A modified relative dose-response assay employing 3,4-didehydroretinol (vitamin A2) in rats

3,4-Didehydroretinol (vitamin A2, DR, dehydroretinol), a naturally occurring analogue of retinol (vitamin A1, R), is active in vision, growth and cellular differentiation but is converted to retinol in very small amounts, if at all. When vitamin A-depleted rats were given 500 micrograms of R acetate, a naturally occurring mixture of 480 micrograms DR ester and 20 micrograms R ester or 500 micrograms DR acetate orally in corn oil, serum levels of all administered retinoids peaked between 3.5 and 5 h and then declined. When an oral dose of 600 micrograms DR/kg body wt was administered to rats with various liver reserves of vitamin A, the serum ratio of DR to R at 3.5 h was inversely related to the liver reserves of vitamin A below approximately 2 micrograms/g liver. Because the administration of DR does not affect serum R values, a single blood sample taken at 3.5 h might provide information analogous to that obtained from two blood samples in the conventional relative dose-response method.