(Received October 17; accepted for publication December 2, 1969.)
ADDRESS: (R.D.F.) St. Louis Children’s Hospital, 500 South Kingshighway Boulevard, St. Louis, Missouri 63110.
PEDIATRICS, Vol. 45, No. 5, May 1970 782
CIRCADIAN
PERIODICITY
OF
BLOOD
AMINO
ACIDS
IN
THE
NEONATE
Ralph D. Feigin, M.D., and Morey W. Haymond, M.D.
Froni time Division of Infectious Diseases, Department of Pediatrics, Washington Uniuer.sit,j
School of Medicine, St. Louis Children’s Hospital, St. Louis, Missouri
ABSTRACT. Blood amino acids were obtained
every 4 hours for 24 hours from 46 full-term
in-fants who were between 1 hour and 120 hours of
age when first sampled. Blood was also obtained at
0400 and 1200 hours on the same day from 10
ad-ditional infants, aged 48 to 72 hours at the time of
study, for more detailed analysis of individual
blood amino acids. Periodicity of total blood amino
acids was demonstrated as early as the first day of
life in some infants. This blood amino acid
rhyth-micity was similar but not identical to that
pre-viously observed in adults and older children.
Con-centrations of blood amino acids were minimal at
0400 hours and peaked between 1200 and 2000
hours. Periodicity of individual blood amino acids
was similar to that for total blood amino acids but
much less consistent. The presence of periodicity
for plasma tyrosine was demonstrable even in two
patients with neonatal tyrosinemia.
Since plasma amino acids vary normally as a function of time, “normal values” must be
standard-ized for time of day. Pediatrics, 45:782, 1970, BLOOD
AMINO ACIDS, CIRCADIAN, PERIODICITY, NEWBORN INFANTS.
P
HYSIOLOCIC rhythms have been thesub-ject of considerable interest in recent
years. The term “circadian,” first proposed
by Halberg,1 has been used to refer to those
biological rhythms which have a period of
about
( circa ) a day
( diem )
. Theimpor-tance of circadian rhythms in man should
not be underestimated because reports of
circadian periodicity of RNA and DNA
me-tabolism confirm their presence, even on a
subcellular level.2 An understanding of
these rhythms may be important in relation
to an evaluation of normal physiologic
re-sponses and to the pathogenesis and
ther-apy of disease.
Circadian periodicity of blood amino
acids in man was first described by Feigin,
et al., and these findings were confirmed by
Wurtman
and his
associates.4 These andad-ditional studies5 designed to evaluate the
factors affecting blood amino acid
rhythmi-city were performed in adult subjects. This
understanding of normal blood amino acid
periodicity permitted a systematic
evalua-tion of blood amino acid changes in human
infection68 and the documentation that
these changes are a sensitive biochemical
indicator of both viral and bacterial
infec-tion in adult subjects. Blood amino acid
changes may occur in the absence of overt
disease or cultural or serological evidence
of infection.
Studies of blood amino acids in children 3
to 9 years of age, immunized with HPV-77
rubella vaccine, have been reported
recently.#{176} Normal blood amino acid
rhyth-micity in unimmunized controls and a
change in periodicity in immunized
sub-jects was described. These changes in blood
amino acid periodicity were the earliest
recognizable sign of infection and
corre-lated direcfly with having successful
im-munization.
These recent reports suggest that an
evaluation of blood amino acid
concentra-tion and periodicity may be useful in the
rapid diagnosis of infectious disease in
chil-dren. The urgency for early diagnosis of
infection is perhaps most marked in the
neo-natal period. Since interpretation of
infec-tion-related blood amino acid changes is
320
280
24(
200
bc
b200
1600 2000 2400CLOCK HOURS
0400 0800
783
amino acid rhythmicity, a study was
de-signed to determine whether blood amino
acid periodicity was detectable in the
neo-natal period.
MATERIALS
AND
METHODS
Clinical Studies
Parental consent was obtained prior to
accepting any patient for the study group.
Fifty-six healthy, full-term infants (> 2,500
gm, 39 weeks’ gestation), 1 to 5 days of age
were used for study. A patient was included
in the study group only after a pediatrician,
independent of the investigators,
deter-mined that the neonate was in good health
and asserted that pregnancy and delivery
were uneventful. No breast-fed infants
were included in the study population. All
infants resided in the normal, newborn
nur-sery at St. Louis Maternity Hospital and
were subjected to the usual nursery routine.
These nurseries were lighted around the
clock, but lights were dimmed between 10
P.M. (2200 hr) and 4 A.M. (0400 hr). All
infants were fasted for 12 hours; given 5%
dextrose and water every 4 hours for a
sub-sequent period of 12 hours; then fed
En-famil#{176}at 0700, 1100, 1500, 1900, 2300, and
0300 hours until discharge at 5 to 6 days of
age.
In 46 infants, approximately 0.1 ml of
whole blood was obtained by heel stick
every 4 hours around the clock beginning
at 0800 hours and concluding 24 hours
later. Nineteen infants were < 24 hours of
age when first sampled, 9 were 24 to 48 hours
of age, 6 were 48 to 72 hours of age, 5 were
72 to 96 hours of of age, and 7 were 96 to
120 hours of age. The blood obtained was
placed directly on Schleicher and Schuell
903 filter paper for subsequent analysis.
Heparinized blood (2 ml) was obtained by
antecubital veripuncture at 0400 hours and
1200 hours on the same day from 10
addi-tional infants aged 48 to 72 hours at the
time of study. This blood was immediately
spun, plasma was separated and frozen at
- 60#{176}C,and analysis was performed within
48 hours.
* Manufactured b Mead Johnson Company,
2404 Pennsylvania Street, Evansville, Indiana
47721.
FIG. 1. The total integrated value of amino acids/0.006 ml of whole blood
averaged for all 46 infants and days, plotted against hours of the day. The
mean value (dark black line) ± 1 standard error (shaded area) are
TABLE I
SIGNIFICANCE OF TIME DEPENDENT DIFFERENCES IN
BLooD AMINO ACID CONCENTRATIONS
FOR INFANTS OF EACH AGE
Time
0400 vs 0800
0400 vs 1200
0400 vs 1600
0400 vs 2000
2400 vs 1600
2400 vs 2000
Age in flours
0-24
24-48
48-72
72-96
96-120 Number of
Patients
19
9
6
3
7
0400 vs
0400 vs
0400 vs
0400 vs
2000 vs
2400 vs
0800 1200 1600 2000 1200 1200
0400 vs 1200
0400 vs 1600
0400 Vs 2000
0400 vs 1200
0400 vs 1600
0400 vs
0400 Vs
0400 Vs
2400 Vs
0.05
0.05 0.05 0.05 0.01 0.025 0800
1200 1600 1600 784
Laboratory Procedures
Amino acids in approximately 0.006 ml of
whole blood as determined by weight were
measured by the method of Efron, et al.,’#{176}
modified for purposes of semiquantitation
by densitometry as previously reported.’6
This method allows determination of single
amino acids cystine, glutamine, alanine,
alpha amino butyric acid, tryrosine,
phenyl-alanine, and proline;
arginine-lysine-histi-dine, glycine-aspartic-serine,
methionine-va-line-tryptophan, and leucine-isoleucine
were determined as groups. The sum of the
integrated values for each single amino
acid and amino acid group was called the
total integrated value. The error of the
method as calculated from three standard
deviations of the mean total integrated
value of 20 replicate determinations of the
same blood sample on the same day was
2.1%. The error of the method calculated
similarly from replicate determinations of
the same blood sample on 20 different days
was 5.7%. This method has proven
suffi-p Values ciently sensitive to detect even minimal
cir---- cadian changes in blood amino acid
con-0.02 centration and yields results similar to those
0.01 obtained using automated methods.3’
Con-0.01 current analysis of as many as 60 samples
per chromatography tank always permitted
simultaneous analysis of all samples
ob-tamed from a single individual at one time
0.025 and minimized changes attributable to
0.01 methodological variables.
To further document the changes
ob-0
:
served, specific quantitation of individual0.025 and total amino acids was obtained by use
of a Technicon Amino Acid Analyzer.t This
#{149}5 analysis was performed upon plasma
pre-pared for analysis as previously described.1’
RESULTS
Figure 1 illustrates results obtained when
the total integrated value in 0.006 ml of
whole blood is averaged for subjects and
days, with each point representing 46
de-terminations. The periodicity observed was
characterized by the occurrence of maximum
concentrations at 1200 and 1600 hours and
minimal concentrations at 0400 hours. The
difference between results obtained at 0400
and 0800, 1200, 1600, or 2000 hours is
sta-tistically significant (p <0.005). Similarly,
2400 hours concentrations were significantly
less than concentrations obtained at 1200
hours (p <0.005), 1600 hours (p <0.005),
0800 hours (p < 0.025), and 2000 hours
(p <0.01). There were no significant
dif-ferences between concentrations obtained
at 1200, 1600, or 2000 hours.
Figure 2 illustrates results obtained when
the mean total integrated value is plotted
by hours of the day for the subjects
sam-pled on each day. Periodicity of total blood
amino acids similar to that previously
de-+Manufactured by Technicon Corporation,
CLOCK HOURS
scribed is noted and begins during the first
24 hours of life. The significance of
time-dependent differences in blood amino acid
concentrations for infants of each age is
shown in Table I.
Although tile illustration of total blood
amino acid concentrations for neonates 1
through 5 days of age reveals relatively
similar daily results, Table I illustrates that
the data is not homogeneous. The greatest
number of statistically significant
differ-ences is noted for the day on which the
greatest number of subjects was tested,
with increasingly fewer statistically
signifi-cant differences as the number of subjects
tested decreased. Thus, only 13 of 19
sub-jects 24 hours of age at time of sampling
had a total blood amino acid periodicity
similar to the curve representative of the
group mean. Similarly, eight of nine infants
24 to 48 hours of age, four of six infants 48
to 72 hours of age, four of five infants 72 to
96 hours of age, and six of seven infants 96
to 120 hours of age showed minimal
con-centrations of total blood amino acids at
0400 hours and maximal concentrations
be-tween 1200 and 2000 hours.
Analysis of results obtained following
2
quantitation of individual amino acids or
amino acid groups by either the paper
chromatography method or the automated
method revealed much less consistency.
Specific results obtained following
auto-mated analysis of 0400 and 1200 hour
sam-ples in 3 of the 10 children aged 48 to 72
hours are presented in Table II. These
three children were chosen to represent the
spectrum of results obtained. In some
sub-jects, each individually quantitated amino
acid demonstrated periodicity similar to
that described for the total, with
concentra-tions at 0400 hours less than those obtained
at 1200 hours (Table II, Case 1). In others,
as many as 8 of 15 blood amino acids
showed concentrations at 0400 hours equal
to or greater than those obtained at 1200
hours (Table II, Case 2).
Neonatal tyrosinemia was noted in
sev-eral patients. Specific quantitation of blood
amino acids performed on the samples
ob-tained at 0400 and 1200 hours from the
patient with the most marked tyrosinemia
re-vealed normal periodicity of 11 of 15
indi-vidual amino acids including tyrosine
(Table II, Case 3). The likelihood of
find-ing a large number of individual amino
FIG. 2. Total integrated value of amino acids/0.006 ml of whole blood plotted against hours of the day
and corrected for the age of the infant in days at time of sampling. The mean value (dark line) ± 1
standard error (shaded area) are represented. The number of infants sampled at each age is
indi-cated by the circled number. Note the similar periodicity and relatively stable blood amino acid
acids with periodicity which did not
con-form to the periodicity of total blood amino
acid concentration in any infant was as
great for patients sampled at 5 days of age
as for those sampled at 2, 3, or 4 days of
age. The periodicity of individual amino
acids was most frequently nonexistent or
atypical in patients sampled during the first
24 hours of life.
DISCUSSION
Although normal values for plasma
amino acids in man have been established
in a number of studies,”’ information
con-cerning sampling time has not been
in-cluded. Similarly, studies designed to assess
the concentration of plasma amino acids in
the neonatal period have not been
con-trolled with respect to time of sample
19 Previous observations have
established the existence of a circadian
pe-riodicity for total blood amino acids
con-centration in adult subjects such that levels
between 1200 and 2000 hours are
signifi-cantly greater
( p
< 0.01) than
those
ob-served at 0400 or 0800 hours.’ Seventeen
in-dividual blood amino acids also vary with a
periodicity which closely resembles that
originally described for total blood amino
acid concentration.4” The present study
documents the existence of a circadian
pen-odicity for total blood amino acid
concen-tration as early as the first 24 hours of life
in most full-term newborn infants, with
similar but less consistent peniodicity
de-monstrable for the concentration of
individ-ual blood amino acids. The rhythmic
pat-tern observed is similar but not identical to
that described for adult subjects. Maximal
concentrations in both groups were noted
between 1200 and 2000 hours, and minimal
concentrations were seen at 0400 hours. In
the neonate, a brisk increase in blood
amino acid concentration occurred between
0400 and 0800 hours, such that
concentra-tions at 0800 hours more closely
approxi-mated maximal daily concentrations than
did 0800 hour-levels in the adult.
The demonstration of periodicity of total
blood amino acid concentration during the
first week of life was somewhat
unex-pected. Wright2o has stated that the
new-born is lacking in physiologic and behavioral
rhythms. The studies of Hellbrugge2l and
other recent reviews22’23 tend to support
this statement, since the day-night rhythms
of heart rate, urine volume excretion,
rhyth-micity of urinary sodium and potassium
ex-cretion, plasma steroid periodicity,
and
body temperature rhythmicity are not well
established until after the second week of
life and may be delayed until after the
third month of life. In contrast to these
find-ings, a day-night rhythm of electrical skin
resistance has been observed during the
first week of life.2’ Parmelee and
co-work-ens24 and others”,’ have noted that, during
the first 3 days of life, the longest
contin-uous period of sleep was between 11 P.M.
and 7 A.M., suggesting that humans have an
inborn internal circadian periodicity of
ap-proximately 24 hours.26 The sampling of the
largest number of neonates in our study on
day 1 of life was intended to more clearly
define the appearance of blood amino acid
rhythmicity during these early hours of life
as vel1 as to determine the relative
fre-cuency with which a full-term, newborn
in-fant failed to conform to the group pattern.
Twenty-nine percent of the infants first
sampled prior to 24 hours of age
demon-strated either no peniodicity or a
rhythmi-city dissimilar to that of the group.
Hellbnugge2l noted that day-night
rhythms of sleep-wakefulness behavior and
pulse frequency developed later in
prema-tune than in full-term, newborn infants and
concluded that exogeneous environmental
influences are of lesser importance for the
development of a diurnal rhythm than
ma-turing processes. If this were not the case,
the day-night rhythm for any biologic
pro-cess should develop simultaneously and
similarly in premature and full-term,
new-born infants under the equally long and
similar influences of timed stimuli, i.e.,
lighting, feedings, and so forth. Detailed
timed measurements of blood amino acids
in a large number of infants of varying
ges-tational age and weight are needed to
deter-mine the time of appearance of blood amino
Amino Acids
Case 1 Case 2 Case 3
Adult Normal’
M/ml L11/ml iil/ml Jf/ml ll/ml j.il/ml
04tX) 1200 0400 1200 0400 1200 O8 2tXXJ
Tlireonine Serine Glutamicacid Glutamine Proline Glycine Alanine Valine Methionine Isoleucine Leucine Tyrosine Phenylalanine Lysine Histidine Arginine 0.172 0.212 0.100
0.538
0.233 0.186 0.317 0.061 0.023 0.029 0.077 0.180 0.028 0.142 0.053 0.040 0.230 0.249 0.168 0. 606 0.416 0.246 0.421 0.188 0.045 0.094 0.148 0.638 0.092 0.205 0.093 0.049 0.201 0.242 0.096 0. 450 0.268 0.416 0.269 0.115 0.094 0.037 0.073 0.104 0.042 0.153 0.067 0.031 0.236 0.262 0.121 0. 624 0.304 0.337 0.205 0.080 0.106 0.027 0.944 0.052 0.041 0.126 0.089 0.021 0.182 0.229 0.347 0.552 0.170 0.194
0. 560 0. 595
0.248 0.408 0.212 0.198 0.275 0.276 0.184 0.158 0.027 0.040 0.072 0.070 0.117 0.111 1.178 2.510 0.099 0.106 0.172 0.201 0.072 0.090 0.048 0.089 0.165 0.201 0.167 0.308 0.264 0.481 0.267 0.025 0.082 0.155 0.065 0.089 0.00 0.074 0.092 0.255 0.252 0.218 0.385 0.352 0.700 0.373 0.051 0.134 0.244 0.098 0.125 0.281 0.105 0.133
Total 2.391 3.888 2.658 2.675 3.651 5.827
TABLE II
INDIVIDUAL BLoor A1INo AID CONCENTRATIONS IN ThREE REPRESENTATIVE NEWBORN INFANTS DETERMINED BY AUTOMATED ANALYSIS
Inasmuch as circadian rhythms occur in
biologic systems under established patterns
of sleep-wakefulness and light-darkness
routines, previous study of the influence of
such factors upon blood amino acid
period-icity have been reported.5 A 12-hour shift in
the sleep and wakefulness cycle resulted in
a rapid reversal
( within
48 hours) of
nor-mal circadian periodicity of blood amino
acids, such that peak values were observed
at 0400 rather than at 1200, 1600, or 2000
hours seen in the same subjects on a normal
routine. The speed with which blood amino
acid periodicity adapted to a new cycle
compared with the resistance of body
tem-perature and excretory mechanisms’
sug-gested that blood amino acid periodicity
was more easily influenced by exogeneous
factors than any of the variables noted
here. In this regard, it might be anticipated
that sleep-wakefulness patterns might
influ-ence blood amino acid peniodicity in the
neonate. No attempt was made to evaluate
patterns of sleep-wakefulness in the
patients studied. It is possible that the
new-born infants with a sleep wakefulness
pat-tern similar to those described,21”4’25
devel-oped normal blood amino acid periodicity
promptly, whereas those with a more
aber-rant pattern of sleep and wakefulness did
not. It is also possible that dimming the
nursery lights prompted the development of
day-night rhythmicity.
Additional factors affecting the
concen-tration and periodicity of total or individual
amino acids have been detailed in a
num-ber of publications.273#{176} The influence of
diet upon blood amino acid concentration
has been the subject of a great deal of
study. No attempt will be made to review
this subject because it is not a central issue
in a discussion of periodicity. The precise
role of protein intake in maintainance of
amino acid concentration is an entirely
dif-ferent question from the relationship of the
time of protein ingestion to amino acid
pe-riodicity. In the present study, infants were
fasted for 12 hours, fed 5% glucose and
water for a subsequent period of 12 hours,
around the clock. Although no attempt was
made to control intake, a careful record of
intake was maintained. Subsequent
evalua-tion of the quantity of glucose water or
En-famil ingested with regard to the presence
of periodicity for total or individual amino
acids in any given patient showed no
ap-parent pattern. These findings are in accord
with previous observations that normal or
exaggerated dietary protein intake does not
seem responsible for the cincadian
periodic-ity of blood amino acids’ and that increases
or decreases in the protein content of an
iso-caloric diet did not affect blood amino
acid peniodicity despite an effect upon
ab-solute concentration.’7”#{176}
The role of the adrenal gland as a
pace-maker for circadian sequences of events has
been reviewed.” The extent to which the
peniodicity of the adrenal cortex underlies
the peniodicity of blood amino acids is
un-clear. Corticosteroids may affect the amino
acid poo1 by their influence on protein
syn-thesis
and
gluconeogenesis.
Since humanglucocorticoid secretion peaks during the
early morning hours, it had been suggested
that a relationship may exist between
ste-roid induced protein synthesis and the
tim-ing of minimum blood amino acid
concen-trations.5 Although a relationship between
these two variables might be anticipated,
the manner in which one is dependent
upon the other is uncertain. Our studies of
plasma corticosteroids, hepatic tryptophan
pyrrolase, and whole blood tryptophan in
the mouse with adrenal glands present and
following surgical removal of the adrenals
showed that the periodicity of both the
substrate and enzyme are changed but
are not abolished following
adrenolec-tomy.3’ Similarly, the periodicity of other
blood amino acids in mice were not
abol-ished by adrenalectomy.” Wurtmann, et al.
have commented that the rhythm of plasma
tyrosine in rats persisted despite hypophy-sectomy.’7 Thus, corticosteroid secretion
ap-pears to exert a permissive control over
blood
amino
acid
periodicity,
but
it is not essential for the presence of rhythmicity. Inview of these findings, it is not surprising
that peniodicity of blood amino acids was
demonstrable in the neonatal period prior
to the time that normal plasma
corticoste-noid rhythmicity is anticipated.
Although the rhythmicity of total blood
amino acid concentration might appear to
be no more than the sum of the
concentra-tions of the individual amino acids at any
point in time, this is not the case. Scniver’4
has recently commented on the constancy
of amino acid concentrations in
extracellu-lar fluid despite the fact that man is an
epi-sodic protein consumer and that the influx
of amino acids at mealtime can be many
times their amount in the plasma. Efron, et
a!.” noted that an elevated concentration of
plasma phenylalanine as the result of
phe-nylketonuria or artificially induced by
phe-nylalanine infusion resulted in a marked
decrease in the levels of many other amino
acids, resulting in a tendency for total
amino acid concentration to remain
con-stant. This finding is in accord with
pre-vious observations.#{176} Thus, the organism at-tempts to control the total concentration of
blood amino acids within relatively narrow
limits at the expense of one or more
individ-ual components. The work of Van Slyke
and Meyer,’7 Christensen,’ and most
re-cently Scniver,’4 indicates that this
phe-nomena is most likely the result of
move-ment into and retention of amino acids by
intracellular fluids, a process which occurs
even against a concentration gradient. The
tendency for
total
blood
amino acidperiod-icity in the neonatal period to show greater
consistency than peniodicity of individual
blood
amino
acids
may
be a reflection ofthese and other factors which serve to
care-fully regulate total blood amino acid
con-centration.
The extent to which the peniodicity of
in-dividual blood amino acids is dependent
upon the periodicity of enzymes concerned
with their metabolism has been a source of
speculation. Our studies in mice
demon-strated that plasma tryptophan was
ele-vated when hepatic tryptophan pyrrolase
activity was lowest, and lowest at the time
greatest activity.” Coburn, et al.’9
demon-strated that plasma tyrosine in the rat was
elevated between 2 A.M. and 5 A.M., a
pe-nod when tyrosine transaminase was
low-est, and was lowest between 8 A.M. and 11
P.M., when tyrosine transaminase was
high-est. Although such studies appear to offer
evidence that enzyme periodicity is an
im-portant factor in the rhythmicity of the
cir-culating substrate, the precise
interelation-ship of the two is not clear. Analysis of the
individual amino acid concentrations of
Cases 1 and 3 (Table II
) shows
that
both
infants had neonatal tyrosinemia. Despite
the apparent immaturity of the tyrosine
transaminase and para-hydroxy-phenylpy-ruvic acid oxidase systems in these infants, a periodicity of plasma tyrosine was noted,
with peak values obtained at 1200 hours.
The absolute increase in concentration of
plasma tyrosine in these infants was far
greater than that observed for the amino
acid in the unaffected neonate or adult. If
the peniodicity of enzymes involved in the
metabolism of blood amino acids plays a
prime role in substrate rhythmicity, one
must then assume that immature enzymes
show a peniodicity identical to that found
when full enzyme activity is achieved. In
addition, since most blood amino acids
reach maximal concentrations and decline
to minimal levels almost simultaneously,
one would have to assume that a large
number of enzymes exhibit similar, if not
identical, rhythmicity. It is more likely that
blood amino acid peniodicity is a reflection
of many factors acting concurrently and
that one of these factors, enzyme
periodic-ity, plays a distinct, but not identical, role with respect to each amino acid.
IMPLICATIONS
Circadian studies of physiologic systems
have shown that the organism is ordered in
time as well as in space. It should be
appar-ent that plasma amino acids vary normally
as a function of time and that “normal
values” for the concentration of a given
substance must be standardized for time of
day. Although these studies have
intro-duced the concept of amino acid
periodic-ity
in the neonate, definition of normalcon-centrations and ranges for each time of day
remain a subject for further investigation. Analysis of blood amino acid
concentra-tion and periodicity has proven valuable in
the early diagnosis of infection in adults68
and young children.9 The present study
mdi-cates that such analysis is less likely to yield
reliable data in the neonatal period because
one could not predictably distinguish
be-tween amino acid rhythmicity altered by
infection and physiologic disturbances of
blood amino acid rhythmicity in the
neo-nate.
Understanding the peniodicity of blood
amino acids may be of great importance in
the detection of disorders associated with
transient or permanent enzymatic defects.
Blood tyrosine concentration of 0.180 .M/
ml at 0400 hours with a concentration of
0.638 p.M/mi at 1200 hours was observed in
one of the patients studied
(
Table II, Case1
)
. Although classification of this subject asa case of neonatal tyrosinemia might not
have been warranted if the 0400-hour
spec-imen were the only one available, the
1200-hour specimen more readily permits
an appreciation of the immaturity of the
ty-rosine transaminase system. The results of
loading tests employing single amino acids
are affected by the time of day at which the test is performed.’#{176}”#{176} Although data of this
type are scant, they suggest that
perfor-mance of amino acid loading tests at a time
other than 0800 hours might more readily
permit the identification of individuals who are heterozygote for one of the inherited
disorders of amino acid metabolism.
SUMMARY
Blood amino acids were obtained every 4
hours for 24 hours from 46 infants who
were between 1 hour and 120 hours of age
when first sampled. Periodicity of total
blood amino acids was demonstrated as
early as the first day of life in some infants,
and this periodicity was similar, but not
identical to, that which has previously been
Con-centrations of blood amino acids peaked
between 1200 and 2000 hours, while
mini-mal concentrations occured at 0400 hours.
Rhythmicity of individual blood amino
acids, when present, was similar to that for
total blood amino acids, but it was much
less consistent. Rhythmicity of plasma
tyro-sine was present and exaggerated, even in
two patients with neonatal tyrosinemia. The
presence of blood amino acid peniodicity
during the early days of life lends support
to the concept that dietary protein intake
does not seem solely responsible for the
cm-cadian periodicity of blood amino acids.
Since plasma amino acids vary normally
as a function of time, “normal values” must
be standardized for time of day.
REFERENCES
1. Halberg, F. : Physiologic 24-hour periodicity; general and procedural considerations with
reference to the adrenal cycle. Z. Vitamin
Ilormon Fermentforsch, 10:225, 1959.
2. Barnum, C. P., Jardetzky, C. D., and Halberg,
F. : Time relations among metabolic and
morphologic 2.4-hour changes in mouse liver.
Amer.
J.
Physiol., 195:301, 1958.3. Feigm, R. D., Klainer, A. S., and Beisel, W. R.:
Circadian periodicity of blood amino-acids
in adult men. Nature (London), 215:512, 1967.
4. Wurtman, R. J., Rose, C. M., Chou, C., and
Latin, F. F. : Daily rhythms in the
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Acknowledgment
This work was supported by U. S. Public Health
Service Medical School Ceneral Research Support
Crant No. 53703A and a research grant from the
Lifeseekers, St. Louis, Missouri. The work of Mrs.
Hilary Thirkill is gratefully appreciated. We would
