The effect of single dose of oestrogens administered during the early postnatal period on the DNA content of rat bone epiphyses.
It has been shown previously that the administration of a single dose or oestrogens to male rats during the early postnatal life retards growth, after a latent period lasting several weeks, [slowing down of body weight and body lenth increments]. We therefore studied the effect of a single subcutaneous dose of oestrogens (1.25 mg oestradiol dipropionate) administered on the 5th postnatal day on the DNA content and DNA concentration in the parts of long bones associated with growth (distal epiphysis of the femur, and proximal and distal epiphyses of the tibia together with the epiphyseal plates). The rats were decapitated at the age of 18, 25 and 40 days, the given parts of the bones were immediately dissected out, weighed and their absolute DNA content and DNA concentration were analyzed. The weight of the distal femoral epiphysis of oestrogen-treated rats was found to be significantly lower at 40 days than in the controls. At the same age, its DNA content and concentration were likewise significantly lower in animals given oestrogens on the 5th day of life. The weight of the proximal tibial epiphysis of oestrogen-treated rats was significantly lower from the 25th day, while its DNA content was already significantly lower on the 18th day and the difference was maintained up to the 40th day of life. A significant decrease in the DNA concentration in oestrogen-treated rats did not appear until the 40th day. The weight of the distal tibial epiphysis of experimental rats was also significantly lower from the 25th postnatal day onwards and its DNA content was significantly lower by the 18th day. At 25 days, the DNA content was slightly lower in oestrogen-treated rats, but the significance of the difference disappeared, although it re-appeared on the 40th day of life. As in the two preceding epiphyses, the DNA concentration in the distal tibial epiphysis was not significantly lower in oestrogen-treated animals before the 40th day of life. The results show that the administration of oestrogens in the early postnatal period significantly affects both the absolute DNA content and the DNA concentration in all the epiphyses in question. The reaction does not appear in all the epiphyses at the same time, however. Differences in the degree of maturity of the epiphyses are evidently responsible for the variability of the response as regards the time at which the above changes occur.
D000818:Animals; D000831:Animals, Newborn; D004247:DNA / Q000378:metabolism*; D004838:Epiphyses / Q000187:drug effects / Q000378:metabolism*; D004967:Estrogens / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D009929:Organ Size; D051381:Rats; D013997:Time Factors
D004967:Estrogens; D004247:DNA