Scrotal heat stress effects on sperm viability, sperm DNA integrity, and the offspring sex ratio in mice

Abstract

Evidence exists to suggest detrimental effects of heat stress on male fertility. This study was designed to assess the effects of scrotal heat stress on mature and developing sperm in a mouse model. After receiving shock heat treatment (42 degrees C for 30 min), mature spermatozoa were recovered from the epididymis hours (6) or Days (7, 14, 21, 28, 60) later, to determine the variables: number of spermatozoa, sperm viability, motility and progressive motility, sperm DNA integrity as established by the TUNEL method, embryo implantation rate, and sex ratio of the fetuses conceived using the heat-exposed spermatozoa. Our results indicate that transient mild heat treatment does not affect in the same way the different types of male germ cells. Spermatocytes present within the testis at the time of heat stress resulted into a lower concentration of spermatozoa with reduced viability and low motility. Even though, DNA integrity of spermatozoa resulting from spermatocytes was also compromised by heat stress, the higher degree of DNA damage was found among spermatozoa resulting from spermatids present within the testis at the time of heat stress. At last, heat shock effect on spermatozoa present in the epididymis at the time of thermal stress resulted into a sex ratio distortion. These findings point to a higher sensitivity of spermatocytes to heat exposure and also suggest a different response of X and Y chromosome-bearing spermatozoa to heat stress that warrants further investigation.

A single, mild, transient scrotal heat stress causes DNA damage, subfertility and impairs formation of blastocysts in mice

“…It was therefore concluded that the reduced pregnancy rate in this group was due to preimplantation failure of embryos. Our data is consistent with a recent study by Perez-Crespo et al (2008) which found a decrease in the number of pregnancies and foetuses but no change in resorption rate using a similar heat stress regime to our own.…”

“…35-36 8C) for several hours , Cammack et al 2006. In these studies, the common features of disturbances in testicular function that have been recorded include decreased testicular weights, germ cell loss and increased rates of apoptosis (McLaren et al 1994, Setchell et al 1996, 1998, Lue et al 1999, Banks et al 2005, Perez-Crespo et al 2008. Some studies have reported that pachytene spermatocytes and early spermatids are the cell types most susceptible to testicular heat stress (Setchell 1998).…”

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

“…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.…”

Evidence that mammalian sex ratios at birth are partially controlled by parental hormone levels around the time of conception

“…The author has offered an explanation of the latter data (James 2007). The author suggests that this explanation may apply also to the data of Perez-Crespo et al (2007). The correlation between sperm quality and offspring sex ratio is secondary to correlations of both with paternal testosterone/gonadotrophin ratio.…”

“…Heat stress in mice and sperm quality and fertility -Crespo et al (2007) reported that male mice were exposed to heat stress and then mated 6 h later with unexposed females. These authors noted that heat stress has deleterious effects on sperm quality, and they found that the resulting offspring sex ratio was significantly low.…”