Partial inhibition of nitric oxide synthase activity stimulates the nuclear maturation progression of bovine cumulus-oocyte complex in vitro in the presence of hemisections of the follicular walls.

This study aimed to assess the effects of the inhibition of nitric oxide synthase (NOS) on events that modulate bovine in vitro oocyte maturation. Cumulus-oocyte complexes (COCs) were cultured with hemisections (HSs) of the follicular walls in a maturation medium supplemented with different concentrations (0.1-10.0 mM) of Nω-nitro-l-arginine methyl ester hydrochloride (l-NAME). Controls consisted of COCs cultured in the presence (+HSs) or absence of HSs (-HSs) with no additional l-NAME supplementation. The following parameters were assessed: oocyte nuclear maturation stage; cumulus cell (CC) membrane integrity; nitrate/nitrite, progesterone, and estradiol concentrations in the culture medium at 22 h of cultivation; and the concentrations of cGMP and cAMP in COCs during the first hour of maturation. The addition of 1.0 mM l-NAME increased the percentage of oocytes that reached metaphase II (MII) and the percentage of intact CCs (P < 0.05). All l-NAME concentrations reduced the nitrate/nitrite concentrations (P < 0.05), but none affected steroid concentrations compared with control +HSs (P > 0.05). The addition of 1.0 mM l-NAME reduced cGMP concentrations at 3 h and increased cAMP concentrations in the first hour of culture (P < 0.05). Our findings suggest that the NOS/NO/cGMP pathway participates in meiosis progression (MI to MII) of the bovine oocytes matured in vitro in the presence of hemisections of the follicular walls. Lastly, the mechanisms that lead to the progression of meiosis after NOS inhibition do not involve changes in steroid production.

Luteinizing hormone upregulates NPPC and downregulates NPR3 mRNA abundance in bovine granulosa cells through activation of the EGF receptor.

During folliculogenesis, the luteinizing hormone (LH) surge triggers dynamic events in granulosa cells that culminate with ovulation. The aim of this study was to evaluate if the epidermal growth factor receptor (EGFR) is required for ovulation in cattle, and if it regulates the expression of the natriuretic peptide (NP) system in granulosa cells after gonadotropin-releasing hormone (GnRH)/LH stimulation. It was observed that GnRH induces amphiregulin (AREG) and epiregulin (EREG) mRNA at 3 and 6 h after in vivo treatment, but the expression of these genes was not regulated by atrial (ANP) and C-type (CNP) NPs in granulosa cells cultured in vitro. The abundance of mRNA encoding the NP receptors (NPR1, 2 and 3) was not altered by LH supplementation and/or EGFR inhibition (AG1478; AG) in granulosa cells after 6 h of in vitro culture. However, in the same conditions, mRNA encoding the natriuretic peptide precursor C (NPPC) was upregulated by LH, whereas AG (0.5 and 5 µM) inhibited the LH effect. In order to confirm those results, 5 µM AG or saline were intrafollicularly injected in preovulatory follicles and cows were simultaneously treated with GnRH intramuscularly. Granulosa cells harvested at 6 h after GnRH injection revealed higher NPR3 and lower NPPC mRNA levels in AG-treated, compared to control cows. However, intrafollicular injection of AG did not inhibit GnRH-induced ovulation. In granulosa cells cultured in vitro, ANP associated with LH increased prostaglandin-endoperoxide synthase 2 (PTGS2) mRNA abundance. In conclusion, we inferred that LH modulated NPPC and NPR3 mRNA abundance through EGFR in bovine granulosa cells, but ovulation in cattle did not seem to depend on EGFR activation.

The effect of age and length of gonadotropin stimulation on the in vitro embryo development of Holstein calf oocytes.

The use of oocytes recovered from prepubertal donors for in vitro embryo production has great potential for accelerating the rate of genetic gain in the dairy industry. However, these oocytes are known to be less developmentally competent than those from adult donors. In this study, we investigated the effect of age and gonadotropin stimulation in Holstein heifers subjected to oocyte collection every two weeks between 2 and 6 months of age. In order to assess the effect of gonadotropin stimulation, animals were subjected to one of three treatments, namely Short (ST; 36-42 h), Long (LT; ≥72 h) and No Treatment (NT) prior to laparoscopic ovum pick-up (LOPU). Our results show that the LT significantly improved the proportion of large follicles (>5 mm diameter) present in the ovary (LT 34.0% vs. ST 11.2% vs. NT 2.4%, P < 0.05), as well as the percentage of good-quality cumulus oocyte complexes (COCs) recovered (LT 95.3 ± 18% vs. ST 85.4 ± 22% vs. NT 82.2 ± 14%, P < 0.05) and blastocyst rate (LT 36.7 ± 26% vs. ST 18.3 ± 15% vs. NT 16.7 ± 9%, P < 0.05). Recovery rate was affected by treatment (LT 70.4 ± 25 vs. ST 85.4 ± 29 vs. NT 72.7 ± 23, P < 0.05). To assess the impact of age, data was grouped into <100 days (A), 100-130 days (B) and >130 days (C) of age at LOPU. We found that as animals got older, although the average number of COCs per donor per LOPU declined (A: 17.5 ± 11 vs. B: 14.7 ± 7 vs. C: 11.9 ± 8), the blastocyst rate increased (A: 12.8 ± 20% vs. B: 17.1 ± 21% vs. C: 21.8 ± 25%, P < 0.05). We also evaluated the incidence of polyspermy and confirmed it is a critical limitation for IVF in calf oocytes. The incidence of polyspermy was unaffected by gonadotropin treatment, but significantly decreased with age. The capacity for full development to term of in vitro produced embryos from calf oocytes was tested by embryo transfer into 21 synchronized adult recipients, which resulted in 13 pregnancies (62%), full development to term and healthy calves born. Finally, the study allowed evaluating the safety of the procedure since, on average, each animal was subjected to 8 LOPU procedures over a period of 4 months. Our results showed that the procedure is safe (no incidents during laparoscopy), and was not harmful for the reproductive future of the animals, as those that were bred became pregnant after reaching sexual maturity.

Natriuretic peptides stimulate oocyte meiotic resumption in bovine.

The aim of the present study was to evaluate the expression of mRNA encoding natriuretic peptides (NPs) and their receptors in the cumulus-oocyte complex in cattle, a monovular mammalian species, and also to investigate the role of NPs in oocyte meiotic resumption in vitro. mRNA was observed for the NP precursor type-A (NPPA), type-C (NPPC), NP receptor-1 (NPR-1), receptor-2 (NPR-2) and receptor-3 (NPR-3) in bovine cumulus cells, and NPR-2 mRNA was observed in oocytes. These results are different from those obtained in mouse and pig models. The effects of NPPA, NP precursor type-B (NPPB) and NPPC on the resumption of arrested meiosis maintained by forskolin were studied at three different doses (10, 100 and 1000nM) with a 12h culture system. The germinal vesicle breakdown rates were greater (P≤0.05) in oocytes that were cultured in the presence of one or a combination of NPs (from 44% to 73%) than the negative control (from 24% to 27%). Additionally, it was demonstrated that the concentration of cyclic guanosine 3',5'-monophosphate (cGMP) is increased by NPPA and NPPC in oocytes and cumulus cells after 3h of in vitro maturation. However, in both groups, the concentration of cyclic adenosine 3',5'-monophosphate (cAMP) in the oocyte did not increase between 3 and 6h of culture, even when forskolin was used. In summary, we observed the presence of mRNA for NPs and their receptors in the bovine cumulus-oocyte complex and demonstrated that, in vitro, NPPA, NPPB and NPPC stimulate oocyte meiotic resumption in a monovular species.