Reduced femoral geometry but normal biomechanics in the dorsomedial hypothalamic nucleus-lesioned rat.

Bone geometry, structure, and biomechanical properties were investigated in a model of growth retardation, the dorsomedial hypothalamic nucleus-lesioned (DMNL) weanling rat. Male weanling Sprague-Dawley rats received bilateral electrolytic lesions in the dorsomedial hypothalamic nucleus (DMN) at age 27 days. Sham-operated rats served as controls. All rats were maintained postoperatively for 40 days. Upon sacrifice, DMNL rats weighed less (p < 0.01), were shorter (p < 0.01), and ate less (p < 0.01) when compared to controls, but their body composition was normal. The femora in DMNL were shorter (p < 0.01), had a smaller outer anteroposterior (AP) diameter (p < 0.04), polar moment of the area (p < 0.02), and maximal (p < 0.02) and minimal (p < 0.03) principal moment of the area when compared with sham-operated rats. Notably, mean torque at failure, torsional energy, stiffness, and maximal stress did not demonstrate statistically significant differences between the two groups. These data clearly show that despite the reduced size and bone growth, DMNL rats responded normally to the mechanical challenges applied to test bone biomechanical properties. The data, therefore, add to previous evidence and strengthen the hypothesis that DMNL rats are governed by an "organismic" set point.