Atualização sobre o estresse térmico testicular / Updates on testicular heat stress

Os testículos, são mantidos no escroto a uma temperatura ~3-5°C abaixo da corporal. Quando a temperatura das gônadas se eleva, instala-se um quadro de estresse térmico (ET) testicular. O ET afeta a espermatogênese, e observam-se, já na primeira semana pós-ET, impactos na cinética, concentração e morfologia espermática. Classicamente, tais efeitos eram creditados à incapacidade da circulação local de atender ao aumento do metabolismo testicular devido ao aumento da temperatura local. Contudo, estudos recentes demonstraram que a hipóxia não era a causa da degeneração testicular. Atualmente, credita-se os efeitos deletérios do ET ao aumento local das espécies reativas de O2. Nesta situação, apesar da ativação de mecanismos antioxidantes (aumento das HSP e GPX1) e de proteção do DNA (aumento da P53), estes não são suficientes, sendo desencadeada a apoptose. Os efeitos deletérios do ET testicular podem ser mitigados pela melatonina, que pode ser tanto administrada aos animais ou adicionada ao sêmen para que desencadeie seus efeitos protetores.(AU)

The testes are kept in the scrotum at a ~3-5°C below body core temperature. When the temperature of the gonads increases, a process called heat stress (HS) takes place. The HS impairs spermatogenesis, and in the first week post-HS, impacts in sperm kinetics, concentration, and morphology are observed. Classically, such effects were credited to the incapacity of the local circulation to sustain the higher testicular metabolism due to the increased temperature. However, recent studies demonstrated that it was not the cause of testicular degeneration. The novel perspective credits the deleterious impacts of the HS to the local increase of the reactive oxygen species. Importantly, although there's an activation of antioxidant defenses (increase in HSP and GPX1) and DNA protection (increase in P53), such mechanisms are not sufficient, unfolding the apoptotic cascade. Lastly, some of the negative effects of HS can be mitigated by melatonin, which can either be given to the animals or added to the sperm to exert its protective effects.(AU)

Pathogenesis and mitigation of the deleterious effects of heat stress on bull reproduction / Patogênese e mitigação dos efeitos deletérios do estresse térmico na reprodução de touros

Bull testes must be 2 to 6 0C below body temperature for morphologically normal, motile and fertile sperm. Scrotal/testicular thermoregulation is complex, including a coiled testicular artery, surrounded by the venous pampiniform plexus comprising the testicular vascular cone, a counter-current heat exchanger. In addition, heat radiation from the scrotum, sweating, complementary arterial blood supplies, and temperature gradients in the scrotum and testes all contribute to testicular cooling. Despite a long-standing paradigm that mammalian testes are close to hypoxia and blood flow does not increase in response to testicular heating, in recent studies in mice, rams and bulls, warming the testes stimulated increased blood flow, with no indications of testicular hypoxia. Furthermore, hypoxia did not replicate the changes and hyperoxia did not provide protection. Therefore, we concluded that testicular hyperthermia and not secondary hypoxia affects spermatogenesis and sperm quality. Increasing testicular temperature causes many cellular and subcellular changes. As testicular temperature increases, the proportion of defective sperm increases; recovery is dependent upon the nature and duration of the thermal insult. Environmental control of temperature (shade, sprinklers, air conditioning) and some chemical approaches (e.g., melatonin and L-arginine) have promise in reducing the effects of heat stress on bull reproduction.

Os testículos dos bovinos devem permanecer 2 a 6 ºC abaixo da temperatura corporal para produzirem espermatozoides morfologicamente normais, móveis e férteis. A termorregulação escrotal/testicular é complexa e envolve a enovelada artéria testicular circundada pelo plexo venoso pampiniforme, que constituem o cone vascular, um sistema contracorrente de troca de calor. Adicionalmente, a perda de calor por radiação pelo escroto, sudorese, suprimento sanguíneo arterial complementar, e os gradientes de temperatura no escroto e testículos contribuem para o resfriamento testicular. A despeito do duradouro paradigma de que os testículos estão em uma situação de quase hipóxia e que o fluxo sanguíneo não aumenta em resposta ao aquecimento testicular, em recentes estudos em camundongos, carneiros e touros, o aquecimento testicular estimulou o fluxo sanguíneo sem serem observados sinais de hipóxia. Além disso, a hipóxia não afetou os testículos e a hiperóxia não conferiu proteção. Portanto, concluímos que é a hipertermia testicular, e não a hipóxia secundária, que afeta a espermatogênese e a qualidade seminal. O aumento da temperatura testicular causa muitas mudanças celulares e subcelulares. À medida que a temperatura aumenta, a proporção de espermatozoides defeituosos aumenta. A recuperação depende da natureza e duração do insulto térmico. O controle ambiental (sombra, aspersores de água e ar condicionado) e algumas abordagens químicas (ex., melatonina e L-arginina) são medidas promissoras de redução dos efeitos do estresse térmico na reprodução de touros

Impactos do estresse térmico na reprodução de fêmeas bovinas / Heat stress impact on bovine female reproduction

O estresse por calor (ET) ocorre quando a temperatura ambiente excede a zona de conforto térmico animal. Várias respostas corporais inespecíficas, capitaneadas pelos sistemas nervoso, neuroendócrino e imunológico são acionadas para manter a homeostase e resfriar o animal. O ET afeta o eixo hipotálamo-hipofisário-gonadal, comprometendo a liberação de gonadotrofinas, e promove o acúmulo de espécies reativas de oxigênio e proteínas anormais nas células ovarianas. Em resposta, as células ativam mecanismos antioxidantes e de reparação do DNA, que reduzem o metabolismo celular e aumentam as chances de sobrevivência; quando a reparação não é possível, acontece a apoptose. O ET impacta negativamente a produção de estradiol ovariano, o comportamento do estro, o desenvolvimento folicular, a competência dos oócitos e do embrião, as taxas de concepção, o estabelecimento e a manutenção da gravidez e até mesmo a eficiência reprodutiva da progênie. O combate ao ET inclui estratégias de combate ao aquecimento global progressivo e de manejo para resfriar os animais, e diminuir a produção de calor metabólico. O uso de biotecnologia reprodutiva e estratégias genéticas para gerar animais termotolerantes são também essenciais

Heat stress (HS), a harmful condition affecting animal production, reproduction, and welfare, occurs when an animal is exposed to temperatures that exceed its thermal comfort zone. Several nonspecific body responses involving neural, neuroendocrine, and immune systems are triggered to keep homeostasis in such conditions. These responses, primarily directed to cooling the body, also impact the hypothalamic-pituitary-gonadal axis, compromising the bovine female’s release of gonadotropins. Heat stress also promotes reactive oxygen species accumulation in ovarian cells, impairing protein folding and refolding, triggering antioxidant and DNA protection mechanisms. These mechanisms, directed to reduce cell metabolism and increase survival chances, are not always sufficient to protect the cell and result in apoptosis. Heat stress’s systemic and cellular consequences impact ovarian estradiol production, estrous behaviors, follicular development, oocytes and embryo competence, conception rates, pregnancy establishment and maintenance, and even the future reproductive efficiency of the progenies of cows exposed to HS during pregnancy. The combat of heat stress includes strategies to alleviate the effect of progressive global warming, management strategies to cool the animals, reduced metabolic heat, and methane production dietary approaches. The use of reproductive biotechs and genetic strategies to increase thermotolerant animals are also critical to overcoming the harmful effect of HS.

Inhibition of Na+, K+ -ATPase with ouabain is detrimental to equine blastocysts

Although equine blastocysts ≤ 300 µm in diameter can be successfully vitrified, larger equine blastocysts are not good candidates for cryopreservation. As Na+, K+-ATPase is involved in maintaining blastocyst expansion, perhaps inhibition of this enzyme would be a viable method of reducing blastocyst diameter prior to cryopreservation. Objectives were to evaluate effects of ouabain-induced inhibition of Na+, K+-ATPase in equine blastocysts. Sixteen mares were ultrasonographically monitored, given deslorelin acetate to induce ovulation, and inseminated. Embryos (D7 and D9) were harvested and Na+, K+-ATPase inhibited for 1 or 6 h by exposure to 10-6 M ouabain, either natural ouabain or conjugated to fluorescein (OuabainFL), during incubation at 37° C. Evaluations included morphometric characteristics (bright field microscopy) and viability (Hoescht 33342 + propidium iodide). Blastocysts incubated for 6 h in Holding medium + ouabain (n=3) had, on average, a 45.7% reduction in diameter, with adverse morphologic features and no re-expansion after subsequent incubation in Holding medium for 12 h. In subsequent studies, even a 1-h exposure to Ouabain or OuabainFL, caused similar reductions, namely 38.7 ± 6.7% (n=5) and 33.6 ± 3.3% (n=7) for D7 and D9 blastocysts, respectively. Ouabain binding was confirmed after OuabainFL exposition and all embryos (n=12) lost viability. We concluded that Na+, K+-ATPase inhibition with ouabain caused death of equine blastocysts and therefore was not a viable method of reducing blastocyst size prior to cryopreservation.

Inhibition of Na+, K+ -ATPase with ouabain is detrimental to equine blastocysts

Although equine blastocysts ≤ 300 µm in diameter can be successfully vitrified, larger equine blastocysts are not good candidates for cryopreservation. As Na+, K+-ATPase is involved in maintaining blastocyst expansion, perhaps inhibition of this enzyme would be a viable method of reducing blastocyst diameter prior to cryopreservation. Objectives were to evaluate effects of ouabain-induced inhibition of Na+, K+-ATPase in equine blastocysts. Sixteen mares were ultrasonographically monitored, given deslorelin acetate to induce ovulation, and inseminated. Embryos (D7 and D9) were harvested and Na+, K+-ATPase inhibited for 1 or 6 h by exposure to 10-6 M ouabain, either natural ouabain or conjugated to fluorescein (OuabainFL), during incubation at 37° C. Evaluations included morphometric characteristics (bright field microscopy) and viability (Hoescht 33342 + propidium iodide). Blastocysts incubated for 6 h in Holding medium + ouabain (n=3) had, on average, a 45.7% reduction in diameter, with adverse morphologic features and no re-expansion after subsequent incubation in Holding medium for 12 h. In subsequent studies, even a 1-h exposure to Ouabain or OuabainFL, caused similar reductions, namely 38.7 ± 6.7% (n=5) and 33.6 ± 3.3% (n=7) for D7 and D9 blastocysts, respectively. Ouabain binding was confirmed after OuabainFL exposition and all embryos (n=12) lost viability. We concluded that Na+, K+-ATPase inhibition with ouabain caused death of equine blastocysts and therefore was not a viable method of reducing blastocyst size prior to cryopreservation.(AU)