The effect of different doses of oestradiol-17 beta on collagen synthesis in the femur of castrated female rats.

The effect of different doses of oestradiol-17beta on collagen metabolism in the femur of castrated young mature female rats was studied. The animals received daily injections of the hormone for 21 days and 25 muCi [14C] proline was injected intraperitoneally 24 h before the rats were sacrificed. The rats receiving 1 mug oestradiol per day had a significantly higher specific activity of hydroxyproline in bone compared to the normal and the castrated control rats. At the same time the bone weights and collagen content per femur was less in the rats receiving oestradiol 1 and 2 mug/day than in the control animals. The higher specific activity of bone hydroxyproline in the rats receiving oestradiol-17beta 1 mug/day did not, however, indicate a higher bone collagen accretion rate. As all rats received the same amount of [14C] proline, and the body weights differed considerably at sacrifice, tha naimals probably had different tissue fluid concentrations of [14C] proline. This possibility was supported by the observation that serum concentrations of radioactivity were inversely correlated to body weights. "Correcting" for differences in body weights, the castrated control rats turned out to be the group with the highest specific activity. On doses of 10 and 20 mug oestradiol-17beta per day, the specific activity of hydroxyproline in bone was lower than in the control rats while bone weights and collagen content of the femur were not different from the corresponding values of the castrated controls. This finding suggests a "slow down" of collagen metabolism - both with regard to the accretion and the resorption.