| Research Abstract |
Comparative studies on metabolism and physiological action of the vitamin D_2 and D_3 Related compounds were performed.
In order to obtain the standard compounds of the D_2 compounds, 24R,25(OH)_2D_2 and 24S,25(OH)_2D_2 were chemically syntesized while 25-OH-D_2 and 1,25(OH)_2D_2 were produced by the biochemical methods. When the binding affinity of the D_2 compounds and commercially available D_3 compounds to vitamin D-binding protein (DBP) or 1,25-(OH)_2D receptor was assayed, there was no significant difference between the affinity of 1,25(OH)_2D_2 and 1,25(OH)_2D_3 bound to the recptor whereas 24,25(OH)_2D_3 showed stronger binding affinity to DBP than 24,25(OH)_2D_2. Therefore, when 24,25(OH)_2D_2 is assayed by a competitive protein binding assay method, the calibration curve should be made by using the standard compound while the use of standard compound of 24,25(OH)_2D_3 instead of the D_2 compound will give a significant error. From these results, we have made a multiple assay method of vitamin D_2,D_3 and their metabolites in plasma and applied to the studies on the effect of orally administerd vitamin D_2 on the concentrations of vitamin D_2,D_3 and their metabolites in plasma. The studies on the bioavailability of vitamin D_2 to healthy subjects and the supplementation of vitamin D_2 to healthy lactating mothers were performed, and very intersting results were obtained.
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