Influence of Environmental Temperature on Thyroid Hormone Production in Sheep
Abstract: The effect of high
(28oC) and low (14oC) temperature on thyroid hormone production were studied in
five male sheep since the activity of thyroid releasing hormone (TRH) cell in
the hypothalamus that influence the thyroid stimulating hormone (TSH) production
and release can be affected through the temperature regulatory center. The aim
of this study were to measure the iodine (the core of thyroid hormone)
needed in the
different temperatures, T4
(thyroxine) production, T4 and T3 (triiodotironine) concentration. Two
experiments were performed in both
condition to investigate
the thyroidal 125I
uptake and to measure
T4 production. The
sheep were shorn
at the beginning
of each adaptation period (22oC).
The first treatment was high
temperature and the second
treatment was low temperature. The experiments were done at least five weeks of
each temperature. The mean of rectal temperatures during the warm period were
significantly higher than that in the cold period. The feed intake during the
warm period tend to decrease significantly, but there was no increase during
the cold period. The absolute iodine uptake (AIU) over 24 hours was markedly
increased during the second period (7.94±1.37 -g/24 hr) compare to the first
period (1.65±0.13 -g/24 hr). It means that cold exposure has a potential to
stimulate the thyroid gland in order to uptake more iodide. The mean of T4 concentration was 51.6±2.1 ng/ml during the warm and
61.2±5.5 ng/ml four weeks after shift to the cold period and did not differ,
but four weeks later the concentration
was significantly increased
(77.4±1.47)(33%). The same
pattern occurred to the T3 concentration that the four weeks after
shifting the level of T3 was not significantly increased from value of 0.39
ng/ml to value of 0.51 ng/ml, eight weeks after shifting the T3 value (0.65
ng/ml) was significantly rose. This finding provides convincing evidence that
the T4 and T3 concentration indeed increase during the cold period. The
conclusion that the production of thyroid hormones were
influenced by temperature.
T4 and T3
concentration were increase
during the cold period. The AIU was absolutely higher during the cold period,
that means the amount of iodine needed in high temperature is less than in low
temperature.
Autor: Syafwan
Journal Code: jppeternakangg060001
