Human testicular aromatase: immunocytochemical and biochemical studies

The location of the aromatase enzyme in the testes of human subjects ages 3 months to 72 yr was determined immunocytochemically using a monoclonal antibody specific to human aromatase. In addition, an assay was developed to measure aromatase activity in suspensions of cryosections in order to validate the presence and to quantitate the activity of aromatase in the sections. In mature testes, aromatase immunostain was always associated with Leydig cells and was absent from Sertoli cells. Aromatase activity ranged from 0.014-0.55 pmol estrogen per mg/h and was significantly correlated with the immunostain intensity (P < 0.02). Thus, the aromatase activity provided a semiquantitative estimate of the immunoreaction. Activity and immunostain intensity of aromatase did not correlate with increasing age. Rather, the highest levels were measured in four of six testes of men ages 18-20 yr, three of whom also had the strongest immunostain for aromatase. The Leydig cell clusters of these subjects were larger and more prominent than those in the other specimens. A low level of aromatase activity but no immunostain was detected in prepubertal testes. Aromatase was not detected by either method in normal tissue from the testis of a patient with testicular cancer.