Characterization and physiological validation of a radioimmunoassay for plasma testosterone in the male rat.

A radioimmunoassay (RIA) to measure testosterone concentration in the plasma of male rats was formalized, tested and physiologically validated. The procedure measured testosterone equally well, whether or not estimation of recovery and chromatographic purification preceded the RIA. The results were equivalent to those achieved by the method of competitive protein binding. No 17beta-hydroxy-5alpha-androstan-3-one was found in the plasma of male rats. Adrenalectomy did not significantly decrease plasma testosterone in either male or female rats. The simplified protocol met all requirements of precision, sensitivity, accuracy and specificity. A single investigator can analyze 1,000 plasma samples for testosterone in one week if necessary.