Effect of Cortisol on Bovine Oocytes Maturation and Further Embryonic Development After In vitro Fertilization
Journal Title: Biomedical Journal of Scientific & Technical Research (BJSTR) - Year 2018, Vol 10, Issue 4
Abstract
Oocyte meiotic maturation and further embryonic development after fertilization is one of the most important physiological requirements for species survival. Herein, the aim of the study was to evaluate the effects of the stressful hormone, cortisol, on the nuclear maturation and further embryonic development of bovine oocytes after in vitro fertilization (IVFJ. For such purpose, 1,439 immature oocytes were collected from slaughtered cows and matured in vitro for 24 hours with different concentrations of cortisol (0 (control); 50 μM; 150 μM ;250 μM). Afterwards, 412 oocytes were denuded, dyed with aceto-orcein and evaluated for meiotic development. The other 1027 were submitted to IVF and cultured for 9 days, being evaluated on day 2, 6 and 9, for cleavage, morula and blastocyst, respectively. In the control, 85 % of oocytes reached Metaphase II, decreasing to 49, 32 and 15 % for the concentration of the cortisol (50, 150, and 250 μM, respectively). For the embryos, obtained from the oocytes submitted to IVF, in the control group, 28.3 ± 4.8% reached the stage of blastocyst, while for the concentrations of cortisol this value decreased to 22.1 ± 5.4%, 15.4 ± 6.0% and 6.5 ± 2.1% for 50, 150 and 250 μM of cortisol, respectively). Results of the present study clearly demonstrated that animal's stress and particularly high concentrations of cortisol impair bovine nuclear maturation as well as the further embryonic development after IVF. Stress is a process stimulus activate the entire system and produces an organic response generating negative effects on animal health and production. The hormone mainly produced during stress is the cortisol (C21H30O5) which is secreted by the upper part of the adrenal gland, being an useful indicator as a biomarker to detect stress on the animals [1]. Besides, cortisol plays an important role during the catabolic phase and it negative effect on several metabolism has been well described [2], it is not yet clear the role of this hormone in ovaries and particularly on oocyte nuclear maturation and further embryo development after fertilization. The immature oocytes begin to develop in the ovaries, possessing a large nucleus referred to as germinal vesicle (GV), in which a sequence called germinal vesicle breakdown (GVBD), initiates the process of nuclear oocyte maturation, finishing at the stage of metaphase II just before ovulation [3]. Maturation promoting factor (MPF) is activated at GVBD and increases until it reaches a plateau at the end of the Metaphase I. A transient decline in MPF activity takes place during the transition between meiosis I, arresting at metaphase II. During oocyte maturation, the extracellular signal-regulated kinases (ERKs) are activated and a comprehensive, extensive rearrangement of the cytoskeleton and associated proteins occurs involving a spindle pole close to the cortex [4-6]. After polar body extrusion, chromosomes realign progressing to metaphase II. All meiosis developmental stages occur when follicles are growing from preantral to antral follicles. Moreover, the ovulation occurs when oocyte is in the metaphase II stage [7-8]. At the endocrine level, folliculogenesis is regulated by a central nervous system, anterior pituitary, and ovary cascade mechanism. Specialized hypothalamic neurons secrete pulses of gonadotropin-releasing hormone (GnRH) into the portal blood vessels, which acts on the gonadotrophs to cause a pulsatile release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which act on ovarian follicle cells to control folliculogenesis. Although GnRH, FSH, and LH are critically important in regulating folliculogenesis, hormones and growth factors, which are themselves products of the follicle, can act locally to modulate (amplify or attenuate) FSH and LH action [9-10]. This is the autocrine/paracrine system of developing follicles. It is believed that this local regulatory system plays an important role in the complex mechanisms governing the timing of folliculogenesis and whether a follicle becomes dominant or atretic. An important point is that estradiol produced by the dominant follicle rises production of GnRH, FSH and LH, increasing follicular growth, leading to its rupture/ovulation [11-13]. Stress-like levels of cortisol suppress follicular growth and development and block or delay the preovulatory surge of LH when cortisol is present during the late luteal and early follicular phases of the oestrous cycle [14-16]. In fact, since the last century it has been postulated that stressful stimuli reduce fertility in domestic species, such climatic extremes, transportation or laparoscopy as well as psychological stress suppress or delay expression of behavioural oestrus and ovulation. In addition to reducing fertility, these stressors also stimulate the activity of the hypothalamic-pituitary-adrenal (HPA) axis, and a marked increase in serum concentration of cortisol is commonly associated with management-related stressors [17-19]. Furthermore, cortisol reduces amplitude of GnRH and LH secretion and lowers plasma estradiol levels in follicular-phase and for such reason, high cortisol levels can inhibit the reproduction physiology [20-21]. The effect of cortisol inhibition in the protein ERKs disrupting their functions in meiotic maturation of full- grown oocytes and/or arrest at metaphase of meiosis II prior to fertilization [22-23]. Although the causal link between stress and infertility has not been precisely defined, several studies indicate that glucocorticoids in general and cortisol in particular may contribute to the anti-gonadal effect of stress [24-25]. Additionally, the increasing of cortisol level reduces estradiol production possibly by affecting the granulosa cell functions within the follicle, which results deterioration in oocyte quality, leading to a poorest ability to develop after fertilization [17]. The aim of the present study is to evaluate the role of this hormone on bovine in vitro oocyte nuclear maturation and further embryo development after fertilization.
Authors and Affiliations
Aya KH Mahdy, Maria Helena Moreira da Silva, Fernando Moreira da Silva
Keywords
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- EP ID EP587293
- DOI 10.26717/BJSTR.2018.10.001998
- Views 123
- Downloads 0
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