Metabolism and plasma protein transport of vitamin D3 in the baboon

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Abstract
Plasma protein transport of vitamin D3 was investigated in baboons whose bodily vitamin D3 has been labeled with 14C by feeding 14C-ring-labeled vitamin D3 to young baboons thoroughly depleted of this vitamin. Plasma proteins were separated and identified by ultracentrifugation, gel filtration, DEAE cellulose chromatography, polyacrylamide gel and starch zone electrophoresis, and microimmunoelectrophoresis. More than 60% of the plasma vitamin D3 was associated with a nonlipid containing α1-globulin and most of the remainder with albumin. Transport by lipoproteins was quantitatively greater during the early phase of repletion, only trace quantities thus attached being detected in the subsequent weeks. Thus, plasma transport of vitamin D3 in nonhuman primates is very similar to that which has been described previously for other species. In addition, several aspects of baboon vitamin D metabolism were investigated and were found to be similar to those of man.