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OrganBody-weight relationships in the hamster.

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Organ :Body-Weight Relationships in the Hamster
PAUL F. ROBINSON AND CHARLES G . WILBER
Experimental Zoology Branch, Directorate of Medical Research,
U. S . Army Chemical Research and Development Laboratories,
Army Chemical Center, Maryland
Because of the relatively recent introduction of the hamster as an experimental
animal, there is considerably less basic
physiological data available from this animal than from the other more common
laboratory species. The early preemption
of this species for nutritional investigation
further delayed the establishment of its
biological norms.
Determination of body :organ-weight ratios over a wide range of total body
weights for both male and female hamsters hitherto has been neglected, although
during the past 50 years, many body:organ-weight studies have been carried out
on the other more commonly used laboratory animals (Webster and Liljegren, '49;
Freudenberger, ' 3 2 ) , and even on such
species as the dog-fish (Kearney, '14), frog
(Latimer, '20), turtle (Latimer, '20a) and
wild rodents (Frick, '57a).
Apart from the inherent interest in the
study of normal growth and development,
the ratio between the weight of the whole
organism and that of each of its discrete
components at any particular stage of the
life span is a practical tool of some promise in both nutritional and toxicological
investigation (K aunitz , S1anetz , Johnson
and Guilmain, '56), (Krumholz, '56). For
these reasons it was decided to ascertain
the body: organ-weight ratios in hamsters
of all ages after birth.
METHODS
In the following study, the animals were
obtained immediately after weaning, ( 1415 days), from a commercial breeder who
maintained a random inbred stock of
Cricetus nuratus. The young animals were
maintained in our laboratory on commercial ration. As they matured they were
killed at selected intervals. The animals
were etherized until respiration ceased,
the desired organs were carefully dissected out, freed from extraneous tissue,
blotted on absorbent paper and weighed
at once. The brain, heart, kidneys, liver,
lung and spleen were weighed. Organs
that weighed more than 500 mg were
weighed on a torsion balance with a sensitivity of 2 mg. Lighter organs were
weighed on a torsion balance sensitive to
0.2 mg. The auricles and ventricles of the
heart were slit open and any blood present
expressed before the organ was weighed.
Two persons usually worked together: one
dissected, removing the organs always in
the same order, while the other carried
out the weighing as each organ was removed. In this way, dehydration of the
excised tissues was avoided. The rare animal that showed gross pathology was discarded. In all, 85 male and 99 female
animals were used with a body weight
range of 7 to 150 grams. In compiling the
results, the sexes were tabulated separately and their weights grouped at 10
gram intervals: those weighing 10 to 20
grams in the first group, 20 to 30 grams
in the second group, and so on.
The relationship of body weight to organ
weights was compared using ( a ) absolute
weights and (b) logarithms of the weights.
The least squares method of fitting regression lines was used throughout. Coefficients of determination for the various
calculated regression lines are given in
table 3 .
RESULTS AND DISCUSSION
Table 1 summarizes the results of body
weight measurements for the hamsters.
The data include young animals, 14 days
old and old adults. The ranges of organ
weights are shown in table 2.
31
32
P A U L F. ROBINSON AND CHARLES G . W I L B E R
TABLE 1
Summary of data on hamster body weights
Item
Male
Number of animals
Mean body weight, gm
Range
Mode
Median
Skewness
Standard deviation
of mean
Female
85
76
16-160
74
82
- 0.62
99
70
15-160
45
64
f 0.62
4 29
f29
TABLE 2
Ranges of organ weights in grams for hamsters
Range
Organ
Brain
Heart
Kidney
Liver
Lung
Spleen
Male
Female
0.710-1.110
0.1 12-1.785
0.426-1.380
1.210-6.880
0.124-0.985
0.018-0.278
0.650-1.085
0.094-0.935
0.331-2.000
0.775-8.330
0.142-1.610
0.013-0.690
If logarithms of all weights for the
female hamster are used, the organs studied are clearly related to log of body
weight in a linear fashion (table 3 ) . The
same relationships hold in the male hamster, except for the heart, for which absolute weight increases in weight linearly
with the absolute body weight.
Why does the heart in the male hamster grow at a different rate with respect
to the body than the heart in the female?
A biased sample might be responsible for
the results. If this were true one would
suspect that other organs in addition to
the heart would show differences in male
and female populations. Table 3 emphasizes that although the kidney has a low
coefficient of determination, the male
heart is the only organ which fails to
bear a log-log relationship to body weight
in the hamster. Table 1 indicates that our
samples are truly random.
In certain genetic strains of rabbits the
ventricular walls of the heart are heavier
in females than in males, with greater
variability in the latter (Latimer and
Sawin, '59).
Moreover, most organs in female rabbits
(except gonads, integument and harderian
glands) are heavier than in males. The
heart and the brain in males make up
greater percentages of total body weight
than similar organs in females (Latimer
and Sawin, '55).
Prediction equations for the various organ weights (y) in terms of total body
weight ( x ) were derived (table 4). It is
evident that the growth of all the organs,
except the male heart, follows the equation y = axb; a and b are constants which
were not estimated for this paper because
the logarithmic prediction equations were
more readily handled.
In guinea pigs, the liver, kidneys, lungs,
heart, and spleen conform tolerably well
to the log-log relationship with respect to
body weight (Webster and Liljegren, '49).
In an extensive survey of heart weights
in vertebrates, Hesse ('21) gives values
for body weight and heart weight in 10
male and 8 female specimens of Cricetus
cricetus. The male heart accounts for an
average of 0.42% of the body weight, the
female 0.45%. The estimating equations
derived by us for heart weight in terms of
body weight do not apply with acceptable
precision to individual male hamsters of
the species and strain used by Hesse. In
Hesse's work, the mean body weight of the
female hamster was 251 gm with a mean
heart weight of 1.14 gm. By calculation,
using our prediction equation for females,
TABLE 3
Coeficient of determination (Rz) for linear versus log-log plots of organ weights and
body weights in the hamster
Males
Organ
Brain
Liver
Heart
Kidney
Lung
Spleen
c
Females
_
Log-log
Linear
0.a327
0.9444
0.1269
0.4706
0.8m3
0.6808
0.1978
0.9126
0.6933
0.0077
0.8118
0.5510
Log-log
Linear
0.8652
0.8945
0.8688
0.6579
0.8530
0.5~~99
0.5925
0.1939
0.0875
0.6259
0.6268
0.0500
ORGAN :BODY-WEIGHT RELATIONSHIPS I N THE HAMSTER
33
TABLE 4
Prediction equations for organ weights (y) in terms of body weight ( x ) in male and
in female hamsters
Equation
Organ
Brain
Liver
Heart
Kidney
Lung
Spleen
Male
Female
log y = 0.299 log x - 0.605
log y = 1.031 log x - 1.385
y = 0.0046 x
0.0046
logy = 0.767 log x - 1.493
log y = 0.607 log x - 1.468
log y = 0.574 log x - 1.217
logy = 0.188 log x - 0.376
log y = 0.844 log x - 1.005
log y = 0.810 log x - 2.000
log y = 0.529 lag x - 1.057
log y = 0.720 log x - 1.670
logy z 0.874 log x - 2.612
+-
the mean heart weight was 1.13 gm. For
Hesse's male hamsters, our equation gave
a calculated mean heart weight of 1.39
gm, whereas the observed mean heart
weight was 1.20 gm.
Frick ('57), in a study of Ethiopian
mammals, found that various organs were
related to body weight according to the
equation, y = axb, where y is the organ
weight, x the body weight, a the organ
constant and b the body exponent. The
constant ( a ) which varied with sex and
organs, was found to range from 0.01 to
0.049 for the heart. The exponent (b)
was found to be: heart, 0.83; liver, 0.92;
kidneys, 0.92. The ranges for these constants are broad enough so that similar
constants calculated from our data fall
within the limits. For example, taking
( b ) as 0.83 for the hamster heart, (a)
is calculated to range between 0.01 and
0.03. Similarly for the liver, taking (b)
as 0.92, calculated ( a ) falls between 0.06
and 0.09.
Our results show that in the normal
hamster organ weight: body weight ratios
are the same as those in other mammals.
The fact that the hamster is a hibernator
and that it is peculiarly resistant to many
toxicants is not reflected significantly in
the weight relationships of various organs
to total body weight. The linear relationship of absolute heart weight to absolute
body weight in the male hamster, in the
face of the log-log relationship of all other
organs in both sexes, cannot be explained
at this time. We doubt that a biased
sample or diseased animals are factors
which can explain our results.
SUMMARY
1. Body weights and weights of the following organs were recorded for 85 male
and 99 female hamsters: brain, heart,
kidney, liver, lung and spleen.
2. Prediction equations for the various
organs in terms of body weight were
derived. The growth of all organs, except
the male heart follows the usual equation
y axb.
LITERATURE CITED
Freudenberger, C. F. 1932 A comparison of
the Wistar albino and the Long-Evans hybrid
strain of the Norway rat. Am. J. Anat., 50:
293-349.
Frick, H. 1957 Quantitative Untersuchungen
an athiopischen Saugetieren. I. Absolute und
relative Gewichte von Herz, Leber, Milz und
Nieren. Anat. Anz., 104: 305-333.
1957a Betrachtungen uber die Beziehungen Zwischen Korpergewicht und Organgewicht. 2. Saugetierk., 22: 193-207.
Hesse, R. 1921 Das Herz gewicht der Wirbeltiere. Zool. Jb. Abt. Allg. Zool., 38: 243-364.
Kaunitz, H., C. A. Slanetz, R. E. Johnson and
J. Guilmain 1956 Infiuence of diet composition on caloric requirements, water intake
and organ weights of rats during restricted
food intake. J. Nutrition, 60: 221-228.
Kearney, H. L. 1914 On the relative growth
of the organs and parts of the embryonic and
young dogfish (Mustelus canis). Anat. Rec.,
8: 271-297.
Krumholz, L. A. 1956 Observations on the
fish population of a lake contaminated by
radioactive wastes. Bull. Am. Mus. Nat. Hist.,
110: 283-367.
Latimer, H. B. 1920 The weights of the viscera of the common frog. Anat. Rec., 18:
35-46,
1920a The weights of the viscera of
the turtle. Ibid., 19: 347-360.
Latimer, H. B., and P. B. Sawin 1959 Morphogenetic studies of the rabbit. XXI. The weight
and thickness of the ventricular walls in the
rabbit heart. Ibid., 134: 141-147.
1955 Morphogenetic Studies of the
Rabbit. XII. Organ size in relation to bodv
weights in adults of small sized race X. Ibid:,
123: 81-102.
Webster, S. H., and E. J. Liljemen 1949 Organ:body weight ratios for cgrtain organs of
laboratory animals. 11. Guinea pig. Am. J .
Anat., 85: 199-230.
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