Long-term effects of high or low Ca intakes and of lack of parathyroid function on rat femur biomechanics

Abstract

In order to assess the repercussion of chronically affected parathyroid function on bone biomechanics, 3-point flexion tests were carried out with fresh, whole femurs of young, intact rats fed diets with low, normal, or high Ca contents, and thyroparathyroidectomized (TPTX) rats fed normal Ca diet. Ca-restriction reduced, and TPTX augmented, inertial parameters and load-resistance of the whole femurs, not affecting the bending stress or the modulus of elasticity of the bone material, suggesting that parathyroid status affected bone mass and architecture without biomechanical alteration of bone tissue. High-Ca feeding enhanced tissue strength and stiffness as a direct effect, not altering bone geometry. The relationships between the energy-absorbing capacity of the whole bones or of the bone tissue, and the moment of inertia of the fracture sections in weight-paired animals showed that (1) in intact rats under normocalcic diet, the inertia of the section was unrelated to the whole-bone biomechanical performance, while bone section architecture depended on bone tissue biomechanical quality; and (2) in the absence of the parathyroids, or in chronically-induced hyperparathyroidism, this last relationship did not apply, but section architecture had a major influence on the whole-bone biomechanics, independently of physiological stresses. The evidence obtained can be interpreted to indicate that architectural changes brought about by the parathyroids contribute to the regulation of bone biomechanics by adapting organ inertial parameters to tissue quality.

Biomechanical performance of diaphyseal shafts and bone tissue of femurs from hypothyroid rats

“…The finding that the adverse effect of hypothyroidism disappears when parameters indicative of bone extrinsic mechanical properties are normalized for body mass, gives support to this concept. The natural stimuli for the bone mechanostat would be the strain of bone tissue, sensed by osteocytes that are induced by both gravitational forces and contractions of regional muscles [17]. Therefore, on a wearing-weight bone as the femur, different body weights will produce different loads and strains.…”

“…Measurements were taken with a digital caliper with the aid of a magnifier 409. This procedure enabled calculation of the amount of diaphyseal bone mass (CSA) and the second moment of inertia of the cross-section in relation to the horizontal axis [17]. The volume of bone between supports (Lp (HB -hb), the entire crosssectional area (CSA) (p/4 BH), the medullary area (MA) (p/4 bh) and the cortical area (CtA) (CSA -CtA) were also calculated.…”

Diachronic patterns of change in structural properties of the femur in the prehistoric American Southwest

“…These factors could include declining nutritional quality through time that was especially poor during the Abandonments period. A gross dietary deficiency or a change in dietary intake of calcium, protein, or phosphorous may lead to a loss of bone density (Avioli, 1977;Ferretti et al, 1985;Marie, 1982). The literature on the negative effects of protein-calorie malnutrition on bone loss is extensive (Crosby et al, 1985;Garn, 1970;Garn and Kangas, 1981;Garn et al, 1976).…”

Dietary intake and stress fractures among elite male combat recruits

“…Studies on bone density have been contradictory [14], and biochemical markers of bone turnover are also probably not related to stress fractures [15]. Calcium deficiency has been found deterrent to bone quality in animal models [16,17] but studies on athletes and soldiers have been less conclusive. Calcium and vitamin D are probably important in women [18] and in Finnish males (who may be effected by the latitude) [19], but in general, there is not enough data on males.…”