Effects of androgens, progesterone and their antagonists on the developmental competence of in vitro matured bovine oocytes

The aim of the present study was to determine whether androgens and progest erone influence the in vitro maturation of bovine oocytes as assessed by cl eavage rates and competence to form blastocysts after in vitro fertilizatio n. Bovine cumulus-oocyte complexes were cultured (n = 20 per drop) for 22-2 4 h at 38.5 degrees C in TCM-199 medium supplemented with 10% oestrous cow serum, eCG (2.5 iu ml(-1)) and a range of treatments that included aromatiz able (testosterone; 100 nmol l(-1)) and non-aromatizable (dihydrotestostero ne; 100 nmol l(-1)) androgens, an androgen antagonist (flutamide; 36 mu mol l(-1)), progesterone (300 nmol l(-1)) and a progesterone antagonist (mifep risone, RU486; 100 nmol l(-1)). Production of inhibin A, total a-subunit, a ctivin A and follistatin by each group of cumulus-oocyte complexes was also measured, since inhibin-related peptides have been implicated as modulator s of oocyte maturation and their production may be influenced by steroids a nd anti-steroids. Both testosterone and dihydrotestosterone increased oocyt e cleavage rate (25%; P < 0.01) and dihydrotestosterone also increased (24% ; P < 0.05) the proportion of oocytes that reached the greater than or equa l to eight-cell stage. However, neither androgen affected blastocyst yield, or the proportion of blastocysts that hatched. The stimulatory effect of d ihydrotestosterone on cleavage rate was reduced by flutamide but the antian drogen had no effect when tested alone. Treatment with testosterone, but no t dihydrotestosterone, decreased (P < 0.05) endogenous follistatin and incr eased (P < 0.05) the activin A:follistatin ratio in maturation medium. Conc entrations of inhibin A, total alpha-subunit and activin A were not affecte d significantly by androgen or flutamide. Addition of progesterone or the a nti-progestin mifepristone to cumulus-oocyte complexes had no effect on cle avage rate. However, progesterone reduced by approximately 40% (P < 0.05) t he proportions of both total oocytes and cleaved oocytes that formed blasto cysts. This effect was partially reversed by mifepristone. Neither progeste rone nor mifepristone affected inhibin A, activin A or follistatin producti on. However, total a-subunit concentration was significantly greater in the progesterone-treated group than in the controls (50%; P < 0.05), indicatin g that the negative effect of progesterone on blastocyst yield may be media ted by increased inhibin a-subunit expression by cumulus cells.