Interactions of circulating estradiol and progesterone on pituitary responsiveness to GnRH and changes in endometrial area

• Autor(a) principal: Motta, Jéssica Cristina Lemos
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: http://www.teses.usp.br/teses/disponiveis/11/11139/tde-17092019-154944/
• topic: FSH; FSH; LH; LH; Proestro; Proestrus; Útero; Uterus

Changes in circulating progesterone (P4) and estradiol (E2) during proestrus produce dynamic changes in endometrial function and pituitary release of gonadotropins. Independent and combined effects of P4 and E2 on endometrium and pituitary were evaluated. In Exp.1, an exogenous hormone model of proestrus was created by removal of CL and follicles >=5 mm followed by gradual removal of intravaginal P4 implants during 18h and treatment with increasing doses of estradiol benzoate during 48h to mimic proestrus using HighE2 (n=9) or LowE2 (n=9). Decreased P4, increased E2, and increased endometrial area (EA) simulated proestrus values in HighE2 cows and this was used subsequently. Experiment 2 used a 2x2 factorial design with: HighE2&LowP4 (n=11); HighE2&HighP4 (n=11); LowE2&HighP4 (n=11); LowE2&LowP4 (n=10). At 48h, GnRH-induced LH and FSH release was determined. Variables were analyzed using PROC MIXED of SAS and AUC calculated with MESS. The EA increased dramatically during 48h only in HighE2&LowP4 cows. For FSH, HighE2 cows had greater AUC and FSH peak after GnRH than LowE2 groups, with mild negative effects of HighP4. For LH, concentration at peak and AUC were 2-fold greater in HighE2 compared to LowE2 groups, with HighP4 reducing in a similar proportion compared to LowP4 groups. Thus, maximal changes in uterus and pituitary during proestrus depend on both LowP4 and HighE2 but E2 and P4 have different actions. Changes in endometrium depend on LowP4 and HighE2, whereas GnRH-induced FSH secretion primarily depends on HighE2, and GnRH-induced LH secretion is independently increased by HighE2 or reduced by HighP4.