The subcellular distribution of physiological doses of vitamin D₃

When physiological doses of tritiated vitamin D₃ are administered to rachitic chicks, the small intestine accumulates a large portion of the dose. The subcellular distribution of the ³H-vitamin D₃ within the intestinal mucosa cells shows the radioactivity to be primarily associated with the nuclear fraction. The radioactivity is retained in this fraction when it is purified by sedimentation in 2 m sucrose. In vitro incubation of ³H-vitamin D₃ with homogenates of vitamin D-deficient and normal chick mucosa cells indicates a selective binding of the vitamin to the nuclear fraction derived from the rachitic chicks.