On the existence of lipid peroxides in rat tissue.

1. The colorimetric micro-adaption of the iodometric method and the colorimetric thiocyanate method for the determination of lipoperoxides were compared. Similar results were obtained when methyl linoleate hydroperoxide was tested, but when lipid from rat liver, muscle, kindney and testes was examined, substantial amounts were found by the iodometric, but almost nothing by the thiocyanate method.2. The main reason for the discrepancy between the methods seems to be that the iodometric micromethod also estimates substances other than true lipoperoxides. The presence of ubiquinone and vitamin A in the organ extracts was shown to interfere in this way in the method.3. The yellow colour which develops when retinol and its esters are tested by the iodometric micromethod is due not to liberated iodine but to conversion products of retinol.4. It is concluded that the occurrence of substantial amounts of lipoperoxides in vivo has so far been demonstarted only in the adipose tissue, and not in the parenchymatous organs of the rat.