17 beta-hydroxysteroid dehydrogenase type 1, 2, 3, and 4 expression and enzyme activity in human anterior pituitary adenomas

17 beta-Hydroxysteroid dehydrogenase (17 beta HSD) isoforms reversibly cata lyze the final step in the formation of estradiol (E-2) from estrone (E-1) and the formation of testosterone from androstenedione, We have investigate d 17 beta HSD type 1, 2, 3, and 4 gene expression and 17 beta HSD estrogeni c activity in human anterior pituitary adenomas. 17 beta HSD messenger ribo nucleic acid (mRNA) expression was studied by RTPCR in 42 pituitary tumors and 3 normal pituitaries, 17 beta HSD activity was studied in II tumors and 17 beta HSD type 1 was immunolocalized in vitro in 6 tumors. 17 beta HSD t ype 1 gene expression was detected in 34 of 42 adenomas in all tumor subtyp es; 17 beta HSD type 2 mRNA was detected in 18 of 42 adenomas, but not in p rolactinomas; 17 beta HSD type 3 mRNA was detected in 12 of 42 adenomas, bu t not in corticotropinomas; 17 beta HSD type 4 was expressed in 20 of 42 ad enomas by all adenoma subtypes. Reversible 17 beta HSD activity was found i n 9 of II adenomas, and 17 beta HSD type 1 immunopositivity was cytoplasmic ally distributed in all 6 adenomas in vitro. All 4 17 beta HSD isoforms are variably expressed in human anterior pituitary adenomas, which also show 1 7 beta HSD enzyme activity, suggesting that 17 beta HSD may play an importa nt role in regulating the local cellular levels of estradiol. (J Clin Endoc rinol Metab 84: 1340-1345, 1999!).