Abstract
BackgroundThe objective of this study was to investigate whether the steroid hormone(s) secreted from cumulus-oocyte complexes (COCs) is a prerequisite for bovine oocyte maturation and cumulus expansion using aminoglutethimide (AGT), a P450 cholesterol side-chain cleavage inhibitor.MethodsIn experiment 1, COCs were cultured in maturation medium with various concentrations of AGT for 22 h to determine the effective concentration of AGT to inhibit steroid hormone secretion, meiotic maturation and cumulus expansion. In experiment 2, COCs were cultured in conditioned medium (CM) and TCM-199 medium with or without 10 mM AGT to check whether steroid hormones secreted from COCs were responsible for oocyte maturation and cumulus expansion. Experiments 3 and 4 were carried out to determine whether exogenous progesterone or estradiol-17beta was able to overcome the inhibitory effects of AGT on oocytes maturation and cumulus expansion. COCs cultured in 10 mM AGT-containing medium supplemented with various concentrations of progesterone or estradiol-17beta for 22 h were examined for oocyte maturation and cumulus expansion.ResultsExperiment 1 showed that a concentration of 10 mM AGT in medium was sufficient to block steroid hormone secretion, oocyte maturation and cumulus expansion, and that these inhibitory effects were fully reversible. In experiment 2, the addition of 10 mM AGT to CM did not significantly prevent oocyte maturation and cumulus expansion, implying that CM contains the steroid hormone(s) secreted from COCs, which are closely associated with oocyte maturation and cumulus expansion. The results in experiments 3 and 4 demonstrated that the addition of any concentration of progesterone or estradiol-17beta in the medium did not reduce the inhibitory effects of AGT on oocyte maturation and cumulus expansion.ConclusionOur results indicate that bovine oocytes surrounded by cumulus cells are prevented from maturation and cumulus expansion through the inhibition of steroid secretion due to AGT, and that these inhibitory effects of AGT on oocyte maturation and cumulus expansions can not be overcome by the addition of either progesterone or estradiol-17beta in the medium. These observations suggest that some steroid hormone(s) other than P4 and E2 secreted from bovine COCs is essential for their meiotic maturation and cumulus expansion.
Highlights
The objective of this study was to investigate whether the steroid hormone(s) secreted from cumulus-oocyte complexes (COCs) is a prerequisite for bovine oocyte maturation and cumulus expansion using aminoglutethimide (AGT), a P450 cholesterol side-chain cleavage inhibitor
The results of the present study have demonstrated that the maturation and cumulus expansion of bovine oocytes surrounded by cumulus cells were prevented from maturation and cumulus expansion through the inhibition of steroid secretion due to 10 mM AGT, and that these inhibitory effect of AGT on oocytes maturation and cumulus expansion can not be overcome by the addition of either P4 or E2 in maturation medium
Concerning of AGT concentration, Lieberman et al [17] have reported that when rat oocytes are cultured in maturation medium with 1.0 mM AGT, the progesterone secretion is reduced to approximately 5% of that in controls without AGT
Summary
The objective of this study was to investigate whether the steroid hormone(s) secreted from cumulus-oocyte complexes (COCs) is a prerequisite for bovine oocyte maturation and cumulus expansion using aminoglutethimide (AGT), a P450 cholesterol side-chain cleavage inhibitor. The maturation was controlled by many factors including steroid hormone in vivo and in vitro [[2,3] and [4]]. In vitro maturation of mammalian oocytes has been commonly performed using medium covered by paraffin oil or mineral oil. In previous studies using medium covered with oil, it has been reported that the addition of progesterone (P4) to the maturation medium stimulates meiotic re-initiation of bovine oocytes, regardless of the presence or absence of gonadal hormones [5], and that the addition of estradiol-17β (E2) with FSH in the maturation medium increases the maturation, morula, and blastocyst rates in bovine oocytes [6]. It is thought that the effects of steroids on the maturation of oocytes cultured in medium covered by oil are unreliable
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
