ESTROGEN DOES NOT INCREASE BONE-FORMATION IN GROWING RATS

The purpose of these experiments was to test the hypothesis that estrogen has an anabolic effect on cancellous bone formation in long bones Of growing rats. In the present studies, estrogen decreased measurements related to cancellous bone formation, including osteoblast number, fluorochrome-labeled bone perimeter, and incorporation of [H-3]proline into osteoid. Steady state mRNA levels for bone matrix proteins and mineral apposition rate were unchanged or reduced. The [H-3]thymidine labeling index for osteoblasts was very low and was reduced by estrogen treatment. Finally, estrogen decreased the rate of removal of tetracycline previously incorporated into cancellous bone as well as the growth-dependent decrease in cancellous bone area, indicating that hormone treatment reduced net bone resorption. In summary, no evidence was secured to support the hypothesis that estrogen has an anabolic action on bone formation; the results obtained in these studies consistently demonstrated a pronounced inhibitory action of the hormone on bone turnover.