close

Вход

Забыли?

вход по аккаунту

?

Effects of reproductive activity on the weight of adrenal glands in microtus montanus.

код для вставкиСкачать
Effects of Reproductive Activity on the Weight of
Adrenal Glands in Microtus montanus
STURGIS McKEEVER
Department o f Zoology, University o f California, Davis'
From a review of the literature, it is
evident that the cortex of adrenal glands
from sexually active animals differs in size,
and presumably in activity, from that of
sexually quiescent individuals. These differences are not consistent in the various
species of mammals. The male of most
mammals has a smaller adrenal than the
female, and testoids decrease adrenal size
while folliculoids increase it (Selye, '50).
It follows that the adrenals of males should
become smaller and that adrenals of females should enlarge during periods of
sexual activity. All investigators agree that
this enlargement is due to greater thickness of the cortex. A progressive increase
in the size of adrenal glands with progressive decrease in size of the organs of reproduction of both wild and white male
mice has been demonstrated by Christian
('55a). Female wild mice also exhibited
adrenal enlargement with suppression of
reproductive activity, but to a lesser degree
than males (Christian, '56).
Some investigators have found that the
adrenal cortex is somewhat enlarged during estrus, pregnancy, and lactation (Selye,
'49), but enlargement during pregnancy
has been questioned by Andersen and Kennedy ('33). They found no adrenal hypertrophy during pregnancy of rats; and, from
a critical review of the literature, they
concluded that there was evidence against
this phenomenon in the rat, mouse, rabbit,
and cat. There was evidence for adrenal
enlargment in both sexes of the mole during the season of rut, but not necessarily
of pregnant animals. It has been demonstrated (Zalesky, '34) that there is a significant increase in the size and weight of
the adrenal glands of both male and female thirteen-lined ground squirrels ( Citellus tridecemlineatus) during the breeding
season or as a result of artificial stimula-
tion of the gonads and reproductive accessories during the season of sexual inactivity. An increase in weight of the
adrenal glands with onset of reproduction
has been observed in female Mic~otus
pennsytvanicus (Louch, '56, '58).
Selye ('50) proposed that there is a general adaptation mechanism, acting through
the adreno-pituitary system, which helps
to raise resistance to various forms of
stress. Christian ('50) suggested that the
size of animal populations exerts densitydependent effects on the physiology of individuals. In experimental populations of
mice, he demonstratd (Christian, '55a,
'55b) that there was an increase in adrenal size with increase in population size
until the population reached a point where
there was a breakdown in social organization. He attributed the adrenal enlargement to a degree of stress proportional to
population size. There was an inverse relationship between population size and
sizes of the reproductive organs.
This report presents results of investigations on size of the adrenal glands in
relation to sex and reproductive activity
in natural populations of Microtus montanus in northeastern California.
METHODS
All animals were collected with snap
traps set at 6-foot intervals in meadows or
weed fields. Traps were placed in runways, since the animals were not attracted
to bait. Relative populations were estimated from the number of animals caught
per 100 trap nights on the first night traps
were set in a given locality.
The mice were weighed to the nearest
0.1 gm, adrenals removed and fixed in
In cooperation with the California Forest and
Range Experiment Station, U. S. Forest Service,
Berkeley.
2
STURGIS McKEEVER
weight class ( P < 0.02 for 35-45 gm
females; P < 0.01 for all other classes).
Males and females which were not sexually
active and which weighed less than 25 gm
had approximately the same relative
adrenal weight.
Pregnant animals did not have larger
adrenals than females which exhibited the
other 5 conditions of reproductive activity.
When the weights of adrenals from females which exhibited the 6 conditions of
sexual activity were compared, there was
no significant difference among the means
of the condition classes (table 1 ). In many
animals there was some overlap among reproductive conditions; in those instances,
the animals were assigned to the most
advanced condition class.
Animals were obtained from populations
of two different densities. Trap success in
5 populations averaged 12.7% (range,
10.7-14.4% ), a low density; trap success
RESULTS
in two populations averaged 30.9% (range,
Adrenal weights of sexually active males 30.6-31.1%), a high density. There was
were significantly smaller than those of no significant difference between mean
non-active males, while adrenals of active adrenal weights of animals from populafemales were significantly larger than tions of high and low density, when anithose of non-active females (fig. 1). Fur- mals of the same sex and reproductive
thermore, the adrenals of non-active males condition were compared (table 2).
Histologically, the adrenals of sexually
were significantly smaller than those of
active males showed a zona fasciculata
non-active females ( P < 0.01).
Body weights were grouped by 10-gm approximately two-thirds and a zona reticclasses and the adrenal weights of animals ularis approximately one-third as thick as
in the various classes compared (fig. 2). the corresponding zones in glands from
When the two sexes were considered sepa- non-active animals. In sexually non-active
rately, adrenal weights of reproductively females, the zona fasciculata was approxiactive animals differed significantly from mately two-thirds and the zona reticularis
those of non-active animals for every body approximately one-half as thick as the cor-
10% formalin, and the stomach removed
and weighed to the nearest 0.1 gm. Later,
adrenals were cleaned and the paired
glands weighed to the nearest 0.2 mg on
a torsion balance. The ratio of adrenal
weight in milligrams per gram of body
weight was computed after the stomach
weight was subtracted from the body
weight; this ratio was used for all comparisons.
Reproductive activity of male animals
was determined by the method described
by Jameson ('50). Females were considered to be sexually active if they (1)
were pregnant, ( 2 ) were lactating, ( 3 ) had
an enlarged uterus, ( 4 ) had recent placental scars, ( 5 ) had enlarged mammae,
or ( 6 ) had perforate vaginas.
A number of adrenals were sectioned at
7 and stained with hematoxylin and eosin
for histological examination.
i
v3.
4.
I
I
I
F
1
~
I
I
I
I
0.2
0.4
0.6
0.8
1
I
I0
1.2
ADRENAL W E I G H T
1
I
I
1.4
1.6
1.8
.
I
2.0
2.2
Fig. 1 Adrenal weights in milligrams per gram body weight for Microtus montanus
which were classified according to sex and reproductive condition. The classes, and
sample size of each, were as follows: class 1, sexually active males, 76; class 2, nonactive males, 79; class 3, active females, 62; class 4, non-active females, 56. Median
vertical bar represents the mean, the enclosed area represents two standard errors, and the
horizontal line represents the extremes.
3
ADRENAL WEIGHTS OF MICROTUS MONTANUS
I6
1.6
1.4
?
1.2
c
1.0
-I
2
y
0.8
U
0.6
0.4
0.2
10
20
50
30
40
BODY WEIGHT
,
I
60
70
10
20
I
I
I
30
40
BODY WEIGHT
50
60
70
Fig. 2 Adrenal weight in milligrams per gram body weight, plotted against body weight
in grams. Points represent the means for each 10-gm interval of body weight. Numbers at
each point represent sample size. The left graph presents data for males, the right graph
presents data for females. Sexually active animals are represented by a solid line, nonactive animals are represented by a dotted line. Vertical bars represent two standard errors.
TABLE 1
Adrenal weights in milligrams per gram body weight for sexually active female Microtus montanus
Condition of sexual activity
Characteristic
Pregnant
Number examined
Lactating
1
14
Mean weights f S.E.
-t-
0.597
1.418
min.
Extreme weights
0.883
0.0773
max.
Uterus
enlarged
Recent
Mammae
s c $ ~ ~ ~ enlarged
~ n t
27
7
0.935
-
0.910
k 0.1437
0.671
1.666
-
2
1.082
0.0697
rf:
Perfqrate
vagma
0.583
2.171
-C
11
0.955
0.0580
rf:
0.897
1.014
0.808
0.0873
0.397
1.411
TABLE 2
Mean adrenal weight in milligrams per gram body weight for Mimotus montanus
in populations of different density
Rzft”pSexually active
lation
density
Low
-
Number
examined
”Mean
a,;:
58
2
High
16
Males
Females
Non-active
Number
examined
0.189
0.0077
45
0.186
33
2 0.0257
Sexually active
Number
Mean
Mean
2
2;: examined
YZ;:
0.352
37
f 0.0139
&
0.386
0.0269
2
25
Non-active
Number
examined
0.955
0.0580
41
0.974
10
It 0.0654
Mean
weight
f S.E.
0.452
2 0.0318
0.464
f 0.1090
4
STURGIS McKEEVER
responding zones in active animals. Relative total thickness of the cortex in the 4
classes was: active males, 28; non-active
males, 54; active females, 106; and nonactive females, 55.
DISCUSSION
Chester Jones ('57) demonstrated that
gonadectomy in the male rat resulted in
increased adrenal weight, while in the female gonadectomy was followed by a decline in adrenal weight; injection of the
respective gonadal hormones reversed these
changes. If cessation of reproductive activity is assumed to produce changes in hormone production similar to, but probably
of lesser magnitude than, those brought
about by gonadectomy, then Chester Jones'
explanation of results obtained with gonadectomized animals can be used to explain
changes in both adrenal size and reproductive activity which were exhibited by
Microtus montanus. He suggested that
castration of the female would be accompanied by storage of FSH and LH without
an increase in pituitary weight. This would
divert cells from the secretion of ACTH and
result in a decrease in weight of the adrenals. In the male, castration would be
accompanied not only by storage of FSH
and LH but also by an increase in pituitary
size. Thus, increased storage of gonadotrophic hormones might not reduce ACTH
production in the male. In addition, pituitaries of castrated males secrete large
amounts of LH and FSH, in contrast to
relatively small amounts secreted by pituitaries of castrated females, and these
hormones have the capacity to evoke a
thickening of the zona fasciculata in some
species. Testosterone reduces the size of
the pituitary, lowers LH secretion, and results in a decrease of the zona fasciculata.
Estrogens, however, sometimes aid in the
secretion of gonadotrophins and ACTH,
thus stimulating an increase in size of
both the gonads and the adrenals.
Although no data are available for pituitary size or hormone production in Microtus montanus, the foregoing hypothesis is
considered to be an adequate explanation
for observed changes in adrenal size and
reproductive activity.
Atrophy of the gonads and hypertrophy
of the adrenals have been attributed to a
shift in pituitary production during periods
of stress, and malnutrition is considered
to be a form of stress (Selye, '50). Ershoff
('52) demonstrated that under conditions
of caloric restriction, the gonads become
castrate in type because of reduction in
circulating gonadotrophins. It is logical to
assume that a drought or shortage of food
in winter could lead to malnutrition, accompanied by gonadal atrophy. Data herein presented for Microtus montanus suggest that stress through malnutrition would
result in a significant increase i n adrenal
size in males but a decrease of even greater
proportions in the adrenal size of females.
In natural populations of Microtus pennsyluanicus, Louch ( ' 5 8 ) found that during
a period of drought there was a sharp decline in the percentage of sexually active
animals and, at the same time, a significant increase in the adrenal weights of
males. Onset of reproductive activity in
the spring was accompanied by an increase
in adrenal weight of female animals.
SUMMARY
In natural populations of Microtus montukus, the adrenals of sexually active males
were significantly smaller than non-active
males; adrenals of active females were
significantly larger than those of nonactive females. Adrenals of non-active
males were significantly smaller than nonactive females ( P < 0.01). Pregnant animals did not have larger adrenals than
those females which exhibited other conditions of sexual activity.
Since gonadal atrophy occurs during
periods of stress and since female Microtus
montanus show marked adrenal hypertrophy when sexually active, it is evident
that stress does not produce hypertrophy
of the adrends in both sexes of alI species
of mammals.
LITERATURE CITED
Andersen, D. H., and H.S. Kennedy 1933 The
adrenal cortex in pregnancy and lactation. J.
Physiol. (Lond)., 77: 159-173.
Chester Jones, I. 1957 The Adrenal Cortex.
Cambridge Univ. Press, Cambridge, pp. 10%
104.
Christian, J. J. 1950 The adreno-pituitary system and population cycles in mammals. J.
Mamm., 31: 247-259.
ADRENAL WEIGHTS OF MICROTUS MONTANUS
1955a Effects of population size on the
adrenal glands and reproductive organs of mice
in populations of fixed size. Am. J. Physiol.,
182: 292-300.
1955b Effect of population size on the
weights of the reproductive organs of white
mice. Ibid., 181: 477-480.
1956 Adrenal and reproductive responses to population size in mice from freely
growing populations. Ecology, 37: 258-273.
Ershoff, B. H. 1952 Nutrition and anterior
pituitary with special reference to the general
adaptation syndrome. Vitam. and Horm., 10:
79-140.
Jameson, E. W., Jr. 1950 Detennining fecundity in male small mammals. J. Mamm., 31:
433-436.
5
Louch, C. D. 1956 Adrenocortical activity in
relaton to the density and dynamics of three
confined populations of Microtus pennsylZ J C L T Z ~ C ~ SEcology,
.
37: 701-713.
1958 Adrenocortical activity in two
meadow vole populations. J. Mamm., 39: 109116.
Selye, H. 1949 Textbook of Endocrinology, 2nd
edition. Acta Endocrinologica, Inc., Montreal,
p. 135.
1950 The Physiology and Pathology of
Exposure to Stress. Acta Endocrinologica Inc.,
Montreal, pp. 47-360.
Zalesky, M. 1934 A study of the seasonal
changes in the adrenal gland of the thirteenlined ground squirrel (Citellus tridecemlineatus) with particular reference to its sexual
cycle. Anat. Rec., 60: 291-321.
-
Документ
Категория
Без категории
Просмотров
2
Размер файла
349 Кб
Теги
effect, gland, weight, activity, adrenal, microtus, reproduction, montanus
1/--страниц
Пожаловаться на содержимое документа