6.8

250

KN

40

F

6.9

500

150

3.4

GG

55

F

4.4

460

92

WC

31

F

6.5

500

93

WC

42

M

8.1

600

CT

26

F

5.0

LB

51

M

EB

37

F

*From Mikkelson&al?' tFrom Smithand S~ott.?~ fFrom Seegmilleretal!6

96.3

167

96.5

152

14.9

94.2

158

5.8

117.3

165

116

4.4

107.6

178

700

165

5.9

135.2

168

5.7

700

132

6.5

100.1

163

9.0

200

97

1.6

107.0

173

URIC ACID DURING

553

FASTING

ment. For the acetylsalicylic acid test, three successive 2-hr clearance periods were employed beginning at 0800 hr. Six hundred milliliters of water were ingested from 0700 to 0800 hr. Blood was collected at the midperiod on three occasions by separate venepuncture. After the first 2-hr period 600 mg acetylsalicylic acid were administered orally. No adverse effects occurred during or after the period of study in any subject, except for mild tingling of the extremities in two subjects following the infusion of bicarbonate. Similar studies employing lactate, bicarbonate, and acetylsalicylic acid were performed under identical conditions following an overnight fast. Blood samples were drawn and distributed as follows: (1) anaerobically into heparinized syringes for pH and pco, determinations, (2) into tubes without anticoagulant for the determination of serum sodium, potassium, chloride, creatinine, and uric acid, and (3) immediately placed in an equal volume of lOoA perchloric acid at 4°C for determination of lactate, pyruvate, acetoacetate, and @-hydroxybutyrate. Aliquots of voided urine were immediately distributed into tubes, for sodium, potassium, chloride, phosphate, creatinine. and uric acid determination. An aliquot was immediately diluted in an equal volume of 10% perchloric acid and frozen at -20°C. For 24-hr collections, urine was collected without preservative, kept refrigerated, and then aliquots were frozen at - 20°C for subsequent assay. The serum and urine uric acid were assayed by the uricase method” in the acute studies. The urine oxypurines were measured by an enzymatic spectrophotometric procedure.‘* Creatinine from acute studies was quantified by the method of Brod and Sirota.” Lactate, pyruvate, acetoacetate, and P-hydroxybutyrate were determined by enzymatic fluorimetric microtechniques.’ Samples of both blood and urine for pyruvate and acetoacetate were assayed on the same day, and all other determinations were performed on specimens which had been frozen at -20°C for no longer than 7 days. Other measurements were performed by standard autoanalyzer techniques. Urate binding protein was assayed at 4°C with 15 mg/lOO ml of uric acid using the equilibrium dialysis method of Klinenberg and Kippen.” Statistical analysis was performed using the paired or unpaired two-tailed Student’s t test where appropriate. RESULTS

Serum and Urine Uric A cid (Fig. 1) During the first week of fasting the following changes were observed in 11 patients: (1) the serum uric acid concentration increased from 5.9 f 0.4 to 12.5 * 1.0 mg/lOO ml (p < O.Ol), (2) the clearance of uric acid (Curate) decreased from 5.5 S=0.9 to 1.8 f 0.2 ml/min (p < O.Ol), (3) the serum creatinine concentration rose from 0.9 f 0.1 to 1.2 f 0.1 mg/lOO ml (p < 0.01) while the creatinine clearance (Ccreatinine) decreased from 114 + 11 to 80 f 6 ml/min ( p < 0.01) (4) the percentage Curate:Ccreatinine diminished from 5.4 f 1.3 to 2.4 f 0.3% (p < 0.05), and (5) the blood P-hydroxybutyrate and acetoacetate concentrations increased to 4.2 f 0.3 and 0.9 f 0.07 mM. From day 7 to day 28 of fasting the following changes occurred: (1) the serum uric acid concentrations diminished to 7.7 f 1.3 mg/lOO ml (p < O.Ol), (2) Curate increased to 4.4 A 1.3 mg/lOO ml ( p < 0.05), a value not different from day 0, (3) Ccreatinine remained low at 64 + 6.3 ml/min, (4) the percentage Curate:Ccreatinine increased to 9.1 * 3.7”/0 (p < 0.05), (5) the concentrations in the blood of P-hydroxybutyrate ranged between 4.2 f 0.3 to 4.8 A 0.5 mM and of acetoacetate ranged between 0.91 + 0.05 and 1.19 f 0.28 mM, and (6) the clearance of acetoacetate and @-hydroxybutyrate did not increase after the first week of fasting. The clearance values for /3-hydroxybutyrate are given in Table 2. During this time one patient (CC) became hypouricemic with a serum uric acid of 1.5 mg/lOO ml, a Curate of 14.8 ml/min and a Curate:Ccreatinine of 32.8%. There was no evidence of generalized proximal tubular dysfunction as in-

FOX ET AL

”

a

IO

0

20

30

DAYS Fig. 1. Serum uric acid and uric acid clearance during starvation. Eleven patients were studied during total therapeutic fasting. The mean values plus or minus the standard error of the mean are shown for the serum uric acid (A), the renal clearance of uric acid and creatinine (B), and the blood values of p-hydroxybutymte and acetoacetate (C).

dicated by glycosuria, bicarbonaturia, or increased phosphaturia during the fasting period. The urine uric acid excretion did not decrease after the first week of fasting despite the reduction in the serum uric acid (Table 3). Urine oxypurines in two patients were decreased from 228 to 90 and from 256 to 64 @moles/24 hr from day 0 to day 21 of fasting. Table 2. Clearance of &Hydroxybutymte

During Starvation CleOrOnCe

Fasting Day

mljmin

l13.1 f A.7

1

*Values

are expressed

os plus

3

13.4 f A.3

5

29.4 f A.6

7

30.3 zt 3.8

14

22.9

i

21

21.5

i

2.9

28

25.2

f

A.6

or minus

the

standard

error

2.5

of the mean for the

11 patients

studied.

URIC ACID DURING

555

FASTING

Table 3. Urine Uric Acid Excretion During Starvation

Fasting Do7

Serum Uric

Urine Uric

Uric Acid

Creatinine

Acid

Acid

Cl~DKl~C~

CbXCJiKe

(mg/lOO

ml)

(ml/min)

hg/do7)

(mljmin)

0

6.2 f 0.5*

449 f 57

5.5 * 0.9

114*

12

3

a.4 f 0.8

236 i

36

2.1 i 0.3

100*

12

5

11 .o f 0.9

249 f

39

1.6 * 0.2

103 f

7

12.5 i

316 i

46

1.8 f 0.2

80 f

6

14 21 20

1.0

12

10.5 * 0.9

281 i 47

1.9 + 0.2

71 f

7

a.5 rt

i .2

261 + 47

2.7 zt 0.6

71 i

5

7.7 f

1.3

329 i

4.4 i

64 f 6

48

1.5

*Values are expressed as plus or minus the standard errar of the mean far the 11 patients studied.

Renal Handling of Uric Acid The diminution of the serum uric acid together with an increase in the Curate: Ccreatinine which occurred beyond 7 days of fasting might have been mediated by an alteration in urate binding protein or a change in the renal tubular handling of uric acid or both. However, there was no significant decrease in the urate bound during the time when the serum uric acid was diminishing (Table 4). The renal handling of uric acid was evaluated after 3 wk of fasting (Fig. 2). The infusion of sodium lactate resulted in a 63% decrease of Curate:Ccreatinine during the l-2 hr collection period in the overnight fasted state as has been previously observed.r6 In the prolong ed fasted state the same lactate infusion caused a 63% increase of Curate:Ccreatinine, a value significantly different from the overnight fasted state (p < 0.02). The blood lactate concentrations rose from a mean vaiue of 802 A 92 to a steady-state value of 2045 f 200 ~h4 and the pyruvate concentrations from 50 i 9 to 115 f 20 PM. Four to 7 days after refeeding, ketosis was no longer present and the response to a sodium lactate infusion was similar to that observed in the overnight fasted state with a 440/d, decrease of Curate:Ccreatinine during the l-2 hr collection period. The systemic acid base changes induced by the sodium lactate were reproduced by an infusion of sodium bicarbonate. This resulted in a 91% increase in Curate: Ccreatinine (p < 0.01) during the 2-3 hr collection period, a value similar to fable 4. Urate Binding Protein During Fasting Uric Acid Bound’ Da7

0

W)

11.4 i 1.5

3

11.1 i 1.7

8

12.5 zt1.8

14

11.9 10.6

33

14.9 il.1

*Values are mean f

SE from seven patients.

556

FOX

ET AL.

I

0

2

4

0 t,me

2

4

(hours)

The renal handling of uric acid. Patients were either in the prolonged fasting (x -x) fasting (e-e) state. The Curate:Ccnatinine is expressed as a percentage of the control value plus or minus the standard error of the mean. (A) Sodium lactate 167 mEq was infused into four prolonged fasting and three overnight fasting subjects during O-2 hr. (B) Sodium bicarbonate 150 mEq was infused into three prolonged fasting and three overnight fasting subjects during O-2 hr. (C) Acetylsalicylic acid 600 mg was given orally at 0 hour to five prolonged fasting and four overnight fasting subjects. (D) Sodium chloride 155 mEq was infused into four prolonged fasting subjects during O-2 hr. Fig. 2.

or overnight

the effect observed with sodium lactate. The bicarbonate infusion had no effect on the renal excretion of uric acid in the overnight fasted state. The response of the renal handling of uric acid to 600 mg of acetylsalicylic acid was also evaluated. In the overnight fasted state there was a 28% reduction in Curate: Ccreatinine during the 2-4 hr collection period, whereas in the prolonged fasted state there was a 65% increase in Curate:Ccreatinine. These values were significantiy different (p < 0.05). To evaluate the possible role of extracellular fluid volume expansion induced by the lactate infusion an equivalent quantity of isotonic saline was infused. This produced a small but insignificant increase in Curate:Ccreatinine during the l-2 hr collection period. In vitro studies of urate binding protein showed no significant inhibition by lactate in concentrations up to 20 mM. During these acute studies there was no significant change in the glomerular filtration rate, glycosuria was not observed and there was no change in the degrees of phosphaturia. DISCUSSION

Uric acid is normally excreted into the urine by glomerular filtration and bihas been directional tubular transport. 7-9 In the fasted state, ketoacidemia shown to alter the renal clearance of uric acid by an effect on these tubular transport mechanisms.2-6 Hyperuricem i a was observed in the present study but was not sustained (Fig. 1). After the first week the mean serum uric acid concentration gradually diminished and approached normal values within 4 wk. This secondary fall in the serum uric acid is present in the data of others.’ The decrease in the serum uric acid concentration was accompanied by a progres-

URIC ACID DURING

FASTING

557

sive increase in the renal clearance of uric acid which occurred despite a concurrent and sustained fall in the creatinine clearance and sustained ketoacidemia (Fig, 1). A similar reduction in the glomerular filtration rate, as measured by inulin clearances, has been observed previously during fasting” and may be related to the extracellular fluid volume contraction. The renal handling of uric acid was assessed when the serum uric acid was approaching the normal range (Fig. 2). The administration of sodium lactate or low dose acetylsalicylic acid, which ordinarily cause a diminution in the renal clearance of uric acid,‘6.‘8 resulted in a uricosuric effect. The failure of an isotonic sodium chloride infusion to alter significantly the excretion of uric acid tends to exclude extracellular fluid volume expansion as the major explanation for the uricosuric effect of lactate in this study. The similar results obtained with infusions of either sodium lactate or sodium bicarbonate may be explained by the observed decrease in systemic acidemia or urine pH.19 However, acetylsalicylic acid caused similar modifications of the renal handling of uric acid in the absence of acid-base effects. This eliminates acid-base alterations as the only etiologic basis for the uricosuric effects observed. In the overnight fasted state low dose salicylate decreases the Curate:Ccreatinine while high dose salicylate has a uricosuric effect. ” This phenomenon has also been described for other weak organic acids. 20*2’In the prolonged fasted patients low dose salicylate increased the fractional excretion of uric acid (Fig. 2C). Thus salicylate and the ketoacid anions may have an additive effect with the net result being similar to high dose salicylate. However, this mechanism cannot explain the continued increase in the renal clearance of uric acid in the face of a relatively constant ketonemia and ketonuria during 7-28 days of prolonged fasting. The similarities in the influences of the weak organic acids studied upon the renal tubular handling of uric acid suggests that there may be a related renal transport process for these compounds. If this were the case, it would be predicted that the renal handling of other organic acids may be similarly affected. Indeed such effects were observed. The administration of lactate, bicarbonate, or acetylsalicylate resulted in an increase of the renal clearance of lactate, pyruvate, P-hydroxybutyrate and acetoacetate.‘* Although the decrease in serum uric acid during prolonged fasting appears to be accounted for by a modification of the renal tubular handling of uric acid, a diminution in the production of uric acid could theoretically contribute to this decrease. No reduction of the urine uric acid excretion was observed after the first week of fasting (Table 3). However, to interpret this as unchanged urate production is difficult because of the variable factor of intestinal uricolysis and the progressively increasing uric acid clearance. If inhibition of xanthine oxidase accounted for a decrease of uric acid synthesis, then an increase of urine oxypurines would be the result. In fact a decrease in urine oxypurines was observed in the two patients in whom they were determined. However, an inhibition of purine biosynthesis de novo with a subsequent decrease of uric acid synthesis remains a possible contributing factor to the diminution of the serum uric acid in our studies. Although this has been previously observed in fasting rats,23 no data are available for man. The increasing renal clearance of uric acid after the first week of the keto-

FOX ET AL.

558

nemia of starvation may be beneficial to fasting man. This change leads to a progressive diminution in the serum uric acid and thus could prevent the tissue deposition of urate. ACKNOWLEDGMENT The authors wish to thank Dr. David Sinclair for performing the in vitro mate binding protein studies with lactate, Dr. Howard Stein for performing the studies using acetylsalicyhc acid alone, the nursing staff of the Clinical Investigation Unit of the Toronto General Hospital and of Women’s College Hospital, the technical assistance of Thelma Peregrino-Solomon, Maria Leung, Rina Thumm, Nancy Cochron, Arjumand Hasan, and Wayne Chisnell and Janice MacKellar for typing the manuscript.

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purine biosynthesis de novo in the rat spleen. Clin Sci Mol Med 46:37-47, 1974 24. Mikkelsen WM, Dodge HJ, Valkenburg H: The distribution of serum uric acid values in a population unselected as to gout or hyperuricemia. Tecumseh, Mich. 1959-1960, Am J Med 39:242-251, 1965

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subjects.

Ann

AI, Laster L. in gout. J Clin