The Determination of Vitamin D with Radiophosphorus

Abstract

A technique for the bioassay of vitamin D with the use of parenteral radiophosphorus has been described. In this technique young rats are fed a rachitogenic ration (ration 2965) for 16 days. They are then given orally an unknown vitamin D preparation, in a dose ranging in expected potency from one-half to 50 units. Forty-eight hours later this is followed with an intraperitoneal injection of a trace dose of P³². After 10 days of continued feeding of the rachitogenic ration the rats are anesthetized and the radioactivity of a forepaw of the living animal is determined. This is accomplished by placing the rat with a forepaw fixed in a reproducible position on Scotch tape under an end-mica-window Geiger counter. The average count for 10 rats which received the unknown vitamin D is compared with values of a standard reference curve obtained with doses of known potency. This technique gives results which compare in accuracy with wellknown methods and offers some advantages.