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      Factores asociados a la liberación de gonadotrofinas y ovulación después de la administración exógena de GnRH en el Bos Taurus

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          Abstract

          Resumen La hormona liberadora de gonadotropina (GnRH) es un decapéptido, sintetizado por las neuronas GnRH en el hipotálamo, que estimula la síntesis y secreción de gonadotrofinas (hormonas folículo estimulante, FSH y luteinizante, LH) de la hipófisis anterior o adenohipofisis. Agonistas de GnRH con una estructura idéntica o similar a la natural han estado disponible comercialmente desde la década del 70 y han sido utilizadas en un principio para el tratamiento de quistes foliculares y el mejoramiento de la fertilidad en el ganado vacuno (1). La ovulación de folículos ováricos después de la administración de GnRH fue reportada por primera vez por Schams et al. (2) y Britt et al. (3), pero no fue hasta la década del 90 cuando la GnRH se comenzó a utilizar para controlar la dinámica folicular durante el ciclo estral del bovino. Ahora sabemos que una nueva onda folicular emerge dentro de los 2 días después de la ovulación del folículo dominante presente en el momento del tratamiento con GnRH (4,5). Este hallazgo facilitó el desarrollo de protocolos de sincronización a base de GnRH en combinación con prostaglandinas (PGF) que permiten la inseminación artificial a tiempo fijo (IATF), sin necesidad de realizar detección de celo. Estos protocolos a base de GnRH y PGF son parte del manejo reproductivo bovino, sobre todo del ganado lechero, en muchos rodeos comerciales del mundo. Existen numerosos protocolos a base de GnRH y PGF disponibles para la sincronización del estro y la ovulación en el ganado, varios de esos protocolos se han explicado y discutido en detalle en otros artículos (6,7). El objetivo de esta revisión es describir los factores asociados a la liberación de LH y respuesta ovulatoria posterior a la administración de GnRH, dar a conocer información relevante sobre el efecto de las hormonas esteroideas en la respuesta a la GnRH y, por último, brevemente postular estrategias que podrían mejorar la eficacia de los protocolos basados en la aplicación de GnRH y PGF.

          Translated abstract

          Abstract The gonadotropin-releasing hormone (GnRH) is a decapeptide, synthesized by the GnRH neurons in the hypothalamus, which stimulates the synthesis and secretion of gonadotrophins (follicle-stimulating hormone, FSH and luteinizing hormone, LH) from the anterior pituitary or adenohypophysis. GnRH agonists with a structure identical or similar to nature have been commercially available since the 1970’s and were initially used for the treatment of follicular cysts and the improvement of fertility in cattle (1). The ovulation of ovarian follicles after GnRH administration was first reported by Schams et al. (2) and Britt et al. (3), but it was not until the 1990’s that GnRH began to be used to control follicular dynamics during the bovine estrous cycle. Studies have shown that a new follicular wave emerges within 2 days after ovulation of the dominant follicle present at the time of GnRH treatment (4,5). This finding facilitated the development of synchronization protocols based on GnRH in combination with prostaglandins (PGF) that allow fixed-time artificial insemination (FTAI), without the need for heat detection. These GnRH-based protocols are part of the reproductive management, especially in dairy cattle, in many commercial herds around the world. There are several GnRH and PGF-based protocols available for estrus and ovulation synchronization in cattle, most of these protocols have been explained and discussed in detail in other publications (6,7). The objective of this review is to describe the factors associated with the release of LH and ovulatory response after the administration of GnRH, to present relevant information on the effect of steroid hormones on the response to GnRH and, finally, to briefly postulate strategies that could improve the efficacy of GnRH and PGF-based protocols.

          Translated abstract

          Resumo O hormônio liberador de gonadotrofinas (GnRH) é um decapeptídeo, sintetizado pelos neurônios GnRH no hipotálamo, que estimula a síntese e secreção de gonadotrofinas (hormônio folículo-estimulante, FSH e hormônio luteinizante, LH) da hipófise anterior ou adeno-hipófise. Agonistas de GnRH com estrutura idêntica ou semelhante à natureza estão disponíveis comercialmente desde a década de 1970 e foram inicialmente utilizados para o tratamento de cistos foliculares e melhoria da fertilidade em bovinos (1). A ovulação de folículos ovarianos após a administração de GnRH foi relatada pela primeira vez por Schams et al. (2) e Britt et al. (3), mas foi somente na década de 1990 que o GnRH começou a ser usado para controlar a dinâmica folicular durante o ciclo estral bovino. Sabemos agora que uma nova onda folicular surge dentro de 2 dias após a ovulação do folículo dominante presente no momento do tratamento com GnRH. (4,5) Essa descoberta facilitou o desenvolvimento de protocolos de sincronização baseados em GnRH em combinação com prostaglandinas (PGF) que permitem a inseminação artificial em tempo fixo (IATF), sem a necessidade de detecção de cio. Esses protocolos baseados em GnRH e PGF fazem parte do manejo reprodutivo de bovinos, especialmente bovinos leiteiros, em muitos rebanhos comerciais ao redor do mundo. Existem inúmeros protocolos baseados em GnRH e PGF disponíveis para sincronização de estro e ovulação em bovinos, vários desses protocolos foram explicados e discutidos em detalhes em outros artigos (6,7). O objetivo desta revisão é descrever os fatores associados à liberação de LH e resposta ovulatória após a administração de GnRH, apresentar informações relevantes sobre o efeito dos hormônios esteroides na resposta ao GnRH e, por fim, postular brevemente estratégias que possam melhorar a eficácia de protocolos baseados na aplicação de GnRH e PGF.

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          Most cited references36

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          Synchronization of ovulation in dairy cows using PGF2α and GnRH

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            Expression of follicle-stimulating hormone and luteinizing hormone receptor messenger ribonucleic acids in bovine follicles during the first follicular wave.

            The objective of the present study was to characterize expression of mRNAs encoding FSH and LH receptors during follicular development and at different stages of the first follicular wave in cattle. Following estrus, groups of heifers (3-5 per group) were ovariectomized on the day of initiation of the first follicular wave (as determined by ultrasonography; Day 0), or on Days 2, 4, 6, 8, or 10 after initiation of the first wave. FSH and LH receptor mRNAs were detected within follicles > or = 4 mm and in some smaller follicles by in situ hybridization and were quantified by image analysis. FSH receptor mRNA was expressed in granulosa cells of all growing follicles, starting in some follicles with only one layer of granulosa cells. Irrespective of day of the follicular wave, the level of expression of FSH receptor mRNA in granulosa cells of healthy antral follicles ranging from 0.5 to 14 mm in diameter did not vary significantly with follicular size (r = 0.02, p > 0.10). Expression of LH receptor mRNA was first observed in theca interna cells of follicles shortly after antral formation. Irrespective of day of the follicular wave, the levels of LH receptor mRNA in theca interna cells of healthy antral follicles ranging from 0.5 to 14 mm increased with follicular size (r = 0.39, p 9 mm in diameter and was first observed in the dominant follicles collected on Day 4. Expression of mRNA for LH receptor, but not for FSH receptor, changed (p < 0.01) with the stage of the first follicular wave.(ABSTRACT TRUNCATED AT 250 WORDS)
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              Molecular Mechanisms of Gonadotropin-Releasing Hormone Signaling: Integrating Cyclic Nucleotides into the Network

              Gonadotropin-releasing hormone (GnRH) is the primary regulator of mammalian reproductive function in both males and females. It acts via G-protein coupled receptors on gonadotropes to stimulate synthesis and secretion of the gonadotropin hormones luteinizing hormone and follicle-stimulating hormone. These receptors couple primarily via G-proteins of the Gq/ll family, driving activation of phospholipases C and mediating GnRH effects on gonadotropin synthesis and secretion. There is also good evidence that GnRH causes activation of other heterotrimeric G-proteins (Gs and Gi) with consequent effects on cyclic AMP production, as well as for effects on the soluble and particulate guanylyl cyclases that generate cGMP. Here we provide an overview of these pathways. We emphasize mechanisms underpinning pulsatile hormone signaling and the possible interplay of GnRH and autocrine or paracrine regulatory mechanisms in control of cyclic nucleotide signaling.
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                Author and article information

                Journal
                civet
                Ciencia Veterinaria
                Cienc. vet.
                Universidad Nacional de La Pampa. Facultad de Ciencias Veterinarias (General Pico, La Pampa, Argentina )
                1515-1883
                1853-8495
                December 2022
                : 24
                : 2
                : 9
                Affiliations
                [2] orgnameUniversity of Saskatchewan, Saskatoon, Canada Canadá
                [1] orgnameUniversity of Alberta, Edmonton, Canada Canadá
                Article
                S1853-84952022000200009 S1853-8495(22)02400200009
                10.19137/cienvet202224208
                b9691a68-f6a3-4554-b536-a2090ad40956

                This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

                History
                : 08 August 2022
                : 23 June 2022
                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 37, Pages: 1
                Product

                SciELO Argentina

                Categories
                Articulo de revisión

                Dinámica folicular,Inseminación artificial,Liberación de LH,Progesterona,Estrógeno,Inseminação artifícial,Dinâmica folicula,Liberação de LH,Estrogênio,Artificial insemination,Follicular dynamics,LH release,Progesterone,Estrogen

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