Activity of 17β-hydroxysteroid oxidoreductase in tissues of the human fetus

Abstract

The interconversion of oestrone and oestradiol, androstenedione and testosterone, and dehydroepiandrosterone and 5-androstene-3 beta,17 beta-diol in mammalian tissues is catalysed by 17 beta-hydroxysteroid oxidoreductase (17 beta-HSOR). To identify tissue sites of 17 beta-HSOR activity in the human fetus, microsomal fractions from 15 different fetal tissues obtained from first and second trimester pregnancies were used for evaluation of enzymatic activity by use of [17 alpha-3H] oestradiol as the substrate and NADP+ as the co-factor. With these reagents, the enzyme-catalysed reaction led to the production of both non-radiolabelled oestrone and NADP3H in equimolar amounts; the radioactivity associated with NADP3H was used to quantify 17 beta-HSOR activity. Activity of 17 beta-HSOR was present in microsomes of all the tissues evaluated. The specific activity of the enzyme was highest in liver and placental microsomes. The interconversion of oestradiol and oestrone in microsomal fractions of nine different fetal tissues was studied by the use of substrates labelled with tritium at stable nuclear positions ([6,7-3H]oestradiol and [6,7-3H]oestrone). The products, [3H]oestrone and [3H]oestradiol, were quantified by the use of established techniques; other metabolites formed in these incubations were not identified. The reductive pathway of metabolism (oestrone to oestradiol) appeared to be favoured in microsomal fractions prepared from placenta, fetal zone of the adrenal gland and, possibly, lung. The oxidative pathway (oestradiol to oestrone) appeared to be favoured in microsomes prepared from liver, intestine, stomach, kidney, brain and heart. 17 beta-HSOR activity in fetal liver also was assessed by the use of fresh and frozen-thawed tissue, homogenate, subcellular fractions, and, also, in primary hepatocytes maintained in culture; the specific activity of the enzyme was highest in the microsomal fraction of liver tissue and 17 beta-HSOR activity in liver microsomes was linear with time of incubation up to 1 h. In hepatocytes, the enzymatic activity was linear with time of incubation up to 2 h and with cell number up to 2.5 x 10(5) cells/ml; the apparent Michaelis constant of hepatocyte 17 beta-HSOR for oestradiol was 11 mumol/l. The specific activity of 17 beta-HSOR did not change after pretreatment of hepatocytes for 24 h with insulin, glucagon or dexamethasone.

Differential expression of 17beta-hydroxysteroid dehydrogenases types 2 and 4 in human endometrial epithelial cell lines

“…The type 1 isozyme was the first 17 -HSD isozyme identified in endometrium (Mäentausta et al 1991). The importance of its function in this tissue is controversial, because it is expressed at very low levels compared with the other isozymes (Milewich et al 1989, Casey et al 1994, Zeitoun et al 1998. This was confirmed in our study, since the expression of both 17 -HSD types 2 and 4 is much higher in human endometrial tissue and in cell lines.…”

Cloning of mouse 17β-hydroxysteroid dehydrogenase type 2, and analysing expression of the mRNAs for types 1, 2, 3, 4 and 5 in mouse embryos and adult tissues

“…Previous activity measurements have shown the existence of 17HSD activity in both human and rodent fetuses [30,31]. However, in these previous studies the type of enzyme expressed could not be determined.…”

Characterization of 17β‐Hydroxysteroid Dehydrogenase Activity in Brain Tissue: Testosterone Formation in the Human Temporal Lobe

“…Although the formation of 17 β ‐HSD metabolites in the CNS was reported for the first time in the late 1960s ( 9), only little data are available concerning 17 β ‐HSD activity in human brain tissue ( 17, 18). Androgenic and oestrogenic 17 β ‐HSD in‐vitro activities have been demonstrated in the brain of rat and rhesus monkey ( 19, 20) and cells containing 17 β ‐HSD were immunohistochemically localized in the brain of rat, frog and the human foetus when antiserum against human 17 β ‐HSD type 1 was used ( 21–24).…”