The estimation of small amounts of corticosterone in rat plasma.

Many of our investigations involving adrenal physiology have been carried out in the rat (14). Since corticosterone is the preponderant adrenal steroid found in rat plasma, l it became essential to develop a rapid, valid method for its determination. The Silber-Porter method (5) is inadequate for studies in the rat because it is neither sensitive nor specific enough. The method of Sweat (B), although demonstrating the usefulness of sulfuric acid-induced fluorescence for analysis of plasma corticosteroids, has not been found practical. Our method uses the double extraction technique of Silber and Porter and a modification of the fluorescence technique described by Sweat (7).