THE EFFECT OF DIFFERENT DOSES OF OESTRADIOL-17β ON COLLAGEN SYNTHESIS IN THE FEMUR OF CASTRATED FEMALE RATS

Abstract

ABSTRACT The effect of different doses of oestradiol-17β 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 μCi [14C]proline was injected intraperitoneally 24 h before the rats were sacrificed. The rats receiving 1 μg 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 were less in the rats receiving oestradiol 1 and 2 μg/day than in the control animals. The higher specific activity of bone hydroxyproline in the rats receiving oestradiol-17β 1 μg/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, the animals 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 μg oestradiol-17β 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. At high doses – 10 and 20 μg oestradiol per animal per day – the percentage of incorporated 14C found as [14C]hydroxproline was reduced. The reason for this altered total-C14/[14C]hydroxyproline ratio is at present unknown.