The influence of estradiol and testosterone on body growth of young male Wistar rats was investigated. In the first experiment, estradiol was given to intact ad libitum fed male rats at 32, 37 and 42 days of age. Moreover, two untreated groups of animals were used: one was fed rcstrictedly according to the food intake of animals receiving estradiol and another was fed ad libitum. The animals were sacrificed at 47 days of age. Both untreated groups of animals achieved significantly higher body weight and length of tibia than estradiol treated animals. Also the growth of the tail of untreated animals was more intensive than that of estradiol treated animals. In the second experiment, estradiol was given to intact ad libitum fed male rats at 30, 35 and 45 days of age. Moreover, testosterone was given to a half of these animals at 45, 50 and 55 days of age. The animals were sacrificed at 60 days of age. Administration of testosterone significantly increased the growth of the tail and tibia in comparison to the animals which did not receive testosterone after estradiol administration. The results of the present study show that the inhibitory effect of estradiol on body growth of young male rats is not only the result of decreased food intake and that testosterone can improve the skeletal growth of male rats altered by previously given estradiol.
The effect of oestradiol administration and restricted feeding on longitudinal tibia growth was investigated in immature male rats. The restrictedly fed animals had a significantly longer tibia, greater thickness of the growth plate, faster rate of longitudinal tibial growth as well as the greater rate of [methyl-3H]thymidine incorporation into the growth plate of the tibia compared with oestradiol-treated animals. The results indicate that, in immature male rats, exogenous oestradiol can decrease the longitudinal growth of the tibia (at least partly due to inhibition of cell proliferation in the growth plate) independently of its anorexic effect.