Reduction of the developmental competence of sheep oocytes by inhibition of LH pulses during the follicular phase with a GnRH antagonist

Abstract

were collected by flushing the oviducts 28 h after the LH surge, and were fertilized and cultured in vitro for 7 days. Ovulation and cleavage rates were not significantly different among the three groups but a higher rate of blastocysts (P < 0.01) was obtained after Antarelix treatment when LH pulsatility was re\ x=req-\ established (group B). Oestradiol concentration was strongly depressed (P < 0.0003) after Antarelix treatment in group A, but was maintained after injection of LH pulses in group B, although at a lower value than before the preovulatory surge in the control group. In conclusion, inhibition of endogenous LH pulses 1 day before the preovulatory surge was not essential for ovulation and in vitro fertilization but was associated with a decrease in plasma oestradiol concentrations and inferior embryo development both in vivo and in vitro. When LH pulsatility was re-established, oestradiol concentrations increased and embryo development was restored.

Comparison of the effects of two GnRH antagonists on LH and FSH secretion, follicular growth and ovulation in the mare

“…Similar effects are observed in gilts [4]. But other experiments report an indirect stimulating effect of GnRH antagonists on FSH, caused by a decrease in the negative feedback of estradiol induced by the inhibition of LH: thus when ewes receive the antagonist at the onset of oestrus, an increase in FSH is observed [27]. When ewes are additionally treated with exogenous LH, FSH concentrations are depressed [10].…”

“…Antarelix (Ac-D-Nal, D-Phe(pCI), D-Pal, Ser, Tyr, D-Hci, Leu, Lys-(iPr), Pro, D-Ala-NH 2, Teverelix, Europeptides, Argenteuil, France) is a water soluble GnRH antagonist [9], which has been tested in some domestic species: gilts [4,11], ewes [27], cows [26] and more recently in mares [33]. Cetrorelix (Ac-D-Nal, D-Phe(pCI), D-Pal, Ser, Tyr, D-Hci, Leu, Arg, (iPr), Pro, D-Ala-Nh 2, Asta Medica, Frankfurt Germany) is also a water soluble GnRH antagonist used in rodents for experimental purposes [31], in superovulated zebu calves [23], and in humans for clinical uses [1].…”

Cryopreservation of Sheep Produced Embryos – Current and Future Perspectives

“…Although allowing good estrus synchronization, the fertility is usually lower compared to natural estrus [55]. Several reasons have been raised to explain this lower fertility, including (a) the asynchrony between the beginning of estrus and the ovulation time [56], (b) a negative influence on the transport of spermatozoa [57], (c) the reduced expression of estradiol and progesterone receptors in oviduct and endometrial cells, (d) a reduced progesterone secretion by the corpus luteum (CL) [58], (e) an inadequate process of maturation and acquisition of competence by the oocyte [59,60], and (f) the development and lack of ovulation of large persistent follicles [53,[59][60][61] due to altered levels of progesterone after the first 6 days of treatment [62].…”

“…According to González-Bulnes et al [58,84], the presence of a CL at the beginning of FSH treatment may improve the number of viable embryos. Moreover, before the application of the multiple ovulation treatment and to improve the superovulatory response, GnRH agonists or antagonists can also be administered [59]. These latter strategies intend to inhibit the final stage of follicular development [75], suppress-ing the existence of follicles more than 3 mm [85] and simultaneously implementing the development of small follicles [86].…”

Effect of GnRH and its antagonist (Antarelix) on LH release from cultured bovine anterior pituitary cells

“…In contrast to GnRH agonists, treatment with antagonists like Antarelix (Deghenghi et al, 1993) inhibited gonadotropin secretion followed by a change in follicular growth and development (Driancourt et al, 1995;Campbell et al, 1997;Dobson et al, 1997;Fike et al, 1997;Patterson-Bay et al, 1997;Oussaid et al, 1999;Schneider et al, 1999;Acta Veterinaria Hungarica 50, 2002Brüssow et al, 2001). Antagonists to GnRH inhibit gonadotropin secretion, presumably by competing with GnRH for its receptor on the pituitary gonadotrope.…”