Intl. J. of Molecular Zoology, 2013, Vol.3, No.2, 4
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Figure 4 Hormonal concentration of Thyroid hormone and TSH
during various phases pregnancy
2
Discussion
Thyroid gland secretes thyroglobulin, triiodothyronine
and thyroxin. Thyroxin plays an important role in
metabolism of the body (Turner, 1966). Thyroid gland
is metabolically important and essential for the normal
maintenance of reproductive function, impairment of
thyroid activity may be inhibitory to reproduction
(
Peebles et al., 1984; Jannini et al., 1995).
Pregnancy alters thyroid status in rodents. In the rat,
pregnancy results in decreased total T4 and T3
concentrations and enlarged thyroid gland volume.
However, unlike the case of humans, iodine up take is
decreased in pregnant rats, and urinary iodide
excretion remains unaltered the last days of gestation
(
Calvo et al., 1990, Feldman, 1958, Versloot et al.,
1997).
In
Taphozous kachhensis
,
the location of thyroid gland
in the body is similar to other large animals like cattle
and buffaloes (Getty et al., 1986) and Camel (Kausar
and shahid, 2006) i.e., with the first ring of trachea
and consisted of two lobes on both side and an
isthmus connecting these lobes. In
Taphozous
kachhensis
the gland appeared reddish brown in
colour which is in concordance with the findings of
Schwartz and Dioli (1992). The present study also
showed a close relationship between changes in the
weight and morphological features of the thyroid and
the ovarian cycle of
Taphozous kachhensis
.
Histological studies revealed similar results as
reported in camel (Abdel-Magied et al., 2000; Atoji et
al., 1999) i.e. the gland consisted of follicles of
variable sizes with small size follicle lined by high
cuboidal epithelium to columnar epithelial cells, while
the larger ones were lined by low cuboidal epithelial
cells. Medium size follicles were lined by cuboidal
epithelium. Similar observation were reported in
Taphozous longimanus
(
Nerkar, 2007),
Megaderma
lyra
(
Sonwane, 2010).
In present study the thyroid hormone show marked
seasonal variation. The concentrations of TSH, T3,
and T4 show significant seasonal changes. The hormonal
level of TSH, T3, T4 changes during early pregnancy
and observed 1.7 ng/mL, 54 ng/mL and 2.9 ng/mL
respectively. During mid pregnancy the T3 level is found
to be 69 ng/mL and 60 ng/mL during late pregnancy. T4
level is highest during early and late pregnancy (2.9 ng/mL)
and lowest during mid-pregnancy (1.5 ng/mL). The T3
level is higher than T4 level during reproductive cycle.
The serum T3 and T4 concentration showed
significant variation with changes in reproductive
cycle of bat,
Taphozous longimanus
(
Singh et al.,
2005).
The thyroid hormones are important for regulation of
nutrient assimilation, metabolism, calorigenesis
(
Todini et al., 2007), reproduction (Blaszczyk et al.,
2004).
The report of thyroid hormone on pregnancy
was reported in
Macrotus californicus
(
Burn et al.,
1972).
Thyroid hormone plays an important role in the
central regulation of body temperature, stimulating the
thermogenesis and regulating cellular metabolism
(
Seitz et al., 1985). The metabolism hormone
Thyroxin (T4) has been implicated in the
physiological regulation of energy balance as well as
maintaining normal reproductive function in mammals
(
Bosewell et al., 1994).
In ewes, plasma T4 levels are lower during the luteal
phase; T3 concentrations were higher during the luteal
phase, this observation supports the present study.
During pregnancy, thyroid activity and circulating
hormone levels are reported to increase in all the
investigated mammalian species. Several mechanisms
have been claimed to explain these observations.
Towards the end of pregnancy, the goat foetus (es)
should play a competitive role (higher thyroid activity,
iodine affinity and uptake than maternal ones), so that