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

Abstract

The bone changes in hypothyroidism are characterized by a low bone turnover with a reduced osteoid apposition and bone mineralization rate, and a decreased osteoclastic resorption in cortical bone. These changes could affect the mechanical performance of bone. The evaluation of such changes was the object of the present investigation. Hypothyroidism was induced in female rats aged 21 days through administration of propylthiouracil in the drinking water for 70 days (HT group). Controls were untreated rats (C group). Right femur mechanical properties were tested in 3-point bending. Structural (load bearing capacity and stiffness), geometric (cross-sectional area and moment of inertia) and material (modulus of elasticity) properties were evaluated. The left femur was ashed for calcium content determination. Plasma T(4) concentration was significantly decreased in HT rats. Body and femur weight and length in HT rats were also reduced. Femoral calcium concentration in ash was higher in HT than in C rats. However, the femoral calcium mass was significantly lower in HT than in C rats because of the reduced femoral size seen in the former. The stiffness of bone material was higher in HT than in C rats, while the bone geometric properties were significantly lower. The "load capacity" was between 30 and 50% reduced in the HT group, although, the differences disappeared when the values were normalized per 100-g body weight. The lowered biomechanical ability observed in the femoral shafts of HT rats seems to be the expression of a diminished rate of growth. Qualitative alterations in the intrinsic mechanical properties of bone tissue were observed in HT rats, probably because the mineral content and the modulus of elasticity were positively affected. The cortical bone of the HT rat thus appears as a bone with a higher than normal strength and stiffness relative to body weight, probably due to improvement of bone material quality due to an increased matrix calcification.

Effect of radioactive iodine-induced hypothyroidism on longitudinal bone growth during puberty in immature female rats

“…Indeed, a number of clinical studies reported increased body weight gain in adult and children with hypothyroidism [ 14 , 31 ]. In contrast, most animal studies found decreased body weight both in adult [ 3 ] and immature [ 9 , 33 ] rats, in agreement with our results ( Fig. 1B ).…”

“…As expected, we found impaired long bone growth in RAI-treated immature rats ( Figs. 2 and 3 ) as consistent with previous reports [ 9 , 20 ]. On the other hand, BMC mainly increases during the pubertal growth spurt [ 12 ] and thyroid hormone has opposing effects on bone mineralization depending on bone maturational status [ 7 ].…”

“…Terminal blood samples were collected by heart puncture and the serum samples were stored at −70°C. The experimental 4 week-period corresponded to the time of rapid skeletal growth during puberty in rats (from 22 to 62 days of age) [ 9 ].…”

Effects of the combined extracts of Herba Epimedii and Fructus Ligustri Lucidi on bone mineral content and bone turnover in osteoporotic rats

“…The biomechanical properties of the right femur were assessed using a diaphysis bending test [ 18 ] on a WD-1 Universal Testing Apparatus (KeXin Testing Machine Co., Ltd., Changchun, China) that was equipped with calculation and analysis software. The two ends of the right femur were horizontally fixed on the three-point bending platform, and a vertical compression load was then applied to the mid-point of the femur at a displacement rate of 2 mm/min.…”

Experimental Models of Developmental Hypothyroidism

“…Hypothyroidism was implicated in the reduction of body temperature; in increase in sensitivity of receptors dopaminergic agonists to certain drugs like apomorphin, quinpyrole, and 3-benzopine; and in reduction of antagonistic receptors in other studies done in PTU treated young rats [ 63 ] . In addition, studies carried out by various researchers in rats showed that hypothyroidism provokes bone tissue changes characterized by rigidity in bone movement due to reduced osteoid and mineralization index of the bones, and osteoclastic absorption [ 64 ] . Other studies performed in mice with TTF-1 and PAX 8 defi ciencies, 2 transcriptional factors known to be essential for organogenesis with diff erential function in thyroid glands, gave the evidence of the mutagenic origin of CH by dysgenesis of thyroid gland [ 65 ] .…”