Reproduction Abstracts

Introduction: Tone of glucocorticoid action in target organs is regulated by relative activity of 11βHSD type1 (11HSD1), a bidirectional oxidoreductase that mainly converts cortisone to active cortisol, and type 2 (11HSD2), an oxidase that inactivates cortisol to cortisone. We have demonstrated that bovine cumulus–oocyte complex (COC) expresses 11HSDs and both reductive and oxidative activities are present in COC undergoing IVM. In the present study we investigated relative role of these 11HSDs and their localization in the bovine COC.

Materials and methods: Bovine COCs were matured in M199. Activities of 11HSDs were determined by measuring conversion of ³H-labelled cortisol/cortisone/dexamethasone to respective metabolites in intact COC/denuded oocyte (DO)/dispersed cumulus cell (DCC). To discriminate oxidative activities of 11HSD1 and 2, COCs were treated with 11-keto-progesterone (11KP), a selective inhibitor of 11HSD2. The presence of 11HSDs in the oocyte was examined using immunohistochemistry.

Results and discussion: The reductive activity led by 11HSD1 increased as IVM progressed while the oxidative activity was unchanged. 11KP equally suppressed oxidation of cortisol and dexamethasone, a selective substrate for 11HSD2. DO showed oxidative activity comparable to that of intact COC but not reductive activity. DCC did not show either activity. A strong signal of 11HSD2 was observed in oocyte. These results indicate that the bovine COC possesses both activating and inactivating abilities led by 11HSD1 and 11HSD2. Oocyte is the main site of oxidation where 11HSD2 is expressed while CC appears to be the site of 11HSD1 led reductive activity although integration of COC is necessary for 11HSD1 action.