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Journal of Neurology, Neurosurgery, and Psychiatry, 1976, 39, 61-65
Parallel variation of ventricular CSF tryptophan and
free serum tryptophan in man'
SIMON N. YOUNG,2 SAMARTHJI LAL, FRANCOIS FELDMULLER,
THEODORE L. SOURKES, ROBERT M. FORD, MAUREEN KIELY,
AND JOSEPH B. MARTIN
From the Department of Psychiatry, McGill University, and the Departments of Psychiatry, Neurology,
and Neurosurgery, Montreal General Hospital, Montreal, Quebec, Canada
Tryptophan was measured in the ventricular CSF and serum, and the neutral amino
acids leucine, isoleucine, valine, phenylalanine, and tyrosine were measured in the serum of two cases
with ventricular drains. Samples were taken every two hours for 24 hours in one case and for 16
hours in the other. The CSF tryptophan was correlated significantly with the free-that is, nonalbumin-bound-serum tryptophan but not with the total serum tryptophan. CSF tryptophan was
not correlated significantly with the ratio of free serum tryptophan to the sum of the neutral amino
acids. These data suggest that, in man, brain tryptophan concentrations are influenced by the free
and not the total serum tryptophan and that physiological variations of the neutral amino acids do
not appreciably influence the concentration of brain tryptophan.
SYNOPSIS
In experimental animals tryptophan hydroxylase,
the first and rate-limiting enzyme on the pathway to 5-hydroxytryptamine (5-HT), is not saturated with its substrate tryptophan in the brain
(Friedman et al., 1972). Because of this, the
brain 5-HT concentration can be affected by
even quite small changes in the brain tryptophan
concentration (Fernstrom and Wurtman, 1971).
The same is probably true in man, as tryptophan
administration will increase the concentration
of the 5-HT metabolite 5-hydroxyindoleacetic
acid (5-HIAA) in lumbar CSF. In this situation,
after tryptophan administration, the CSF 5HIAA and tryptophan concentrations are positively and significantly correlated (Ashcroft
et al., 1973). Thus, it is of interest to know what
controls the CNS tryptophan and, therefore,
the 5-HT concentration in the central nervous
system. This has recently been a subject of much
controversy.,
'This investigation received financial support from the Medical
Research Council (Canada) through grants to S. Lal and T. L. Sourkes,
A preliminary report of this work was presented at the meeting of
the Canadian Federation of Biological Sciences, Hamilton, June 1974.
2 Address for reprints: Laboratory of Neurochemistry, Allan Memorial Institute of Psychiatry, 1033 Pine Avenue West, Montreal,
Quebec, Canada.
(Accepted 13 August 1975.)
61
Most of the tryptophan in serum is bound to
albumin and only a small portion is in free solution. Some evidence suggests that it is the free
(non-albumin-bound) serum tryptophan concentration that controls the brain concentration
(Curzon and Knott, 1974; Gessa and Tagliamonte, 1974). However, conflicting reports suggest that it is the total and not the free serum
tryptophan that is important in regulating the
brain level (Fernstrom et al., 1974). The situation is further complicated by the possible involvement of the large neutral amino acids
(NAA), leucine, isoleucine, valine, phenylalanine, and tyrosine. These amino acids are probably transported into brain by the same carrier
system as tryptophan (Kiely and Sourkes, 1972).
Certain results suggest that there is competition
between all these amino acids for the transport
sites. Consequently, one suggestion is that the
brain tryptophan concentration follows the ratio
of the total serum tryptophan to the sum of the
large neutral amino acids (Fernstrom et al.,
1974).
The situation has been investigated in man by
taking blood and CSF samples from patients
before and after a meal (Perez-Cruet et al.,
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62
Simon N. Young et al.
1974). It was concluded that, in man, the lumbar
CSF tryptophan concentration is controlled by
the ratio of the free serum tryptophan to the sum
of the neutral amino acids.
We have now obtained further evidence on
the control of CSF (and perhaps brain) tryptophan concentration in man by serial sampling of
CSF and blood in two patients with ventricular
drains.
CASE REPORTS
CASE 1 This 59 year old man was in good
health until four weeks before admission, when he
developed ataxia on the left side, nystagmus on right
lateral gaze, and upgoing plantar reflex on the right.
A tumour of the left cerebellar hemisphere was removed and during surgery a ventricular drain was
inserted because of obstructive hydrocephalus. The
patient remained semicomatose after the operation.
Twelve days after surgery, ventricular CSF
samples (3 ml) were taken every two hours for 24
hours. These samples were taken through the ventricular drain. The fluid in the tubing was first discarded and the CSF for analysis was taken directly
from the ventricle. The total CSF passing down the
drain during the 24 hours of the study was about
200 ml.
During the study, the patient was given dexamethasone (4 mg every six hours, administered at 6 am,
12 noon, 4 pm, and 11 pm). He received glucose
intravenously (5%4 solution with 2000 units heparin
per litre) at the rate of 800 ml during the 24 hours.
Two hundred millilitres of Sustagen high protein
supplement (Mead Johnson) at half strength was
administered through a nasogastric tube at 5 pm,
9 pm, 8 am, and 12 noon. This volume contained 6 g
protein, 0.9 g fat, 16.6 g carbohydrate, 2.2 mmol
sodium, and 4.9 mmol potassium.
CASE 2 This 21 year old man was admitted in coma
with decerebration from acute meningitis. Development of obstructive hydrocephalus required insertion of a ventricular drain six days later. Samples of
CSF were taken every two hours for 16 hours as
described above, one day after the drain was inserted. The CSF was slightly xanthochromic. The
total volume passing down the drain over the 16
hours was about 300 ml. During this time the patient
received 1,550 ml 10%4 glucose containing 15 units
crystalline zinc insulin (Connaught) and 20 mmol
potassium per litre by continuous intravenous infusion. Every three hours he received a one-hour
infusion containing 3 megaunits ampicillin trihy-
drate. During the study at 9 pm and 9.15 am he
received a 600 mg aspirin suppository.
In addition, single ventricular CSF samples were
taken during ventriculography from 12 patients. The
diagnoses in these cases were subarachnoid haemorrhage (two cases), acute subdural haematoma,
carcinoma of lung with probable brain metastases, a
thalamic tumour, a recurrent left cerebellar astrocytoma, an aneurysm of the carotid bifurcation,
normal pressure hydrocephalus (two cases), and an
acoustic neuroma. In two cases CSF was taken
during revision of ventriculoperitoneal shunt. Of
these patients, six were male and six female. Their
average age was 48 years ± 11 (SD).
METHODS
Tryptophan was determined by the method of
Denckla and Dewey (1967). Free serum tryptophan
was taken as the tryptophan concentration in an
ultrafiltrate of serum. Serum was equilibrated with
5%0 CO2 at 37°C and the ultrafiltration was performed at 37°C using an Amicon propellantpressurized ultrafiltration cell with UM 10 membranes (nominal molecular weight cut-off 10,000).
Blood samples were taken within five minutes of the
CSF and put on ice immediately. The ultrafiltration
was performed within two hours.
5-HIAA was measured fluorimetrically after
partial purification on a column of Bio-Rex 5 resin,
as described previously (Young et al., 1975).
Homovanillic acid (HVA), the dopamine metabolite, was measured fluorimetrically after partial
purification by ethyl acetate extraction as described
by Papeschi and McClure (1971).
Serum amino acids were measured on a Beckman
120 C amino acid analyzer using the method of
Stein and Moore (1954).
RESULTS
Table 1 shows the concentration of tryptophan
and 5-HIAA in ventricular CSF of patients
TABLE 1
CONCENTRATION OF TRYPTOPHAN IN SERUM VENTRICULAR
CSF AND 5-HIAA IN VENTRICULAR CSF OF PATIENTS UNDERGOING VENTRICULOGRAPHY
Free serum tryptophan
Total serum tryptophan
% Serum tryptophan in free form
CSF tryptophan
CSF 5-HIAA
2,170 ± 1,540
12,600 ± 8,600
19.5 ± 8.7
1,620 ± 1,900
98 ± 71
Values (ng/ml) are the mean for 12 patients ± SD.
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Parallel variation of ventricular CSF tryptophan and free serum tryptophan in man
TABLE 2
100 <
z
63
CORRELATION COEFFICIENTS BETWEEN VARIABLES IN SERUM
AND CSF OF CASES 1 AND 2
50-
Case
Variables
0-L
14
-
CSF tryptophan
CSF tryptophan
CSF tryptophan
CSF tryptophan
CSF tryptophan
12-
10
°°.
6
E
v. total serum tryptophan
v. total serum tryptophan
Sum of NAA
v. free serum tryptophan
free serum tryptophan
V.
Sum of NAA
v. CSF 5-HIAA
1
2
0.28
-0.46
0.26
-0.45
0.57*
0.76*
0.01
0.04
0.17
-
Correlations are for 13 pairs of measurements in case 1 and nine in
case 2.
*P < 0.05.
co
2-
1.81.6 U,
0
1.4
-
1 .2 L
3
pm
-
I
I
.6
9
12
3
am
6
9
12
3
pm
shows the same for case 2. Table 2 gives correlations between some of the measured variables.
In both cases, CSF tryptophan is significantly
correlated with free serum tryptophan but not
with total serum tryptophan. In neither case is
the ratio of the free serum tryptophan to the sum
FIG. 1 Variation in CSF tryptophan, free and total
serum tryptophan, and serum NAA in case 1. The
patient was fed through a nasogastric tube as described in the case report at the times indicated by the
arrows.
60 z
40 -
undergoing neuroradiology. The mean for ventricular CSF tryptophan is above the mean reported previously of 860 + 68 (SE) ng/ml (Young
et al., 1974). However, in the present study,
seven of the 12 values were below 860 with the
other five values 1 120 ng/ml (from both the patient
with metastases and the one with a thalamic
tumour), 1730 (subarachnoid haemorrhage),
4490 (acute subdural haematoma), and 6520 ng/
ml (left cerebellar astrocytoma). Thus, the mean
in the present study probably does not reflect
the mean CSF tryptophan in healthy individuals.
Perhaps for this reason, there is no significant
correlation between any pair of the measured
variables given in Table 1.
Figure 1 shows the changes in the tryptophan
concentration of serum and CSF in case 1. Also
shown is the concentration in the serum of the
neutral amino acids (NAA) leucine, isoleucine,
valine, phenylalanine, and tyrosine. Figure 2
-j10`
8-
3LX
cc
-
2-
0.8
-
n6-
0.6
8
pm
FIG. 2
serum
10
12
2
4
6
8
10
12
am
Variation in CSF tryptophan, free and total
tryptophan, and serum NAA in case 2.
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Simon N. Young et al.
64
150
100
Le
50Oa
I
150
100-
E;n
3
pm
FIG.
3
6
9
12
3
am
6
9
12
3
pm
Variation ofCSFHVA and S-HIAA in case 1.
of the neutral amino acids significantly correlated with the CSF tryptophan.
Figure 3 shows the variation of 5-HIAA and
HVA in the ventricular CSF of case 1. There is a
fairly close correlation between 5-HIAA and
HVA in the first nine samples (r = 0.67, P < 0.05)
but not for the whole series of thirteen samples
(r= -0.15).
It was not possible to make similar measurements on CSF from case 2 because the CSF was
slightly xanthochromic and because the patient
had received aspirin which interferes with the
assay procedure.
DISCUSSION
This study shows a relationship between CSF
and free serum tryptophan concentrations in two
individuals. While this is not proof that a similar
relationship holds in the general population, it
does support the idea that free, and not total,
serum tryptophan is a factor controlling the ventricular CSF tryptophan concentration. We did
not find that the NAA influence the CSF tryptophan concentration. This is unlike the conclusions of Perez-Cruet et al. (1974). They made pre-
and postprandial measurements in plasma and
lumbar CSF and concluded that the CSF
tryptophan concentration follows the ratio of
the free plasma tryptophan to the sum of NAA.
In their study, the mean NAA changed from
57.0 to 81.5 ,ug/ml. In our study, the sum of NAA
varied from a low of 20.4 to a high of 90.6
,ug/ml in case 1 and from 34.8 to 57.8 tg/ml in
case 2. Therefore, our findings that the NAA do
not influence CSF tryptophan was not due to a
small range of NAA concentration.
In our present study, the relationship that is
revealed between free serum tryptophan and CSF
tryptophan in the two longitudinal studies is not
apparent in the cross-sectional study (Table 1
and text), nor was any such relationship revealed
in a previous cross-sectional study with lumbar
CSF (Young et al., 1975). Thus, the baseline
concentrations probably vary too greatly to show
up any relationship such as can be found in
longitudinal studies.
In our previous work (Young et al., 1975), we
found no change in lumbar CSF tryptophan
after three days of probenecid administration,
although the free serum tryptophan increased.
Even in the present study, the CSF tryptophan
concentration does not follow the free serum
tryptophan very closely. For example, in case 1
a decline in free serum tryptophan from 5400
ng/ml to 1800 ng/ml (a 67% decrease) was
accompanied by a decline in CSF tryptophan
from 1730 ng/ml to only 1300 ng/ml (a 25%
decrease). There are obviously other factors influencing CSF tryptophan concentrations, especially over longer time periods.
In this investigation, tryptophan was measured
in the CSF, as CSF is the closest approach to the
brain available in living humans. It is likely that
changes in ventricular CSF tryptophan concentration do reflect changes in brain tryptophan.
In the rat changes in cisternal CSF tryptophan
concentration tend to follow changes in the brain
tryptophan (Young, Etienne, and Sourkes, in
preparation). Thus, our results on the control of
CSF tryptophan in man probably also apply to
the brain tryptophan.
It is impossible to say if the very high tryptophan concentrations found in the CSF of a small
number of the patients undergoing neuroradiological investigation reflect similarly high brain
concentrations. Although the cause of these high
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Parallel variation of ventricular CSF tryptophan andfree serum tryptophan in man
values is unknown, it is probably related to the
underlying brain pathology, as no such high
values have been found in lumbar CSF except in
patients with a specific clinical condition, hepatic
cirrhosis (Young et al., 1975). The high ventricular CSF tryptophan may be related to tissue
damage, as rats with a unilateral hemisection
of the brain have high brain tryptophan concentrations on the side of the lesion (Bedard et
al., 1972). The mean ventricular CSF tryptophan
concentration that we reported previously
(Young et al., 1974) may be an overestimate of
the concentration found in healthy individuals,
as that study may also have included some individuals with pathologically elevated CSF
tryptophan. Although none of the patients in
that study had a very high value, two were above
1000 ng/ml. Thus the small gradient of tryptophan concentration that we reported previously
between ventricles and lumbar CSF may not
exist. The absence of any gradient is consistent
with the finding that CSF tryptophan was the
same in cisternal and lumbar CSF in a patient
with a complete block of CSF flow at the
thoracic level (Young et al., 1973).
The correlation between CSF 5-HIAA and
HVA that occurred for part of the time in case 1
was possibly due to variations in the activity of
the uptake system that removes these compounds
from CSF. If this were so, variations in the
5-HIAA concentration in CSF would not have
been a good index of variations in brain 5-HT
turnover. This might explain why the CSF
tryptophan and 5-HIAA concentrations were
not correlated.
We would like to thank M-W Hfiung for skilful technical assistance.
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Downloaded from http://jnnp.bmj.com/ on March 6, 2016 - Published by group.bmj.com
Parallel variation of ventricular
CSF tryptophan and free serum
tryptophan in man.
S N Young, S Lal, F Feldmuller, T L Sourkes, R M
Ford, M Kiely and J B Martin
J Neurol Neurosurg Psychiatry 1976 39: 61-65
doi: 10.1136/jnnp.39.1.61
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