BIOLOGICAL TRACE ELEMENT RESEARCH 2, 193-198 (1980)
Rubidium--A Possible Essential Trace Element 1. The Rubidium Content of Whole Blood of Healthy and Dietetically Treated Children I N G R I D L O M B E C K , l'*
K.
KASPEREK, 2
L. E. FEINENDEGEN, 2 AND n.
J. BREMER l
l University Children's Hospital C, University of DiJsseldorf Moorenstrasse 5, D-4000 Dfzsseldorf 1, Federal Republic of Germany, and 2Medical Institute, Nuclear Research Centre of JiJlich GmbH, D-5170 JiJlich, Federal Republic of Germany Received March 3, 1980; Accepted April 16, 1980
Abstract The rubidium content of whole blood was estimated by instrumental neutron activation analysis. In 46 healthy children it amounts to = I 1.47 _ 2.88 X 10-6g/g dry weight. There was no difference between the values found for infants, toddlers, and school children. In 29 dietetically treated patients with phenylketonuria and maple-syrup-urine disease the values were significantly lower than in healthy children. During the first three months of diet therapy the rubidium levels remained in the lower range of the normal values, decreasing to about 60% of the mean of normal values later on. With increasing length of diet therapy these values tended to decrease. It remains questionable whether these decreased levels reflect only an induced biochemical phenomenon without biological importance, or whether they are the first signs of a deficiency syndrome.
Index Entries: Rubidium, as a potential essential trace element; blood, rubidium content of; childhood, rubidium levels in blood during; normal values, of rubidium in blood; dietary treatment of rubidium deficiency. 9 1980 The Humana Press Inc. All rights of any nature whatsoever reserved.
0163-4984/80/06004)193502.00
193
194
LOMBECK ET AL.
Introduction Rubidium, a heavier alkali element, has similar biochemical properties to those of potassium. Therefore, its radioisotope, rubidium-86, is often used to trace potassium metabolism. Rubidium substitutes potassium to some extent, but has certain effects on growth and longevity that preclude full interchangeability. Purified diets containing 0.02% or more rubidium decrease survival time of rats (4, 12). Mammals including monkeys first show irritability, hyperactivity, aggressiveness and convulsions. Purified diets containing 0.2% rubidium are not toxic (4). Contradictory information exists on the biological effects of trace amounts of rubidium. It is not clear whether rubidium levels of 0.01% or less are a dietary essential and stimulatory amount for animals or not (4, 11). Previously published work neglected the biological functions of rubidium, while recent research postulates essentiality (4, 6, 15, 17). One main feature of all essential trace elements is fulfilled by rubidium: It occurs in all tissues examined. The concentrations exhibit a low relative variance (1, 13, 14). The fact that significant differences in rubidium content occur not only in different organ systems (13, 24), but also in different inbred strains (17) strongly supports the notion of its essentiality and suggests that its concentration is genetically controlled. At the moment then, rubidium may be said to belong to those trace elements with suspected biological function, and is a possible essential trace element (16, 21). The whole rubidium content of human adults is assumed to be 0.36 + 0.09 g (24). The main excretory route is through the urine, and the rate of clearance is slightly less than that of potassium (8). Following intravenous administration of rubidium-86, 39-134 days were required for one-half to be excreted in the urine and feces (2), while 30 min after intravenous administration less than 5% remained in the total circulatory blood (12). In humans, the red cells show a maximum uptake within 30 min, and maintain this content despite a rapidly decreasing plasma level. The blood uptake at 24 h, however, was lower than that of any other tissue examined except that of the brain (19). Rubidium treatment is said to enhance the turnover of brain norepinephrine (18), but its mechanism of action is not known. The intracellular distribution reveals the highest content in the supernatant fraction; mitochondrial and sacortubular fractions have a reduced content compared to the heart as a whole (21). In brain tissue, the content was found to differ significantly between defined functional regions and to decrease with increasing age (5, 6). In general on a dry basis, soft tissues contain more rubidium than bone (4). The rubidium content of whole blood is mainly determined by the rubidium content of the erythrocytes (1, 20, 23). Our studies were undertaken to estimate the normal values of rubidium in the whole blood of healthy children at various ages. These values were
RUBIDIUM--APOSSIBLEESSENTIALTRACEELEMENT
195
compared to those from patients with phenylketonuria or maple-syrupurine disease treated with semisynthetic diets.
Material and Methods Blood samples were taken from 46 infants and children of various ages between 8 and 9 AM while they were still in the fasting state. These samples were aliquots of those taken for routine analysis before minor operations, e.g., uncomplicated hernia. Samples containing 0.5-1.0 mL of whole blood were kept in weighed silicon tubes and dried at 100~C for 48 h. Instrumental neutron activation analysis was performed as described by Kasparek (7). The neutron flux was 5 X 10~3n/cmLs, and the activation time was 48 h. After a decay time of about 30-40 days, the rubidium content was determined by measuring the gamma rays of S6Rb by a multichannel impulse height analyzer combined with a 90 cm 3well-type Ge(Li)-detector for 3000 s. The relative error of analysis was less than 5%. In addition, blood samples from four patients with maple-syrup-urine disease and 25 patients with phenylketonuria were taken during routine monitoring of their plasma amino acid concentrations. With the exception of four patients, they were treated by approved dietary methods (9) for more than 3 months (3 months to 8 years). During this time, 60-80% of their protein need was provided by amino acid mixtures and by protein hydrolysates free of phenylalanine or the branched chain amino acids. These basal diets were supplemented by vitamins, minerals, and eight trace elements known to be essential for mammalian life, and did not contain extra rubidium. In addition, the patients were given vegetables, fruits, low-protein bread and small amounts of cow's milk according to their individual need for the respective amino acids. The patients thrived well during the time of observation. The rubidium concentration values of the healthy children and those of the dietetically-treated patients were compared by the Wilcoxon rank test.
Results (1) The rubidium content of the whole blood of healthy children (n = 46) amounts to ~ = 11.47 ___2.88 • 10-6g/g dry weight. The values are distributed normally (Fig. 1). There is no significant difference between the values found in infants, toddlers, and school children (Table 1). (2) The rubidium content of whole blood was significantly lower (p < 0.01) in 29 dietetically-treated patients with phenylketonuria or maple-syrup-urine disease than in healthy children (Table 1). In infant
196
LOMBECK ET AL.
percentage 30-
Rubidium content of w h o l e b l o o d
20-
10-
-7 I
i
'
'
I
'
'
'
10
5
'
I
15
. . . .
I
20 Rb 10-6 gig dry weight
FIG. 1. Rubidium content in the whole blood of healthy children and its distribution (n = 46). TABLE 1 Rubidium Content of Whole Blood
Age, Years
Number of patients sampled Diet therapy
Rubidium content of whole blood, 10-6/g dry weight Mean
SD
Range
0.1-1 0.1-1
8 9
0 +
11.41 a 7.50a
3.22 2.16
9.7-16.7 4.9-13.0
1-5 1-5
19 14
0 +
11.65~ 6.24~
2.87 1.09
7.9-16.3 4.9-8.6
5-12 5-12
10 5
0 +
11.55~ 5.00~
2.62 1.50
10.1-14.1 3.5-7.0
"p ~0.01. patients during the first three months of dietary therapy the values remain in the lower range of the normal values. With increasing length of diet therapy the values tend to decrease further in later childhood. There is no difference between the rubidium content of whole blood in patients treated for phenylketonuria or for maple-syrup-urine disease.
RUBIDIUM--A POSSIBLE ESSENTIAL TRACE ELEMENT
197
Discussion The levels of rubidium in the whole blood of healthy children reveal no agedependency. Our values are in good agreement with those cited in literature for adults (1, 3). Dietetically-treated patients with phenylketonuria and maple-syrupurine disease reveal reduced whole blood rubidium content. These differences were obvious after a period of dietary treatment of more than 1-3 months. The potassium intake, however, is not known to show significant differences from that of healthy children. Therfore, a reduced rubidium intake owing to the use of a special diet is the most likely reason for the reduced rubidium content in whole blood, just as has been found for reduced selenium content (9). Industrial processing is known to change the rubidium content of infant food (10). In humans, reduced rubidium contents of serum and muscles were reported in chronic uremic patients before and during dialysis (14). An increased urinary excretion and a decreased serum concentration of rubidium were reported in hypertensive patients during treatment with chlorthalidone (22). The significance of these findings is far from being clear. As long as our knowledge of the biological effects of rubidium is so incomplete, we do not know whether or not deficiency states exist. Further research is needed to learn more about the biochemical actions of rubidium in adults and growing children.
Acknowledgment The authors gratefully acknowledge the support of the Deutsche Forschungsgemeinschaft.
References 1. G. Bertrand and D. Bertrand, Ann. Inst. Pasteur 80, 227, 339 (1951). 2. G.E. Burch, S. A. Threefoot, and C. T. Ray, J. Lab. Clin. Med. 45, 371 (1955). 3. C. Chechan, X. Marchandise, and J. Lekieffre, C. R. Soc. BioL 169, 991 (1975). 4. B. L. Glendening, W. G. Shrenk, and D. B. Parrish, J. Nutr. 60, 563 (1956). 5. G. Henke, H. M611mann, and H. Aires, Z. Neurol. 199, 283 (1971). 6. A. H6ck, U. Demmel, H. Schicha, K. Kasperek, and L. E. Feinendegen, Brain 98, 49 (1975). 7. K. Kasperek, In Proceedings o f the Second International Conference on Nuclear Methods in Environmental Research, U.S. Energy Research and Development Administration, Conf. 740701, 1974.
198
LOMBECK ET AL.
8. A. S. Kunin, E. H. Deaborn, B. A. Burrows, and A. S. Relman, Am. J. Physiol. 197, 1297 (1959). 9. I. Lombeck, K. Kasperek, H. D. Harbisch, K. Becket, E. Schumann, W. Schr6ter, L. E. Feinendegen, and H. J. Bremer, Eur. J. Pediatr. 128, 213 (1978). 10. I. Lombeck, unpublished data. 11. W. D. Love and G. E. Butch, J. Lab. Clin. Med. 41, 351 (1953). 12. P. H. Mitchell, J. W. Wilson, andR. E. Stanton, J. Gen. Physiol. 4, 171 (1921). 13. L. O. Plantin, in Trace Elements in Relation to Cardiovascular Diseases, Technical Report, IAEA, Vienna, 1973, p. 91. 14. H. Rudolph, A. C. Alfrey, and W. R. Smythe, Trans. Am. Soc. Artif. Intern. Organs 19, 456 (1973). 15. H. Schicha, W. Mfiller, K. Kasperek, and R. Schr6der, Beitr. Path. 151, 281 (1974). 16. K. Schwarz, personal communication, Jiilich, 1975. 17. M. P. Siegers, K. Kasperek, H. J. Heiniger, and L. E. Feinendegen, in TEMA3, M. Kirchgessner, ed., Freising-Weihenstephan, (1978), p. 188. 18. J. M. Stolk, W. J. Nowack, and J. D. Barchas, Science 168, 501 (1970). 19. A. S. Freedberg, H. B. Pinto, and A. Zipser, Fed. Proc. 11, 49 (1952). .20. J. Versieck, H. Hoste, F. Barbier, H. Michels, and J. De Rudder, Clin. Chem. 23, 1301 (1977). 21. P. O. Wester, Acta Med. Scand. 439, 7 (1965). 22. P. O. Wester, Acta Med. Scand. 194, 505 (1973). 23. O. L. Wood, Biochem. Med. 3, 458 (1970). 24. N. Yamagata, J. Radiat. Res. 3, 9 (1962).
Rubidium--A Possible Essential Trace Element 1. The Rubidium Content of Whole Blood of Healthy and Dietetically Treated Children I N G R I D L O M B E C K , l'*
K.
KASPEREK, 2
L. E. FEINENDEGEN, 2 AND n.
J. BREMER l
l University Children's Hospital C, University of DiJsseldorf Moorenstrasse 5, D-4000 Dfzsseldorf 1, Federal Republic of Germany, and 2Medical Institute, Nuclear Research Centre of JiJlich GmbH, D-5170 JiJlich, Federal Republic of Germany Received March 3, 1980; Accepted April 16, 1980
Abstract The rubidium content of whole blood was estimated by instrumental neutron activation analysis. In 46 healthy children it amounts to = I 1.47 _ 2.88 X 10-6g/g dry weight. There was no difference between the values found for infants, toddlers, and school children. In 29 dietetically treated patients with phenylketonuria and maple-syrup-urine disease the values were significantly lower than in healthy children. During the first three months of diet therapy the rubidium levels remained in the lower range of the normal values, decreasing to about 60% of the mean of normal values later on. With increasing length of diet therapy these values tended to decrease. It remains questionable whether these decreased levels reflect only an induced biochemical phenomenon without biological importance, or whether they are the first signs of a deficiency syndrome.
Index Entries: Rubidium, as a potential essential trace element; blood, rubidium content of; childhood, rubidium levels in blood during; normal values, of rubidium in blood; dietary treatment of rubidium deficiency. 9 1980 The Humana Press Inc. All rights of any nature whatsoever reserved.
0163-4984/80/06004)193502.00
193
194
LOMBECK ET AL.
Introduction Rubidium, a heavier alkali element, has similar biochemical properties to those of potassium. Therefore, its radioisotope, rubidium-86, is often used to trace potassium metabolism. Rubidium substitutes potassium to some extent, but has certain effects on growth and longevity that preclude full interchangeability. Purified diets containing 0.02% or more rubidium decrease survival time of rats (4, 12). Mammals including monkeys first show irritability, hyperactivity, aggressiveness and convulsions. Purified diets containing 0.2% rubidium are not toxic (4). Contradictory information exists on the biological effects of trace amounts of rubidium. It is not clear whether rubidium levels of 0.01% or less are a dietary essential and stimulatory amount for animals or not (4, 11). Previously published work neglected the biological functions of rubidium, while recent research postulates essentiality (4, 6, 15, 17). One main feature of all essential trace elements is fulfilled by rubidium: It occurs in all tissues examined. The concentrations exhibit a low relative variance (1, 13, 14). The fact that significant differences in rubidium content occur not only in different organ systems (13, 24), but also in different inbred strains (17) strongly supports the notion of its essentiality and suggests that its concentration is genetically controlled. At the moment then, rubidium may be said to belong to those trace elements with suspected biological function, and is a possible essential trace element (16, 21). The whole rubidium content of human adults is assumed to be 0.36 + 0.09 g (24). The main excretory route is through the urine, and the rate of clearance is slightly less than that of potassium (8). Following intravenous administration of rubidium-86, 39-134 days were required for one-half to be excreted in the urine and feces (2), while 30 min after intravenous administration less than 5% remained in the total circulatory blood (12). In humans, the red cells show a maximum uptake within 30 min, and maintain this content despite a rapidly decreasing plasma level. The blood uptake at 24 h, however, was lower than that of any other tissue examined except that of the brain (19). Rubidium treatment is said to enhance the turnover of brain norepinephrine (18), but its mechanism of action is not known. The intracellular distribution reveals the highest content in the supernatant fraction; mitochondrial and sacortubular fractions have a reduced content compared to the heart as a whole (21). In brain tissue, the content was found to differ significantly between defined functional regions and to decrease with increasing age (5, 6). In general on a dry basis, soft tissues contain more rubidium than bone (4). The rubidium content of whole blood is mainly determined by the rubidium content of the erythrocytes (1, 20, 23). Our studies were undertaken to estimate the normal values of rubidium in the whole blood of healthy children at various ages. These values were
RUBIDIUM--APOSSIBLEESSENTIALTRACEELEMENT
195
compared to those from patients with phenylketonuria or maple-syrupurine disease treated with semisynthetic diets.
Material and Methods Blood samples were taken from 46 infants and children of various ages between 8 and 9 AM while they were still in the fasting state. These samples were aliquots of those taken for routine analysis before minor operations, e.g., uncomplicated hernia. Samples containing 0.5-1.0 mL of whole blood were kept in weighed silicon tubes and dried at 100~C for 48 h. Instrumental neutron activation analysis was performed as described by Kasparek (7). The neutron flux was 5 X 10~3n/cmLs, and the activation time was 48 h. After a decay time of about 30-40 days, the rubidium content was determined by measuring the gamma rays of S6Rb by a multichannel impulse height analyzer combined with a 90 cm 3well-type Ge(Li)-detector for 3000 s. The relative error of analysis was less than 5%. In addition, blood samples from four patients with maple-syrup-urine disease and 25 patients with phenylketonuria were taken during routine monitoring of their plasma amino acid concentrations. With the exception of four patients, they were treated by approved dietary methods (9) for more than 3 months (3 months to 8 years). During this time, 60-80% of their protein need was provided by amino acid mixtures and by protein hydrolysates free of phenylalanine or the branched chain amino acids. These basal diets were supplemented by vitamins, minerals, and eight trace elements known to be essential for mammalian life, and did not contain extra rubidium. In addition, the patients were given vegetables, fruits, low-protein bread and small amounts of cow's milk according to their individual need for the respective amino acids. The patients thrived well during the time of observation. The rubidium concentration values of the healthy children and those of the dietetically-treated patients were compared by the Wilcoxon rank test.
Results (1) The rubidium content of the whole blood of healthy children (n = 46) amounts to ~ = 11.47 ___2.88 • 10-6g/g dry weight. The values are distributed normally (Fig. 1). There is no significant difference between the values found in infants, toddlers, and school children (Table 1). (2) The rubidium content of whole blood was significantly lower (p < 0.01) in 29 dietetically-treated patients with phenylketonuria or maple-syrup-urine disease than in healthy children (Table 1). In infant
196
LOMBECK ET AL.
percentage 30-
Rubidium content of w h o l e b l o o d
20-
10-
-7 I
i
'
'
I
'
'
'
10
5
'
I
15
. . . .
I
20 Rb 10-6 gig dry weight
FIG. 1. Rubidium content in the whole blood of healthy children and its distribution (n = 46). TABLE 1 Rubidium Content of Whole Blood
Age, Years
Number of patients sampled Diet therapy
Rubidium content of whole blood, 10-6/g dry weight Mean
SD
Range
0.1-1 0.1-1
8 9
0 +
11.41 a 7.50a
3.22 2.16
9.7-16.7 4.9-13.0
1-5 1-5
19 14
0 +
11.65~ 6.24~
2.87 1.09
7.9-16.3 4.9-8.6
5-12 5-12
10 5
0 +
11.55~ 5.00~
2.62 1.50
10.1-14.1 3.5-7.0
"p ~0.01. patients during the first three months of dietary therapy the values remain in the lower range of the normal values. With increasing length of diet therapy the values tend to decrease further in later childhood. There is no difference between the rubidium content of whole blood in patients treated for phenylketonuria or for maple-syrup-urine disease.
RUBIDIUM--A POSSIBLE ESSENTIAL TRACE ELEMENT
197
Discussion The levels of rubidium in the whole blood of healthy children reveal no agedependency. Our values are in good agreement with those cited in literature for adults (1, 3). Dietetically-treated patients with phenylketonuria and maple-syrupurine disease reveal reduced whole blood rubidium content. These differences were obvious after a period of dietary treatment of more than 1-3 months. The potassium intake, however, is not known to show significant differences from that of healthy children. Therfore, a reduced rubidium intake owing to the use of a special diet is the most likely reason for the reduced rubidium content in whole blood, just as has been found for reduced selenium content (9). Industrial processing is known to change the rubidium content of infant food (10). In humans, reduced rubidium contents of serum and muscles were reported in chronic uremic patients before and during dialysis (14). An increased urinary excretion and a decreased serum concentration of rubidium were reported in hypertensive patients during treatment with chlorthalidone (22). The significance of these findings is far from being clear. As long as our knowledge of the biological effects of rubidium is so incomplete, we do not know whether or not deficiency states exist. Further research is needed to learn more about the biochemical actions of rubidium in adults and growing children.
Acknowledgment The authors gratefully acknowledge the support of the Deutsche Forschungsgemeinschaft.
References 1. G. Bertrand and D. Bertrand, Ann. Inst. Pasteur 80, 227, 339 (1951). 2. G.E. Burch, S. A. Threefoot, and C. T. Ray, J. Lab. Clin. Med. 45, 371 (1955). 3. C. Chechan, X. Marchandise, and J. Lekieffre, C. R. Soc. BioL 169, 991 (1975). 4. B. L. Glendening, W. G. Shrenk, and D. B. Parrish, J. Nutr. 60, 563 (1956). 5. G. Henke, H. M611mann, and H. Aires, Z. Neurol. 199, 283 (1971). 6. A. H6ck, U. Demmel, H. Schicha, K. Kasperek, and L. E. Feinendegen, Brain 98, 49 (1975). 7. K. Kasperek, In Proceedings o f the Second International Conference on Nuclear Methods in Environmental Research, U.S. Energy Research and Development Administration, Conf. 740701, 1974.
198
LOMBECK ET AL.
8. A. S. Kunin, E. H. Deaborn, B. A. Burrows, and A. S. Relman, Am. J. Physiol. 197, 1297 (1959). 9. I. Lombeck, K. Kasperek, H. D. Harbisch, K. Becket, E. Schumann, W. Schr6ter, L. E. Feinendegen, and H. J. Bremer, Eur. J. Pediatr. 128, 213 (1978). 10. I. Lombeck, unpublished data. 11. W. D. Love and G. E. Butch, J. Lab. Clin. Med. 41, 351 (1953). 12. P. H. Mitchell, J. W. Wilson, andR. E. Stanton, J. Gen. Physiol. 4, 171 (1921). 13. L. O. Plantin, in Trace Elements in Relation to Cardiovascular Diseases, Technical Report, IAEA, Vienna, 1973, p. 91. 14. H. Rudolph, A. C. Alfrey, and W. R. Smythe, Trans. Am. Soc. Artif. Intern. Organs 19, 456 (1973). 15. H. Schicha, W. Mfiller, K. Kasperek, and R. Schr6der, Beitr. Path. 151, 281 (1974). 16. K. Schwarz, personal communication, Jiilich, 1975. 17. M. P. Siegers, K. Kasperek, H. J. Heiniger, and L. E. Feinendegen, in TEMA3, M. Kirchgessner, ed., Freising-Weihenstephan, (1978), p. 188. 18. J. M. Stolk, W. J. Nowack, and J. D. Barchas, Science 168, 501 (1970). 19. A. S. Freedberg, H. B. Pinto, and A. Zipser, Fed. Proc. 11, 49 (1952). .20. J. Versieck, H. Hoste, F. Barbier, H. Michels, and J. De Rudder, Clin. Chem. 23, 1301 (1977). 21. P. O. Wester, Acta Med. Scand. 439, 7 (1965). 22. P. O. Wester, Acta Med. Scand. 194, 505 (1973). 23. O. L. Wood, Biochem. Med. 3, 458 (1970). 24. N. Yamagata, J. Radiat. Res. 3, 9 (1962).
