In the present study recipient

In the present study, recipient oestradiol serum levels on the day of donor oocyte retrieval or warming were found to be significantly higher in the antagonist group and higher than 100 pg/ml in all cases. Serum oestradiol level has been reported to have no effect on endometrial receptiveness in oocyte donation cycles (); however, it has been routinely used as a marker of adequate endometrial preparation in recipients of oocyte donation. Retrospective studies (Younis et al., 1996, Remohi et al., 1997) have failed to show that serum oestradiol level or endometrial thickness are able to predict implantation in recipients of oocyte donation. Additionally, in oocyte recipients sharing oocytes from single donors, the discordant pregnancy outcome in the recipients could not be explained by serum oestradiol level or endometrial thickness (). Premature luteinization was observed only in one woman in the antagonist group. Previously published data about the incidence of herpes simplex virus cancellation as a result of luteinization in the unsuppressed groups ranged between 1.9% and 4.3% (Simon et al., 1998, Dal Prato et al., 2002), and in 5.3% of unsuppressed cycles displayed follicular growth, although not ovulation (); Also, 21.9% of women unsuppressed by agonists GnRH showed serum progesterone levels greater than 1 ng/ml (). These studies have confirmed that total pituitary desensitization is not always achieved with oestradiol-only therapy (Simon et al., 1998, Remohi et al., 1993, Dal Prato et al., 2002). Other studies have confirmed that the 0.25 mg GnRH antagonist multiple dose did not completely suppress gonadotrophin and steroid activity during the entire treatment in all participants (; Sagnella, 2009). Follicular development was delayed in most cases; however, in some patients, the start of follicular growth and corresponding increasing oestradiol concentrations were observed during GnRH antagonist treatment. With early follicular GnRH antagonist administration, the most pronounced suppression of FSH was obtained at 6 h, and the duration of suppressive effect of GnRH antagonist was short, mean 24 h with 0.25 mg; however, suppression of LH concentrations was more pronounced than FSH concentrations (). Patients should be advised that the interval between doses must not exceed 24 h to avoid spontaneous FSH surges. Administration of high oestradiol doses in conjunction with GnRH antagonist administration could delay the start of follicular development. Recently, a depot formulation of GnRH antagonist (degarelix 2.5 mg) has been developed. This formulation induces more sustained LH suppression during 7 days compared with daily administration of a low daily dose of GnRH antagonist (). This approach could be explored in future studies being more convenient for the patients and minimizing the number of injections.
Acknowledgements
Introduction Gonadotropin-releasing hormone (GnRH) is an important regulator of reproduction through its actions on pituitary luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion as well as synthesis. The first GnRH peptide isolated was LHRH (denoted as mammalian (m)GnRH hereafter; see Table 1 for a list of abbreviations) (Schally et al., 1971). Elucidating the signal transduction mechanisms responsible for GnRH actions in the pituitary is an integral part of understanding the neuroendocrine control of reproduction. The majority of information on GnRH post-receptor signal transduction in the pituitary is derived largely from mammalian gonadotrope models and often uses immortalized gonadotrope-derived cell lines; these models have been extensively reviewed in the recent past (Counis et al., 2005, Pawson and McNeilly, 2005, Finch et al., 2010, Melamed et al., 2012, Naor and Huhtaniemi, 2013). Among non-mammalian vertebrates, studies in a small number of teleost fishes model systems represent some of the best characterized models of GnRH-stimulated signalling and include an evaluation of GnRH effects on pituitary cell-types other than gonadotropes (e.g., Chang et al., 2009, Chang et al., 2012, Canosa et al., 2007). This review highlights the importance of comparative studies findings from teleosts as they contribute to our physiological understanding of GnRH signalling in the pituitary of vertebrates.