Discrimination in the metabolism of orally dosed ergocalciferol and cholecalciferol by the pig, rat and chick

Abstract

Vitamin D-deficient pigs, rats and chicks were repleted with four daily oral doses of crystalline ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3) containing equal concentrations of each. At 24 h after the last dose, the plasma of each species was analysed for vitamin D and 25-hydroxyvitamin D by standard methods. The mean (+/- S.D.) ratios of plasma cholecalciferol to ergocalciferol concentration were 1.5 +/- 0.1 (pig). 1.7 +/- 0.1 (rat) and 6.3 +/- 1.2 (chick). The mean ratios of plasma 25-hydroxycholecalciferol to 25-hydroxyergocalciferol concentration were 4.0 +/- 0.1 (pig), 0.4 +/- 0.02 (rat) and 10.7 +/- 3.4 (chick). The mean plasma cholecalciferol/ergocalciferol ratios for the 24,25-dihydroxy-, 25,26-dihydroxy- and 1,25-dihydroxy-derivatives in the pig were 2.6 +/- 0.6, 5.8 +/- 1.3 and 5.8 +/- 0.8 respectively. This is the first evidence that mammals other than the New World monkey, like birds, discriminate between ergocalciferol and cholecalciferol. These data, therefore, suggest that species discrimination between the different forms of vitamin D is probably a general phenomenon in mammals. Moreover, this is the first indication of a species (rat) that discriminates against a cholecalciferol metabolite in favour of an ergocalciferol metabolite. Species discrimination against particular forms of vitamin D may be important to the choice of experimental animal models for studying the regulation of vitamin D metabolism and may also be an important consideration in dietary vitamin supplementation.

Vitamin D supplementation improves pathophysiology in a rat model of preeclampsia

“…Although VD2 and VD3 are commercially available as supplements, clinical data have implicated that VD3 may be a better therapeutic for humans (42,61). In contrast, VD2 may be more efficiently metabolized in rats (26). In accordance with these reports, our data showed that VD2 lowered blood pressure, AT 1 -AA, and sFlt-1 to a greater extent than VD3 in RUPP rats.…”

Stereochemistry of 25‐hydroxyvitamin D3—26,23‐lactone and 1α,25—dihydroxyvitamin D3—26,23‐lactone in rat serum

“…We obtained the highly purified 25OH-Ds-26,23-lactone from rat serum as in [9] with slight modifications. The natural metabolite was directly compared to 2 diastereoisomers, 23(S)25@)-25-OH-Da-26,23-lactone and 23@)25(S)-25-OH-Ds-26,23-lactone stereospecifically synthesized by [7,8].…”

The Pharmacology of Vitamin D

“…For a bioassay yielding "units," equivalence is not the same thing as equivalence per milligram or per mole. Furthermore, all species tested show differences between the vitamin D 2 and vitamin D 3 [90,91], so why should humans be any different? Despite these obvious problems about units, the very conservative approach used by those who frame official statements about nutrients has remained unchanged, that one international unit of vitamin D is equivalent to 25 nanograms of either vitamin D 2 or vitamin D 3 [72,89].…”