Journal of Clinical Endocrinology and Metabolism Printed in U.S.A. Copyright © 1997 by The Endocrine Society Prostaglandin E 2 Stimulates Aromatase Expression in

C19 steroids are converted to estrogens by aromatase P450 (P450arom). Aromatase expression in humans is regulated by use of tissue-specific promoters in the placenta (promoter I.1), adipose tissue (promoters I.4, I.3, and II), and gonads (promoter II). The use of each promoter gives rise to a population of P450arom messenger ribonucleic acid (mRNA) species with a unique untranslated 5�-terminus. Aromatase is not expressed in the endometrium of disease-free women. We demonstrated, however, the presence of P450arom mRNA in pelvic endometriotic implants and eutopic endometrial curettings of women with endometriosis. In the current report, aromatase activity and P450arom gene expression were investigated in cultured stromal cells derived from eutopic endometrium and ovarian endometriomas of women with pelvic endometriosis. We also investigated the hormonal regulation of aromatase expression and alternative