If you thought the heat outside was just driving you crazy, you should know that it does much more than that. Researchers in Japan have found that even slight changes in temperature impair the ability of the testicles to produce sperm, which dramatically affects rates of male fertility.
Hot and bothered
The new study published in the journal Communications Biology found that at a temperature of 34° Celsius the testes can successfully produce healthy sperm. However, at temperatures between 37° and 38° this process is severely damaged and can lead to infertility.
Sperm is produced in the testes at a temperature lower than the average body temperature. In the testes there is a unique network of blood tubes that eliminate excess heat, and another mechanism by which the scrotal sac becomes loose when exposed to heat, which helps keep the testicles ventilated.
"We didn’t expect such a subtle set of temperature-dependent events to be based on this well-known phenomenon."
Shoshi Yoshida of the National Institute of Basic Biology
The scrotum contracts and brings the testicles closer to the body at low temperatures. So, an increase in body temperature may impair sperm quality.
Can't take the heat
The new study used testicular cultures to support full sperm inside an incubator by cultivating mouse testicles at different temperatures. The team found that sperm failed in several stages as temperatures rose from 30° to 40°.
"We didn’t expect such a subtle set of temperature-dependent events to be based on this well-known phenomenon. This discovery could only have been achieved through an organ culture system," said study editor Shoshi Yoshida of the National Institute of Basic Biology in a press release.
The group further revealed that meiosis, through which homologous chromosomes separate into fluid seed, was severely damaged at the temperature of 37-38°.
Researchers added that “it was surprising that vital processes, like meiosis, can be easily damaged at normal body core temperatures. Using the combined functions of the scrotum and barrier, only semen developed at low temperatures fertilizes eggs to create the next generation. Key questions for future studies include the molecular mechanism of heat sensitivity and the biological significance of low temperatures in sperm production.”