Intl. J. of Molecular Zoology, 2013, Vol.3, No.2, 4
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http://ijmz.sophiapublisher.com
5
reduction in the secretion and plasma levels of
gonadotrophins was associated with hypothyroidism
(
Hagino, 1971; LaRochelle and Freeman, 1974;
Buchanan et al., 1977). Likewise, Dunn et al. (1976)
have reported that the daily rhythmic release of
luteinizing hormone (LH) and prolactin in rats was
altered by thyroidectomy.
Thyroid hormones have a significant mode of action
on seasonal reproduction. In 1994, work by researchers
in Michigan implicated thyroid hormones as having a
role in decreasing LH secretion at the end of the
breeding season, resulting in the normal cessation of
follicular activity and ovulation. Along with follicle
stimulating hormone (FSH), luteinizing hormone (LH)
and indirectly, gonadotropin-releasing hormone
(
GnRH) are hormones responsible for follicle growth
and ovulation
.
1
Results
1.1
Gross Observations
Gross studies of thyroid gland of female bat
Taphozous kachhensi
s revealed that the gland was
located near the first ring and third ring of trachea and
consisted of two lobes. An isthmus connected these
lobes to each other. The colour of the gland was
reddish brown.
1.2
Seasonal Changes in Body, Ovary, and Thyroid
Weights
The weights (mean±SEM) of the body, ovary, and
thyroid during reproductive phases are shown in Table
1
and Figure 1. There was not much difference in
weight of thyroid gland of adult female bats caught
during different phases of pregnancy. The thyroid
weight showed two peaks coinciding with the peaks of
ovary weight during early pregnancy and mid
pregnancy. Both thyroid and ovary began to increase
in weight from early pregnancy (January to February)
and attained a peak during mid pregnancy (Late
February to Middle April). Thyroid weights declined
during late pregnancy similarly to ovary weight
(
Figure 1).
1.3
Histology
The thyroid gland of the female bat is studied
Table 1 The mean weights of the body, ovary, and thyroid
during different phases of pregnancy
Early
pregnancy
(
mg)
Mid
pregnancy
(
mg)
Late
pregnancy
(
mg)
Thyroid
2.24
± 0.120 2.88 ± 0.051
2.70
± 0.067
Ovary
2.38
± 0.086 2.49 ± 0.075
1.49
± 0.064
Body
50.00
45.00
39.00
Figure 1 The mean weights of the body, ovary, and thyroid
during different phases of pregnancy
histologically; it showed marked seasonal variation in
quantity of colloid, epithelial cell height and plasma
concentration of thyroid hormones. Diameter of
colloid in large, medium and small size follicle of
thyroid gland shows variations, with higher value
during early pregnancy and lower value during mid
pregnancy in large follicle, while in medium size
follicle higher value of colloid during late pregnancy
and lower during mid pregnancy. Small size follicle
shows higher value of colloid during late pregnancy
and lower during early pregnancy (Table 2). Thyroid
follicular epithelial cells height also showed marked
variations during various period of pregnancy. The
large size follicles were lined by low cuboidal
epithelium having flattened nuclei and 3.6 µm, 4 µm
and 4 µm in diameter during early, mid and late
pregnancy respectively and were assumed to be
inactive. The medium size follicles were lined by
cuboidal epithelium having darkly stained nuclei
and 4 µm, 8 µm and 8 µm in diameter during early,
mid and late pregnancy respectively. The small size
follicles were lined by high cuboidal epithelium with
rounded nuclei having diameter 12 µm, 12 µm and 8 µm
during early, middle and late pregnancy respectively
(
Figure 2, Table 2, Figure 3).