The thyroid gland synthesizes mainly T4 and releases it into the
circulation. T4 is converted to T3 in peripheral tissues. Many investigations
have demonstrated that NO3–N could induced a significant
decrease in T3 and T4 levels and might be considered as a
goitrigenic factor in rat (Zaki et al., 2004; Mukhopadhyay et al.,
2005). Our report clearly observed that treatment with 100 NO3–
N can significantly decline T4 and T3 levels, which is consistent
with all the above results. However, our result also showed that
exposure to 100 mg/L NO3–N could increase the T3/T4 ratio. At
metamorphic climax, which corresponds with the emergence of
forelimbs (G42), there is a corresponding peak in the primary circulating
thyroid hormone, T4. T4 contains iodine, and nitrate can
impair the formation of thyroid hormones through the inhibition of iodine uptake and transport (Boas et al., 2012). We proposed
that high dose nitrate decreased T4 levels more sharply than T3
levels, leading to increased T3/T4 ratio.
The thyroid gland synthesizes mainly T4 and releases it into thecirculation. T4 is converted to T3 in peripheral tissues. Many investigationshave demonstrated that NO3–N could induced a significantdecrease in T3 and T4 levels and might be considered as agoitrigenic factor in rat (Zaki et al., 2004; Mukhopadhyay et al.,2005). Our report clearly observed that treatment with 100 NO3–N can significantly decline T4 and T3 levels, which is consistentwith all the above results. However, our result also showed thatexposure to 100 mg/L NO3–N could increase the T3/T4 ratio. Atmetamorphic climax, which corresponds with the emergence offorelimbs (G42), there is a corresponding peak in the primary circulatingthyroid hormone, T4. T4 contains iodine, and nitrate canimpair the formation of thyroid hormones through the inhibition of iodine uptake and transport (Boas et al., 2012). We proposedthat high dose nitrate decreased T4 levels more sharply than T3levels, leading to increased T3/T4 ratio.
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