Vitamin D uptake by the perfused rat liver is determined by its transport protein.

Radiolabelled vitamin D3 and 25(OH)vitamin D3 (25(OH)D) were added to an isolated perfused rat liver, bound either to lipoproteins or lipoprotein-free plasma. The disappearance of vitamin D and 25(OH)D from the perfusate was determined. When vitamin D or 25(OH)D were added to the perfusate on lipoproteins there was a rapid decline in the amount present in the perfusate, as compared to when they were added bound to lipoprotein-free plasma. The uptake of vitamin D and 25(OH)D by the liver from lipoproteins was associated with a transfer of radioactivity from the lipoprotein portion to the lipoprotein-free portion of the perfusate. These results demonstrate the importance of the vitamin D transport protein to its uptake by the liver.