Oophorectomy and cortical bone remodeling in the beagle

Abstract

Cortical bone remodeling measurements were carried out on the ribs of 6 spayed and five control Beagle dams which had been subjected to a period of observation equal to more than one sigma of cortical bone remodeling activity. The results of the measurements of static and dynamic parameters indicate that the lack of ovarian hormones does not produce a major alteration in the rates of cortical bone remodeling, but does result in an increase in the number of resorption spaces per mm2 of cortical bone without altering the parameters of bone function. This latter fact supports the hypothesis that decreased levels of circulatory ovarian hormones may influence the duration of the resorption activity as well as possibly uncoupling the resorption/formation (R/F) mechanism of the bone remodeling unit.

Modulation of bone loss during disuse by pulsed electromagnetic fields

“…Ovariohysterectomy does not have a major effect on cortical bone remodeling parameters in the beagle, although there may be a slight increase in the resorption phase (20). However the principal benefit of ovariohysterectomy is the abolition of the estrous cycle.…”

“…However the principal benefit of ovariohysterectomy is the abolition of the estrous cycle. The female beagle has a 6 month estrous cycle and the natural estrogen levels fluctuate over this period (20). To our knowledge, there have been no studies of changes in remodeling parameters in relation to this fluctuation.…”

Review of Nonprimate, Large Animal Models for Osteoporosis Research

“…Although it can vary widely among dogs, heat cycles include a long anestrus interval of up to 150 days, during which circulating estradiol concentrations remain comparatively low because of ovarian quiescence. During most canine bone loss experiments in which peripheral estradiol concentrations were measured after ovary removal, significant reductions in estradiol have been reported based on comparisons to sham dogs, (24)(25)(26) although in one experiment a significant drop in estradiol concentrations took up to 10 wk to become apparent. (27) Ovariohysterectomy (OHX) or spaying entails physical removal of the ovaries, oviducts, uterine horns, and the uterus.…”

“…(55) The fallibility of the castrated dog model for bone loss research may have evolved more as a result of inconsistent study designs rather than an inherent unreliability of the dog itself. A systematic comparison of available OVX and OHX dog studies (24)(25)(26)(27)(42)(43)(44)(45)(46)(47)(48)(59)(60)(61)(62)(63) showed that the age range of animals has often been wide, the numbers of dogs in experimental groups are sometimes small, use of histomorphometric endpoints (e.g., BV/TV) for small group sizes requires very large differences given the high SD (∼25%) for this method of assessment, (57) the site examined may not be representative of bone loss at other sites, dietary calcium is often overabundant or indeterminable, complete extrication of ovarian tissue is not routinely confirmed at necroscopy, and the timing of ovariectomy may not have been well planned in relation to estrous cycle stage. Castration during times of peak progesterone concentrations can potentially result in heterogeneous hormonal profiles among dogs in shorter-term experiments.…”

Bone quality in animal models of osteoporosis

“…When the role of local factors is considered as influential to bone formation rate to any significant degree, then it is appropriate to employ tissue from a model taken from sites where there are loading dynamics not dissimilar to the human. In this regard, the NHP is superior to other models such as the rat [Danielsen et al, 1992;Jee et al, 1990;Kalu, 1991] and the dog [Faugere et al, 1990;Snow et al, 1984], which have significant shortcomings in terms of biomechanics, growth properties, endocrinology, and cortical bone tissue morphology. The femoral neck of the NHP has the basic triangular shape of the human, with variation in cortical thickness [Hotchkiss, 1999], as opposed to the round shape with uniform cortical thickness seen in rats [Bagi et al, 1997].…”