AJP - Endocrinology and Metabolism, Vol 244, Issue 3 266-E271, Copyright © 1983 by American Physiological Society
Apparent [3H]1,25-dihydroxyvitamin D3 uptake by canine and rodent brain
M. Gascon-Barre and P. M. Huet
The brain uptake of [3H]1,25-dihydroxyvitamin D3 ([3H]1,25(OH)2D3) was
studied during steady-state conditions using the multiple-indicator
dilution technique in dogs. The fractional [3H]1,25(OH)2D3 uptake was
evaluated at 0.8 +/- 0.15% during a single passage through the dog brain.
Evaluation of the [3H]1,25(OH)2D3 uptake by the vitamin D-replete and
vitamin D-depleted rat brain indicated that 30 min after its injection, the
fractional uptake was not influenced by the vitamin D status of the animals
or by the amount of [3H]-1,25(OH)2D3 injected. In the rodent the fractional
[3H]-1,25(OH)2D3 brain accumulation was between 0.16 and 0.20%, whereas the
brain-to-serum ratio varied between 5 and 6%. Protein-binding studies of
serum [3H]1,25(OH)2D3 indicated that, at 37 degrees C, 94.8 +/- 0.4% of the
hormone was protein bound 30 min after its intravenous injection. These
observations suggest that 1,25(OH)2D3 is able to cross the blood-brain
barrier. However, its limited brain uptake in relation to its serum
concentration suggests that the hormone does not penetrate freely into the
central nervous system and that its brain uptake may be related to the free
circulating 1,25(OH)2D3 concentration perfusing the blood-brain barrier.
