Download Plasma Glucose, Non-Esterified Fatty Acids and Amino Acids in

Clinical Science and Molecular Medicine (1977) 52, 3 11-3 18.
Plasma glucose, non-esterified fatty acids
and amino acids in Huntington’s chorea
0.T. PH I L L I PSO N * A N D E. I). B I R D
MRC Neurochemical Pharmacology Unit, Department of Pharmacology,
Medical School, University of Cambridge, Cambridge, (I.K.
(Received 18 May 1976; accepted 22 October 1976)
Key words: amino acids, glucose, Huntington’s
chorea, insulin provocation test, non-esterified
fatty acids, tryptophan.
S-W
1. The metabolic responses to an oral glucose
tolerance test (100 g) and an intravenous insulin
provocation test (0.1 i.u./kg) were studied in
nine control subjects and nine patients with
Huntington’s chorea.
2. Plasma glucose responses to these stimuli
were identical in both groups.
3. High fasting concentrations of non-esterified fatty acid (NEFA) were recorded in the
choreic patients when compared with control
subjects. This difference was maintained under
hypoglycaemic conditions. However, during
hyperglycaemia the differences in NEFA
concentrations between the groups was abolished.
4. Total plasma tryptophan concentrations
were equal in the two groups. Free plasma
tryptophan, however, was markedly reduced in
the choreic group, and this appeared to be a
result of a disturbed relationship between free
tryptophan and NEFA concentrations. The
abnormalities in free tryptophan values were
sensitive to plasma glucose concentrations, as
hyperglycaemic conditions markedly reduced
the differences between the choreic and control
group.
5 . Patients with Huntington’s chorea showed
reduced fasting plasma concentrations of leucine, isoleucine and valine.
Abbreviation: NEFA, non-esterified fatty acids.
Introduction
In an earlier investigation of the characteristics
of growth hormone secretion in patients with
Huntington’s chorea (Phillipson & Bird, 1976)
it was found that patients with this disorder had
high fasting levels of growth hormone in plasma
and abnormal hormone responses both to an
oral glucose load and to intravenous insulin.
The present work investigates some of the consequences of these abnormalities in the same
group of subjects.
Growth hormone is known to be involved in
the release of free fatty acids from adipose
tissue stores (Raben & Hollenberg, 1959). In
the first part of our study, therefore, we examined the blood glucose and plasma NEFA
response to oral glucose and intravenous insulin
in patients with Huntington’s chorea and in
control subjects. The results show marked
abnormalities in plasma NEFA concentrations.
The influence of NEFA on the distribution of
free and bound tryptophan has been extensively
reviewed (Curzon & Greenwood, 1974). This
amino acid is particularly relevant as it appears
to play a part in the control of S-hydroxytryptamine (serotonin) synthesis in the brain (Knott
& Curzon, 1972; Biggio, Fadda, Fanni,
Tagliamonte & Gessa, 1974; Curzon & Knott,
* Present address: Department of Anatomy, Karolinska Institute, Stockholm, Sweden.
Correspondence: Dr Edward D. Bird, Department
of Neurological Surgery and Neurology, Addenbrookes
Hospital, Hills Road, Cambridge CB2 ZQQ, U.K.
31 I
312
0.T. Phillipson and E. D. Bird
1974). The chief effect of increased plasma
NEFA concentration is to decrease the degree
to which tryptophan is bound to plasma albumin
(Curzon, Friedel, Kantamaneni, Greenwood &
Lader, 1974). Furthermore, the degree of
plasma binding of tryptophan partly determines
the amount of free tryptophan available for
intracellular metabolism and synthesis of
5-hydroxytryptamine in brain. In addition to
these factors, however, tryptophan entry into
brain can be competitively inhibited by other
neutral amino acids, notably the branchedchain amino acids leucine, isoleucine and valine
(Fernstrom & Wurtman, 1972). The ratio of
tryptophan to these amino acids in plasma is
therefore important in controlling the rate of
tryptophan entry into brain (Fernstrom, Faller
& Shabshelowitz, 1975). T. L. Perry has shown
that the concentrations of several plasma amino
acids including leucine, isoleucine and valine
are reduced in patients with Huntington’s
chorea (Perry, Hansen, Diamond & Stedman,
1969). In the second part of the study we therefore present data on the concentrations of free
and total tryptophan in plasma and of the
amino acids which compete for the uptake of
tryptophan into the brain.
Methods
Criteria used for the diagnosis of Huntington’s
chorea were a positive family history, progressive chorea and progressive dementia. Nine
patients with the disease and nine age- and sexmatched control subjects were given a glucose
tolerance test (100 g orally) followed by an
insulin provocation test (0.1 i.u./kg, intravenously) the following day. None of the subjects was taking any drugs, with the exception
of three control subjects (treated with dihydrocodeine, ethinyloestradiol and clonidine) and
these three patients did not take any drugs on
the day of the tests. None of the subjects was
obese (i.e. greater than 15% over the ideal body
weight) and none of the controls had a history
of metabolic or endocrine abnormality. The
mean age of the choreic group was 43 years and
that of the control group 41 years. The mean
weight of the control group was 66 kg and that
of the choreic group 56 kg.
Patients had been eating their normal diets
before the tests. After an overnight period of
fasting, an indwelling cannula was inserted into
a forearm vein and connected to a slowly
running infusion of sodium chloride solution
(154 mmol/l; saline). Both control and choreic
groups received about the same volume of
saline throughout the tests. The patient was
then allowed to become accustomed to the
experimental situation for a further 30 min, after
which three base-line blood samples were
withdrawn at - 30, - 15 and 0 min before
either glucose or insulin was given. Blood was
taken thereafter every 30 min for 4 h. Samples
were kept at 4°C until centrifuged for 10 min at
room temperature at lo00 g. Plasma was then
separated and stored at -20°C until analysis.
Glucose was assayed in whole blood on a
Technicon Autoanalyser mark 2 by the standard
Neocuproine method (AA11-02).
NEFA were assayed by a colorimetric micromethod based on the formation of NEFAcopper soaps (Laurel1 & Tibbling, 1967). Total
and free tryptophan were determined by the
method of Denckla & Dewey (1967). Values for
free tryptophan obtained by this method were
found to be reproducibly lowered by the
increase in pH of the plasma from pH 7.9 to
about pH 8.1 which occurred before assay. The
characteristics of this change were studied and a
correction was made to obtain the true free
tryptophan value at pH 7.4 (G. Curzon, personal communication). Amino acids were
assayed on a Durrum D500 Automatic Amino
Acid Analyser after precipitation of plasma
proteins with equal volumes of trichloroacetic
acid (100 g/l). Plasma albumin was assayed by
a Bromocresol Green dye-binding method.
Consent for the studies was obtained both
from the patients and control subjects, and from
the Ethical Committee of the Hospital.
Significance of results was assessed by the use
of Student’s t-test.
Results
Plasma glucose (Fig. 1)
Fasting glucose concentrations before both
tests were similar in both the choreic group and
control subjects. In the glucose tolerance test,
the rise in glucose was slightly, but not significantly, faster in the choreic group compared
with control subjects, but the rest of the plasma
glucose curve was the same in both groups. In
the insulin provocation test there were no
significant differences between the groups.
Metabolic features of Huntington's chorea
313
.
Glucose
I
'4'/4
0"
I
2
4
3
Time ( h )
FIG. 1. (a) Glucose tolerance test (100 g of glucose orally) on the first day; (b) insulin provocation test
( 0 1 i.u. of insulin/kg, intravenously) on the second day. The histogram bars represent the mean* SEM of
plasma glucose in patients with Huntington's chorea, and the shaded area represents the width of the
SEM about the mean values for the plasma glucose in the control group.
--.
Glucose
r
Insulin
(a)
1
r
(b)
T
1
Trt
500
'
I
'/*
'40"
I
2
3
4
Time ( h )
FIG.2. Concentration of plasma NEFA in response to (a) oral glucose and (b) intravenous insulin.
Details are explained in the legend to Fig. 1.
Plasma NEFA (Fig. 2)
Fasting NEFA concentrations were significantly higher in the choreic group both before
the glucose tolerance test and the insulin
provocation test (P~ 0 . 0 1for
) all mean fasting
values of NEFA. However, in the glucose
tolerance test, 1 h after oral glucose, NEFA
concentrations in the choreic group were not
significantly different from in control subjects
and remained so for a further 2 h. Thereafter
NEFA in the choreic group increased to significantly higher concentrations than in control
subjects, as they approached their high fasting
values again.
In the insulin tolerance test, the differences
between fasting NEFA in choreic and control
groups were maintained throughout the whole
test. All mean values for choreic patients were
significantly different from control subjects
(PcOX)O5 for all mean values). Furthermore,
the degree of difference was maintained throughout the test, the mean values for choreic patients
being three to four times higher than control
values at each time-point.
0 . T. Phiflipson and E. D. Bird
314
Insulin
Glucose
(a)
I,
v.2
'v4 0"
I
2
3
'2
4
0"
3
2
I
4
Time ( h )
FIG.3. Plasma total tryptophan in response to (a) oral glucose and (b) intravenous insulin. Details are
explained in the legend to Fig. I .
Insulin
k2 '4 0"
(b)
I
I
2
3
4
Time(h)
FIG.4. Response of plasma free tryptophan to (a) oral glucose and (b) intravenous insulin. Details are
explained in the legend to Fig. 1.
Total tryptophan (Fig. 3)
Free tryptophan (Fig. 4)
There were no marked differences between
choreic and control groups in either the fasting
total tryptophan concentrations or the response
to either glucose or insulin. Indeed, theresponses
to the different stimuli were quite similar, the
total tryptophan tending to fall during the course
of both tests, the maximum fall in the glucose
tolerance test being 28% at 34 h and 34% at 3
h in the insulin test. There was a slight tendency
for the rate of fall to be greater in the control
subjects than in choreic patients in both tests.
In both the glucose tolerance test and insulin
test, fasting free tryptophan concentrations in
the choreic group were significantly lower than
in control subjects for all the mean fasting
values (P<O.o05 for all points). In the disease
group, the mean reduction in free tryptophan
for all fasting values was 43%. As with the
NEFA results, the differences between the two
groups was either reduced or abolished after
oral glucose, but were maintained significantly
throughout the insulin test.
Metabolic features of Huntington’s chorea
315
15r
t
0
I
I
I
0.1
0.2
0.3
I
I
I
0.4 0.5
0.6
NEFA ( m m l / l )
I
0.7
I
0.0
I
0.9
FIG.5. Relationship between plasma NEFA and free tryptophan in choreic patients ( 0 ) and control
subjects (A).
In the glucose tolerance test, there was a sharp
fall in free tryptophan in control subjects
compared with a slower fall in the choreic
group. In both groups intravenous insulin
caused a sharp fall in free tryptophan, followed
by a return of free tryptophan to normal concentrations at the time when NEFA values were
rising sharply. Throughout the test, the control
values were between 1.5 and 2.0 times those of
the disease group. Thus the shape of the curve
was identical in the two groups after insulin, but
differed after glucose.
A line with the best fit for each group of points
was calculated by linear regression analysis.
The value obtained for r was 0.71 in control
group and 0.74 in the choreic group. These
figures show that there is a relationship between
free tryptophan and NEFA in both groups, and
that the relationship is significant at the 1%
level. Both lines intercept t h e y axis at approximately the same point. However, the slope of
the lines appears quite different, so that increasing NEFA values cause very little change in
free tryptophan in the choreic group when
compared with the control group.
Relation between NEFA and plasma free
tryptophan (Fig. 5 )
Amino acid analyses (Table 1)
The values for the mean NEFA
tions at each time-point in both
plotted against the values for the
tryptophan at each corresponding
These analyses were performed on a separate
group of control subjects and choreic patients
from those studied for the glucose tolerance and
insulin provocation tests. In this case eight
concentratests were
mean free
time-point.
TABLE1. Plasma amino acids
Values represent fasting plasma amino acid concentration as
mean+sEM. * P<O.O5;** P < O O l .
Amino acid umol/l)
Control
Tyrosine
Phenylalanine
Leucine
isoleucine
Valine
4 6 2 + 3.6
43.2+ 1.8
95.2+40
56%+ 5-2
214.0+ 19.2
Huntington’s Reduction
chorea
(%)
39.2_+4.4
43.2_+3.6
85*0+54
39.8+3.2**
173-8+90*
11
30
19
316
0.T. Phillipson and E. D. Bird
controls and eight age- and sex-matched
patients with Huntington’s chorea were studied
and plasma was obtained by venepuncture
after an overnight fast. None of the control
subjects had a history of endocrine or metabolic
abnormalities and none of the subjects was
being treated with drugs. The procedure for
obtaining plasma was as described in the
Methods section. Significant reductions were
seen in the early morning fasting plasma concentrations of leucine (1 1%), isoleucine (30”,)
and valine (19%). Tyrosine and phenylalalanine
concentrations, however, were not affected
significantly.
Plasma albumin
Early morning fasting plasma albumin
concentrations were measured in the plasma
samples used for the amino acid analyses. The
mean value for the control group was 46.2 k 1.7
g of albumin/l compared with 45.5 f 0 . 9 g/l in
the choreic group.
Discussion
The main finding in the present study was that
concentrations of NEFA in fasting plasma
samples from patients with chorea were two- to
four-fold those in control subjects. We have
previously shown (Phillipson & Bird, 1976) that
the mean fasting plasma growth hormone
concentrations are raised in patients with
Huntington’s chorea. Abnormal growth hormone secretion has also been reported by other
workers (Podolsky & Leopold, 1974; Leopold
& Podolsky, 1975; Keogh, Johnson, Nanda &
Sulaiman, 1976). Growth hormone is known to
cause the release of NEFA from peripheral fat
depots (Raben & Hollenberg, 1959). It therefore
seems likely that the raised NEFA result at
least in part from increased growth hormone
secretion, although other factors such as
adrenocorticotrophic hormone or circulating
adrenaline, which are known to influence
circulating NEFA, cannot be excluded. It is
noteworthy that the differences in NEFA in
choreic patients and control subjects disappear
during the hyperglycaemic phase of the glucose
tolerance test, and re-appear as plasma glucose
concentrations return to normal (Fig. 2). On
the other hand, under hypoglycaemic conditions
during the insulin tolerance tests, the difference
between NEFA concentrations in control
subjects and choreic patients is qualitatively and
quantitatively maintained throughout the test.
The responses to insulin are therefore in marked
contrast to those obtained in the glucose tolerance test. It would seem therefore that the
metabolic abnormalities resulting in increased
circulating NEFA were corrected under hyperglycaemic conditions.
In our series of patients, there were no significant differences in plasma glucose responses in
either the glucose tolerance test or the insulin
provocation test when patients with Huntington’s chorea were compared with control
subjects. Podolsky, Leopold & Sax (1972)
reported that in a sub-group of patients with
Huntington’s chorea there was an exaggerated
increase in plasma glucose in response to oral
glucose. Even when we removed from our group
those patients who had the highest plasma
glucose concentrations in this test there did not
appear to be any difference from the control
group. Furthermore, there was no correlation
between duration of choreic symptoms and the
maximum blood glucose concentrations. The
reason for the difference in results is therefore
not clear, but may be a result of patient selection. To establish this possibility, studies of
much larger groups of choreic patients than the
ten studied by Podolsky et al. (1972), or the nine
in our group, will be necessary.
The second main difference between control
subjects and choreic patients in this study was
the reduced free tryptophan concentrations in
patients with Huntington’s chorea (Fig. 4).
Other workers have previously reported small
reductions in plasma tryptophan concentrations
(Perry et al., 1969). However, it is not certain
with their method that only free tryptophan was
being measured. It is clear from our results,
however, that total tryptophan concentrations
are normal in choreic patients and that only
free tryptophan is reduced. The distribution of
tryptophan in plasma, and in particular the
equilibrium between tryptophan bound to
plasma protein and free tryptophan, depends on
several factors. Since free and bound tryptophan
dissociate reversibly from plasma albumin
according to the laws of mass action, there is a
linear relation between the amount of free and
bound tryptophan. This relation holds experimentally both in vitro and in vivo (Curzon et al.,
1974), provided that amounts of tryptophan
Metabolic features of Huntington’s chorea
added do not saturate the binding sites on the
protein molecules. Since albumin is the chief
site of tryptophan binding to plasma and since
there appears to be only one binding site per
molecule (Curzon et al., 1974; McMenamy &
Oncley, 1958), alterations in plasma albumin
concentration may cause alterations in free
tryptophan. Our results indicate, however, that
plasma albumin concentrations are the same in
choreic patients and in control subjects.
The concentration of NEFA has been shown
to affect the degree of tryptophan binding to
purified albumin preparations (McMenamy,
1965) and whole human plasma. When NEFA
were added to human plasma at concentrations
within the physiological range (Curzon et al.,
1974) the amount of free tryptophan was
increased; furthermore, in whole animals in
which plasma NEFA were increased physiologically this was associated with increased free
tryptophan concentrations (Knott & Curzon,
1972; Curzon et al., 1974) and drugs affecting
plasma NEFA also cause corresponding changes
in free tryptophan concentrations (Curzon &
Knott, 1974). Thus there is a large body of
evidence showing a correlation between physiologically induced changes in plasma NEFA and
plasma free tryptophan. The correlation between
reduced NEFA and reduced free tryptophan
was shown to occur after oral glucose by Lipsett,
Madras, Wurtman & Munroe (1973). We
con6rm this result in our glucose tolerance test
both in patients with Huntington’s chorea and
control subjects and show in addition that the
relationship also holds true in the insulin
tolerance test (Fig. 4). However, although it was
expected that free tryptophan would be increased in choreic patients we found that the
free tryptophan decreased. The reason for this
puzzling result can be understood from Fig. 5.
Thus although choreic patients show, like
control subjects, a significant positive correlation between plasma free tryptophan and
NEFA, the slope of the line relating the two
variables is altered such that, despite a high
fasting concentration of NEFA in choreic
patients, the free tryptophan concentration is
reduced compared with control subjects. At low
NEFA concentrations and at high plasma
glucose concentrations these differences, however, tend to disappear. These results suggest
that the normal equilibrium between free and
bound tryptophan, and in particular its relation
317
to plasma NEFA, is disturbed. One possibility
is that the characteristics of tryptophan binding
to the albumin molecule are abnormal. A
second possibility, which we have been able to
test, is that the transport of free tryptophan out
of the plasma compartment, under conditions
of raised NEFA concentrations, is abnormally
rapid. Fernstrom & Wurtman (1972) proposed
that one factor controlling tryptophan transport
into brain was the concentrations of chiefly the
branched-chain amino acids (leucine, isoleucine
and valine), which compete for the same sites as
tryptophan for uptake into brain. This view has
gained support in other laboratories, for rats
(Biggio et al., 1974; Gessa, Biggio, Fadda,
Corsini & Tagliamonte, 1974) and man (PerezCruet, Chase & Murphy, 1974).
Thus, in brain, in the presence of lowered
concentrations of the branched-chain amino
acids it would be expected that tryptophan
transport out of the plasma compartment would
be increased and the amount of free tryptophan
lowered. Since we have shown that concentrations of all three branchedchain amino acids
are lowered, it is possible that this factor results
in the lowered free tryptophan observed in
choreic patients.
Huntington’s chorea is frequently associated
with increased appetite, increased food intake
and weight loss. The patients appear, in some
ways, to be starving. The biochemical features
of starvation in man have been thoroughly
studied. Among a wide range of biochemical
changes there are prolonged increases in growth
hormone output (Reichlin, 1973), increases in
plasma free fatty acids, which generate ketone
acids necessary for use as the main oxidative
fuel for the brain (Owen, Morgan, Kemp,
Sullivan, Herrera & Cahill, 1967), and reductions in plasma concentrations of leucine, isoleucine, valine and alanine (Felig, Owen,
Wahren & Cahill, 1969). We have previously
described increases in growth hormone secretion in choreic patients (Phillipson & Bird,
1976), and Perry et al. (1969) have described
reductions in plasma alanine, leucine, isoleucine
and valine concentrations. Our present results
show changes in plasma NEFA and confirm and
extend Perry’s observations on plasma amino
acids. The similarity between a metabolic
response to starvation and these results indicates
the need for further study of this area.
318
0 . T. Phillipson and E. D . Bird
Acknowledgments
We thank Dr Anthony Healey and Janet Baker
for expert advice and technical assistance with
the NEFA and tryptophan estimations, the
Department of Clinical Biochemistry, New
Addenbrooke’s Hospital for carrying out blood
glucose and albumin estimations, and Mr K.
Edwards, at the MRC Laboratory for Molecular
Biology, for the amino acid analyses.
References
Brccio, G., FADDA,
F., FANNI,P., TAGLIAMONTE,
A. &
GESSA,G.L. (1974) Rapid depletion of serum tryptophan, brain tryptophan, serotonin and 5-hydroxyindolacetic acid by a tryptophan-free diet. Life
Sciences, 14, 1321-1 329.
CURZON,
G., FRIEDEL,J., KANTAMANENI,
B.D., GREENWOOD, M.H. & LADER,M.H. (1974) Unesterified
fatty acids and the binding of tryptophan in human
plasma. Clinical Science and Molecular Medicine, 47,
415424.
CURZON,
G. & GREENWOOD,
M.H. (1974) Plasma protein binding: free and bound tryptophan. In:
Exerpta Medica International Congress Series no.
359, Proceedings of the I X Congress of the Collegium
Internationale Neuropsychopharmacologium, pp. 108116. Excerpta Medica.
CURZON,G. & KNOTT,P.J. (1974) Effects on plasma
and brain tryptophan in the rat of drugs and hormones that influence the concentration of unesterified fatty acid in the plasma. British Journal of
Pharmacology, 50, 197-204.
DENCKLA,
W.D. & DEWEY,
H.K. (1967) The determination of tryptophan in plasma, liver and urine. Journal
of Laboratory and Clinical Medicine, 69, 160-1 69.
FELIG,P., OWEN,O.E., WAHREN,
J. & CAHILL,G.F.,
J R (1969) Amino acid metabolism during prolonged
starvation. Journal of Clinical Investigation, 48, 584594.
FERNSTROM,
J.D., FALLER,
D.V. & SHABSHELOWITZ,
H.
(1975) Acute reduction of brain serotonin and 5HIAA
following food consumption: correlation with the
ratio of serum tryptophan to the sum of competing
neutral amino acids. Journal of Neural Transmission, 36, 113-121.
FERNSTROM,
J D. & WURTMAN,R.J. (1972) Brain
serotonin content: physiological regulation by
plasma neutral amino acids. Science, 178, 414-416.
GESSA,G.L., BIGGIO,G., FADDA,
F., CORSINI,G.U. &
TAGLIAMONTE,
A. (1974) Effect of the oral adminis-
tration of tryptophan-free amino acid mixtures on
serum tryptophan, brain tryptophan and serotonin
metabolism. Journal of Neurochemistry, 22, 869-870.
KEOGH,H.J., JOHNSON,R.H., NANDA,R.N. & SULAIMAN, W.R. (1976) Altered growth hormone release in
Huntington’s chorea. Journal of Neurology, Neurosurgery and Psychiatry, 39, 244-248.
KNOTT, P.J. & CURZON,G. (1972) Free tryptophan in
plasma and brain tryptophan metabolism. Nature
(London), 239,452453.
LAURELL,
S . & TIBBLING,
G. (1967) Colorimetric microdetermination of free fatty acids in plasma. CIinica
Chimica Acta, 16, 57-62.
LEOPOLD,N.A. & PODOLSKY,
S. (1975) Exaggerated
growth hormone response to arginine infusion in
Huntington’s disease. Journal of Clinical Endocrinology and Metabolism, 41, 160-163.
LIPSETT,D., MADRAS,
B., WURTMAN,
R.J. & MUNROE,
H.N. (1973) Serum tryptophan level after carbohydrate ingestion: Selective decline in non-albumin
bound tryptophan coincident with reduction in serum
free fatty acids. Life Sciences, 12. 57-64.
MCMENAMY,
R.H. (1965) Binding of indole analogues
to human serum albumin. Effect of fatty acids.
Journal of Biological Chemistry, 240, 4235-4243.
MCMENAMY,
R.H. & ONCLEY,
J.L. (1958) The specific
binding of L-tryptophan to serum albumin. Journal
of Biological Chemistry, 238, 3241-3248.
OWEN,O.E., MORGAN,A.P., KEMP,H.G., SULLIVAN,
J.M., HERRERA,
M.G. & CAHILL,G.F., JR (1967)
8-Hydroxybutyrate and acetoacetate replace glucose
as the brain’s primary fuel during starvation. Journal
of Clinical Investigation, 46, 1589-1595.
PEREZ-CRUET,
J., CHASE,T.N. & MURPHY,
D.L. (1974)
Dietary regulation of brain tryptophan metabolism
by plasma ratio of free tryptophan and neutral
amino acids in humans. Nature (London), 248.
693-695.
PERRY,T.L., HANSEN,
S.,DIAMOND,
S. & STEDMAN,
D.
(1969) Plasma amino acid levels in Huntington’s
chorea. Lancet, I, 806-808.
PHILLIPSON,
O.T. & BIRD,E.D. (1976) Plasma growth
hormone concentrations in Huntington’s chorea.
Clinical Science and Molecular Medicine, 50, 55 1-554.
PODOLSKY,
S. & LEOPOLD,
N.A. (1974) Growth hormone
abnormalities in Huntington’s chorea: effect of
L-dopa administration. Journal of Clinical Endocrinology and Metabolism, 39, 36-39.
PODOLSKY,
S., LEOPOLD,N.A. & SAX, D.S. (1972)
Increased frequency of diabetes mellitus in patients
with Huntington’s chorea. Lancet, i, 1356-1358.
RABEN,M.S. & HOLLENBERG,
C.H. (1959) Effect of
growth hormone on plasma fatty acids. Journal of
Clinical Investigation, 38, 484488.
REICHLIN,S. (1973) Physiology of growth hormone
regulation: pre- and post-immunoassay eras.
Metabolism, 22, 987-993.