The metabolism and biological activity of esterified vitamin D in the rat

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Abstract
1. [I-3H]Cholecalciferol and [I-3H]cholecalciferol palmitate in amounts equivalent to 2 μg cholecalciferol were injected into rachitic rats as aqueous preparations (intravenously) or in arachis oil (intramuscularly).2. The radioactive faecal metabolites collected for up to 17 days were fractionated according to their polarity. The same pattern of excreted radioactivity was seen with intravenous and intramuscular cholecalciferol and intravenous cholecalciferol palmitate. Intramuscular chole-calciferol palmitate produced a higher proportion of the most polar metabolites in faeces.3. Parenterally administered cholecalciferol palmitate in a rickets-healing biological assay had activity equivalent to unesterified cholecalciferol.4. Vitamin D ester synthesized in vivo is considered to be eventually metabolized as vita- min D alcohol and to be available to vitamin D-requiring processes.