The effects of 17β-estradiol and progestagen on trabecular bone remodeling in oophorectomized dogs

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Abstract
We present the results of the static and dynamic histomorphometric analyses of parameter measurements of trabecular bone remodeling activity in nonoophorectomized, untreated oophorectomized, 17β-estradiol-supplemented oophorectomized, as well as progestagen-supplemented oophorectomized beagle dams. If the spayed beagle dam can be considered a model in which one may equivalate bone changes occurring in the ovarian hormone-deficient human female, we reach the following conclusions: (1) The presence or absence of quasi-physiological levels of single ovarian hormones do affect the status of trabecular bone. (2) The evidence indicates that the presence or absence of individual ovarian hormones do not have a simple effect on trabecular bone remodeling. Apart from affecting the numbers of new bone remodeling units (BMUs) that are initiated in unit time, their effect is seen to be extended to the working efficiency of existing osteoclasts and osteoblasts. The effect is also manifest on the total amount of work performed by the collections of osteoclasts and osteoblasts that provide the respective resorptive and formation phases of the BMU. (3) Finally, we are led to believe that there may be a close interdependence both in physiological activity and therapeutic response between the four active bone envelopes. Such protean effects have hitherto not received their due consideration from researchers in this field.