RESUMEN
Osteoporosis and associated fractures are major public health concerns, and as such require appropriate large animal models to further our understanding of this disease. Although sheep appear to be an ideal model with which to study bone loss caused by estrogen depletion, limited data are available concerning the long-term effect of ovariectomy on bone in sheep. The goal of the present study was to observe the ovariectomy-induced changes in bone mass, structure, and metabolism in sheep over a period of 18 months. Six ewes were ovariectomized (OVX) and compared to an age-matched control group by analyzing bone mineral density, trabecular structure, biochemical markers of bone formation and resorption, and plasma estrogen levels. Bone loss (13%, P < 0.01) occurred during the first 4 months after surgery, then stabilized and returned to pre-OVX levels for the remainder of the study. Trabecular architecture was also altered and tended toward osteopenia with recovery to baseline values. Markers of bone formation and resorption were elevated up to 6 months postovariectomy, after which time levels returned to baseline values. Although estradiol measurements demonstrated a clear decline following surgical ovariectomy, levels returned to normal after 6 months. Therefore, the detrimental effect of ovariectomy on sheep bone metabolism seems to be reversible, with normal bone parameters being reestablished within 6 months after surgery. These data seem to indicate that the sheep is not an appropriate model for human postmenopausal osteoporosis.
Asunto(s)
Huesos/metabolismo , Ovariectomía , Ovinos/metabolismo , Factores de Tiempo , Factores de Edad , Animales , Densidad Ósea , FemeninoRESUMEN
There is a great need for animal models of osteoporosis and sheep are a suitable large animal that meets most requirements. Since it is known that bone mass in humans responds to seasonal changes, this study investigated natural bone metabolism in sheep in order to better define the sheep as a model for osteoporosis. Bone mineral density (BMD), trabecular structure, biochemical markers of bone formation and resorption and estrogen were analysed over a period of 18 months. The lowest BMDs, measured by peripheral quantitative computed tomography (pQCT), were observed during winter. Thereafter, a 5.1% increase in BMD was observed during spring and summer (P<0.05). Bone resorption markers showed a variable pattern, with higher values in spring compared to autumn (P<0.001). The physiological estrus phase during autumn was detected by serum estrogen levels. The findings show that it is necessary to take seasonal variations into account if sheep are used to establish an animal model for osteoporosis.