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.