Exp. Anim. 39(2), 239-248,
Spontaneous
Lesions
Hideki
in Beagle
MORISHIMA,
Dogs Used
Takashi NONOYAMA, and Hiroaki MIYAJIMA
Drug Safety Research Laboratories, Takeda 6-10-1 Himuro-cho, Takatsuki-shi, (Received 26 September
in Toxicity Satoshi
1 December
Studies
SASAKI,
Chemical Industries, Osaka 569, Japan
1989/Accepted
1990
Co., Ltd.,
1989)
Spontaneous histopathologic lesions were examined in 276 young beagle dogs (8 to 15 months old) used in toxicity studies. Mononuclear cell infiltration in the liver was observed with the highest incidence (more than 95%). Calcium deposition in the kidney, mononuclear cell infiltration in the salivary glands, pigmentation in the spleen, and cortical atrophy in the thymus were seen with relatively high incidences (more than 30%). The incidence of mononuclear cell infiltration in the gallbladder, vacuolization of the tubular epithelium in the kidney, and vacuolization of the zona glomerulosa cell in the adrenal gland showed differences between the sexes. No abnormalities were seen in the spinal cord, sternum, and femur. Although most lesions observed are considered to be age-related, several were considered to be due to congenital anomalies observed in some organs.
The importance of beagle dogs as experimental animals in toxicologic and medical studies is well established. Background information on this breed has been extensively accumulated [1, 5, 10, 13, 14]. Although the recognition of subclinical spontaneous lesions in dogs used in drug-safety evaluation studies and the differentiation of these lesions from drug-induced alterations are very important, only a few histopathologic surveys of spontaneous lesions in beagle dogs are found in the literature [7, 8,11,12,15], but control data may take many forms and include variables such as the source and age of animals and diet. In this report, the histopathology of spontaneous subclinical lesions found in young beagle dogs (8 to 15 months old) used in drugsafety evaluation studies is described.
and
leptospirosis,
serologically
and
Methods
were
proved
Brucella
canis
to
be
by
the
After the animals arrived at our laboratory, they were quarantined and acclimatized to the environmental conditions for at least one month before they were used in the studies. During this period, all animals were considered to be normal on the basis of body weight, heart rate, body temperature, ophthalmoscopy, hematology, blood chemistry, examination for Brucella canis in the serum, examination for salmonellosis and the eggs of parasites in the feces, and the absence of clinical signs of disease. The metal
10-20
animals
cages
ditioned
tion
1. Animals : Two hundred and seventy-six beagle dogs (144 males and 132 females) used in drug-safety evaluation studies are the subjects of this report. The animals were obtained from Japan Experimental Dog and Monkey Co., Ltd. or White Eagle Laboratories, Inc. at 5-6 months of age. The animals were vaccinated against canine distemper, infectious hepatitis,
from
breeder.
were
housed
(650•~580•~800mm)
room
a relative
Materials
and
free
with
humidity
times/hr, light/dark
a temperature of
and
in in
55•}15%,
a 12 hr
individual an of
air-con23•}3•Ž,
air-changes
fluorescent
of
illumina-
cycle.
Each animal was fed daily a mixture of 260g of a pellet diet (CD-5, CLEA Japan, Inc. ), 100g of a canned meat (Kal Kan (R), Kal Kan Foods Co., U. S. A.), and 360g of warm tap water in the afternoon. They were allowed free access to tap water. The ages of the from 8 to 15 months.
dogs
at
autopsy
ranged
240
2.
Histopathologic
mination was
Procedures
of
each
anesthetized
sacrificed and
with
by
of
and
f ormalin
the
fixed
10
uterus,
testis/ovary,
gallbladder, lymph node, glands
at
ixed in specimens
sectioned with
at
cord,
pH
formalin,
tract and
for
about
of eosin
infiltration•h
of •gMononuclear in
beagle
cell
dogs
and for
stained histopa-
sternum, by
and
f ormalin. paraffin,
in
(H-E)
The
were
15 min
4 ƒÊm,
decalcified they
Table
mesenteric salivary sublingual
thickness
were
colon),
mammary
a
before
para-
and trachea. The phosphatebuffered
7.1
examination. trachea
dogs
liver,
skin,
neutral buffered were embedded
and
Incidence
in beagle
prostate/
and
5%
hematoxylin
thologic
lung,
ileum,
femur, in 4%
2.
lesions
were
thyroid,
gland
sternum, were fixed
glutaraldehyde postf All
heart, kidney,
spinal
Common
buffered
bone marrow (femur), urinary bladder, tongue,
esophagus,
gland, eyeballs
organs neutral
duodenum,
(submaxillary
gland),
1.
artery,
gastrointestinal
pylorus,
Table
sodium,
carotid
vagina,
adrenal,
(fundus,
%
thymus,
ter-
animal
immediately.
pituitary,
pancreas,
thyroid,
the
following
in
: brain,
spleen,
and
of
examined
portions
obtained
the
each
thiopental
incision
macroscopically
Small
After
experiment,
femur, formic
embedded
acidin
para-
ffin.
If there was any suspicion that a lesion might be related to drug-treatment, it was not considered to be spontaneous. Differences between the sexes in the incidence of each lesion were statistically analyzed using the Chi-square test. Results Various observed spinal
histopathologic in
cord,
all
organs
sternum,
lesions examined
and
except
were the
femur.
Table 1 shows the common lesions that were observed in several organs. Mononuclear cell infiltration was the most common lesion observed in 21 organs (Fig. 1, 2) ; the incidence in each organ was relatively high (Table 2), but the severity was minimal to mild. In the salivary glands, most of the mononuclear cell infiltration observed was in the sublingual gland. The cells which infiltrated the sublingual gland had abundant basophilic cytoplasm, a wheel-like nucleus, and resembled plasma cells (Fig. 3, 4). In the gallbladder, the incidence of mononuclear cell infiltration in males (20.8%) was significantly higher than that in females
* : Significant
difference
male and female
in incidence
between
(P