An in vivo study of the carrier proteins of 3H-vitamins D3 and D4 in rat serum

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Abstract
The distribution of radioactivity among rat serum proteins separated by disc electrophoresis was studied in vitro, 1/2 and 24 hr. after intravenous injection of vitamins D3-3H or D4-3H. The radioactivity was found associated with 5 of the 12 serum protein fractions. Of these, four were shown to be or to contain lipoproteins. The fifth was shown to be a nonlipoprotein, [alpha]-globulin. In vitro, the lipoprotein fractions were associated with 47-56% of the radioactivity. In vivo, there was an increasing association of radioactivity with the nonlipoprotein, [alpha] -globulin with time (from 50 to 80%). The shift from lipoprotein to nonlipoprotein was shown to be purely time-after-dose related, being independent of amount of dose and the prior vitamin D status of the animals. It was further shown that this nonlipoprotein, [alpha] -globulin is also associated with a major biologically active metabolite of the vitamin.

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