11β-hydroxysteroid dehydrogenase is a predominant reductase in intact rat leydig cells

Abstract

11β-Hydroxysteroid dehydrogenases (11β-HSDs) interconvert active corticosterone and inert 11-dehydrocorticosterone. In tissue homogenates, 11β-HSD type 1 (11β-HSD-1) exhibits both 11β-dehydrogenase (corticosterone inactivating) and 11β-reductase (corticosterone regenerating) activities, whereas 11β-HSD type 2 (11βHSD-2) is an exclusive dehydrogenase. In the rat testis, 11β-HSD has been proposed to reduce glucocorticoid inhibition of testosterone production, promoting puberty and fertility. This hypothesis presupposes dehydrogenation predominates. 11β-HSD-1 immunoreactivity has been localised to Leydig cells. However, recent studies suggest that 11β- HSD-1 is predominantly an 11β-reductase in many intact cells. We therefore examined the expression and reaction direction of 11β-HSD isozymes in cultures of intact rat Leydig cells. Reverse transcriptase PCR demonstrated expression of 11β-HSD-1, but not 11β-HSD-2 mRNA in rat testis. Primary cultures of intact rat Leydig cells showed pre- dominant 11β-reductase activity, activating 50-70% of 11-dehydrocorticosterone to corticosterone over 3 h, whereas 11β-dehydrogenation was <5%. Although both dexamethasone (10 nM) and corticosterone (1 μM) modestly inhibited LH-stimulated testosterone production by Leydig cells, inert 11-dehydrocorticosterone (1 μM) had similar effects, suggesting 11β-reductase is functionally important. Carbenoxolone (10-5 M) inhibited 11β-reduction in intact Leydig cells. However, although carbenoxolone reduced Leydig cell testosterone production, this also occurred in the absence of glucocorticoids, suggesting effects distinct from modulation of corticosteroid access to Leydig cells. In conclusion, rat Leydig cell 11β-HSD-1 is unlikely to reduce glucocorticoid access to testicular receptors. More likely, 11β-reductase amplifies glucocorticoid action, perhaps to maintain Leydig cell metabolic and endocrine functions.