3²-Hydroxysteroid dehydrogenase activity in glandular and extraglandular human fetal tissues

The expression of 3²-hydroxysteroid dehydrogenase (3²HSD) in steroidogenic tissues is an absolute requirement for mammalian reproduction, fetal growth, and life maintenance. We sought to identify extraglandular tissue sites in the human fetus where 3²HSD is expressed. To this effect, we conducted in vitro studies by use of homogenates prepared from second trimester fetal tissues. To facilitate the determination of 3²HSD activity, an abbreviated technique was developed that consisted in the use of [3±-^3H]dehydroepiandrosterone ([3±-^3H] DHEA) as the substrate and NAD⁺ as the cofactor. With these reagents, the enzymatic reaction leads to the production of both nonradiolabeled androstenedione and NAD³H in equimolar amounts, and the radioactivity associated with NAD³H is used for quantification of 3²HSD activity. The kinetic isotope effect introduced by substitution of tritium for hydrogen at the C-3± position of DHEA, determined with six different tissues, was 2.5 ± 0.7 (mean ± sd). The specific activities of the enzyme in peripheral tissues and ovary were relatively low, in the range of 0.03 nmol/mg protein h for stomach (n = 2) to 0.18 ± 0.14 nmol/mg protein h for liver (mean ± sd; n = 13), while in fetal testis and placenta the specific activities were relatively high, viz. 3.4 ± 0.7 nmol/mg protein h (mean ± sd; n = 4) and 2.8 ± 1.8 nmol/mg protein h (mean ± sd; n = 13), respectively. The findings of this study serve to demonstrate that 3²HSD is distributed widely among tissues of the human fetus. Although the enzymatic activity was easily demonstrated in peripheral tissues by the use of radiolabeled DHEA as the substrate, 3²HSD protein was not readily detected by Western analysis.