Effect of heat acclimatization on testicular enzymes involved in androgen biosynthesis via the 5-ene pathway.

The metabolism of 3beta-hydroxy-5-ene steroids by testicular homogenates of heat-acclimatized and control mice was investigated in vitro. Acclimatization was achieved by keeping the animals in a hot room (33-35 degrees C, 25-40% R.H.) for 5 weeks. The control animals were kept in a temperate environment (20-22 degrees C, 30-50% R.H.). Some of the heat-acclimatized animals were supplied with additional water in a trough placed inside each cage (HAII mice). This source of water was used by the mice mainly for body cooling. A pronounced decrease in body weight and testis weight, and a smaller decrease in the weight of seminal vesicles which was associated with atrophy of the seminiferous tubules and hyperplasia of the Leydig cells was characteristic of heat-acclimatized mice with only drinking water available (HAI), but not of HAII mice. Although body cooling abolished the adverse physiological response described, it did not prevent specific changes in enzyme activity associated with androgen production. There was increased activity of 3beta-hydroxysteroid dehydrogenase and isomerase, and of 5-ene-17beta-hydroxysteroid dehydrogenase. These data offer partial explanation for the lower peripheral blood testosterone level observed in some species of heat-acclimatized mammals.