Testicular steroidogenesis is decreased by hyperthermia in old rats

To evaluate the effects of hyperthermia on testicular steroidogenesis in a rat model.

Three-month-old and 20-month-old male Sprague-Dawley rats were randomly divided into 4 groups of 10 rats each, a control group and a hot-bath group for each age. The rats in the hot-bath groups received multiple 10-min treatments in a hot bath (41-43 degrees C) over a period of 4 weeks. Testicular testosterone, serum testosterone and serum luteinizing hormone levels were measured. The protein levels of 2 steroidogenic enzymes, StAR and P450c17, were measured by Western blot. The testes were examined histologically by light microscopy.

Testicular testosterone levels of the 20-month-old, but not the 3-month-old, rats in the hot-bath group were significantly lower than those in the control group (p < 0.05). Serum testosterone levels of both the old and the young hot-bath groups tended to decrease compared with their corresponding controls, although the differences were not statistically significant. Serum luteinizing hormone levels changed insignificantly after the hot baths in both age groups. The hot-bath treatment had no significant effect on P450c17 protein levels, whereas the protein level of StAR was significantly lower in the old hot-bath group than in the same-age control group (p < 0.05).

Hyperthermia significantly decreased the testicular testosterone level in old male rats and significantly lowered the StAR protein level. These data imply that frequent hot baths might impair testicular steroidogenesis, especially in old men.