Effect of type 3 and type 4 phosphodiesterase inhibitors on the maintenance of bovine oocytes in meiotic arrest.

The use of broad-spectrum inhibitors first suggested that phosphodiesterases (PDEs) are involved in the maturation of bovine oocytes. Modulation of individual PDE families is now possible with the use of newly developed type-specific PDE inhibitors. This study evaluated the role of type 3- and type 4-specific PDE inhibitors on the meiotic arrest of bovine cumulus-oocyte complexes (COCs) and denuded oocytes (DOs). It also evaluated the role of these specific inhibitors on meiotic arrest when COCs are incubated in the presence or absence of theca cell monolayers. Bovine COCs were aspirated from ovaries collected at the abattoir. Denuded oocytes and COCs were incubated for 12 h in culture medium alone or culture medium containing the type 3 PDE inhibitors cilostamide (10 and 20 microM) or milrinone (10 and 50 microM) or the type 4 PDE inhibitor rolipram (10 and 50 microM). Oocytes were then fixed and classified according to the status of nuclear maturation. Cumulus-oocyte complexes were coincubated with untreated theca cell monolayers or theca cell monolayers treated with the different specific PDE inhibitors. Bovine COCs or DOs incubated in culture medium resumed meiosis, but supplementation of the culture medium with the PDE3 inhibitors cilostamide or milrinone resulted in meiotic arrest. On the other hand, supplementation of the culture medium with rolipram did not prevent oocyte maturation. Furthermore, PDE3 inhibitors, but not PDE 4 inhibitors, had an additive effect on the inhibitory action of theca cell monolayers on oocyte maturation. These data support the hypothesis that inhibition of PDE3 prevents the meiotic resumption of bovine oocytes, whereas inhibition of PDE4 does not block oocyte maturation even under normally inhibitory conditions. The additive effect of PDE3 inhibitors on the ability of theca cells to maintain bovine oocytes in meiotic arrest suggests that type 3 PDE has an important role in meiotic resumption of bovine oocytes.