LOCALIZATION OF AROMATASE IN EQUINE LEYDIG-CELLS

Stallion testes secrete large amounts of estrogens, but the cellular l ocation of the enzyme that converts androgens to estrogens, cytochrome P-450 aromatase, has not been determined. The goal of the present stu dy was to immunocytochemically localize stallion testicular aromatase using a polyclonal antibody generated against human placental cytochro me P-450 aromatase. Testes were obtained from 12 stallions from 2 to 2 3 years of age, during both the breeding and non-breeding seasons. Imm unoreactivity was confined to the Leydig cells in all testes examined. No immunostaining was observed in the Sertoli or germ cells. Heteroge neity in the level of immunostaining among individual Leydig cells was observed. The results of this study indicate that in postpubertal, ad ult, and aged stallions, testicular aromatase is located in Leydig cel ls.