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Influence of circulating concentrations of estradiol and progesterone on endometrial thickness and LH and FSH concentrations after GnRH treatment

Grant number: 17/16701-9
Support type:Scholarships in Brazil - Master
Effective date (Start): November 01, 2017
Effective date (End): August 31, 2019
Field of knowledge:Agronomical Sciences - Veterinary Medicine - Animal Reproduction
Principal Investigator:Roberto Sartori Filho
Grantee:Jéssica Cristina Lemos Motta
Home Institution: Escola Superior de Agricultura Luiz de Queiroz (ESALQ). Universidade de São Paulo (USP). Piracicaba , SP, Brazil
Associated scholarship(s):18/09266-7 - Comparing and improving techniques for progesterone and estradiol assays using bovine plasma samples from previous experiments that evaluated the influence of these steroids on endometrial thickness, BE.EP.MS

Abstract

The uterine and hormonal dynamics throughout the estrous cycle of bovine females has been extensively studied. At the end of the cycle, in proestrus, there is a gradual reduction of circulating concentrations of progesterone (P4), due to the luteolysis process, and a progressive increase in estradiol (E2) concentrations. Simultaneously with these changes in the hormonal environment, an increase in endometrial thickness and endometrial vascular perfusion is observed. However, it is not possible to distinguish which of the steroids is responsible for these endometrial changes, in other words, whether it is the reduction of P4, or the increase of E2, or the combination of both. Parallel to the advances in the understanding of bovine reproductive physiology, studies aimed at manipulating the estrous cycle in an attempt to synchronize ovulation intensified. Since the establishment of the first protocol that effectively promoted ovulation synchronization, Ovsynch, GnRH analogs have been widely used with the aim of stimulating the release of peak of luteinizing hormone (LH) and consequently ovulation of the dominant follicle. Studies have reported that high concentrations of P4 at the time of treatment with GnRH caused a reduction in the peak of LH and consequently of ovulation by a probable blockade of GnRH receptors in the adenohypophysis. Nonetheless, the studies did not consider E2 concentrations at the time of GnRH treatment, only the P4 concentration, which turns it difficult the clarification of the role of both steroids in the GnRH response. In addition, the studies did not assess FSH concentrations after GnRH treatment. Thus, to understand the influence of circulating concentrations of P4, E2 and the combination of both on the uterine dynamics and in response to GnRH, experiments will be performed using exogenous sources of steroids, in order to avoid variations in the circulating concentrations inherent to each animal. Non-lactating Holtein cows will be used. In experiment 1, 12 cows will have uterine (perfusion and endometrial thickness) and ovarian dynamics evaluated daily in an interval between two ovulations (complete estrous cycle), and daily blood samples (P4, E2, FSH and LH analysis) will be collected. For experiment 2, 12 cows will be treated with a pre-synchronization protocol followed by a protocol that will simulate the proestrus: D0: two intravaginal devices (IVD) containing 2 g of P4 each, follicular aspiration (OPU) and prostaglandin F2± i.m. (PGF); D1: PGF; D4: OPU; D5: OPU and removal of an IVD; removal of the second IVD 18 hours later; D6: OPU; D5 to D7: estradiol benzoate (EB) distributed in 8 injections in an interval of 6 hours each. Two doses of EB will be tested, and that one which reaching a peak close to 8 pg/mL of circulating E2 will be used in experiment 3. Blood samples for P4 and E2 analysis will be collected and endometrial thickness and vascular perfusion will be evaluated via ultrasonography. In experiment 3, 20 cows will be used and distributed in four groups, with each cow going through two treatments (n = 10 per treatment). The protocols will be similar to experiment 2, but with GnRH treatment on D7 and the groups will differ according to concentration of P4 and E2 at the time of GnRH: high P4 and high E2; Low P4 and high E2; Low P4 and low E2, high P4 and low E2. Endometrial dynamics (thickness and perfusion), circulating concentrations of P4 and E2, and LH and FSH concentrations in response to GnRH will be evaluated. In this way, it will be possible to effectively understand the influence of P4 and E2 on the cited variables.

Academic Publications
(References retrieved automatically from State of São Paulo Research Institutions)
MOTTA, Jéssica Cristina Lemos. Interactions of circulating estradiol and progesterone on pituitary responsiveness to GnRH and changes in endometrial area. 2019. Master's Dissertation - Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz Piracicaba.

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