Effects of 1,25-dihydroxycholecalciferol administration on the rat renal vitamin K-dependent carboxylating system

AbstractWe have shown previously that the in vitro activity of the renal vitamin K-dependent γ-glutamyi carboxylase toward synthetic oligopeptide substrates is stimulated by administration of either parathyroid hormone (PTH) or 1,25-dihydroxycholecalciferol [1,25 (OH)2D3] to rats [(1983) J. Biol. Chem. 258, 12783-12786]. Here we report that administration of 1,25(OH)2D3 to rats increases their levels of endogenous carboxylase substrate as well. Rats fed a vitamin D-deficient diet had highly elevated serum PTH levels while vitamin D-replete animals had undetectable levels. Furthermore, since PTH increases 1,25(OH)2D3 levels by stimulating renal 25-hydroxy vitamin D-1α-hydroxylase, it is very likely that the stimulatory effects of PTH on the renal vitamin K-dependent carboxylating system are mediated by 1,25(OH);,D3