Ascorbic acid effects on vitamin D hormone metabolism and binding in guinea pigs.
Ascorbic acid deficiency in guinea pigs fed a vitamin D-replete diet caused a moderate reduction of Ca level in serum and bone; 25-hydroxy-cholecalciferol or 25-hydroxyergocalciferol (25-OHD) serum concentration tended to decline; renal 25-hydroxycholecalciferol-1-hydroxylase (1-OHase) activity decreased 50%; and 25-hydroxycholecalciferol-24-hydroxylase activity increased 1.6-fold. Chromatin 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] receptor concentration in the intestinal mucosa decreased 20-30%, and the percentage of occupied receptors decreased from 12-15% to 6-8%. Receptor affinity for 1,25-(OH)2D3 did not change (Kd = 0.24-0.26 nmol/L, Kd2 = 0.06-0.10 nmol/L), but the cooperativity coefficient decreased from 1.7 to 1.4. Vitamin C deficiency potentiated effects of vitamin D deprivation and impaired a restorative action of vitamin D. It was accompanied by a marked delay in the elevation of 25-OHD concentration in serum as well as decreased 1-OHase activity in kidneys and a lower concentration of occupied 1,25-(OH)2D3 receptors in the intestinal mucosa. The data demonstrate a critical role for ascorbic acid in vitamin D metabolism and binding.
Sergeev
I N
IN
Institute of Nutrition, Academy of Medical Sciences of the USSR, Moscow.
Arkhapchev
Y P
YP
Spirichev
V B
VB
D015652:25-Hydroxyvitamin D 2 / Q000378:metabolism; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000378:metabolism; D000818:Animals; D001206:Ascorbic Acid Deficiency / Q000378:metabolism*; D001842:Bone and Bones / Q000737:chemistry / Q000378:metabolism; D002112:Calcifediol / Q000378:metabolism; D002118:Calcium / Q000032:analysis / Q000097:blood; D006168:Guinea Pigs; D007413:Intestinal Mucosa / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D008297:Male; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000378:metabolism; D014807:Vitamin D / Q000008:administration & dosage / Q000378:metabolism*; D014808:Vitamin D Deficiency / Q000378:metabolism*
D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; D014807:Vitamin D; D015652:25-Hydroxyvitamin D 2; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D002112:Calcifediol; D002118:Calcium