Two healthy dogs weighing 18 kg and 13
kg each received an intravenous injection of 7 μg/kg 25-hydroxyvitamin D3 (25OHD3). Subsequently,
they were blood-sampled
in order to determine the plasma levels of 25(OH)D3 over 4-hourly
time intervals and for a time period of 24 hours. After a period of 18 days
since the last blood sampling, the animals were brought to a hyperthyroid state
and the intravenous injection of 7 μg/kg 25OHD3 was repeated. Blood sampling was performed every 4
hours and over a time period of 24 hours in order to determine the levels of
25OHD3. The graphic plotting of plasma levels of 25OHD3 in the euthyroid state did not differ from that in the hyperthyroid state. This
finding in dog animal experimentation is indicative that the increased levels
of thyroid hormones did not affect the activity of CYP27B1 and CYP24A1 enzymes
that are related to the catabolism of 25OHD3 over a minimum of 24
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