Severe Thyrotoxicosis Does Not Accelerate 1a-Hydroxylation of 25-Hydroxyvitamin D3 in Dogs. Experimental Study
542
3) The significant increase in supply of 25OHD3 to the
CYP27B1 enzyme inhibited or slowed down the enzyme
activity.
4) The thyroid hormones have no effect on the hy-
droxylating enzymes of 25OHD in dogs. FGF23-cIotho
reduces the blood levels of 1,25(OH)2D3 [12]. There is a
lack of data in literature for the correlation of thyroxine
and the axis of osteoblasts-osteocytes-PTH-FGF23-clotho
and 1,25(OH)2D.
7. Addendum
In 1633 Galileo Galilei quoted the historical phrase “Ep-
pure si muove (still it moves, and yet it moves) when he
was forced from “Holy Inquisition” to recant his belief
that the earth moves around the sun (The event was first
reported in English print in 1757 by Giuseppe Baretti)
[13]. A minor yet similar event occurred to me as well. In
my case, the “Holy Inquisition” was my research study
that forced me to state that the increased levels of thyroid
hormones in dogs do not influence the metabolism of
25OHD3. On the contrary, I believe that the increased
blood levels of thyroid hormones in the body accelerate
the catabolism of vitamin D to give the end products of
calcitroic acid and lactones [14]. In favour of this theory
are: 1) the accelerated hydroxylation of Vitamin D on
C25 position in thyrotoxicosis, 2) the depressed levels of
1,25(OH)2D3 again in thyrotoxicosis, 3) the increased
1,25(OH)2D3 blood levels in hypothyroidism [15]. I be-
lieve that a more detailed investigation in human subjects
will clarify these issues in the future.
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