Extraction of [14C] vitamin A from rat liver and kidney during processing for transmission electron microscopy

The retention of radioisotope-labeled vitamin A during processing for electron microscopy was investigated using the livers and kidneys of vitamin A deficient rats. [15-14C]Retinol (3muCi/animal) was administered by esophageal intubation to male rats which had been maintained on a vitamin A deficient diet for five or six weeks postweaning. Glutaraldehyde- or osmium-fixed tissue was processed by three methods: a) routine (a graded series of ethanols, propylene oxide and epoxy), b) rapid (75% and 95% ethanol with three changes of epoxy), or c) water-soluble embedding (70% and 80% hydroxypropyl methacrylate). Water-soluble embedding retained the highest percentage of label in the tissue (liver: 96.31%; kidney: 98.68%). Inclusion of osmium tetroxide in the processing sequence and minimal exposure of tissue to lipid solvents were necessary for good retention of labeled vitamin A in tissues.