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Increased urinary excretion of glycerol: Metabolic studies on a patient
391
Clinica Chimica Acta, 80 (1977) 391-393 @ Elsevier/North-Holland Biomedical Press
SHORT COMMUNICATION CCA 8893
INCREASED URINARY EXCRETION STUDIES ON A PATIENT
J. PALO
*, C. SERVO,
E. PITKANEN
OF GLYCEROL:
METABOLIC
and P. TAMMISTO
Department of Neurology and Fourth Department of Medicine, University of Helsinki, and Research Department, Rinnekoti Institution for the Mentally Retarded, Helsinki (Finland) (Received
May 6th, 1977)
Among 900 mentally retarded patients four individuals were discovered who excreted large amounts of glycerol in the urine [l]. The identity of the compound was confirmed with chromatographic and enzymatic tests, and possible artifactual sources were excluded. The 24-h excretion varied between 1130 pmol and 4100 pmol, in contrast to normal controls who only excreted from 6.7 pmol to 33.3 pmol per day. The plasma glycerol values varied between 58 pmol/l and 105 pmol/l in the patients and between 27 pmol/l and 78 pmol/l in the controls. The observation period extended up to 1.5 years. No association was found between excretion and mental retardation. It was suggested that the excretion was due to inability to reabsorb glycerol from the glomerular filtrate
[Il. No other cases of increased urinary excretion of glycerol have meanwhile been reported. Because the patients seemed thus to represent a unique metabolic aberration the urine specimens of the four retarded patients were now re-examined. Two of the retarded patients were male and two were female. They were born between 1947 and 1959. One represented Down’s syndrome (mongolism) and three suffered from severe cerebral palsy due to premature birth or unknown aetiology. A more detailed description of the patients was given in the previous paper [ 11. The excretion of glycerol had remained on the same level in all four patients, i.e., it exceeded 1130 pmol per day. Routine clinical examinations, including differential cell count of the blood, urine sediment, and serum creatinine levels, X-ray of the skull, spine, chest and long bones, as well as electroencephalography and neuropsychological tests, revealed no signs of progressive neurological, haematological or kidney disease.
* Correspondence 00290
Helsinki,
to Dr. J. Palo. Finland.
Department
of Neurology,
University
of Helsinki,
Haartmaninkatu
4.
392
One of the retarded patients, a male born in 1959, was selected for a special examination. A retarded female of the same age and living in the same ward was selected as a control. The renal function of both subjects was normal. Plasma, urine and cerebrospinal fluid (CSF) glycerol was determined with an enzymatic micro method [ 21. For basal plasma and CSF levels, and for urinary excretion of glycerol both subjects were followed up for 7 h on a randomlyselected day. Seven different plasma and urine samples and one CSF specimen were collected during that period. In fructose and glycerol loading tests 1 g of each substance was given per 1 kg body weight after overnight fasting. The plasma levels of glycerol were measured 30, 60 and 120 min after the oral dose. Urine was collected for 5 to 13 h after the beginning of the loading test and 2 to 4 different samples were obtained. Glycerol was measured from each specimen. The basal plasma levels of glycerol were similar in the patient and in the control (Table I). No glycerol was found in their CSF. The excretor’s urine contained ca. 30 times more glycerol than that of the control. The estimated filtration rate of glycerol was approximately similar in the two subjects but the estimated fraction excreted from the filtrate into the urine was near 100% in the excretor while it appeared to be only 10% in the control. A slight and transient increase was observed in the plasma glycerol concentration of both subjects after the fructose and glycerol loads but the total amount of glycerol excreted into the urine remained essentially unchanged (Table I). The estimated fraction excreted of the filtrate varied from 13 to 40%
TABLE
1
The basal plasma, cerebrospinal fluid (CSF). and urinary concentrations of glycerol (~~mol, mean and range) in one patient with increased urinary excrrtion of glycerol (cxcretor) and in one control. The measurements were made from 5 different blood and urine specimens and from one CSF of both subjects. The estimated glomerular filtration. calculated as plasma level X creatinine clearance (~mol/sec, range), and the estimated fraction of glycerol excreted into the urine (~mol/sec, mean) are also given. Except for CSI’, the same determinations were made on both subjects after oral loading tests with fructose> and glycerol. The plasma values represent the mean and range of 3 specimens and those for urine the mean and range of 2 to 4 specimens (see the text for other details). The endogenous creatinine clearance of the rxcrrtor was 2.3 ml/set and that of the control 1.45 ml/set.
Basal conditions Plasma glycerol CSF‘ glywrol Urinary glycerol Filtration Excretion intu urine F’ructosr loading Plasma glycerol Urinary
glvrcrol
Filtration Excretion Glvwrol
into
urine
Exrretor
Control
65 (45-110) 0 1 R80 (900-2550) 0.05~xI.5 0.14
6.5 (25.-95) 0 60 (50-65) 0.03--0.12 0.008
95 (85-100) 1580 (1170~1800) 0.10 0.23 0.36
85 (80--100) 60 (55-65) o.oc,~-~.l 3 0.016
111) (X5-170) 1 x55 (1 500~-2200) 0.1 o-o.45 0.60 ~~~
115(110~120) 90 (SO -100) 0.08--0.09 0.01 2
loading
Plasma g.lycerol Urinarv glyccr<,l Filtratinn Excwtion into urme
~~
393
in the control while at least 100% of the estimated filtrate was constantly excreted by the patient, Less than 1% of the glycerol administered orally to the patient was found in the urine during a follow-up of 5 h. The main source of blood glycerol (mol. wt. 92.10) is the adipose tissue where during lipolysis both free fatty acids and glycerol are formed. Glycerol is converted into glucose during gluconeogenesis where glycerokinase (GK) is required 133. The normal turnover is about 1.8 pmol/s but can increase fourfold during fasting [4]. Intravenous glycerol is known to become partly reabsorbed in the proximal tubuli [ 51. A defect in the metabolism of glycerol can lead into increased amounts of glycerol in the organism if the phosphorylation of glycerol is impaired. This phospho~lation is dependent on GK which is found in the liver and kidney [ 31. A decreased activity of GK in the kidney should therefore result in an accumulation of glycerol in the kidney and possibly increased excretion of glycerol into the urine. The very slight increase of plasma glycerol in the glycerol loading test, comparable to that of the control patient, did not support this hypothesis. It seemed during the glycerol loading test that the excreted glycerol fraction (0.60 pmol/sec) exceeded the estimated glomerular filtration of the patient (0.10-0.45 pmol/sec) suggesting also tubular excretion of glycerol but, since glomerular filtration rate was determined after and not during the glycerol loading, the possibility must be considered that glycerol itself increased the glomerular filtration rate. Fructose is known to be split into three-carbon fragments by kidney aldolase. A metabolic derangement in the tubular cells might lead into increased levels of a-glycerophosphate with subsequently increased urinary excretion of glycerol. Therefore, an increase in the excretion of glycerol during the fructose loading test. might have been anticipated but no such increase was observed. It thus appears that the glyceroluria is due to a disturbed reabsorption capacity of the tubuli rather than to a metabolic defect in the tubular cells. Furthermore, this disturbance seems not to be directly connected with a neurological disease and no clinical signs of a kidney disease have developed in the patient during an observation period of more than 10 years. Since the disturbance has recently been detected also in an apparently healthy female with normal intelligence it may be concluded that it is a harmless phenomenon. No hereditary features have been found. The activity of GK and an analysis of renal biopsies will be the subjects of further studies. Acknowledgements We thank Professor A. Pasternack for advice and Mrs. H. Jorasmaa for tcchnical assistance. This study was supported by grants from the National Research Council for Medical Sciences and the Rinnekoti Research Institute. References 1
PitkXnen,
2
Sheath.
E. and
3
WinklPr,
4
Bortz..,
5
Kruh#ffrr.
J.B. B.,
Palo,
(1970) Rathgeb.
W.M.,
Paul, P.
J.
(1967) Ann.
CIin.
Biochem.
I.. Steele. P.,
Haff,
R.
A.C.
and Nissan, 0.1.
Med.
Exp.
Fenn.
45.
SO-93
3, 339-341 and
and
(1963)
Altszuler,
Holmes, Acta
N. W.L.
Physiol.
(1970)
Am.
J. Physical.
(1972)
J. CLin.
Invest.
Stand.
59, 284-294
219, 51,
497-502
1537-1546
Clinica Chimica Acta, 80 (1977) 391-393 @ Elsevier/North-Holland Biomedical Press
SHORT COMMUNICATION CCA 8893
INCREASED URINARY EXCRETION STUDIES ON A PATIENT
J. PALO
*, C. SERVO,
E. PITKANEN
OF GLYCEROL:
METABOLIC
and P. TAMMISTO
Department of Neurology and Fourth Department of Medicine, University of Helsinki, and Research Department, Rinnekoti Institution for the Mentally Retarded, Helsinki (Finland) (Received
May 6th, 1977)
Among 900 mentally retarded patients four individuals were discovered who excreted large amounts of glycerol in the urine [l]. The identity of the compound was confirmed with chromatographic and enzymatic tests, and possible artifactual sources were excluded. The 24-h excretion varied between 1130 pmol and 4100 pmol, in contrast to normal controls who only excreted from 6.7 pmol to 33.3 pmol per day. The plasma glycerol values varied between 58 pmol/l and 105 pmol/l in the patients and between 27 pmol/l and 78 pmol/l in the controls. The observation period extended up to 1.5 years. No association was found between excretion and mental retardation. It was suggested that the excretion was due to inability to reabsorb glycerol from the glomerular filtrate
[Il. No other cases of increased urinary excretion of glycerol have meanwhile been reported. Because the patients seemed thus to represent a unique metabolic aberration the urine specimens of the four retarded patients were now re-examined. Two of the retarded patients were male and two were female. They were born between 1947 and 1959. One represented Down’s syndrome (mongolism) and three suffered from severe cerebral palsy due to premature birth or unknown aetiology. A more detailed description of the patients was given in the previous paper [ 11. The excretion of glycerol had remained on the same level in all four patients, i.e., it exceeded 1130 pmol per day. Routine clinical examinations, including differential cell count of the blood, urine sediment, and serum creatinine levels, X-ray of the skull, spine, chest and long bones, as well as electroencephalography and neuropsychological tests, revealed no signs of progressive neurological, haematological or kidney disease.
* Correspondence 00290
Helsinki,
to Dr. J. Palo. Finland.
Department
of Neurology,
University
of Helsinki,
Haartmaninkatu
4.
392
One of the retarded patients, a male born in 1959, was selected for a special examination. A retarded female of the same age and living in the same ward was selected as a control. The renal function of both subjects was normal. Plasma, urine and cerebrospinal fluid (CSF) glycerol was determined with an enzymatic micro method [ 21. For basal plasma and CSF levels, and for urinary excretion of glycerol both subjects were followed up for 7 h on a randomlyselected day. Seven different plasma and urine samples and one CSF specimen were collected during that period. In fructose and glycerol loading tests 1 g of each substance was given per 1 kg body weight after overnight fasting. The plasma levels of glycerol were measured 30, 60 and 120 min after the oral dose. Urine was collected for 5 to 13 h after the beginning of the loading test and 2 to 4 different samples were obtained. Glycerol was measured from each specimen. The basal plasma levels of glycerol were similar in the patient and in the control (Table I). No glycerol was found in their CSF. The excretor’s urine contained ca. 30 times more glycerol than that of the control. The estimated filtration rate of glycerol was approximately similar in the two subjects but the estimated fraction excreted from the filtrate into the urine was near 100% in the excretor while it appeared to be only 10% in the control. A slight and transient increase was observed in the plasma glycerol concentration of both subjects after the fructose and glycerol loads but the total amount of glycerol excreted into the urine remained essentially unchanged (Table I). The estimated fraction excreted of the filtrate varied from 13 to 40%
TABLE
1
The basal plasma, cerebrospinal fluid (CSF). and urinary concentrations of glycerol (~~mol, mean and range) in one patient with increased urinary excrrtion of glycerol (cxcretor) and in one control. The measurements were made from 5 different blood and urine specimens and from one CSF of both subjects. The estimated glomerular filtration. calculated as plasma level X creatinine clearance (~mol/sec, range), and the estimated fraction of glycerol excreted into the urine (~mol/sec, mean) are also given. Except for CSI’, the same determinations were made on both subjects after oral loading tests with fructose> and glycerol. The plasma values represent the mean and range of 3 specimens and those for urine the mean and range of 2 to 4 specimens (see the text for other details). The endogenous creatinine clearance of the rxcrrtor was 2.3 ml/set and that of the control 1.45 ml/set.
Basal conditions Plasma glycerol CSF‘ glywrol Urinary glycerol Filtration Excretion intu urine F’ructosr loading Plasma glycerol Urinary
glvrcrol
Filtration Excretion Glvwrol
into
urine
Exrretor
Control
65 (45-110) 0 1 R80 (900-2550) 0.05~xI.5 0.14
6.5 (25.-95) 0 60 (50-65) 0.03--0.12 0.008
95 (85-100) 1580 (1170~1800) 0.10 0.23 0.36
85 (80--100) 60 (55-65) o.oc,~-~.l 3 0.016
111) (X5-170) 1 x55 (1 500~-2200) 0.1 o-o.45 0.60 ~~~
115(110~120) 90 (SO -100) 0.08--0.09 0.01 2
loading
Plasma g.lycerol Urinarv glyccr<,l Filtratinn Excwtion into urme
~~
393
in the control while at least 100% of the estimated filtrate was constantly excreted by the patient, Less than 1% of the glycerol administered orally to the patient was found in the urine during a follow-up of 5 h. The main source of blood glycerol (mol. wt. 92.10) is the adipose tissue where during lipolysis both free fatty acids and glycerol are formed. Glycerol is converted into glucose during gluconeogenesis where glycerokinase (GK) is required 133. The normal turnover is about 1.8 pmol/s but can increase fourfold during fasting [4]. Intravenous glycerol is known to become partly reabsorbed in the proximal tubuli [ 51. A defect in the metabolism of glycerol can lead into increased amounts of glycerol in the organism if the phosphorylation of glycerol is impaired. This phospho~lation is dependent on GK which is found in the liver and kidney [ 31. A decreased activity of GK in the kidney should therefore result in an accumulation of glycerol in the kidney and possibly increased excretion of glycerol into the urine. The very slight increase of plasma glycerol in the glycerol loading test, comparable to that of the control patient, did not support this hypothesis. It seemed during the glycerol loading test that the excreted glycerol fraction (0.60 pmol/sec) exceeded the estimated glomerular filtration of the patient (0.10-0.45 pmol/sec) suggesting also tubular excretion of glycerol but, since glomerular filtration rate was determined after and not during the glycerol loading, the possibility must be considered that glycerol itself increased the glomerular filtration rate. Fructose is known to be split into three-carbon fragments by kidney aldolase. A metabolic derangement in the tubular cells might lead into increased levels of a-glycerophosphate with subsequently increased urinary excretion of glycerol. Therefore, an increase in the excretion of glycerol during the fructose loading test. might have been anticipated but no such increase was observed. It thus appears that the glyceroluria is due to a disturbed reabsorption capacity of the tubuli rather than to a metabolic defect in the tubular cells. Furthermore, this disturbance seems not to be directly connected with a neurological disease and no clinical signs of a kidney disease have developed in the patient during an observation period of more than 10 years. Since the disturbance has recently been detected also in an apparently healthy female with normal intelligence it may be concluded that it is a harmless phenomenon. No hereditary features have been found. The activity of GK and an analysis of renal biopsies will be the subjects of further studies. Acknowledgements We thank Professor A. Pasternack for advice and Mrs. H. Jorasmaa for tcchnical assistance. This study was supported by grants from the National Research Council for Medical Sciences and the Rinnekoti Research Institute. References 1
PitkXnen,
2
Sheath.
E. and
3
WinklPr,
4
Bortz..,
5
Kruh#ffrr.
J.B. B.,
Palo,
(1970) Rathgeb.
W.M.,
Paul, P.
J.
(1967) Ann.
CIin.
Biochem.
I.. Steele. P.,
Haff,
R.
A.C.
and Nissan, 0.1.
Med.
Exp.
Fenn.
45.
SO-93
3, 339-341 and
and
(1963)
Altszuler,
Holmes, Acta
N. W.L.
Physiol.
(1970)
Am.
J. Physical.
(1972)
J. CLin.
Invest.
Stand.
59, 284-294
219, 51,
497-502
1537-1546