Quantitative Evaluation of Virilizing Activity of Steroids by Measuring Morphological Changes in Uro-genital Region of Rats

A new technique to measure the uro-genital parameters such as the lengths of urovaginal septum, corpora cavernosa and anogenital distance on the sagittal sections of the pelvic region of female fetus of rat under microscope equipped with a micrometer was developed. In the examination of 180 normal female fetuses on the 21st day of gestation, relationships were observed between the fetal body weight and the length of urovaginal septum as well as anogenital distance, but not on the length of corpora cavernosa. Following maternal subcutaneous administration of various doses of 17α-methyltestosterone between the 17th and 20th day of gestation, dose-dependent abridgment in urovaginal septum length and extensions in corpora cavernosa length and anogenital distance were observed in female fetus on the 21st day's examination. When these three parametars were calculated on the relative value to the fetal body weight, however, linear relationships against log-dose were observed in all parameters. Among these three parameters the abridgment in urovaginal septum was shown to be the most sensitive. A quantitative assay of virilizing activity of steroids in female fetuses was examined on rats treated subcutaneously with 17α-methyltestosterone and norethandrolone. Linear regressions against the log-doses of both steroids were demonstrated in urovaginal septum length, and parallelism was noted between both regression lines. The relative potency of norethandrolone to 17α-methyltestosterone calculated on urovaginal septum length was 0.354 with fiducial limits of 0.293-0.446, and it was suggested that the virilizing activities of steroids can be evaluated quantitatively.