17 beta-hydroxysteroid dehydrogenase type 2 expression and enzyme activityin the human gastrointestinal tract

The 17 beta -hydroxysteroid dehydrogenases (17 beta HSDs) play an important role in the regulation of intracellular levels of biologically active sex steroid hormones in various human tissues. To date, eight distinctive 17 be ta HSD enzymes have been cloned and characterized in humans. Among these is oenzymes, 17 beta HSD type 2 (17 beta HSD2) catalyses the conversion of tes tosterone into androstenedione and/or oestradiol into oestrone in various t issues, and it has thus been suggested to be involved in the biological ina ctivation of these sex steroids. The human gastrointestinal tract and liver are considered as the principle sites of inactivation and metabolism of va rious forms of orally administered sex steroids. We therefore examined 17 b eta HSD2 expression and activity in human adult non-pathological gastrointe stinal tract in order to clarify further the biological significance of thi s enzyme. A total of 80 specimens (40 from males and 40 from females) of no rmal oesophageal, stomach, duodenal, ileal, colonic and rectal tissues were examined for immunohistochemistry. Altogether, 17 tissue specimens were us ed for enzyme assay, and eight for RNA analysis. 17 beta HSD2 activity was detected in the stomach, duodenum, ileum, colon and rectum. 17 beta HSD2 mR NA was most abundant in the small intestine. 17 beta HSD2 immunoreactivity was localized almost exclusively to the absorptive epithelium, which may be involved in the inactivation of excessive endogenous and exogenous active sex steroids. Results from the present study thus suggest that the human ga strointestinal tract is an important sex steroid metabolizing organ in huma ns.