11-BETA-HYDROXYSTEROID DEHYDROGENASE IS A PREDOMINANT REDUCTASE IN INTACT RAT LEYDIG-CELLS

11 beta-Hydroxysteroid dehydrogenases (11 beta-HSDs) interconvert acti ve corticosterone and inert 11-dehydrocorticosterone. In tissue homoge nates, 11 beta-HSD type 1 (11 beta-HSD-1) exhibits bath 11 beta-dehydr ogenase (corticosterone inactivating) and 11 beta-reductase (corticost erone regenerating) activities, whereas 11 beta-HSD type 2 (11 beta-HS D-2) is an exclusive dehydrogenase. In the rat testis, 11 beta-HSD has been proposed to reduce glucocorticoid inhibition of testosterone pro duction, promoting puberty and fertility.. This hypothesis presupposes dehydrogenation predominates. 11 beta-HSD-1 immunoreactivity has been localised to Leydig cells. However, recent studies suggest that 11 be ta-HSD-1 is predominantly an 11 beta-reductase in many intact cells. W e therefore examined the expression and reaction direction of 11 beta- HSD isozymes in cultures of intact rat Leydig cells. Reverse transcrip tase PCR demonstrated expression of 11 beta-HSD-1, but not 11 beta-HSD -2 mRNA in rat testis. Primary cultures of intact rat Leydig cells sho wed predominant 11 beta-reductase activity, activating 50-70% of 11-de hydrocorticosterone to corticosterone over 3h, whereas 11 beta-dehydro genation was <5%. Although both dexamethasone (10 nM) and corticostero ne (1 mu M) modestly inhibited LH-stimulated testosterone production b y Leydig cells, inert 11-dehydrocorticoscerone (1 mu M) had similar ef fects, suggesting 11 beta-reductase is functionally important. Carbeno xolone (10(-5) M) inhibited Ilpreduction in intact Leydig cells. Howev er, although carbenoxolone reduced Leydig cell testosterone production , this also occurred in the absence of glucocorticoids, suggesting eff ects distinct from modulation of corticosteroid access to Leydig cells . In conclusion, rat Leydig cell 11 beta-HSD-1 is unlikely to reduce g lucocorticoid access to testicular receptors. More likely, 11 beta-red uctase amplifies glucocorticoid action, perhaps to maintain Leydig cel l metabolic and endocrine functions.