Evaluation of Lasting Effects of Heat Stress on Sperm Profile and Oxidative Status of Ram Semen and Epididymal Sperm

Abstract

Higher temperatures lead to an increase of testicular metabolism that results in spermatic damage. Oxidative stress is the main factor responsible for testicular damage caused by heat stress. The aim of this study was to evaluate lasting effects of heat stress on ejaculated sperm and immediate or long-term effects of heat stress on epididymal sperm. We observed decrease in motility and mass motility of ejaculated sperm, as well as an increase in the percentages of sperm showing major and minor defects, damaged plasma and acrosome membranes, and a decrease in the percentage of sperm with high mitochondrial membrane potential in the treated group until one spermatic cycle. An increased enzymatic activity of glutathione peroxidase and an increase of stressed cells were observed in ejaculated sperm of the treated group. A decrease in the percentage of epididymal sperm with high mitochondrial membrane potential was observed in the treated group. However, when comparing immediate and long-term effects, we observed an increase in the percentage of sperm with low mitochondrial membrane potential. In conclusion, testicular heat stress induced oxidative stress that led to rescuable alterations after one spermatic cycle in ejaculated sperm and also after 30 days in epididymal sperm.

Hyperthermia and not hypoxia may reduce sperm motility and morphology following testicular hyperthermia

“…Similar changes occurred at corresponding times in previous studies that involved increased testicular temperatures in bulls and rams (Howarth 1969;Meyerhoeffer et al 1985;Saab et al 2011;Rocha et al 2015;Hamilton et al 2016) with some apparent differences in the magnitude of changes and the interval from the thermal insult to recovery, attributed to the degree and duration of testicular heating and perhaps species-specific characteristics (Skinner and Louw 1966;Rathore 1970;Brito et al 2004;Nichi et al 2006). Furthermore, in this study, sperm damage occurred during the final stages of spermatogenic development in the testis (Howarth 1969;Cardoso and Queiroz 1988;Senger 2003).…”

“…Furthermore, in this study, sperm damage occurred during the final stages of spermatogenic development in the testis (Howarth 1969;Cardoso and Queiroz 1988;Senger 2003). Although sperm at various stages of development or in the epididymis may be affected by increased testicular temperature (Lue et al 1999;Perez-Crespo et al 2008;Hamilton et al 2016), in our study, due to the delay from testicular heating to appearance of abnormalities, there was no apparent effect on sperm present in the epididymis. However, in a previous study in bulls with scrotal insulation (Vogler et al 1991), sperm present in the epididymis were apparently unaffected when fresh, unfrozen sperm were evaluated, although changes were evident after sperm cryopreservation, thawing, and incubation for 3 h at 37 °C.…”

“…Semen was collected by electroejaculation on two occasions (14 and seven days before scrotal insulation was applied) and starting at seven days after the onset of scrotal insulation, semen collection was done bi-weekly for four weeks and then weekly for an additional two weeks. All heat-stress induced damage to sperm was due to increased temperature per se and not due to testicular hypoxia as reported (Waites and Setchell 1964;Paul et al 2009;Hamilton et al 2016). …”

“…Although some studies have been conducted, there is still a relative lack of information regarding how high and low O 2 availability in vivo impact sperm. Furthermore, an increase in reactive oxygen species (ROS) and an impact on sperm mitochondria was observed after long term exposure to increased intra-testicular temperature (approximately 33.5 °C), but no observation on the O 2 availability was taken (Hamilton et al 2016). Important modifications of the proteomic profile of seminal plasma were related to semen quality parameters after testicular heat stress in rams (Rocha et al 2015), indicating another potential mechanism for the observed damage that is not necessarily caused by hypoxia.…”

“…However, blood flow is reported to remain relatively constant and therefore the resulting hypoxia is regarded as the basis for decreases in sperm motility and morphology (Waites and Setchell 1964;Paul et al 2009;Hamilton et al 2016). Regardless, to the authors' knowledge, this has never been critically tested.…”