Existence of vitamin D3 and 25-hydroxyvitamin D3 in rat lymph.

The transport forms of vitamin D3 and 25-hydroxyvitamin D3 [25 (OH) D3] in lymph were studied in rats with thoracic duct cannulas. Under in vitro and in vivo conditions, the majority of vitamin D3 recovered from lymph was found in the chylomicrons and other lipoproteins fractions. On the other hand, the major fraction containing 25 (OH) D3 corresponded to the albumin and α-globulin fractions. In order to confirm the presence of binding protein having affinity to 25 (OH) D3 in lymph, the binding protein was isolated and purified by procedures of gel filtration, affinity and ion exchange chromatography from the incubated mixture of thoracic duct lymph with 25 (OH) D3. The purified binding protein showed a single band of protein on disc and sodium dodecyl sulfate-disc gel electrophoreses. Furthermore, the protein also gave a single peak on highperformance liquid chromatography (HPLC) using a gel permeation column. The molecular weight of the protein was calculated from the results of HPLC as 57000, a value which is apparently different from that of lymph albumin. These results suggest that vitamin D3 and 25 (OH) D3 are mainly transported from the intestine to the liver via the lymph duct by different carrier mediators as lipoprotein complex and protein-bound forms, respectively, in rats.