RELATIONSHIP BETWEEN SERUM CONCENTRATION OF GONADOTROPINS AND TESTOSTERONE IN HEAT-EXPOSED AGING MALE-RATS

Serum follicle stimulating hormone (FSH), luteinizing hormone (LH) and testosterone of control rats (20-22°C, 30-50% relative humidity) did not vary at 4, 6 and 10 months of age. Prolonged maintenance of rats in a hot environment (33-35°C, 25-40% relative humidity) was accompanied by a significant decrease in testosterone concentration, irrespective of the animal's age or duration of exposure to heat (1, 2 and 7 months), whereas the concentration of FSH and LH remained relatively unaffected. Activity of 17β-hydroxysteroid oxidoreductase (17β-HSD) in the testes of control rats was inversely related to the animals' age. In most cases prolonged exposure to heat augmented the decline in activity of 17β-HSD associated with ageing. These data suggest that increasing in age is accompanied by a decrease in the activity of testicular 17β-HSD without affecting the concentration of FSH, LH and testosterone in blood serum. It is concluded that, within the age limits used in the present experiment, the significant drop in serum testosterone concentration characterizing rats exposed to heat is independent of serum gonadotropin concentration and testicular acitivity of 17β-HSD, as well as the animal's age. © 1979.