Abstract
BackgroundNatriuretic peptides (NPs), brain and C type NPs (BNP and CNP), were involved in the maintenance of porcine oocyte meiotic arrest. The present study investigated the effects of NPs on developmental competence of immature porcine oocytes with follicles of different sizes.MethodsFollicular fluid NP levels were examined by radioimmunoassay. The developmental competence of porcine oocytes was evaluated by cleavage and blastocyst developmental rates after in vitro fertilization (IVF) or parthenogenetic activation (PA) of cumulus oocyte complexes (COCs), which were recovered from follicle with different sizes. NP levels were examined and classified according to the cleavage potential after IVF with COCs released from these follicles.ResultsThe BNP and CNP concentrations were increased with follicular size in follicular fluid and sustained at the set ranges of 3.0 – 6.0 mm follicles compared to 6.1 – 8.0 mm follicles. The oocytes developed from 3.0 to 6.0 mm follicles demonstrated increased embryo cleavage and blastocyst ratios after IVF, with an increased follicle size (P < 0.05). Moreover, BNP and CNP significantly promoted the blastocyst developmental rates of 3.0 – 6.0 mm follicles, but could not improve the developmental competence of oocytes from 6.1 to 8.0 mm follicles due to low NP levels. The COCs from 3.0 to 4.0 mm follicles were pre-incubated in 100 ng/ml of BNP and CNP media for 20 h before regular in vitro maturation, which demonstrated 2 to 3 folds higher developmental competencies in both PA and IVF groups compared to respective controls (P < 0.01).ConclusionsThe effects of BNP and CNP supplementation in the pre-maturation culture media (PMC) on porcine developmental competence from COCs in follicles of different sizes were different and improved the developmental competence of porcine oocytes from small antral follicle in vitro.
Highlights
Natriuretic peptides (NPs), brain and C type NPs (BNP and C-type natriuretic peptide (CNP)), were involved in the maintenance of porcine oocyte meiotic arrest
Previous studies have demonstrated that only a small portion of in vitro matured (IVM) oocytes develop into blastocysts, whereas those oocytes matured in vivo counterparts have much higher embryo developmental rates in several species [2, 4]
Expression of NPPB and Natriuretic peptide precursor C (NPPC) mRNA in the cumulus and granulosa cells as well as the NP levels inside the follicular fluid with follicular size could be associated with the oocyte developmental competence The results showed that the cleavage and blastocyst rates were increased with the dimension of the follicle from 3.0 to 6.0 mm
Summary
Natriuretic peptides (NPs), brain and C type NPs (BNP and CNP), were involved in the maintenance of porcine oocyte meiotic arrest. During the retrieval process of oocytes from their follicles, the GV-stage oocytes spontaneously undergo nuclear maturation in vitro, where it progresses through the first meiotic division and reach till the second metaphase (MII). Previous studies have demonstrated that only a small portion of in vitro matured (IVM) oocytes develop into blastocysts, whereas those oocytes matured in vivo counterparts have much higher embryo developmental rates in several species [2, 4] This indicated poor nuclear and/or cytoplasmic maturation in the current oocyte IVM systems [2,3,4]
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