In vitro studies on collagen metabolism in metaphyseal rat bone. C. The effect of oestradiol-17 beta in hypophysectomized and in thyro-parathyroidectomized animals.

Oestradiol-17 beta has been administered to hypophysectomized/castrated and to thyro-parathyroidectomized/castrated young mature female rats. Treatment with oestradiol-17 beta 5 mug/day per animal, was continued for 3 weeks. Bone pieces from tibia/femur metaphyses were incubated in vitro for 3 h in order to establish the bone collagen synthesis and resorption rates. The results were compared to results from a previous study on castrated female rats with intact hypophysis, thyroid and parathyroid glands. Bone from the thyro-parathyroidectomized/castrated rats treated with oestradiol-17 beta had a significantly reduced collagen resorption rate in vitro as compared to their paired controls. This is a result consistent with that of castrated female rats with intact thyroid and parathyroid glands treated with oestradiol. Oestradiol-17 beta had no detectable effect upon collagen metabolism in the hypophysectomized/castrated rats. It is concluded that the effect of oestradiol on bone resorption is not exerted via the parathyroid glands or parathyroid hormone. The possibility that oestrogens may act on bone via the hypophysis is discussed.