title: Evidence that discrimination against ergocalciferol by the chick is the result of enhanced metabolic clearance rates for its mono- and dihydroxylated metabolites.
abstract: Studies on the discrimination between ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3) by chickens have led to conflicting conclusions. To investigate this problem in more detail, radiolabeled vitamin D and vitamin D metabolites were administered intravenously, which allowed determination of their relative plasma clearance rates. The study involved three groups of adult male chickens (five per group). Birds in group 1 were co-dosed with [3H]vitamin D2 and [3H]vitamin D3. Birds in group 2 were co-dosed with [3H]25-dihydroxyvitamin D2 and [3H]25-dihydroxyvitamin D3 and birds in group 3 were co-dosed with [3H]1,25-dihydroxyvitamin D3 and [3H]1,25-dihydroxyvitamin D2. The results indicated that the plasma turnover rate of [3H]vitamin D2 is 1.5 times faster than that of [3H]vitamin D3. Plasma turnover of the 25-hydroxylated metabolites differed, with [3H]25-dihydroxyvitamin D2 clearing faster (11 times) than [3H]25-dihydroxyvitamin D3. The largest difference appeared in the 1,25-dihydroxyvitamin D2 turnover rates with 1,25-dihydroxyvitamin D2 clearing approximately 33 times faster then [3H]1,25-dihydroxyvitamin D3. These data, therefore, indicate that discrimination against vitamin D2 sterols in the chick occurs primarily between steps in the metabolism of vitamin D and not at the point of metabolism or excretion of the parent vitamin.
authors.affiliation: National Animal Disease Center, U.S. Department of Agriculture, Ames, IA 50010.
authors.forename: D A
authors.initials: DA
authors.lastname: Hoy
authors.forename: C F
authors.initials: CF
authors.lastname: Ramberg
authors.forename: R L
authors.initials: RL
authors.lastname: Horst
mesh_terms: D015652:25-Hydroxyvitamin D 2; D000818:Animals; D002112:Calcifediol / Q000493:pharmacokinetics; D002117:Calcitriol / Q000493:pharmacokinetics; D002645:Chickens / Q000378:metabolism*; D002762:Cholecalciferol / Q000493:pharmacokinetics*; D004872:Ergocalciferols / Q000031:analogs & derivatives / Q000493:pharmacokinetics*; D008297:Male; D008657:Metabolic Clearance Rate
chemical_list: D004872:Ergocalciferols; D002762:Cholecalciferol; D015652:25-Hydroxyvitamin D 2; C003564:1,25-dihydroxyergocalciferol; D002117:Calcitriol; D002112:Calcifediol