Mechanism of action
·
Dihydrotachysterol is a synthetic analogue of
vit D2 that is much less active in antirachitic tests but after hydroxylated
to 25-hydroxydihydrotachysterol, the modified drug binds to the vitamin
D receptor.
·
The
bound form of the vitamin D receptor serves a transcriptional regulator of bone
matrix proteins, inducing the expression of osteocalcin and suppressing
synthesis of type I collagen.
·
Vitamin
D (when bound to the vitamin D receptor) also stimulates the expression of a
number of proteins involved in transporting calcium from the lumen of the
intestine, across the epithelial cells and into blood. This stimulates
intestinal calcium absorption and increases renal phosphate excretion. These
are functions that are normally carried out by the parathyroid hormone.
Reference: Tripathi
K.D., "Essentials of medical pharmacology", Jaypee brothers medical
publishers, Seventh edition, New Delhi, page no. 342-343
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