ResumoCondições ambientais adversas, tais como altas temperaturas e umidade relativa, causam aumento da temperatura corporal interna (hipertermia) de vacas lactantes, que resultam em estresse térmico e diminuição dos índices de gestação. A susceptibilidade embrionária à temperatura elevada já foi bem caracterizada tanto em experimentos in vivo quanto in vitro. A exposição de embriões bovinos em estágios de zigoto e duas células à temperatura elevada diminui o desenvolvimento embrionário até o estágio de blastocisto. No entanto, o embrião torna-se mais resistente aos efeitos deletérios da temperatura elevada à medida que progride no desenvolvimento. A redução na competência de desenvolvimento embrionária causada pelo estresse térmico deve-se, em parte, às inúmeras alterações citoplasmáticas e nucleares induzidas pela temperatura elevada. No citoplasma embrionário, o choque térmico aumenta o número de mitocôndrias edemaciadas, desorganiza os microtúbulos e os filamentos de actina. No compartimento nuclear, a temperatura elevada induz a fragmentação de DNA característica de apoptose. Essa forma de morte celular é um fenômeno regulado ao longo do desenvolvimento embrionário pré-implantacional, visto que altas temperaturas não ativam a cascata de apoptose em embriões de duas ou quatro células. A apoptose embrionária induzida pelo choque térmico em embriões > 16 célu-las pode ser considerada um mecanismo de controle de qualidade para remoção dos blastômeros danificados, já que o bloqueio da apoptose nestes embriões aumenta ainda mais a susceptibilidade ao choque térmico. Além disso, o estresse térmico também pode afetar o estado redox do embrião, levando a um consequente estresse oxidativo. Palavras-chave:Estresse térmico. Embrião. Bovino. Alterações celulares. AbstractAdverse environmental conditions such as high temperature and humidity increase internal body temperature (hyperthermia) of lactating dairy cows resulting in heat stress and decreased pregnancy rates. Embryonic susceptibility to elevated temperature has been well characterized both in vivo and in vitro. Exposure of zygote and two cells stage bovine embryos to elevated temperature decreases embryonic development to the blastocyst stage. However, the bovine embryo becomes more resistant to the deleterious effects of heat stress as it proceeds in its development. The heat-induced reduction in embryonic developmental competence is due, at least in part, to the numerous cytoplasmic and nuclear changes induced by high temperature. In the embryo cytoplasm heat shock increases the number of swollen mitochondria, disrupts microtubules and microfilaments. In the nuclear compartment, elevate temperature induces DNA fragmentation characteristic of apoptosis. This form of cell death is a phenomenon regulated throughout the preimplantation embryonic development, since high temperatures do not trigger apoptosis in embryos of two or four cells. Heat-induced apoptosis in embryos > 16 cells can be seen as a quality control mechanism for removing damaged blastomeres, sinc...
Summary Although bovine embryo in vitro production (IVP) is a common assisted reproductive technology, critical points warrant further study, including sperm traits and oxidative status of sperm for in vitro fertilization (IVF). Our aim was to evaluate whether the lipid peroxidation index of commercial bull semen is influenced by sperm traits and oxidative status of sperm populations selected using Percoll® gradient. Semen straws from 48 batches from 14 Nelore bulls were thawed individually, analyzed for motility and subjected to Percoll selection. After Percoll, the lipid peroxidation index of the extender was evaluated, whereas selected sperm were analyzed for motility, acrosome and membrane integrity, mitochondrial membrane potential, chromatin resistance and oxidative potential under IVF conditions. Batches were divided retrospectively in four groups according to lipid peroxidation index. Sperm from Group 4 with the lowest index of lipid peroxidation had, after Percoll selection, greater plasma membrane integrity (81.3%; P = 0.004), higher mitochondrial potential (81.1%; P = 0.009) and lower oxidative potential (135.3 ng thiobarbituric acid reactive substances (TBARS)/ml; P = 0.026) compared with Group 1 with highest lipid peroxidation index (74.3%, 73% and 213.1 ng TBARS/ml, respectively). Furthermore, we observed negative correlations for the lipid peroxidation index with motility, membrane integrity and mitochondrial potential, and positive correlations with oxidative potential. In conclusion, oxidative stress in semen straws, as determined using lipid peroxidation in the extender, is associated with sperm traits and their oxidative potential under IVF conditions. These results provided further insights regarding the importance of preventing oxidative stress during semen handling and cryopreservation, as this could affect sperm selected for IVF. Finally, Percoll selection did not completely remove sperm with oxidative markers.
quando da predominância do rano lateral, 9,0; 9,0; 11,0 e 10,0, quando da predominância do ramo mediai e 11,0; 11,5; 10,0 e 9,5, quando a artéria testicular emite número variado de ramos laterais (1 a 5) e mediais (2 a 4).
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