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Compact bone changes in cold-exposed rats.

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Compact Bone Changes in Cold-exposed Rats
ALPHONSE RIESENFELD
D e p a r t m e n t of Anthropology, Hunter College of the C i t y University of
N e w Y o r k , nnd i n s t i t u t e of Applied Biology, N e w Yor k
KEY WORDS
Compact bone reduction . R a t s . Experiment . Cold.
ABSTRACT
Rats exposed to cold stress show a reduction of relative cortical
thickness i n their long bones. T h e reaction resembles reduction of cortical thickness observed i n Asiatic h u m a n s of t h e Mongoloid race, in whom many morphological features have been postulated to be cold-adaptive. However, until it c a n
be established that the physiological processes underlying the experimental a n d
phylogenetic condition a r e similar, n o extrapolation c a n be attempted from the
one to the other.
In a paper dealing with compact bone in
Chinese and Japanese, Garn et al. ('64;
Garn, '71) found that these Asiatics whether American-born or born abroad showed
lesser amounts of compact bone than Americans of European descent. Since the differences appear even under conditions of
adequate calcium intake, the authors attribute the difference to genetic factors rather
than to limiting nutrients. Ericksen ('72),
who studied long bones in Alaskan Eskimos
and Pueblo Indians, found that cortical
bone was lost with age in both populations
with some differences according to sex and
specific long bone involved.
It is common knowledge that a number
of morphological features in Mongoloids
have been interpreted as cold-adaptive in
nature, and the validity of these interpretations has been strengthened by the fact that
many of these cold responses could be
duplicated in experimental cold-exposure
of rats (Steegmann and Platner, '68; Riesenfeld, '73). The present analysis was
undertaken to determine possible changes
of compacta thickness in experimentally
cold-stressed rats.
MATERIALS AND METHODS
The right and left femora of normal control rats of the Wistar variety (30d and
300) and of cold-exposed Wistar rats ( 2 5 d
and 300) were used. All animals were fed
the same Purina rat diet and all were six
months old at the time of sacrifice. Temperature condition of cold-exposed rats was
38 "F 2 average humidity was 65% , and
all conditions of housing were the same a s
*
O ,
AM. J. PHYS. ANTHROP..44: 111-112
those described in detail in my previous
study (Riesenfeld, '73). The femur was
selected because of its large size. The bones
were sectioned exactly at the midpoint of
their shaft. The thickness of compacta was
measured with specially constructed Helios
dial calipers with horizontally opposing
points and the antero-posterior diameter of
the shaft at midpoint was measured with
regular Helios dial calipers. All measurements were accurate to 0.01 mm. Both absolute measurements are reported a s well
as the indices relating cortical thickness to
midpoint diameter.
RESULTS
Table 1 indicates that cold females show
a significantly lesser absolute thickness of
the compacta and a significantly greater
antero-posterior diameter of the shaft than
normal controls. Males show the same trend
but the absolute differences are not significant.
When cortical thickness was related to
total antero-posterior diameter of the shaft,
that index for relative cortical thickness
was significantly reduced in cold-exposed
rats of both sexes, the reduction being more
pronounced in females than in males. This
observation is reminiscent of the finding of
my previous study on the effect of cold exposure (Riesenfeld, '73) according to which
a number of responses to experimental
cold stress were considerably more pronounced in female than in male rats. The
exact physiological etiology of cortical reduction under experimental cold stress and
in the phylogenetic situation is not known
111
112
ALPHONSE RIESENFELD
TABLE 1
Meitn, stctndard devicctions crnd t-tests of femoru of normctl cind cold-exposed ruts
Normal
Cortical thickness
Mean
S.D.
0.70
0.63
0.08
0.08
0.67
0.57
0.10
0.08
1 .89
4.78 2
3.02
2.79
0.33
0.19
3.09
2.89
0.25
0.18
1.05
2.75 1
8 23.48
3.11
2.97
21.55
19.61
2.16
2.38
3.16 1
6.152
8
0
A-P d i a m e t e r
d
P
100
X
(Thicknessldiameter)
9 22.82
I
2
Cold
S.D.
Mean
t
p c 0.01,
p s 0.001,
at present and neither is its adaptive advantage in the phylogenetic condition. Until it
can be established that the underlying physiological processes are similar in both, no
extrapolation can be attempted from the
experimental to the phylogenetic situation.
LITERATURE CITED
Erickseii. R1. t'. 1972 A c o m p a r a t i v e study o f c o r tical bone involution in t w o aboriginal Amer-
ican populations ( a b s t r a c t ) . Am. J Phys. Anthrop.. 37: 436.
C;;irn. S. M .
1971 H u m a n Kaces. Charles C
T h o m a s . Publisher. Springfield. 111.
C a m . S. M.. E. M . Pao a n d M. E . Rihl 1964 Compact bone in Chinese and J a p a n e s e . Science. 1 4 3 :
1439-1440.
Kicsc~rifeld.A 1973 T h e effect of e x t r e m e tempera t u r e s and starvation on t h e body proportions
of t h e r a t . Am. J . Phys. Anthrop.. 39: 427460.
S t e e g m a n n . A . T.. a n d W . S. P l a t n e r 1968 Experi m e n t a l cold modification of cranio-faclal morphology. Am. J . Phys. Anthrop.. 2 8 . 17-30.
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