3-BETA-HYDROXYSTEROID DEHYDROGENASE-ACTIVITY IN GLANDULAR AND EXTRAGLANDULAR HUMAN FETAL TISSUES

The expression of 3-beta-hydroxysteroid dehydrogenase (3-beta-HSD) 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 3-beta-HSD 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 3-beta-HSD activity, an abbreviated technique was developed that consisted in the use of [3-alpha-H-3]dehydroepiandrosterone ([3-alpha-H-3] DHEA) as the substrate and NAD+ as the cofactor. With these reagents, the enzymatic reaction leads to the production of both nonradiolabeled androstenedione and (NADH)-H-3 in equimolar amounts, and the radioactivity associated with (NADH)-H-3 is used for quantification of 3-beta-HSD activity. The kinetic isotope effect introduced by substitution of tritium for hydrogen at the C-3-alpha 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 3-beta-HSD 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, 3-beta-HSD protein was not readily detected by Western analysis.