ABSTRACT
Here we describe further experiments to support our hypothesis that bidirectional 11ß-HSD1-dehydrogenase in Leydig cells is a NADP(H) regenerating system. In the absence of androstenedione (AD), substrate for 17ß-HSD3, incubation of Leydig cells with corticosterone (B) or several C(19)- and C(21)-11ß-OH-steroids, in the presence of [(3)H]-11-dehydro-corticosterone (A), stimulated 11ß-HSD1-reductase activity. However, in presence of 30 µM AD, testosterone (Teso) synthesis is stimulated from 4 to 197 picomole/25,000 cells/30 min and concomitantly inhibited 11ß-HSD1-reductase activity, due to competition for the common cofactor NADPH needed for both reactions. Testo production was further significantly increased (p<0.05) to 224-267 picomole/25,000 cells/30 min when 10 µM 11ß-OH-steroids (in addition to 30 µM AD) were also included. Similar results were obtained in experiments conducted with lower concentrations of AD (5 µM), and B or A (500 nM). Incubations of 0.3-6.0 µM of corticosterone (plus or minus 30 µM AD) were then performed to test the effectiveness of 17ß-HSD3 as a possible NADP(+) regenerating system. In the absence of AD, increasing amounts (3-44 pmol/25,000 cells/30 min) of 11-dehydro-corticosterone were produced with increasing concentrations of corticosterone in the medium. When 30 µM AD was included, the rate of 11-dehydro-corticosterone formation dramatically increased 1.3-5-fold producing 4-210 pmol/25,000 cells/30 min of 11-dehydro-corticosterone. We conclude that 11ß-HSD1 is enzymatically coupled to 17ß-HSD3, utilizing NADPH and NADP in intermeshed regeneration systems.
