Aspectos fisiológicos e reprodutivos da exposição de vacas leiteiras ao estresse térmico
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Data
2016-12-22
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Universidade Estadual Paulista (Unesp)
Resumo
O estresse térmico reduz a eficiência reprodutiva em vacas leiteiras. O fluido folicular (FF) contém proteínas envolvidas na atividade e diferenciação celular do folículo e maturação oocitária. A caracterização das proteínas do FF pode contribuir para melhor compreensão dos mecanismos fisiológicos envolvidos na foliculogênese e comprometimento da função reprodutiva durante o estresse térmico. No primeiro experimento avaliou-se o perfil proteomico do FF de vacas em diferentes estágios do desenvolvimento folicular (pré-desvio, desvio, dominância e pré-ovulatório) e foi testada a associação das proteínas com as concentrações intrafoliculares de hormônios esteroides. Foram encontradas 22 proteínas diferentemente expressas (P < 0.05) entre as categorias foliculares, sendo o desvio um momento-chave na determinação da expressão das proteínas. Além disso, três proteínas foram correlacionadas (P < 0.05) com as concentrações intrafoliculares de estradiol, enquanto dezesseis foram correlacionadas (P < 0.05) com as concentrações locais de progesterona. A análise de vias canônicas identificou a ativação/inibição das vias associadas com a resposta de fase aguda, sistema de coagulação, sistema complemento, receptor X do fígado e retinóide e produção de óxido nítrico e espécies reativas de oxigênio. No segundo experimento, testou-se o efeito do estresse térmico sobre a expressão das proteínas do FF de vacas. Na validação do modelo experimental, foi observado que a exposição contínua ao estresse térmico afetou os mecanismos termorregulatórios, levando a um aumento pronunciado da frequência respiratória, seguido pelo aumento da temperatura retal. As variáveis ambientais do dia anterior foram mais importantes para explicar as respostas do parâmetros fisiológicos e ingestão de matéria seca, sendo a temperatura ambiente o principal fator envolvido na troca de calor. Embora a exposição prolongada ao estresse térmico indicar um ajuste adaptativo, neste estudo foi observada apenas aclimatação parcial. O crescimento folicular das vacas expostas ao estresse térmico foi afetado e pode, em parte, ser explicado pela expressão alterada das proteínas do FF. As 28 proteínas diferentemente (P < 0.05) expressas no FF de vacas estressadas por calor foram associadas, principalmente, as vias da função imune e cascata da coagulação. Tais achados indicam potenciais mecanismos moleculares e vias de sinalização envolvidos na foliculogênese e redução da fertilidade observada durante o verão.
Heat stress reduces the reproductive efficiency in dairy cows. Follicular fluid (FF) contains proteins involved in the follicle activity and cell differentiation and oocyte maturation. The characterization of the proteome of FF may contribute to a better understanding of the physiological mechanisms involved in folliculogenesis and impairment of reproductive function during heat stress. In the first experiment, the FF proteomic profile of cows at different stages of follicle development (pre-deviation, deviation, dominance and pre-ovulatory) was evaluated and the association of proteins with intrafollicular concentrations of steroid hormones was tested. Twenty-two differentially expressed proteins (P < 0.05) were found among the follicular categories, with deviation being a critical time-point in the determination of protein expression. In addition, three proteins were correlated (P < 0.05) with the intrafollicular concentrations of estradiol, while sixteen were correlated (P < 0.05) with the local concentrations of progesterone. The canonical pathway analysis identified the activation/inhibition of the pathways associated with acute phase response, coagulation system, complement system, liver X receptor and retinoid, and production of nitric oxide and reactive oxygen species. In the second experiment, the effect of heat stress on the expression of cow FF proteins was tested. In the experimental model validation, we observed that the continuous exposure to heat stress affected thermoregulatory mechanisms,leading to a marked increase in respiratory rate, followed by an increase in rectal temperature. The influence of environmental variables from the previous day on physiological parameters and dry matter intake were more important than the immediate effect and ambient temperature represented the most determinant factor for heat exchange. Although prolonged exposures to heat stress indicate an adaptive adjustment, in this study the acclimation process was only partial. The follicular growth of cows exposed to heat stress was affected and may be partly explained by the altered expression of the FF proteins. The 28 differentially (P < 0.05) expressed proteins in FF from heat stressed cows were closely associated to the immune function and the coagulation cascade pathways. Such findings indicate potential molecular mechanisms and signaling pathways involved in folliculogenesis and reduction fertility observed during the summer.
Heat stress reduces the reproductive efficiency in dairy cows. Follicular fluid (FF) contains proteins involved in the follicle activity and cell differentiation and oocyte maturation. The characterization of the proteome of FF may contribute to a better understanding of the physiological mechanisms involved in folliculogenesis and impairment of reproductive function during heat stress. In the first experiment, the FF proteomic profile of cows at different stages of follicle development (pre-deviation, deviation, dominance and pre-ovulatory) was evaluated and the association of proteins with intrafollicular concentrations of steroid hormones was tested. Twenty-two differentially expressed proteins (P < 0.05) were found among the follicular categories, with deviation being a critical time-point in the determination of protein expression. In addition, three proteins were correlated (P < 0.05) with the intrafollicular concentrations of estradiol, while sixteen were correlated (P < 0.05) with the local concentrations of progesterone. The canonical pathway analysis identified the activation/inhibition of the pathways associated with acute phase response, coagulation system, complement system, liver X receptor and retinoid, and production of nitric oxide and reactive oxygen species. In the second experiment, the effect of heat stress on the expression of cow FF proteins was tested. In the experimental model validation, we observed that the continuous exposure to heat stress affected thermoregulatory mechanisms,leading to a marked increase in respiratory rate, followed by an increase in rectal temperature. The influence of environmental variables from the previous day on physiological parameters and dry matter intake were more important than the immediate effect and ambient temperature represented the most determinant factor for heat exchange. Although prolonged exposures to heat stress indicate an adaptive adjustment, in this study the acclimation process was only partial. The follicular growth of cows exposed to heat stress was affected and may be partly explained by the altered expression of the FF proteins. The 28 differentially (P < 0.05) expressed proteins in FF from heat stressed cows were closely associated to the immune function and the coagulation cascade pathways. Such findings indicate potential molecular mechanisms and signaling pathways involved in folliculogenesis and reduction fertility observed during the summer.
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Palavras-chave
Estresse térmico, Termorregulação, Foliculogênese, Proteômica, Bovino, Heat stress, Thermoregulation, Folliculogenesis, Proteomics, Bovine